K _Ca 3.1 upregulation preserves endothelium‐dependent vasorelaxation during aging and oxidative stress

Abstract

SummaryEndothelial oxidative stress develops with aging and reactive oxygen species impair endothelium‐dependent relaxation (EDR) by decreasing nitric oxide (NO) availability. Endothelial KCa3.1, which contributes to EDR, is upregulated by H2O2. We investigated whether KCa3.1 upregulation compensates for diminished EDR to NO during aging‐related oxidative stress. Previous studies identified that the levels of ceramide synthase 5 (CerS5), sphingosine, and sphingosine 1‐phosphate were increased in aged wild‐type and CerS2 mice. In primary mouse aortic endothelial cells (MAECs) from aged wild‐type and CerS2 null mice, superoxide dismutase (SOD) was upregulated, and catalase and glutathione peroxidase 1 (GPX1) were downregulated, when compared to MAECs from young and age‐matched wild‐type mice. Increased H2O2 levels induced Fyn and extracellular signal‐regulated kinases (ERKs) phosphorylation and KCa3.1 upregulation. Catalase/GPX1 double knockout (catalase−/−/GPX1−/−) upregulated KCa3.1 in MAECs. NO production was decreased in aged wild‐type, CerS2 null, and catalase−/−/GPX1−/− MAECs. However, KCa3.1 activation‐induced, NG‐nitro‐l‐arginine‐, and indomethacin‐resistant EDR was increased without a change in acetylcholine‐induced EDR in aortic rings from aged wild‐type, CerS2 null, and catalase−/−/GPX1−/− mice. CerS5 transfection or exogenous application of sphingosine or sphingosine 1‐phosphate induced similar changes in levels of the antioxidant enzymes and upregulated KCa3.1. Our findings suggest that, during aging‐related oxidative stress, SOD upregulation and downregulation of catalase and GPX1, which occur upon altering the sphingolipid composition or acyl chain length, generate H2O2 and thereby upregulate KCa3.1 expression and function via a H2O2/Fyn‐mediated pathway. Altogether, enhanced KCa3.1 activity may compensate for decreased NO signaling during vascular aging.

Calcium and electrical signaling in arterial endothelial tubes: New insights into cellular physiology and cardiovascular function

“…In old age and chronic disease, oxidative signaling increases via superoxide (O 2 •− ) production from a variety of intracellular sources (NADPH oxidases, mitochondria, uncoupled nitric oxide synthase, and xanthine oxidase) which inactivates nitric oxide to peroxynitrite (75, 77). Via superoxide dismutase, O 2 •− is rapidly converted to the relatively stable intermediate H 2 O 2 [spontaneous breakdown product: hydroxyl radical (OH • )] (74, 78) which increases SK Ca /IK Ca (primarily IK Ca ) channel function (71, 128). While upregulation of SK Ca /IK Ca channel function may be viewed as a compensatory mechanism for sustaining local vasodilation (67), this may be at the expense of a restricted spatial domain of the spread of hyperpolarization and vasodilation via appreciable loss of charge via “leaky” endothelial plasma membranes (3, 50, 71).…”

“…75,[125][126][127][128] In comparison with findings for actions of NO, how aging and conditions of high risk during old age (eg diabetes, hypertension) impact EDH through SK Ca /IK Ca channel activation is less clear. Some studies indicate a loss of endothelial SK Ca /IK Ca -dependent vasodilation, [129][130][131][132][133] whereas others have found an enhancement in SK Ca /IK Ca channel function of intact vessels 128,[134][135][136][137][138][139] and isolated endothelial tubes. 71 This discrepancy in conclusions can be attributed to differences in spe- The presence of SMCs presents activity of high conductance BK Ca channels which may mask analysis of the more modest conductance of SK Ca /IK Ca channels in ECs.…”

“…[15][16][17]131 At least in skeletal muscle feed arteries, the underlying components 74,78 which increases SK Ca /IK Ca (primarily IK Ca ) channel function. 71,128 While upregulation of SK Ca /IK Ca channel function may be viewed as a compensatory mechanism for sustaining local vasodilation, 67 this may be at the expense of a restricted spatial domain of the spread of hyperpolarization and vasodilation via appreciable loss of charge via "leaky" endothelial plasma membranes 3,50,71 for gender should be incorporated as male animals have comprised the majority of studies performed thus far (≥80%), 155,156 whereby females (~50% of the population) have been effectively neglected. Altogether, the integration of oxidative, Ca 2+ , and electrical signaling during aging and cardiovascular disease remains a strong avenue of research to be elucidated and employed for therapeutic interventions.…”

“…In particular, conducted vasodilation in response to ACh (120) and ascending vasodilation in response to skeletal muscle contraction (48, 122, 124) are reduced in old mice in comparison to animals 3 to 4 months of age (“young”). It is well known that NO bioavailability decreases in old age and that molecules of oxidative signaling [e.g., hydrogen peroxide (H 2 O 2 )] may play a compensatory role for maintaining vasodilation and tissue perfusion (75, 125-128). …”

“…Some studies indicate a loss of endothelial SK Ca /IK Ca channel-dependent vasodilation (129-133), whereas others have found an enhancement in SK Ca /IK Ca channel function of intact vessels (128, 134-139) and isolated endothelial tubes (71). This discrepancy in conclusions can be attributed to differences in species of experimental animals (e.g., mouse vs. rat), vascular type [(regional differences: e.g., skeletal muscle vs. gut) & (size: aorta & large arteries vs. feed arteries & arterioles)], assigned definitions of “aged” or “old” animals (< 2 > years of age) and/or extent of severity in vascular pathology.…”