Abstract Catalytic stability is the prerequisite for the catalyst to achieve high catalytic efficiency. This study finds a new path that Prussian Blue (PB) ultrathin nanosheet assembly material (PB‐NSa) is designed and used to reach efficient catalysis through continuous interaction with ammonium perchlorate (AP, component to be catalyzed). Based on the strong oxidation environment provided by AP, the decomposition of PB occurs in advance, the product Fe 2 O 3 accelerates the decomposition of AP that can release a large amount of gas, then reacts on Fe 2 O 3 and disperses it near the undecomposed AP, finally realizing continuous and efficient catalysis. The results show that under the catalysis of PB‐N, “deactivation” stage of AP thermal decomposition disappears, showing two consecutive exothermic stages, high temperature decomposition peak of AP is reduced to 341.1 °C, the reduction range is 73.1 °C. Combining kinetic calculation and TG‐IR test, it is found that PB‐NSa can keep excellent catalytic stability, which depends on its special structure and interaction with AP. This research provides a design idea for the material to achieve catalytic stability, which will greatly promote its rapid industrialization.
The design of highly dispersed active sites of hollow materials and unique contact behavior with the components to be catalyzed provide infinite possibilities for exploring the limits of catalyst capacity. In this study, the synthesis strategy of highly open 3-dimensional frame structure Prussian blue analogues (CoFe-PBA) was explored through structure self-transformation, which was jointly guided by template mediated epitaxial growth, restricted assembly and directional assembly. Additionally, good application prospect of CoFe-PBA as combustion catalyst was discussed. The results show that unexpected thermal decomposition behavior can be achieved by limiting AP(ammonium perchlorate) to the framework of CoFe-PBA. The high temperature decomposition stage of AP can be advanced to 283.6 °C and the weight loss rate can reach 390.03% min-1 . In-situ monitoring shows that CoFe-PBA can accelerate the formation of NO and NO2 . The calculation of reaction kinetics proved that catalytic process was realized by increasing the nucleation factor. On this basis, the catalytic mechanism of CoFe-PBA on the thermal decomposition of AP was discussed, and the possible interaction process between AP and CoFe-PBA during heating was proposed. At the same time, another interesting functional behavior to prevent AP from caking was discussed.
Abstract Production of an appropriate number of distinct cell types in precise locations during embryonic development is critical for proper tissue function. Homeostatic renewal or repair of damaged tissues in adults also requires cell expansion and transdifferentiation to replenish lost cells. However, the responses of diverse cell types to tissue injury are not fully elucidated. Moreover, the molecular mechanisms underlying transdifferentiation remain poorly understood. This knowledge is essential for harnessing the regenerative potential of individual cell types. This study investigated the fate of pulmonary neuroendocrine cells (PNECs) following lung damage to understand their plasticity and potential. PNECs are proposed to carry out diverse physiological functions in the lung and can also be the cells of origin of human small cell lung cancer. We found that Notch signaling is activated in proliferating PNECs in response to epithelial injury. Forced induction of high levels of Notch signaling in PNECs in conjunction with lung injury results in extensive proliferation and transdifferentiation of PNECs toward the fate of club cells, ciliated cells and goblet cells. Conversely, inactivating Notch signaling in PNECs abolishes their ability to switch cell fate following lung insult. We also established a connection between PNEC transdifferentiation and epigenetic modification mediated by the polycomb repressive complex 2 and inflammatory responses that involve the IL6-STAT3 pathway. These studies not only reveal a major pathway that controls PNEC fate change following lung injury but also provide tools to uncover the molecular basis of cell proliferation and fate determination in response to lung injury.
Article Figures and data Abstract Editor's evaluation eLife digest Introduction Results Discussion Materials and methods Appendix 1 Data availability References Decision letter Author response Article and author information Metrics Abstract Alveolar formation requires coordinated movement and interaction between alveolar epithelial cells, mesenchymal myofibroblasts, and endothelial cells/pericytes to produce secondary septa. These processes rely on the acquisition of distinct cellular properties to enable ligand secretion for cell-cell signaling and initiate morphogenesis through cellular contraction, cell migration, and cell shape change. In this study, we showed that mitochondrial activity and distribution play a key role in bestowing cellular functions on both alveolar epithelial cells and mesenchymal myofibroblasts for generating secondary septa to form alveoli in mice. These results suggest that mitochondrial function is tightly regulated to empower cellular machineries in a spatially specific manner. Indeed, such regulation via mitochondria is required for secretion of ligands, such as platelet-derived growth factor, from alveolar epithelial cells to influence myofibroblast proliferation and contraction/migration. Moreover, mitochondrial function enables myofibroblast contraction/migration during alveolar formation. Together, these findings yield novel mechanistic insights into how mitochondria regulate pivotal steps of alveologenesis. They highlight selective utilization of energy in cells and diverse energy demands in different cellular processes during development. Our work serves as a paradigm for studying how mitochondria control tissue patterning. Editor's evaluation This paper will be of interest to the large class of scientists interested in lung development and disease. It explores the under-investigated role of mitochondrial activity and subcellular distribution for alveolar formation, by using a variety of transgenic mouse models to delete two specific mitochondrial proteins. The data support a role for mitochondria distribution and function in postnatal lung development in the mice. https://doi.org/10.7554/eLife.68598.sa0 Decision letter Reviews on Sciety eLife's review process eLife digest The lungs display an intricate, tree-shaped structure which enables the complex gas exchanges required for life. The end of each tiny 'branch' hosts delicate air sacs, or alveoli, which are further divided by internal walls called septa. In mammals, this final structure is acquired during the last stage of lung development. Then, many different types of cells in the immature alveoli multiply and reach the right location to start constructing additional septa. While the structural changes underlining alveoli maturation are well-studied, the energy requirements for that process remain poorly understood. In particular, the exact role of the mitochondria, the cellular compartments that power most life processes, is still unclear. Zhang et al. therefore set out to map, in detail, the role of mitochondria in alveolar development. Microscope imaging revealed how mitochondria were unevenly distributed within the lung cells of newborn mice. Mitochondria accumulated around the machinery that controls protein secretion in the epithelial cells that line the air sacs, and around the contractile apparatus in the underlying cells (the 'myofibroblasts'). Genetically altering the mice to reduce mitochondrial activity or perturb mitochondrial location in these two cell types produced defective alveoli with fewer septa, but it had no effect on lung development before alveoli formation. This suggests that the formation of alveoli requires more energy than other steps of lung development. Disrupting mitochondrial activity or location also compromised how epithelial cells produced chemical signals necessary for the contraction or migration of the myofibroblasts. Together, these results highlight the importance of tightly regulating mitochondrial activity and location during lung patterning. In the future, this insight could lay the groundwork to determine how energy requirements in various tissues shape other biological processes in health and disease. Introduction Production of alveoli during development and following lung injury is essential for lung function (Burri, 2006; Chao et al., 2016; Whitsett and Weaver, 2015; Pan et al., 2019; Rippa et al., 2021). Defective alveologenesis underlies bronchopulmonary dysplasia (BPD) (Silva et al., 2015), and ongoing destruction of alveoli is characteristic of chronic obstructive lung disease (COPD) (Patel et al., 2019). COPD is a major cause of morbidity and mortality globally (Barnes et al., 2015; Rodríguez-Castillo et al., 2018). During alveolar formation, alveolar epithelial cells (type I [AT1] and type II [AT2] cells), myofibroblasts, and endothelial cells/pericytes undergo coordinated morphogenetic movement to generate secondary septa within saccules. As a result, secondary septa are comprised of a layer of alveolar epithelial cells that ensheathes a core of myofibroblasts and endothelial cells/pericytes. Secondary septa formation (or secondary septation) is the most important step during alveolar formation. Platelet-derived growth factor (PDGF) produced by alveolar epithelial cells is a key player in controlling myofibroblast proliferation and contraction/migration during alveologenesis (Boström et al., 1996; Lindahl et al., 1997). In response to PDGF signaling, the traditional model posits that myofibroblasts proliferate and migrate to the prospective site of secondary septation and secrete elastin. Myofibroblasts and endothelial cells/pericytes are subsequently incorporated with alveolar epithelial cells to form secondary septa. All of these principal components play a key role in driving secondary septa formation (Chao et al., 2016). Generation of alveoli increases the surface area and efficiency of gas exchange, enabling high activity in terrestrial environments. Despite the progress that has been made, our mechanistic understanding of alveologenesis remains incomplete. Mitochondrial activity is essential for every biological process, and mitochondria provide a major source of ATP production through oxidative phosphorylation (OXPHOS) (Labbé et al., 2014; Chan, 2020). Unexpectedly, we have limited mechanistic insight into how mitochondria control cellular processes in vivo. In particular, little is known about whether certain cellular processes have a higher energy demand during alveolar formation. Many genetic and molecular tools have been developed in mice to study mitochondrial function. They offer a unique opportunity to address the central question of how mitochondria control alveologenesis at the molecular level. Mitochondria exhibit dynamic distribution within individual cells. This process is mediated by the cytoskeletal elements that include microtubules, F-actin and intermediate filaments. For instance, Rhot1 (ras homolog family member 1), which is also called Miro1 (Mitochondrial Rho GTPase 1), encodes an atypical Ras GTPase and plays an essential role in mitochondrial transport (Devine et al., 2016). RHOT1 associates with the Milton adaptor (TRAK1/2) and motor proteins (kinesin and dynein), and tethers the adaptor/motor complex to mitochondria. This machinery facilitates transport of mitochondria via microtubules within mammalian cells. Whether regulated mitochondrial distribution is essential for lung cell function during alveologenesis is unknown. In this study, we have demonstrated a central role of mitochondrial activity and distribution in conferring cellular properties to alveolar epithelial cells and myofibroblasts during alveolar formation. In particular, PDGF ligand secretion from alveolar epithelial cells and motility of myofibroblasts depend on regulated activity and distribution of mitochondria. Moreover, loss of mitochondrial function does not have a uniform effect on cellular processes, indicating diverse energy demands in vivo. We also reveal regulation of mitochondrial function by mTOR complex 1 (mTORC1) (Laplante and Sabatini, 2012; Land et al., 2014) during alveolar formation and establish a connection between mitochondria and COPD/emphysema. Taken together, these findings provide new insight into how different cell types channel unique energy demands for cellular machinery into distinct cellular properties during alveolar formation. Results Mitochondria display dynamic subcellular distribution in alveolar epithelial cells and mesenchymal myofibroblasts during alveolar formation To uncover the functional role of mitochondria during alveologenesis, we first examined the distribution of mitochondria in murine lung cells involved in alveolar formation. We used antibodies against mitochondrial components to visualize the distribution of mitochondria in lung epithelial cells and myofibroblasts. For instance, we performed immunostaining on lung sections derived from Sox9Cre/+; ROSA26mTmG/+ mice with anti-mitochondrial pyruvate carrier 1 (MPC1) and anti-mitochondrially encoded cytochrome c oxidase I (MTCO1) (Varuzhanyan et al., 2019). In particular, anti-MPC1 serves as a general marker for mitochondria. Lung epithelial cells were labeled by GFP produced from the ROSA26mTmG reporter (Muzumdar et al., 2007) due to selective Cre expression in SOX9+ epithelial cells (Akiyama et al., 2005). We found that mitochondria were widely distributed in alveolar epithelial cells (distinguished by T1α and SPC for AT1 and AT2 cells, respectively) and myofibroblasts (marked by PDGF receptor A [PDGFRA] and smooth muscle actin [SMA]) (Sun et al., 2000; Gouveia et al., 2017; Figure 1A). This is consistent with an essential role of mitochondrial activity in proper functioning of lung cells. In addition, we observed an uneven subcellular distribution of mitochondria (Figure 1A and B). For instance, mitochondria were concentrated in areas adjacent to the trans-Golgi network (TGN38+) in alveolar epithelial cells (especially AT1 cells) where proteins were sorted to reach their destinations through vesicles and in areas that surrounded SMA in myofibroblasts (Figure 1A and B). This finding suggests that localized mitochondrial distribution is required for cellular function in mammalian lungs. Figure 1 Download asset Open asset Mitochondria display subcellular concentration in alveolar epithelial cells and mesenchymal myofibroblasts of mouse lungs. (A) Immunostaining of lung sections collected from Sox9Cre/+; ROSA26mTmG/+ mice at 18.5 days post coitus (dpc) and different postnatal (P) stages as indicated. The GFP signal identified alveolar epithelial cells (alveolar type I [AT1] and alveolar type II [AT2] cells) while myofibroblasts were characterized by smooth muscle actin (SMA) expression. Moreover, mitochondria were labeled by MPC1; the trans-Golgi network was visualized by TGN38. Enhanced MPC1 signal was distributed nonuniformly in both alveolar epithelial cells and myofibroblasts. (B) Transmission electron micrographs of lungs collected from wild-type mice at P3. Prominent features in a given lung cell type include lamellar bodies in AT2 cells, elongated cell membrane in AT1 cells, and actin bundles and collagen fibers in myofibroblasts. RBC, red blood cell. Compromised mitochondrial activity in the postnatal murine lung leads to defective alveologenesis We first tested if mitochondrial activity is required for alveologenesis by inactivating Tfam (transcription factor A, mitochondria), which encodes a master regulator of mitochondrial transcription (Bouda et al., 2019), in the mouse lung after birth. We produced CAGGCreER/+; ROSA26mTmG/+ (control), and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ mice. Tamoxifen was administered to neonatal mice to activate CreER and lungs were collected at postnatal (P) day 10 (Figure 2A). CreER expression under the CAGG promoter/enhancer (Hayashi and McMahon, 2002) was ubiquitous in lung cells, including NKX2.1+ epithelial cells and PDGFRA+ fibroblasts/myofibroblasts, and converted a floxed allele of Tfam (Tfamf) (Hamanaka et al., 2013) into a null allele (Figure 2B). We noticed that multiple regions in the lungs of mutant mice displayed alveolar defects concomitant with an increased mean linear intercept (MLI), a measure of air space size (Campbell and Tomkeieff, 1952; Escolar et al., 1994; Figure 2C and D). Alveolar defects were associated with disorganized SMA (Figure 2E). We anticipated that Tfam removal led to shutdown of mitochondrial transcription and reduction of mitochondrial activity. Indeed, the relative ratio of mitochondrial DNA (mtDNA) (Venegas and Halberg, 2012), 16S rRNA, and mitochondrially encoded NADH dehydrogenase 1 (mtND1), to nuclear DNA (nDNA), hexokinase 2 (Hk2), was reduced in Tfam-deficient lungs compared to controls (Figure 2F). Loss of Tfam was accompanied by diminished immunoreactivity of MTCO1, the expression of which is controlled by Tfam (Figure 2G). Together, these results indicate that mitochondrial activity is required for alveolar formation. Figure 2 Download asset Open asset Global inactivation of Tfam in postnatal mice results in alveolar defects. (A) Schematic diagram of the time course of postnatal (P) administration of tamoxifen and harvest of mouse lungs. (B) Immunostaining of lungs collected from CAGGCreER/+; ROSA26mTmG/+ (control) and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ mice at P10 that had received tamoxifen at P0. The GFP signal represents sites of induced CreER activity. Nuclear NKX2.1 staining marked all lung epithelial cells while PDGFRA immunoreactivity labeled mesenchymal fibroblasts/myofibroblasts. (C) Hematoxylin and eosin-stained lung sections of control and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ mice at P10. Histological analysis revealed the presence of enlarged saccules and retarded development of secondary septa in the mutant lungs. (D) Measurement of the mean linear intercept (MLI) in control and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ lungs at P10 (n = 4 for each group). The MLI was increased in Tfam-deficient lungs. (E) Immunostaining of lung sections collected from control and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ mice at P10. Smooth muscle actin (SMA) expression was characteristic of myofibroblasts and phalloidin stained the actin filaments. (F) Quantification of the relative ratio of mitochondrial DNA (mtDNA), 16S rRNA, and mitochondrially encoded NADH dehydrogenase 1 (mtND1), to nDNA (nuclear DNA), hexokinase (Hk2), in lysates derived from control and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ lungs (n = 4 for each group). (G) Immunostaining of lung sections collected from control and Tfamf/f; CAGGCreER/+; ROSA26mTmG/+ mice at P10. MPC1 antibodies marked mitochondria; MTCO1 antibodies detected cytochrome c oxidase, the expression of which was controlled by Tfam. All values are mean ± SEM. *p<0.05; **p<0.01 (unpaired Student's t-test). Figure 2—source data 1 Mean linear intercept and relative mitochondrial DNA (mtDNA)/nuclear DNA (nDNA) ratio. https://cdn.elifesciences.org/articles/68598/elife-68598-fig2-data1-v2.xlsx Download elife-68598-fig2-data1-v2.xlsx Selective reduction of mitochondrial activity in the lung epithelium disrupts alveologenesis To investigate the function of mitochondrial activity in distinct compartments, we selectively reduce mitochondrial activity in either the lung epithelium or mesenchyme. We produced control and Tfamf/f; Sox9Cre/+ mice to establish a platform for mechanistic studies on mitochondrial activity in lung epithelial cells during alveolar formation. The Sox9Cre mouse line (Akiyama et al., 2005) is highly efficient in removing sequences flanked by loxP sites in the distal lung epithelium. Sox9-Cre is active at or later than 11.5 days post coitus (dpc) and converted Tfamf into a null allele and compromised mitochondrial activity (Figure 3—figure supplement 1A). Tfamf/f; Sox9Cre/+ mice were born at the expected Mendelian frequency and could not be distinguished from their wild-type littermates by their outer appearance at birth. Moreover, histological analysis revealed no difference between control and mutant lungs prior to P5, confirming that branching morphogenesis and saccule formation were unaffected by inactivating Tfam in SOX9+ cells (Figure 3—figure supplement 2A). In addition, differentiation of alveolar type I and type II cells proceeded normally in Tfamf/f; Sox9Cre/+ lungs (Figure 3—figure supplement 2B). These results highlight a difference in dependence on mitochondrial activity in distinct cellular processes during development. To uncover the cellular processes that are highly dependent on mitochondrial activity, we investigated alveolar formation in control and Tfamf/f; Sox9Cre/+ lungs. After P5, Tfamf/f; Sox9Cre/+ mice could be discerned by their slightly reduced body size in comparison with the littermate controls. Histological analysis of Tfamf/f; Sox9Cre/+ lungs at various postnatal stages revealed defects in secondary septa formation with an increased MLI (Figure 3A and B) and reduced primary septal thickness (Figure 3C). In this setting, primary septal thickness (P2–P7) appears to be an earlier and more sensitive indicator than MLI in detecting defects in secondary septation. No apparent difference in cell death was noted between control and Tfamf/f; Sox9Cre/+ lungs (Figure 3—figure supplement 3A), suggesting that mitochondria-mediated apoptosis was not activated. Moreover, lysates from Tfamf/f; Sox9Cre/+ lungs displayed a reduction in mtDNA/nDNA ratio (Figure 3D), mitochondrial complex I activity (Figure 3E) and ATP production (Figure 3F). By contrast, loss of epithelial Tfam did not affect the major regulators of mitochondrial fusion and fission such as OPA1 processing and DRP1 phosphorylation (Chan, 2020; Figure 3—figure supplement 4). Together, these findings are consistent with reduced mitochondrial activity in Tfamf/f; Sox9Cre/+ lungs and reveal a critical role of mitochondrial activity in lung epithelial cells during alveologenesis. We noted that removal of Tfam in T cells by Foxp3-Cre (Rubtsov et al., 2008) or Cd4-Cre (Lee et al., 2001) and in macrophages by activated Cx3cr1-CreER (Yona et al., 2013) did not exhibit alveolar defects (Figure 3—figure supplement 5; Fu et al., 2019; Gao et al., 2022). Histological analysis revealed no difference between control and Tfamf/f; Foxp3Cre/+ and Tfamf/f; Cd4Cre/+ lungs, and between control and Tfamf/f; Cx3cr1CreER/+ lungs that had received tamoxifen (Figure 3—figure supplement 5). This suggests that structural components of the secondary septa are more susceptible to reduced mitochondrial function. Figure 3 with 5 supplements see all Download asset Open asset Elimination of Tfam or Rhot1 in the epithelium of mouse lungs disrupts alveolar formation. (A) Hematoxylin and eosin-stained lung sections of control and Tfamf/f; Sox9Cre/+ mice at different postnatal (P) stages as indicated. Histological analysis revealed the presence of enlarged saccules and failure in secondary septation in the mutant lungs. (B) Measurement of the mean linear intercept (MLI) in control and Tfamf/f; Sox9Cre/+ lungs at P3–P10 (n = 3 for each group). The MLI was increased in Tfam-deficient lungs. (C) Measurement of the primary septal thickness in control and Tfamf/f; Sox9Cre/+ lungs at P3–P7 (n = 3 for each group). (D) Quantification of the relative ratio of mitochondrial DNA (mtDNA), 16S rRNA, and mitochondrially encoded NADH dehydrogenase 1 (mtND1), to nuclear DNA (nDNA), hexokinase 2 (Hk2), in lysates derived from control and Tfamf/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). (E) Quantification of the relative enzymatic activity of mitochondrial complex I and complex IV in control and Tfamf/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). (F) Measurement of relative ATP production in control and Tfamf/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). (G) Hematoxylin and eosin-stained lung sections of control and Rhot1f/f; Sox9Cre/+ mice at different postnatal stages as indicated. Histological analysis detected enlarged saccules and lack of secondary septa in the mutant lungs. (H) Measurement of the MLI in control and Rhot1f/f; Sox9Cre/+ lungs at P3–P10 (n = 3 for each group). The MLI was increased in Rhot1-deficient lungs. (I) Measurement of the primary septal thickness in control and Rhot1f/f; Sox9Cre/+ lungs at P5–P7 (n = 3 for each group). (J) Quantification of the relative ratio of mtDNA, 16S rRNA, and mtND1, to nDNA, Hk2, in lysates derived from control and Rhot1f/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). (K) Quantification of the relative enzymatic activity of mitochondrial complex I and complex IV in control and Rhot1f/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). (L) Measurement of relative ATP production in control and Rhot1f/f; Sox9Cre/+ lungs at P5 (n = 5 for each group). All values are mean ± SEM. **p<0.01; ***p<0.001; ns, not significant (unpaired Student's t-test). Figure 3—source data 1 Mean linear intercept, primary septal thickness, relative mitochondrial DNA (mtDNA)/nuclear DNA (nDNA) ratio, relative enzymatic activity, and relative ATP production. https://cdn.elifesciences.org/articles/68598/elife-68598-fig3-data1-v2.xlsx Download elife-68598-fig3-data1-v2.xlsx Disruption of mitochondrial distribution in the lung epithelium disturbs alveologenesis As described above, mitochondria display dynamic distribution in lung cells, raising the possibility that proper subcellular distribution of mitochondria is vital for cellular function during alveolar formation. To test this hypothesis, we generated control and Rhot1f/f; Sox9Cre/+ mice. Sox9Cre converted a floxed allele of Rhot1 (Rhot1f) (Nguyen et al., 2014) to a null allele in SOX9+ alveolar epithelial cells. Loss of Rhot1 is expected to perturb normal subcellular distribution of mitochondria. Rhot1f/f; Sox9Cre/+ mice were born at the expected Mendelian frequency and cannot be distinguished from their wild-type littermates by their outer appearance or activity at birth. Similarly, no difference between control and mutant lungs prior to P5 was detected by histological analysis (Figure 3—figure supplement 2C and D). After P5, Rhot1f/f; Sox9Cre/+ mice displayed defects in secondary septation (Figure 3G) with an increased MLI (Figure 3H) and reduced primary septal thickness (Figure 3I). Loss of epithelial Rhot1 did not induce cell death (Figure 3—figure supplement 3B). The alveolar phenotypes could first appear anywhere between P5 and P12 (Figure 3G–I). As expected, mitochondrial activity was unperturbed by disrupting epithelial Rhot1. No changes in mtDNA/nDNA ratio, mitochondrial complex I activity, or ATP production were observed in lysates from Rhot1f/f; Sox9Cre/+ lungs (Figure 3J–L). These results support the notion that localized mitochondrial distribution plays a functional role in alveolar formation. We noticed that the alveolar defects in Rhot1f/f; Sox9Cre/+ lungs were less severe than those in Tfamf/f; Sox9Cre/+ lungs. This is likely due to the fact that only the distribution and not the activity of mitochondria was perturbed in Rhot1f/f; Sox9Cre/+ lungs. PDGF signal reception is perturbed and the number of mesenchymal myofibroblasts is reduced in the absence of proper mitochondrial activity or distribution in the lung epithelium We examined various lung cell types in Tfamf/f; Sox9Cre/+ lungs to explore the molecular basis of their alveolar phenotypes. Interestingly, the number of fibroblasts/myofibroblasts marked by PDGFRA was reduced in the absence of epithelial Tfam (Figure 4A and D). Likewise, we found that the number of fibroblasts/myofibroblasts was reduced in Rhot1f/f; Sox9Cre/+ lungs where epithelial Rhot1 was lost (Figure 4G and I). A diminished population of fibroblasts/myofibroblasts in Tfamf/f; Sox9Cre/+ and Rhot1f/f; Sox9Cre/+ lungs prompted us to investigate whether PDGF signaling was disrupted. Figure 4 with 1 supplement see all Download asset Open asset Loss of epithelial Tfam or Rhot1 compromises PDGF release. (A) Immunostaining of lungs collected from control and Tfamf/f; Sox9Cre/+ mice at postnatal (P) day 5 or 10, some of which were injected with EdU as indicated. (B) Immunostaining of lungs collected from control and Tfamf/f; Sox9Cre/+ mice at P5. (C) LacZ staining (blue) of lung sections collected from Sox9Cre/+; Pdgfaex4COIN/+ (control) and Tfamf/f; Sox9Cre/+; Pdgfaex4COIN/+ mice. The slides were counterstained with eosin (red). No difference in the intensity of LacZ staining in the lung was noted between these two mouse lines. (D) Quantification of fibroblast/myofibroblast proliferation in control and Tfamf/f; Sox9Cre/+ lungs at P5, P7, and P10 (n = 3 for each group). The rate of fibroblast/myofibroblast proliferation was calculated as the ratio of the number of EdU+ fibroblasts/myofibroblasts (EdU+ PDGFRA+) to the number of fibroblasts/myofibroblasts (PDGFRA+). The percentage of proliferating fibroblasts/myofibroblasts was reduced in Tfamf/f; Sox9Cre/+ compared to controls at P7 and P10. (E) qPCR analysis of gene expression in control and Tfamf/f; Sox9Cre/+ lungs at P5 (n = 3 for each group). While no difference in expression levels was noted for Pdgfa and Pdgfra between control and Tfamf/f; Sox9Cre/+ lungs, the expression levels of Acta2 (smooth muscle actin [SMA]) and Eln (elastin) were significantly reduced in the absence of Tfam. (F) Western blot analysis of cell lysates and supernatants from control and Tfam-deficient cells (n = 4 for each group) lentivirally transduced with PDGFA-expressing constructs. The amount of PDGFA released into the media was reduced in Tfam-deficient cells compared to controls. α-Tubulin served as a loading control. (G) Immunostaining of lungs collected from control and Rhot1f/f; Sox9Cre/+ mice at P5, P7, or P10, some of which were injected with EdU as indicated. (H) Immunostaining of lungs collected from control and Rhot1f/f; Sox9Cre/+ mice at P5. (I) Quantification of fibroblast/myofibroblast proliferation in control and Rhot1f/f; Sox9Cre/+ lungs at P7 and P10 (n = 3 for each group). The percentage of proliferating fibroblasts/myofibroblasts was reduced in Rhot1f/f; Sox9Cre/+ compared to controls at P7 and P10. (J) qPCR analysis of gene expression in control and Rhot1f/f; Sox9Cre/+ lungs at P5 (n = 3 for each group). The expression levels of Pdgfa and Pdgfra were unaltered between control and Rhot1f/f; Sox9Cre/+ lungs; the expression levels of Acta2 and Eln were significantly reduced in the absence of Rhot1. (K) Western blot analysis of cell lysates and supernatants from control and Rhot1-deficient cells (n = 4 for each group) lentivirally transduced with PDGFA-expressing constructs. The amount of PDGFA released into the media was reduced in Rhot1-deficient cells compared to controls. α-Tubulin served as a loading control. All values are mean ± SEM. *p<0.05; ns, not significant (unpaired Student's t-test). Figure 4—source data 1 EdU quantification, relative transcript levels, and quantification of PDGFA secretion. https://cdn.elifesciences.org/articles/68598/elife-68598-fig4-data1-v2.xlsx Download elife-68598-fig4-data1-v2.xlsx Phosphorylation of PDGFRA (p-PDGFRA), indicative of PDGF signaling, was reduced in Tfamf/f; Sox9Cre/+ or Rhot1f/f; Sox9Cre/+ lungs (Figure 4A and G). This observation suggests that PDGF signal reception by fibroblasts/myofibroblasts was impaired in Tfamf/f; Sox9Cre/+ or Rhot1f/f; Sox9Cre/+ lungs. Defective PDGF signal reception in fibroblasts/myofibroblasts could be due to lack of PDGF production, trafficking, or release. We found that production of the PDGF ligand (PDGFA) in alveolar epithelial cells was unaffected in Tfamf/f; Sox9Cre/+ or Rhot1f/f; Sox9Cre/+ lungs by qPCR analysis (Figure 4E and J). To substantiate this model, we utilized a PDGF reporter mouse line (Pdgfaex4COIN) (Andrae et al., 2014) that faithfully recapitulates the spatial and temporal expression of Pdgfa. Of note, no reliable PDGF antibody is available to detect PDGF in lungs or other tissues (Gouveia et al., 2017; Andrae et al., 2014). We generated Pdgfaex4COIN/+; Sox9Cre/+ (control) and Tfamf/f; Pdgfaex4COIN/+; Sox9Cre/+ mice. Cre recombinase activated β-galactosidase (lacZ) expression in Pdgfa-expressing cells from the Pdgfaex4COIN allele. We found that LacZ expression in Pdgfa-expressing cells (i.e., alveolar epithelial cells) displayed a similar pattern and intensity between control and Tfam-deficient lungs (Figure 4C, Figure 4—figure supplement 1A). Together, these results pointed to disrupted PDGF trafficking or release. This defect would subsequently disturb signal reception in mesenchymal fibroblasts/myofibroblasts of Tfamf/f; Sox9Cre/+ and Rhot1f/f; Sox9Cre/+ lungs. PDGF secretion from lung cells is diminished without proper mitochondrial activity or distribution Our model posits that secretion of PDGF ligand from Tfam- and Rhot1-deficient alveolar epithelial cells is compromised. To test this idea, we derived Tfam- and Rhot1-deficient cells from Tfamf/f; PdgfraCre/+ and Rhot1f/f; PdgfraCre/+ lungs (see below), respectively. We transduced control and Tfam- and Rhot1-deficient cells with lentiviruses that produced epitope-tagged PDGF (Figure 4—figure supplement 1B). Using this assay, we determined the amount of PDGF released from control and Tfam- and Rhot1-deficient cells (Figure 4F and K). PDGF levels in the conditioned media derived from Tfam- or Rhot1-deficient cells were reduced compared to controls (Figure 4F and K). These findings support a model in which loss of mitochondrial activity or distribution results in a failure of vesicular transport and PDGF release from alveolar epithelial cells. We surmise that these defects are in part due to an incapacitated a
Lung branching morphogenesis requires reciprocal interactions between the epithelium and mesenchyme. How the lung branches are generated at a defined location and projected toward a specific direction remains a major unresolved issue. In this study, we investigated the function of Wnt signaling in lung branching in mice. We discovered that Wnt5a in both the epithelium and the mesenchyme plays an essential role in controlling the position and direction of lung branching. The Wnt5a signal is mediated by Vangl1/2 to trigger a cascade of noncanonical or planar cell polarity (PCP) signaling. In response to noncanonical Wnt signaling, lung cells undergo cytoskeletal reorganization and change focal adhesions. Perturbed focal adhesions in lung explants are associated with defective branching. Moreover, we observed changes in the shape and orientation of the epithelial sheet and the underlying mesenchymal layer in regions of defective branching in the mutant lungs. Thus, PCP signaling helps define the position and orientation of the lung branches. We propose that mechanical force induced by noncanonical Wnt signaling mediates a coordinated alteration in the shape and orientation of a group of epithelial and mesenchymal cells. These results provide a new framework for understanding the molecular mechanisms by which a stereotypic branching pattern is generated.
Alveolar formation requires coordinated movement and interaction between alveolar epithelial cells, mesenchymal myofibroblasts, and endothelial cells/pericytes to produce secondary septa. These processes rely on the acquisition of distinct cellular properties to enable ligand secretion for cell-cell signaling and initiate morphogenesis through cellular contraction, cell migration, and cell shape change. In this study, we showed that mitochondrial activity and distribution play a key role in bestowing cellular functions on both alveolar epithelial cells and mesenchymal myofibroblasts for generating secondary septa to form alveoli in mice. These results suggest that mitochondrial function is tightly regulated to empower cellular machineries in a spatially specific manner. Indeed, such regulation via mitochondria is required for secretion of ligands, such as platelet-derived growth factor, from alveolar epithelial cells to influence myofibroblast proliferation and contraction/migration. Moreover, mitochondrial function enables myofibroblast contraction/migration during alveolar formation. Together, these findings yield novel mechanistic insights into how mitochondria regulate pivotal steps of alveologenesis. They highlight selective utilization of energy in cells and diverse energy demands in different cellular processes during development. Our work serves as a paradigm for studying how mitochondria control tissue patterning.
ABSTRACT Mitochondrial cristae are critical for efficient oxidative phosphorylation, however, how cristae architecture is precisely organized remains largely unknown. Here, we discovered that Mic19, a core component of MICOS (mitochondrial contact site and cristae organizing system) complex, can be cleaved at N-terminal by mitochondrial protease OMA1. Mic19 directly interacts with mitochondrial outer-membrane protein Sam50 (the key subunit of SAM complex) and inner-membrane protein Mic60 (the key component of MICOS complex) to form Sam50-Mic19-Mic60 axis, which dominantly connects SAM and MICOS complexes to assemble MIB (mitochondrial intermembrane space bridging) supercomplex for mediating mitochondrial outer- and inner-membrane contact. OMA1-mediated Mic19 cleavage causes Sam50-Mic19-Mic60 axis disruption, which separates SAM and MICOS and leads to MIB disassembly. Disrupted Sam50-Mic19-Mic60 axis, even in the presence of SAM and MICOS complexes, causes the abnormal mitochondrial morphology, loss of mitochondrial cristae junctions, abnormal cristae distribution and reduced ATP production. Importantly, Sam50 displays punctate distribution at mitochondrial outer membrane, and acts as an anchoring point to guide the formation of mitochondrial cristae junctions. Therefore, we propose a model that Sam50-Mic19-Mic60 axis mediated SAM-MICOS complexes integration determines mitochondrial cristae architecture.
Abstract Burning rate of solid propellants can be effectively improved by adding catalysts and using smaller size ammonium perchlorate (AP). Although few reports, the exploration of changing the size of AP primary particles by catalysts is of great significance for improving combustion performance. Here, taking Co‐bipy as an example, the potential advantages of such materials as AP decomposition catalysts are reported. Due to the existence of NO 3 − combined with oxygen rich environment provided by AP, the structural self‐transformation from micronrods to nanoparticles can be quickly realized during the heating process. More importantly, when Co‐bipy decomposes, it can play the role of “scalpel” and in situ cut AP particles. Results show that high‐temperature decomposition of Co‐bipy/AP occurs at 305.8 °C, which is 137.5 °C lower than that of pure AP. Catalytic mechanism is discussed by in situ IR and TG‐IR, CoO can effectively increase the content of reactive oxygen species and weaken the N–H bond, realizing the rapid oxidation of NH 3 . Eventually, the behavior of Co‐bipy cutting AP particles is tested. This interesting catalyst structure self‐transformation behavior can not only realize the influence on AP, but also perform a positive function in the combustion process of solid propellants, such as opening the adhesive AP interface.
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