Fibrodysplasia ossificans progressiva (FOP), a rare disease characterized by progressive heterotopic ossification of muscle and connective tissues, is caused by autosomal dominant activating mutations in the type I receptor, ACVR1/ALK2. The classic human FOP variant, ACVR1
Introduction: Individual blood pressure (BP) response to high salt intake varies from minimal to substantial and is largely genetically determined. More than 50% of hypertensive patients are salt sensitive (SS) and respond to high salt intake by increasing their BP compared to only 10% in the normotensive population. ENaC is involved in sodium transport in the distal nephrons of the kidney as well as in the CNS in the choroid plexus and hypothalamic neurons. In turn, ENaC is controlled by the E3 ubiquitin ligase protein - NEDD4L. The functional NEDD4L SNP rs4149601 (G/A) influences the ability of NEDD4L to regulate ENaC expression and is associated with high blood pressure and salt sensitivity. We hypothesize that NEDD4L rs4149601 genotype is an independent predictor of BP response to salt intake in hypertensives. Methods: Daytime BP was measured using 24hr ABPM in 191 young (<60 years old) Caucasian hypertensives (BP ≥130/85 mmHg). 24hr urine Na and K + , blood Na + and K + , and BMI were collected. Patient genotyping for the rs4149601 (G/A) SNP was done using TaqMan MGB probe based RT PCR. Linear regression analyzed (SAS Software) the influence of urine Na + , urine K + , blood K + ,blood Na + , age, gender, and BMI on blood pressure traits. Results: In hypertensive rs4149601 G carriers (n=169), systolic BP (SBP) varied significantly with salt intake (p=0.0088) while diastolic BP did not (p=0.7198). An SBP increase of 2.34 mmHg per 50 mmol Na was observed when urine Na alone is considered. Age (p=0.0002) and blood K + (p=0.0466) were also significant determinants of SBP in patients with the G allele. Only blood K + was a significant predictor of diastolic BP (DBP) in hypertensive G allele carriers. None of the factors tested influenced either SBP or DBP in hypertensive patients who are carriers of the A allele. Conclusion: The functional NEDD4L rs4149601 SNP influences individual daytime BP response to salt intake. This result supports the hypothesis that NEDD4L rs4149601 G carriers with intact C2 domain express higher levels of ENaC and therefore are more sensitive to salt intake. Thus, NEDD4L rs4149601 polymorphism genotyping may allow for identification of hypertensive individuals who will benefit to a greater extent from reducing the amount of salt in their diet.
The non-histone chromatin binding protein High Mobility Group AT-hook protein 2 (HMGA2) has important functions in chromatin remodeling, and genome maintenance and protection. Expression of HMGA2 is highest in embryonic stem cells, declines during cell differentiation and cell aging, but it is re-expressed in some cancers, where high HMGA2 expression frequently coincides with a poor prognosis. The nuclear functions of HMGA2 cannot be explained by binding to chromatin alone but involve complex interactions with other proteins that are incompletely understood. The present study used biotin proximity labeling, followed by proteomic analysis, to identify the nuclear interaction partners of HMGA2. We tested two different biotin ligase HMGA2 constructs (BioID2 and miniTurbo) with similar results, and identified known and new HMGA2 interaction partners, with functionalities mainly in chromatin biology. These HMGA2 biotin ligase fusion constructs offer exciting new possibilities for interactome discovery research, enabling the monitoring of nuclear HMGA2 interactomes during drug treatments.
Dilated cardiomyopathy (DCM) is one of the leading causes of heart failure and heart transplant. Mutations in 60 genes have been associated with DCM. Approximately 6% of all DCM cases are caused by mutations in the lamin A/C gene (LMNA). LMNA codes for type-V intermediate filaments that support the structure of the nuclear membrane and are involved in chromatin structure and gene expression. Most LMNA mutations result in striated muscle diseases while the rest affects the adipose tissue, peripheral nervous system, multiple tissues or lead to progeroid syndromes/overlapping syndromes. Patients with LMNA mutations exhibit a variety of cellular and physiological phenotypes. This paper explores the current phenotypes observed in LMNA-caused DCM, the results and implications of the cellular and animal models of DCM and the prevailing theories on the pathogenesis of laminopathies.
The lamin A/C (LMNA) gene codes for nuclear intermediate filaments constitutive of the nuclear lamina. LMNA has 12 exons and alternative splicing of exon 10 results in two major isoforms—lamins A and C. Mutations found throughout the LMNA gene cause a group of diseases collectively known as laminopathies, of which the type, diversity, penetrance and severity of phenotypes can vary from one individual to the other, even between individuals carrying the same mutation. The majority of the laminopathies affect cardiac and/or skeletal muscles. The underlying molecular mechanisms contributing to such tissue-specific phenotypes caused by mutations in a ubiquitously expressed gene are not yet well elucidated. This review will explore the different phenotypes observed in established models of striated muscle laminopathies and their respective contributions to advancing our understanding of cardiac and skeletal muscle-related laminopathies. Potential future directions for developing effective treatments for patients with lamin A/C mutation-associated cardiac and/or skeletal muscle conditions will be discussed.
The lamin A/C (LMNA) gene codes for A type lamins which are key components of the nuclear lamina and are involved in maintaining the structure of the nucleus and its processes. Mutations in LMNA cause a group of diseases known as laminopathies. For this project, the lamin A/C variant affecting amino acid 192 is studied. The causal mutation results in an amino acid change from glycine [G] (smaller, non‐polar, uncharged) to aspartic acid [D] (larger, polar, charged). This D192G variant is linked to a severe form of a cardiac disease called Dilated Cardiomyopathy (DCM), where cardiomyocytes are presented with multiple nuclear abnormalities. In vitro experiments with the D192G variant showed abnormal nuclear localization of Protein Kinase C alpha (PKC‐α). PKC‐α is the major protein kinase C isoform found in the heart and skeletal muscles. This enzyme phosphorylates a host of proteins and uses A‐type lamins to reach its nuclear targets. In order to help elucidate the potential role of PKC‐α as the link between the disease phenotype and lamin mutation, a structural comparison between the wild type lamin A and the D192G variant was performed in silico. Moreover, the PKC‐α binding site on the wild type and mutant lamin A were compared in order to determine if a conformation change has occurred. Since there is currently no full‐length crystal structure for either the wild type or D192G lamin A/C variant, the I‐TASSER software suite was used to generate simulated protein structures. The top five structures for the WT and variant simulations were examined. The final models selected to most likely represent reality were chosen based on various factors such as computed C‐score, what is known in literature and human analysis of the simulations. The results show that the D192G variant predominantly takes a globular form which is very comparable to the structure of the wild type lamin A found in the nucleoplasm. This globular form also potentially explains the lamin aggregates found in cells expressing the D192G variant. However, this globular variant conformation significantly differs when compared to the known and prevalent wild type lamin A conformation which is the globular head‐alpha helical rod‐globular tail structure. In particular, the conformation of PKCα binding site on lamin A is also significantly altered. The Ashbury College MSOE Center for BioMolecular Modeling SMART Team used 3‐D modeling and printing technology to examine the structure‐function relationships of the wild type lamin A/C protein and the D192G variant.
Striated muscle laminopathies are cardiac and skeletal muscle conditions caused by mutations in the lamin A/C gene (LMNA). LMNA codes for the A-type lamins, which are nuclear intermediate filaments that maintain the nuclear structure and nuclear processes such as gene expression. Protein kinase C alpha (PKC-α) interacts with lamin A/C and with several lamin A/C partners involved in striated muscle laminopathies. To determine PKC-α's involvement in muscular laminopathies, PKC-α's localization, activation, and interactions with the A-type lamins were examined in various cell types expressing pathogenic lamin A/C mutations. The results showed aberrant nuclear PKC-α cellular distribution in mutant cells compared to WT. PKC-α activation (phos-PKC-α) was decreased or unchanged in the studied cells expressing LMNA mutations, and the activation of its downstream targets, ERK 1/2, paralleled PKC-α activation alteration. Furthermore, the phos-PKC-α-lamin A/C proximity was altered. Overall, the data showed that PKC-α localization, activation, and proximity with lamin A/C were affected by certain pathogenic LMNA mutations, suggesting PKC-α involvement in striated muscle laminopathies.
Abstract Background Lamin A/C gene ( LMNA ) mutations frequently cause cardiac and/or skeletal muscle diseases called striated muscle laminopathies. We created a zebrafish muscular laminopathy model using CRISPR/Cas9 technology to target the zebrafish lmna gene. Results Heterozygous and homozygous lmna mutants present skeletal muscle damage at 1 day post‐fertilization (dpf), and mobility impairment at 4 to 7 dpf. Cardiac structure and function analyses between 1 and 7 dpf show mild and transient defects in the lmna mutants compared to wild type (WT). Quantitative RT‐PCR analysis of genes implicated in striated muscle laminopathies show a decrease in jun and nfκb2 expression in 7 dpf homozygous lmna mutants compared to WT. Homozygous lmna mutants have a 1.26‐fold protein increase in activated Erk 1/2, kinases associated with striated muscle laminopathies, compared to WT at 7 dpf. Activated Protein Kinase C alpha (Pkc α), a kinase that interacts with lamin A/C and Erk 1/2, is also upregulated in 7 dpf homozygous lmna mutants compared to WT. Conclusions This study presents an animal model of skeletal muscle laminopathy where heterozygous and homozygous lmna mutants exhibit prominent skeletal muscle abnormalities during the first week of development. Furthermore, this is the first animal model that potentially implicates Pkc α in muscular laminopathies.
