Within the brain, activating the classical arm of renin angiotensin system (RAS) (ACE/AngII/AT1aR) upregulates, ADAM17, a disintegrin & metalloprotease. ADAM17 sheds ACE2 from the cell membrane compromising compensatory RAS (ACE2/Ang(1–7)/MasR). We have previously published that deleting ADAM17 from the hypothalamus improves autonomic function and attenuates development of DOCA‐salt induced neurogenic hypertension. We hypothesize, ADAM17 containing neurons in the paraventricular nucleus (PVN) contribute to its excitability leading to autonomic dysfunction. Single minded 1 (Sim1) is a transcription factor essential for neurodevelopment of the PVN. This promoter enabled specific labelling of PVN neurons with reporter tdTomato, using cre‐lox mechanism. In another group of mice (named SAT), we conditionally knocked out ADAM17 from Sim1 neurons, keeping tdTomato reporter expression. We identified pre‐sympathetic neurons within the PVN, by injecting a GFP tagged pseudorabies virus in the kidney. These neurons overlapped with Sim1 positive tdTomato reporter neurons in the PVN. The relevance of Sim1‐PVN neurons in blood pressure (BP) was evaluated through an optogenetic approach. Activating Sim1‐PVN neurons with cre driven channelrhodopsin and 20 Hz photo stimulation at 473 nm, led to increased BP, measured with radiotelemetry (+8.2 mmHg, n=1). Ganglionic blockade following chlorisondamine administration prevented this rise in BP, confirming that it is a neuronal response (+ 0.3 mmHg, n=1). Neuron sorting was employed to distinguish the ADAM17 knockout (SAT), Sim1‐tomato PVN neurons from its controls. qRT‐PCR from these neurons confirmed a 4‐fold drop in ADAM17 in knockout mice (p<0.1). Interestingly, at baseline SAT tdTomato neurons in PVN had a 4‐fold decreased FosB expression, a marker of chronic neuronal excitation (p<0.1), indicating that ADAM17 plays a critical role in maintaining neuronal excitability in the PVN. DOCA pellets were implanted in both SAT and control mice. Followed by 15 days of 1% NaCl treatment to induce neurogenic hypertension. DOCA‐salt induced change in RAS within the hypothalamus led to greater drop in ACE (1.7‐fold, p<0.0001) and AT1aR (3.12‐fold, p<0.001) gene expression in SAT mice. Moreover, compensatory ACE2 expression was 6‐fold higher in SAT vs. controls (p<0.05) and MasR expression increased 4.6‐fold in SAT mice (p<0.0001), indicating that deleting ADAM17 preserved the compensatory RAS within SAT during a DOCA‐salt challenge. Though, DOCA‐salt induced change in systolic BP was unchanged between SAT knockouts & controls, optogenetic stimulation and FosB expression presents evidence that the Sim1‐ADAM17 neurons in the PVN contribute to autonomic function through neuronal activation. Future direction includes, studying the interaction of circumventricular injection of AngII with ADAM17 & suppression of AT1R‐induced inflammation with losartan, to understand the mechanism of ADAM17‐induced neuronal activation in the PVN. Clinical relevance is highlighted by the report that enhanced ADAM17‐induced shed ACE2 activity in the cerebrospinal fluid is correlated with systolic BP in hypertensive patients, making ADAM17 a potential new target for the treatment of hypertension. Support or Funding Information NIH/NHLBI HL093178 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
By using pseudorabies virus expressing green fluorescence protein, we found that efferent bone marrow-neural connections trace to sympathetic centers of the central nervous system in normal mice. However, this was markedly reduced in type 1 diabetes, suggesting a significant loss of bone marrow innervation. This loss of innervation was associated with a change in hematopoiesis toward generation of more monocytes and an altered diurnal release of monocytes in rodents and patients with type 1 diabetes. In the hypothalamus and granular insular cortex of mice with type 1 diabetes, bone marrow-derived microglia/macrophages were activated and found at a greater density than in controls. Infiltration of CD45(+)/CCR2(+)/GR-1(+)/Iba-1(+) bone marrow-derived monocytes into the hypothalamus could be mitigated by treatment with minocycline, an anti-inflammatory agent capable of crossing the blood-brain barrier. Our studies suggest that targeting central inflammation may facilitate management of microvascular complications.
The prevalence of metabolic disorders, including type 2 diabetes mellitus, continues to increase worldwide. Although newer and more advanced therapies are available, current treatments are still inadequate and the search for solutions remains. The regulation of energy homeostasis, including glucose metabolism, involves an exchange of information between the nervous systems and peripheral organs and tissues; therefore, developing treatments to alter central and/or peripheral neural pathways could be an alternative solution to modulate whole body metabolism. Liver glucose production and storage are major mechanisms controlling glycemia, and the autonomic nervous system plays an important role in the regulation of hepatic functions. Autonomic nervous system imbalance contributes to excessive hepatic glucose production and thus to the development and progression of type 2 diabetes mellitus. At cellular levels, change in neuronal activity is one of the underlying mechanisms of autonomic imbalance; therefore, modulation of the excitability of neurons involved in autonomic outflow governance has the potential to improve glycemic status. Tissue-specific subsets of preautonomic neurons differentially control autonomic outflow; therefore, detailed information about neural circuits and properties of liver-related neurons is necessary for the development of strategies to regulate liver functions via the autonomic nerves. This review provides an overview of our current understanding of the hypothalamus-ventral brainstem-liver pathway involved in the sympathetic regulation of the liver, outlines strategies to identify organ-related neurons, and summarizes neuronal plasticity during diabetic conditions with a particular focus on liver-related neurons in the paraventricular nucleus.
Increased dietary salt triggers oxidative stress and kidney injury in salt-sensitive hypertension; however, the mechanism for sensing increased extracellular Na(+) concentration ([Na(+)]) remains unclear. A Na(+)-activated Na(+) channel (Na sensor) described in the brain operates as a sensor of extracellular fluid [Na(+)]; nonetheless, its presence in the kidney has not been established. In the present study, we demonstrated the gene expression of the Na sensor by RT-PCR and Western blotting in the Sprague-Dawley rat kidney. Using immunofluorescence, the Na sensor was localized to the luminal side in tubular epithelial cells of collecting ducts colocalizing with aquaporin-2, a marker of principal cells, and in thick ascending limb, colocalizing with the glycoprotein Tamm-Horsfall. To determine the effect of a high-salt diet (HSD) on Na sensor gene expression, we quantified its transcript and protein levels primarily in renal medullas from control rats and rats subjected to 8% NaCl for 7 days (n = 5). HSD increased Na sensor expression levels (mRNA: from 1.2 ± 0.2 to 5.1 ± 1.3 au; protein: from 0.98 ± 0.15 to 1.74 ± 0.28 au P < 0.05) in the kidney medulla, but not in the cortex. These data indicate that rat kidney epithelial cells of the thick ascending limb and principal cells of the collecting duct possess a Na sensor that is upregulated by HSD, suggesting an important role in monitoring changes in tubular fluid [Na(+)].
Deletion of the Angiotensin Converting Enzyme type 2 (ACE2) leads to a genetic background‐dependent increase in baseline blood pressure in mice, which can reach hypertensive levels with age. Recently, we identified a disintegrin and metalloprotease 17 (ADAM17) as a new member of a signaling pathway leading to the development of neurogenic hypertension. In an attempt to pinpoint the origin of developing hypertension in ACE2 knockout mice, we hypothesized that enhanced sympathetic drive could originate from elevated ADAM17 in pre‐sympathetic neurons of the paraventricular nucleus (PVN) of hypothalamus. Adult (10–12 week‐old) wildtype (WT) and ACE2 knockout male mice were used to assess ADAM17 protein expression (immunohistochemistry, Western blot and qPCR) in the PVN while another group was injected in the kidney with a pseudorabies virus encoding a green fluorescent protein, for retrograde labeling of sympathetic neurons. After 4 days, whole‐cell patch‐clamp recordings were conducted from labeled pre‐sympathetic PVN neurons. The resting membrane potential of pre‐sympathetic PVN neurons in WT mice was −49.01 ± 2.09 mV, while −48.9 ± 0.2 mV in ACE2 knockout mice, which may suggest an increased threshold for excitability in pre‐sympathetic PVN neurons. Interestingly, when the inhibitory inputs were analyzed, miniature IPSC frequency was reduced in ACE2 KO compared to WT (0.68 ± 0.29 vs. 1.56 ± 0.28 Hz; P <0.05) suggesting that the ACE2 knockout mice might be more susceptible to excitation, thus contributing to a sympathetic overdrive. Within the hypothalamus, ADAM17 expression showed a 2‐fold increase in ACE2 knockout compared to WT mice ( P <0.05). Using immunohistochemistry, increased ADAM17 expression was confirmed in parvocellular neurons of the PVN. Taken together, our data suggest that enhanced expression of ADAM17 in the parvocellular region of the PVN could be associated with increased excitability of pre‐sympathetic neurons in ACE2 knockout mice. This dysregulation in neuronal activity might alter the intricate pressor homeostasis leading to increased blood pressure. These results suggest that ADAM17 could be a potential new target for the reduction of enhanced sympathetic activity in neurogenic hypertension. Support or Funding Information NIH/NHLBI (HL093178) COBRE (P30GM106392)
Research in preclinical models indicates that estrogens are neuroprotective and positively impact cognitive aging. However, clinical data are equivocal as to the benefits of menopausal estrogen therapy to the brain and cognition. Pre-existing cardiometabolic disease may modulate mechanisms by which estrogens act, potentially reducing or reversing protections they provide against cognitive decline. In the current review we propose mechanisms by which cardiometabolic disease may alter estrogen effects, including both alterations in actions directly on brain memory systems and actions on cardiometabolic systems, which in turn impact brain memory systems. Consideration of mechanisms by which estrogen administration can exert differential effects dependent upon health phenotype is consistent with the move towards precision or personalized medicine, which aims to determine which treatment interventions will work for which individuals. Understanding effects of estrogens in both healthy and unhealthy models of aging is critical to optimizing the translational link between preclinical and clinical research.
