Mechanisms of Vascular CaV1.2 Channel Regulation During Diabetic Hyperglycemia

FXR contributes to obstructive jaundice-induced vascular hyporeactivity in mesenteric arteries by reconstituting BKCa channels

OBJECTIVE

Vascular hyporeactivity increases with the incidence of obstructive jaundice (OJ). Evidence suggests that OJ activates the farnesoid X receptor (FXR) as well as the large-conductance Ca2+-activated K+ (BKCa or MaxiK) channel. This study was designed to explore the role of the FXR in vascular hyporesponsiveness induced by cholestasis.

METHODS

The OJ model rats were constructed by bile duct ligation (BDL) and treated with an FXR agonist or antagonist. Vasoconstriction of the mesenteric arteries (MAs) was assessed in vitro. Whole-cell patch clamp recordings were used to investigate BKCa channel function. Real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot were used to detect mRNA and protein levels.

RESULTS

A significant increase in vascular tone and responsiveness to norepinephrine (NE) was observed after the MaxiK channel blocker (IbTX) was administered. This effect was pronounced in BDL animals and can be mimicked by the FXR agonist GW4064 and inhibited by the FXR antagonist Z-guggulsterone (Z-Gu). GW4064 has a similar effect as cholestasis in promoting MaxiK currents in isolated arterial smooth muscle cells (ASMCs), while Z-Gu blunted this effect. The mRNA and protein expression of FXR and MaxiK-β1, but not MaxiK-α, were significantly increased in the BDL group in comparison to the sham. Furthermore, activation or inhibition of FXR promoted or inhibited the mRNA and protein expression of the MaxiK-β1 subunit, respectively.

CONCLUSION

Activation of FXR enhances the capability of the MaxiK channel to regulate vascular tone and leads to vascular hyporesponsiveness in the MAs of BDL rats, which may be mediated by the nonparallel upregulation of MaxiK-α and MaxiK-β1 subunit expression.

Extracellular glucose and dysfunctional insulin receptor signaling independently upregulate arterial smooth muscle TMEM16A expression

Diabetes alters the function of ion channels responsible for regulating arterial smooth muscle membrane potential, resulting in vasoconstriction. Our prior research demonstrated an elevation of TMEM16A in diabetic arteries. Here, we explored the mechanisms involved in Transmembrane protein 16A (TMEM16A) gene expression. Our data indicate that a Snail-mediated repressor complex regulates arterial TMEM16A gene transcription. Snail expression was reduced in diabetic arteries while TMEM16A expression was upregulated. The TMEM16A promoter contained three canonical E-box sites. Electrophoretic mobility and super shift assays revealed that the -154 nt E-box was the binding site of the Snail repressor complex and binding of the repressor complex decreased in diabetic arteries. High glucose induced a biphasic contractile response in pressurized nondiabetic mouse hindlimb arteries incubated ex vivo. Hindlimb arteries incubated in high glucose also showed decreased phospho-protein kinase D1 and TMEM16A expression. In hindlimb arteries from nondiabetic mice, administration of a bolus dose of glucose activated protein kinase D1 signaling to induce Snail degradation. In both in vivo and ex vivo conditions, Snail expression exhibited an inverse relationship with the expression of protein kinase D1 and TMEM16A. In diabetic mouse arteries, phospho-protein kinase D1 increased while Akt2 and pGSK3β levels declined. These results indicate that in nondiabetic mice, high glucose triggers a transient deactivation of the Snail repressor complex to increase arterial TMEM16A expression independently of insulin signaling. Conversely, insulin resistance activates GSK3β signaling and enhances arterial TMEM16A channel expression. These data have uncovered the Snail-mediated regulation of arterial TMEM16A expression and its dysfunction during diabetes.NEW & NOTEWORTHY The calcium-activated chloride channel, TMEM16A, is upregulated in the diabetic vasculature to cause increased vasoconstriction. In this paper, we have uncovered that the TMEM16A gene expression is controlled by a Snail-mediated repressor complex that uncouples with both insulin-dependent and -independent pathways to allow for upregulated arterial protein expression thereby causing vasoconstriction. The paper highlights the effect of short- and long-term glucose-induced dysfunction of an ion channel expression as a causative factor in diabetic vascular disease.

The mitochondrial regulation of smooth muscle cell proliferation in type 2 diabetes

Background

Type 2 diabetes (T2D) is associated with a strongly increased risk for restenosis after angioplasty driven by proliferation of vascular smooth muscle cells (VSMCs). Here, we sought to determine whether and how mitochondrial dysfunction in T2D drives VSMC proliferation with a focus on ROS and intracellular [Ca 2+ ] that both drive cell proliferation, occur in T2D and are regulated by mitochondrial activity.

Methods

Using a diet-induced mouse model of T2D, the inhibition of the mitochondrial Ca 2+ /calmodulin-dependent kinase II (mtCaMKII), a regulator of Ca 2+ entry via the mitochondrial Ca 2+ uniporter selectively in VSMCs, we performed in vivo phenotyping after mechanical injury and established the mechanisms of excessive proliferation in cultured VSMCs.

Results

In T2D, the inhibition of mtCaMKII reduced both neointima formation after mechanical injury and the proliferation of cultured VSMCs. VSMCs from T2D mice displayed accelerated proliferation, reduced mitochondrial Ca 2+ entry and membrane potential with elevated baseline [Ca 2+ ] cyto compared to cells from normoglycemic mice. Accelerated proliferation after PDGF treatment was driven by activation of Erk1/2 and its upstream regulators. Hyperactivation of Erk1/2 was Ca 2+ -dependent rather than mitochondrial ROS-driven Ca 2+ -dependent and included the activation of CaMKII in the cytosol. The inhibition of mtCaMKII exaggerated the Ca 2+ imbalance by lowering mitochondrial Ca 2+ entry and increasing baseline [Ca 2+ ] cyto , further enhancing baseline Erk1/2 activation. With inhibition of mtCaMKII, PDGF treatment had no additional effect on cell proliferation. Inhibition of activated CaMKII in the cytosol decreased excessive Erk1/2 activation and reduced VSMC proliferation.

Conclusions

Collectively, our results provide evidence for the molecular mechanisms of enhanced VSMC proliferation after mechanical injury by mitochondrial Ca 2+ entry in T2D.