Function (Oxford, England)最新文献

The consensus or canonical model of glucose-stimulated insulin secretion provides that the metabolism of glucose closes KATP channels by increase of the ATP/ADP ratio and that the ensuing depolarization-induced Ca2+ influx through voltage-dependent Ca2+ channels represents the immediate signal for the onset of exocytosis. However, it has been shown earlier that the depolarization-induced secretion can be suppressed by inhibition of the oxidative phosphorylation, pointing to an energy-requiring step presumably located downstream of Ca2+ influx. Here, we have investigated the relation between oxidative phosphorylation and the insulinotropic effect of K+ depolarization to better localize the energy-requiring step. The specific inhibitor of the mitochondrial F1FO ATPase, oligomycin, concentration-dependently and time-dependently inhibited the insulin secretion elicited by a strong K+ depolarization (40 mm). Perifusion with 4 µg/mL of oligomycin for 20, 10, or 5 min prior to the K+ depolarization reduced the amount of insulin secreted from freshly isolated islets from control value to about 5% with a half-time of 1.6 min. 0.4 µg/mL of oligomycin required more time for comparable effects. Cultured islets were less susceptible to the inhibitory action of oligomycin than fresh islets, corresponding to their significantly higher ATP/ADP ratio. The perifusion with oligomycin prior to the K+ depolarization did not decrease the depolarization-elevated cytosolic Ca2+ concentration and did not affect the resting plasma membrane potential and the extent of depolarization by 40 mm KCl. In conclusion, the exocytotic machinery of the beta cell requires a continuously running oxidative phosphorylation to remain responsive to the Ca2+ signal for granule fusion.

Chronic psychological stress has been linked to renal disease and is also associated with the development of hypertension. However, the mechanisms by which chronic stress alters renal function and promotes hypertension is unclear. This study tested the hypothesis that chronic stress causes impaired renal mitochondrial function that can lead to increased arterial pressure. Adult male and female C57BL/6 mice were exposed to a chronic unpredictable stress (CUS), or non-stress control, protocol for 28 consecutive days. The protocol models mild, persistent, and variable stress that is a common occurrence in daily life. The CUS protocol induced anxiety relevant behaviors in both male and female mice. CUS increased blood pressure in both sexes, but the increase was greater in female mice. Renal mitochondrial function was unchanged by CUS in male mice. In contrast, renal mitochondrial function was impaired in the proestrus phase of the estrous cycle in female mice. Female mice exposed to CUS had low renal progesterone. Impaired mitochondrial function correlated with low renal progesterone, which correlated with increased blood pressure. Renal sex steroids were unchanged by CUS in males. Urinary albumin excretion was significantly increased in female mice exposed to CUS. CUS did not affect urinary albumin excretion in male mice exposed to CUS. These data show a direct role for CUS in causing an increase in blood pressure. The mechanisms causing increased pressure in CUS-exposed mice are sex-dependent, with low renal progesterone leading to impaired renal mitochondrial function as a potential mechanism underlying the elevated pressure in female mice.

This review emphasizes the importance of investigating the gut itself-beyond microbiota-centered studies in the context of hypertension. Since the initial discovery of the connection between gut microbiota and blood pressure regulation, research has increasingly focused on understanding the role of gut microbiota and exploring strategies to modify it for better blood pressure management. The intestine as an organ has received comparatively less attention. Yet, hypertension-associated intestinal pathological changes are well documented in both rodent models and human patients. Research to restore the intestinal function may serve as a valuable but unexplored therapeutic target. This underscores the need for a summary of our understanding of the gut's intrinsic physiological and pathological roles in hypertension. To address this, we structured our review to (1) revisit the physiological functions of the intestine; (2) describe the pathological changes that are associated with hypertension; (3) summarize available current studies targeting to restore intestinal function for blood pressure control; and (4) discuss knowledge gaps and future opportunities.

Pattern separation, the ability of a network to distinguish similar inputs by transforming them into distinct outputs, was postulated by the Marr-Albus theory to be realized by divergent feedforward excitatory connectivity. Yet, there is evidence for strong but differential regulation of pattern separation by local circuit connectivity. How do we reconcile the conflicting views on local-circuit regulation of pattern separation in circuits receiving divergent feedforward connectivity? Here, we quantitatively examined a population of heterogeneous dentate gyrus (DG) spiking networks where identically divergent feedforward connectivity was enforced. We generated 20 000 random DG networks constructed with thousands of functionally validated, heterogeneous single-neuron models of 4 different DG neuronal subtypes. We recorded network outputs to morphed sets of input patterns and applied quantitative metrics that we developed to assess pattern separation performance of each network. Surprisingly, only 47 of these 20 000 networks (0.23%) manifested effective pattern separation showing that divergent feedforward connectivity alone does not guarantee pattern separation. Instead, our analyses unveiled strong contributions from the 3 interneuron subtypes toward granule cell sparsity and pattern separation, with pronounced network-to-network variability in such contributions. We traced this variability to differences in local synaptic weights across pattern-separating networks, highlighting synaptic degeneracy as a key mechanism that explains diversity in interneuronal regulation of pattern separation. Finally, we found heterogeneous DG networks to be more resilient to synaptic jitter compared to their homogeneous counterparts. Together, our findings reconcile conflicting evidence by revealing degeneracy in DG circuits, whereby similar pattern separation efficacy can arise through diverse interactions among granule cells and interneurons.

The proper functioning of lymphatic valves is critical for unidirectional lymph transport. Valve development and maintenance depends on multiple genes in lymphatic endothelium, including those controlling the expression of 4 connexin (Cx) isoforms-Cx37, Cx47, Cx43, and Cx45. The relative importance of these isoforms for valve function is undefined, but primary human lymphedema is linked to loss-of-function mutations in Cx47 or Cx43, while deficiencies in Cx43 or Cx45 produce functional valve defects in mice. Tests of back leak and closure for single lymphatic valves from mice with selective deficiency of each Cx isoform revealed defects associated with the loss of Cx37 or Cx43, but not Cx47. Combined deletion of multiple isoforms, including Cx45 but not Cx47, produced even more severe valve defects in certain genotypes, sometimes with nearly complete regression of valves within 6 d. Back leak across connexin-deficient LVs correlated highly with gaps between the commissures formed by leaflet insertion into the vessel wall, indicating that connexin function may be critical for the formation and/or maintenance of leaflet commissures. Our results reveal the following hierarchy of Cx importance in valve function: Cx37 = Cx43 > Cx45 > Cx47 and predict that patients with loss of function mutations in Cx37 (GJA4) should develop lymphedema. We propose a general classification scheme describing 4 stages of progressive valve dysfunction.

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) exhibit cardiorenal protective effects that likely involve mechanisms aside from SGLT2 inhibition. Still, many details surrounding these clinically important pleiotropic effects remain unclear. We previously showed that several SGLT2-independent proximal tubular transport functions are inhibited by canagliflozin, but not empagliflozin. Here, we demonstrate a canagliflozin-specific reduction in Sgk1 abundance in both opossum kidney proximal tubule and mouse cortical collecting duct (mCCDcl1) cells, pointing to a possible underlying mechanism. Given the role of Sgk1 in the distal nephron, we hypothesized that canagliflozin would also inhibit epithelial Na+ channel (ENaC)-dependent Na+ transport. Canagliflozin inhibited ENaC-dependent Na+ transport (amiloride-sensitive short circuit current; ISC) in mCCDcl1 cells while empagliflozin had no effect. Selective membrane permeabilization revealed canagliflozin-induced inhibition of both apical conductance through ENaC and basolateral transport via the Na+/K+ ATPase. These effects were mimicked by the selective Sgk1 inhibitor, GSK650394. Surface labeling studies demonstrated reduced membrane localization of ENaC, but not Na+/K+ ATPase subunits, consistent with a mechanism involving Sgk1. Canagliflozin reduced ISC in the presence and absence of rotenone, suggesting inhibition occurs independently of effects on mitochondrial complex I, another known target of canagliflozin. ENaC activity in mouse distal colon was also inhibited by canagliflozin, confirming these effects in native tissue. We identify Na+ transport through ENaC and the Na+/K+ ATPase as novel targets of inhibition by canagliflozin, with Sgk1 as a likely upstream mechanistic component. Canagliflozin-specific effects on transport mediated via this mechanism may contribute to non-class effects of this drug observed clinically.

Abnormalities of Ca2+ signaling in the heart lead to common cardiac remodeling in the pathogenesis of cardiovascular disorders. The activation of calmodulin-dependent protein kinase II (CaMKII) is regulated by elevated intracellular Ca2+ level in cardiomyocytes, driving the progression of myocardial dysfunction. In this study, using models of β2 adrenergic receptor (β2AR) deficiency in cardiomyocytes (β2AR-CKO), we observed an increased phosphorylation of CaMKII and upregulation of gene expression and protein level of the fibrotic marker connective tissue growth factor (CTGF) in the myocytes. In vivo treatment with the CaMKII inhibitor KN93 attenuated the upregulation of CTGF protein expression in β2AR-CKO hearts. Enhanced L-type calcium channel (LTCC) current was observed in β2AR-CKO cardiomyocytes following adrenergic stimulation, indicating a disruption of Ca2+ signaling. Treatment with the LTCC blocker nifedipine attenuated CaMKII activity and the expression of CTGF in β2AR-CKO hearts, confirming the upstream role of abnormal LTCC-Ca2+ signaling. Additionally, 8-month-old β2AR-CKO mice exhibited cardiac fibrosis and diastolic dysfunction. One month of in vivo nifedipine treatment improved both cardiac dysfunction and fibrosis in β2AR-CKO mice. These findings highlight the critical role of cardiomyocyte β2AR in maintaining LTCC-Ca2+ homeostasis. Loss of β2AR amplifies the Ca2+-CaMKII axis, promoting fibrosis and cardiomyopathy in aging hearts.