Differential targeting and signalling of voltage-gated T-type Cav 3.2 and L-type Cav 1.2 channels to ryanodine receptors in mesenteric arteries

Ion Channels Remodeling in the Regulation of Vascular Hyporesponsiveness During Shock

Shock is characterized with vascular hyporesponsiveness to vasoconstrictors, thereby to cause refractory hypotension, insufficient tissue perfusion, and multiple organ dysfunction. The vascular hyporeactivity persisted even though norepinephrine and fluid resuscitation were administrated, it is of critical importance to find new potential target. Ion channels are crucial in the regulation of cell membrane potential and affect vasoconstriction and vasodilation. It has been demonstrated that many types of ion channels including K+ channels, Ca2+ permeable channels, and Na+ channels exist in vascular smooth muscle cells and endothelial cells, contributing to the regulation of vascular homeostasis and vasomotor function. An increasing number of studies suggested that the structural and functional alterations of ion channels located in arteries contribute to vascular hyporesponsiveness during shock, but the underlying mechanisms remained to be fully clarified. Therefore, the expression and functional changes in ion channels in arteries associated with shock are reviewed, to pave the way for further exploring the potential of ion channel-targeted compounds in treating refractory hypotension in shock.

Senolytics prevent caveolar CaV 3.2-RyR axis malfunction in old vascular smooth muscle

Aging is a major risk factor for cardiovascular diseases. Our previous studies demonstrate that aging impairs the caveolar T-type CaV 3.2-RyR axis for extracellular Ca2+ influx to trigger Ca2+ sparks in vascular smooth muscle cells (VSMCs). We hypothesize that the administration of senolytics, which can selectively clear senescent cells, could preserve the caveolar CaV 3.2-RyR axis in aging VSMCs. In this study, 10-month-old mice were administered the senolytics cocktail consisting of dasatinib (5 mg/kg) and quercetin (50 mg/kg) or vehicle bi-weekly for 4 months. Using VSMCs from mouse mesenteric arteries, we found that Ca2+ sparks were diminished after caveolae disruption by methyl-β-cyclodextrin (10 mM) in cells from D + Q treated but not vehicle-treated 14-month-old mice. D + Q treatment promoted the expression of CaV 3.2 in 14-month-old mesenteric arteries. Structural analysis using electron tomography and immunofluorescence staining revealed the remodeling of caveolae and co-localization of CaV 3.2-Cav-1 in D + Q treatment aged mesenteric arteries. In keeping with theoretical observations, Cav 3.2 channel inhibition by Ni2+ (50 μM) suppressed Ca2+ in VSMCs from the D + Q group, with no effect observed in vehicle-treated arteries. Our study provides evidence that age-related caveolar CaV 3.2-RyR axis malfunction can be alleviated by pharmaceutical intervention targeting cellular senescence. Our findings support the potential of senolytics for ameliorating age-associated cardiovascular disease.

An inactivating human TRPC6 channel mutation without focal segmental glomerulosclerosis

Transient receptor potential cation channel-6 (TRPC6) gene mutations cause familial focal segmental glomerulosclerosis (FSGS), which is inherited as an autosomal dominant disease. In patients with TRPC6-related FSGS, all mutations map to the N- or C-terminal TRPC6 protein domains. Thus far, the majority of TRPC6 mutations are missense resulting in increased or decreased calcium influx; however, the fundamental molecular mechanisms causing cell injury and kidney pathology are unclear. We report a novel heterozygous TRPC6 mutation (V691Kfs*) in a large kindred with no signs of FSGS despite a largely truncated TRPC6 protein. We studied the molecular effects of V691Kfs* TRPC6 mutant using the tridimensional cryo-EM structure of the tetrameric TRPC6 protein. The results indicated that V691 is localized at the pore-forming transmembrane region affecting the ion conduction pathway, and predicted that V691Kfs* causes closure of the ion-conducting pathway leading to channel inactivation. We assessed the impact of V691Kfs* and two previously reported TRPC6 disease mutants (P112Q and G757D) on calcium influx in cells. Our data show that the V691Kfs* fully inactivated the TRCP6 channel-specific calcium influx consistent with a complete loss-of-function phenotype. Furthermore, the V691Kfs* truncation exerted a dominant negative effect on the full-length TRPC6 proteins. In conclusion, the V691Kfs* non-functional truncated TRPC6 is not sufficient to cause FSGS. Our data corroborate recently characterized TRPC6 loss-of-function and gain-of-function mutants suggesting that one defective TRPC6 gene copy is not sufficient to cause FSGS. We underscore the importance of increased rather than reduced calcium influx through TRPC6 for podocyte cell death.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Arterial myogenic response and aging

The arterial myogenic response is an inherent property of resistance arteries. Myogenic tone is crucial for maintaining a relatively constant blood flow in response to changes in intraluminal pressure and protects delicate organs from excessive blood flow. Although this fundamental physiological phenomenon has been extensively studied, the underlying molecular mechanisms are largely unknown. Recent studies identified a crucial role of mechano-activated angiotensin II type 1 receptors (AT1R) in this process. The development of myogenic response is affected by aging. In this review, we summarize recent progress made to understand the role of AT1R and other mechanosensors in the control of arterial myogenic response. We discuss age-related alterations in myogenic response and possible underlying mechanisms and implications for healthy aging.

Deletion of Notch3 Impairs Contractility of Renal Resistance Vessels Due to Deficient Ca2+ Entry

Notch3 plays an important role in the differentiation and development of vascular smooth muscle cells. Mice lacking Notch3 show deficient renal autoregulation. The aim of the study was to investigate the mechanisms involved in the Notch3-mediated control of renal vascular response. To this end, renal resistance vessels (afferent arterioles) were isolated from Notch3^-/- and wild-type littermates (WT) and stimulated with angiotensin II (ANG II). Contractions and intracellular Ca²⁺ concentrations were blunted in Notch3^-/- vessels. ANG II responses in precapillary muscle arterioles were similar between the WT and Notch3^-/- mice, suggesting a focal action of Notch3 in renal vasculature. Abolishing stored Ca²⁺ with thapsigargin reduced Ca²⁺ responses in the renal vessels of the two strains, signifying intact intracellular Ca²⁺ mobilization in Notch3^-/-. EGTA (Ca²⁺ chelating agent), nifedipine (L-type channel-blocker), or mibefradil (T-type channel-blocker) strongly reduced contraction and Ca²⁺ responses in WT mice but had no effect in Notch3^-/- mice, indicating defective Ca²⁺ entry. Notch3^-/- vessels responded normally to KCl-induced depolarization, which activates L-type channels directly. Differential transcriptomic analysis showed a major down-regulation of Cacna1h gene expression, coding for the α_1H subunit of the T-type Ca²⁺ channel, in Notch3^-/- vessels. In conclusion, renal resistance vessels from Notch3^-/- mice display altered vascular reactivity to ANG II due to deficient Ca²⁺-entry. Consequently, Notch3 is essential for proper excitation-contraction coupling and vascular-tone regulation in the kidney.

Evidence for a Physiological Role of T-Type Ca Channels in Ventricular Cardiomyocytes of Adult Mice

T-type Ca channels are strongly expressed and important in the developing heart. In the adult heart, these channels play a significant role in pacemaker tissues, but there is uncertainty about their presence and physiological relevance in the working myocardium. Here, we show that the T-type Ca channel isoforms Cav3.1 and Cav3.2 are expressed at a protein level in ventricular cardiomyocytes from healthy adult C57/BL6 mice. Myocytes isolated from adult wild-type and Cav3.2 KO mice showed considerable whole cell T-type Ca currents under beta-adrenergic stimulation with isoprenaline. We further show that the detectability of basal T-type Ca currents in murine wild-type cardiomyocytes depends on the applied experimental conditions. Together, these findings reveal the presence of functional T-type Ca channels in the membrane of ventricular myocytes. In addition, electrically evoked Ca release from the sarcoplasmic reticulum was significantly impaired in Cav3.2 KO compared to wild-type cardiomyocytes. Our work implies a physiological role of T-type Ca channels in the healthy adult murine ventricular working myocardium.

Aldosterone-Induced Sarco/Endoplasmic Reticulum Ca2+ Pump Upregulation Counterbalances Cav1.2-Mediated Ca2+ Influx in Mesenteric Arteries

In mesenteric arteries (MAs), aldosterone (ALDO) binds to the endogenous mineralocorticoid receptor (MR) and increases the expression of the voltage-gated L-type Ca_v1.2 channel, an essential ion channel for vascular contraction, sarcoplasmic reticulum (SR) Ca²⁺ store refilling, and Ca²⁺ spark generation. In mesenteric artery smooth muscle cells (MASMCs), Ca²⁺ influx through Ca_v1.2 is the indirect mechanism for triggering Ca²⁺ sparks. This process is facilitated by plasma membrane-sarcoplasmic reticulum (PM-SR) nanojunctions that drive Ca²⁺ from the extracellular space into the SR via Sarco/Endoplasmic Reticulum Ca²⁺ (SERCA) pump. Ca²⁺ sparks produced by clusters of Ryanodine receptors (RyRs) at PM-SR nanodomains, decrease contractility by activating large-conductance Ca²⁺-activated K⁺ channels (BK_Ca channels), which generate spontaneous transient outward currents (STOCs). Altogether, Ca_v1.2, SERCA pump, RyRs, and BK_Ca channels work as a functional unit at the PM-SR nanodomain, regulating intracellular Ca²⁺ and vascular function. However, the effect of the ALDO/MR signaling pathway on this functional unit has not been completely explored. Our results show that short-term exposure to ALDO (10 nM, 24 h) increased the expression of Ca_v1.2 in rat MAs. The depolarization-induced Ca²⁺ entry increased SR Ca²⁺ load, and the frequencies of both Ca²⁺ sparks and STOCs, while [Ca²⁺]_cyt and vasoconstriction remained unaltered in Aldo-treated MAs. ALDO treatment significantly increased the mRNA and protein expression levels of the SERCA pump, which counterbalanced the augmented Ca_v1.2-mediated Ca²⁺ influx at the PM-SR nanodomain, increasing SR Ca²⁺ content, Ca²⁺ spark and STOC frequencies, and opposing to hyperpolarization-induced vasoconstriction while enhancing Acetylcholine-mediated vasorelaxation. This work provides novel evidence for short-term ALDO-induced upregulation of the functional unit comprising Ca_v1.2, SERCA2 pump, RyRs, and BK_Ca channels; in which the SERCA pump buffers ALDO-induced upregulation of Ca²⁺ entry at the superficial SR-PM nanodomain of MASMCs, preventing ALDO-triggered depolarization-induced vasoconstriction and enhancing vasodilation. Pathological conditions that lead to SERCA pump downregulation, for instance, chronic exposure to ALDO, might favor the development of ALDO/MR-mediated augmented vasoconstriction of mesenteric arteries.

Involvement of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) in mPRα (PAQR7)-mediated progesterone induction of vascular smooth muscle relaxation

Progesterone acts directly on vascular smooth muscle cells (VSMCs) through activation of membrane progesterone receptor α (mPRα)-dependent signaling to rapidly decrease cytosolic Ca²⁺ concentrations and induce muscle relaxation. However, it is not known whether this progesterone action involves uptake of Ca²⁺ by the sarco/endoplasmic reticulum (SR) and increased sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) activity. The present results show that treatment of cultured human VSMCs with progesterone and the selective mPR agonist Org OD-02-0 (OD 02-0) but not with the nuclear PR agonist R5020 increased SERCA protein expression, which was blocked by knockdown of mPRα with siRNA. Moreover, treatments with progesterone and OD 02-0, but not with R5020, increased phospholamban (PLB) phosphorylation, which would result in disinhibition of SERCA function. Progesterone and OD 02-0 significantly increased Ca²⁺ levels in the SR and caused VSMC relaxation. These effects were blocked by pretreatment with cyclopiazonic acid (CPA), a SERCA inhibitor, and by knockdown of SERCA2 with siRNA, suggesting that SERCA2 plays a critical role in progesterone induction of VSMC relaxation. Treatment with inhibitors of inhibitory G proteins (Gi, NF023), MAP kinase (AZD 6244), Akt/Pi3k (wortmannin), and a Rho activator (calpeptin) blocked the progesterone- and OD 02-0-induced increase in Ca²⁺ levels in the SR and SERCA expressions. These results suggest that the rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.NEW & NOTEWORTHY The rapid effects of progesterone on cytosolic Ca²⁺ levels and relaxation of VSMCs through mPRα involve regulation of the functions of SERCA2 and PLB through Gi, MAP kinase, and Akt signaling pathways and downregulation of RhoA activity.

The mechanism of ions in pulmonary hypertension

Pulmonary hypertension（PH）is a kind of hemodynamic and pathophysiological state, in which the pulmonary artery pressure (PAP) rises above a certain threshold. The main pathological manifestation is pulmonary vasoconstriction and remodelling progressively. More and more studies have found that ions play a major role in the pathogenesis of PH. Many vasoactive substances, inflammatory mediators, transcription-inducing factors, apoptosis mediators, redox substances and translation modifiers can control the concentration of ions inside and outside the cell by regulating the activity of ion channels, which can regulate vascular contraction, cell proliferation, migration, apoptosis, inflammation and other functions. We all know that there are no effective drugs to treat PH. Ions are involved in the occurrence and development of PH, so it is necessary to clarify the mechanism of ions in PH as a therapeutic target for PH. The main ions involved in PH are calcium ion (Ca2+), potassium ion (K+), sodium ion (Na+) and chloride ion (Cl-). Here, we mainly discuss the distribution of these ions and their channels in pulmonary arteries and their role in the pathogenesis of PH.

Aging, calcium channel signaling and vascular tone

Calcium signaling in vascular smooth muscle is crucial for arterial tone regulation and vascular function. Several proteins, including Ca²⁺ channels, function in an orchestrated fashion so that blood vessels can sense and respond to physiological stimuli such as changes in intravascular pressure. Activation of the voltage-dependent Ca²⁺ channel, Cav1.2, leads to Ca²⁺ influx and consequently arterial tone development and vasoconstriction. Unique among Ca²⁺ channels, the vascular Cav3.2 T-type channel mediates feedback inhibition of arterial tone-and therefore causes vasodilation-of resistance arteries by virtue of functional association with hyperpolarizing ion channels. During aging, several signaling modalities are altered along with vascular remodeling. There is a growing appreciation of how calcium channel signaling alters with aging and how this may affect vascular function. Here, we discuss key determinants of arterial tone development and the crucial involvement of Ca²⁺ channels. We next provide an updated view of key changes in Ca²⁺ channel expression and function during aging and how these affect vascular function. Further, this article synthesizes new questions in light of recent developments. We hope that these questions will outline a roadmap for new research, which, undoubtedly, will unravel a more comprehensive picture of arterial tone dysfunction during aging.

Elementary calcium signaling in arterial smooth muscle

Vascular smooth muscle cells (VSMCs) of small peripheral arteries contribute to blood pressure control by adapting their contractile state. These adaptations depend on the VSMC cytosolic Ca²⁺ concentration, regulated by complex local elementary Ca²⁺ signaling pathways. Ca²⁺ sparks represent local, transient, rapid calcium release events from a cluster of ryanodine receptors (RyRs) in the sarcoplasmic reticulum. In arterial SMCs, Ca²⁺ sparks activate nearby calcium-dependent potassium channels, cause membrane hyperpolarization and thus decrease the global intracellular [Ca²⁺] to oppose vasoconstriction. Arterial SMC Ca_v1.2 L-type channels regulate intracellular calcium stores content, which in turn modulates calcium efflux through RyRs. Ca_v3.2 T-type channels contribute to a minor extend to Ca²⁺ spark generation in certain types of arteries. Their localization within cell membrane caveolae is essential. We summarize present data on local elementary calcium signaling (Ca²⁺ sparks) in arterial SMCs with focus on RyR isoforms, large-conductance calcium-dependent potassium (BK_Ca) channels, and cell membrane-bound calcium channels (Ca_v1.2 and Ca_v3.2), particularly in caveolar microdomains.

Age attenuates the T-type CaV 3.2-RyR axis in vascular smooth muscle

Caveolae position Ca_V3.2 (T‐type Ca²⁺ channel encoded by the α‐3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca²⁺ influx to trigger Ca²⁺ sparks and large‐conductance Ca²⁺‐activated K⁺ channel feedback in vascular smooth muscle. We hypothesize that this mechanism of Ca²⁺ spark generation is affected by age. Using smooth muscle cells (VSMCs) from mouse mesenteric arteries, we found that both Ca_v3.2 channel inhibition by Ni²⁺ (50 µM) and caveolae disruption by methyl‐ß‐cyclodextrin or genetic abolition of Eps15 homology domain‐containing protein (EHD2) inhibited Ca²⁺ sparks in cells from young (4 months) but not old (12 months) mice. In accordance, expression of Ca_v3.2 channel was higher in mesenteric arteries from young than old mice. Similar effects were observed for caveolae density. Using SMAKO Ca_v1.2^−/− mice, caffeine (RyR activator) and thapsigargin (Ca²⁺ transport ATPase inhibitor), we found that sufficient SR Ca²⁺ load is a prerequisite for the Ca_V3.2‐RyR axis to generate Ca²⁺ sparks. We identified a fraction of Ca²⁺ sparks in aged VSMCs, which is sensitive to the TRP channel blocker Gd³⁺ (100 µM), but insensitive to Ca_V1.2 and Ca_V3.2 channel blockade. Our data demonstrate that the VSMC Ca_V3.2‐RyR axis is down‐regulated by aging. This defective Ca_V3.2‐RyR coupling is counterbalanced by a Gd³⁺ sensitive Ca²⁺ pathway providing compensatory Ca²⁺ influx for triggering Ca²⁺ sparks in aged VSMCs.

Pathophysiological Role of Caveolae in Hypertension

Caveolae, flask-shaped cholesterol-, and glycosphingolipid-rich membrane microdomains, contain caveolin 1, 2, 3 and several structural proteins, in particular Cavin 1-4, EHD2, pacsin2, and dynamin 2. Caveolae participate in several physiological processes like lipid uptake, mechanosensitivity, or signaling events and are involved in pathophysiological changes in the cardiovascular system. They serve as a specific membrane platform for a diverse set of signaling molecules like endothelial nitric oxide synthase (eNOS), and further maintain vascular homeostasis. Lack of caveolins causes the complete loss of caveolae; induces vascular disorders, endothelial dysfunction, and impaired myogenic tone; and alters numerous cellular processes, which all contribute to an increased risk for hypertension. This brief review describes our current knowledge on caveolae in vasculature, with special focus on their pathophysiological role in hypertension.