Glucose fluctuations promote vascular BK channels dysfunction via PKCα/NF-κB/MuRF1 signaling

Abstract

Glucose fluctuations may contribute to large conductance calcium activated potassium (BK) channel dysfunction. However, the underlying mechanisms remain elusive. The aim of this study was to investigate the molecular mechanisms involved in BK channel dysfunction as a result of glucose fluctuations. A rat diabetic model was established through the injection of streptozotocin. Glucose fluctuations in diabetic rats were induced via consumption and starvation. Rat coronary arteries were isolated and coronary vascular tensions were measured after three weeks. Rat coronary artery smooth muscle cells were isolated and whole-cell BK channel currents were recorded using a patch clamp technique. Human coronary artery smooth muscle cells in vitro were used to explore the underlying mechanisms. After incubation with iberiotoxin (IBTX), the Δ tensions (% Max) of rat coronary arteries in the controlled diabetes mellitus (C-DM), the uncontrolled DM (U-DM) and the DM with glucose fluctuation (GF-DM) groups were found to be 84.46 ± 5.75, 61.89 ± 10.20 and 14.77 ± 5.90, respectively (P < .05), while the current densities of the BK channels in the three groups were 43.09 ± 4.35 pA/ pF, 34.23 ± 6.07 pA/pF and 17.87 ± 4.33 pA/pF, respectively (P < .05). The Δ tensions (% Max) of rat coronary arteries after applying IBTX in the GF-DM rats injected with 0.9% sodium chloride (NaCl) (GF-DM + NaCl) and the GF-DM rats injected with N-acetyl-L-cysteine (NAC) (GF-DM + NAC) groups were found to be 8.86 ± 1.09 and 48.90 ± 10.85, respectively (P < .05). Excessive oxidative stress and the activation of protein kinase C (PKC) α and nuclear factor (NF)-κB induced by glucose fluctuations promoted the decrease of BK-β1 expression, while the inhibition of reactive oxygen species (ROS), PKCα, NF-κB and muscle ring finger protein 1 (MuRF1) reversed this effect. Glucose fluctuations aggravate BK channel dysfunction via the ROS overproduction and the PKCα/NF-κB/MuRF1 signaling pathway. The BK-β1 subunit, encoded by the KCNMB1 gene, can alter the

Neonatal Diabetes in Patients Affected by Liang-Wang Syndrome Carrying KCNMA1 Variant p.(Gly375Arg) Suggest a Potential Role of Ca2+ and Voltage-Activated K+ Channel Activity in Human Insulin Secretion

“…Regarding diabetes, several studies have reported a diminished BKC-mediated vasodilation in coronary micro-vascularization of diabetic patients [18][19][20][21], probably resulting from harmful effects of blood glucose fluctuations leading to overproduction of reactive oxygen species (ROS) and alteration of the protein kinase C α/nuclear factor -κB/muscle ring fingers protein 1 signaling pathway [22] and the consequent ubiquitin-mediated degradation of the channel β1 subunit by the ubiquitin-proteasome system [18]. Unfortunately, the studies on the relationships between BKC inactivation and insulin secretion are very few and mainly performed in cellular and animal models by using channel blockers with different specificity, such as peptide toxins, the alkaloid paxilline and tetraethylammonium [23].…”

Glucose Variability: How Does It Work?

“…The IHG-stimulated activation of NF-κB in cultured HUVECs down-regulated the expression of bcl-2, an antiapoptotic protein [176]. In vascular cells, glucose fluctuations promote the dysfunction of large-conductance, calcium-activated potassium channels via the overproduction of ROS and activation of PKCα/NF-κB/MuRF1 signaling [177]. ROS-mediated NF-κB activation under high-GV conditions up-regulates the receptor for AGEs in podocytes [22].…”

Coronary Large Conductance Ca2+-Activated K+ Channel Dysfunction in Diabetes Mellitus

“…Ca 2+ -activated K + channel currents (I) are determined by the number of activated channels (N), open probability (Po), and channel unitary conductance ( i ), where I=N * Po * i . BK channel current density is reduced in the coronary arteries of T1DM and T2DM animal models and in humans with DM ( Lu et al, 2005 , 2008 , 2010 , 2012 , 2016 , 2017a , 2019 ; Pietryga et al, 2005 ; Burnham et al, 2006 ; McGahon et al, 2007 ; Dong et al, 2008 ; Zhang et al, 2010a ; Nystoriak et al, 2014 ; Yi et al, 2014 ; Li et al, 2017 ; Nieves-Cintron et al, 2017 ; Tang et al, 2017 ; Zhang et al, 2020 ). BK channels are activated by intracellular free Ca 2+ concentration and by membrane depolarization ( Cox et al, 1997 ; Lu et al, 2008 ), and these are impaired in DM ( Lu et al, 2008 , 2019 ).…”

“…Binding of Ang II to AT1R in vascular SMCs activates Gαq which in turn activates the phospholipase C (PLC)-dependent inositol-1,4,5-triphosphate (IP 3 )/diacylglycerol (DAG)-mediated Ca 2+ signaling cascades, causing an increase in protein kinase C (PKC) activity ( De Gasparo et al, 2000 ; Touyz and Schiffrin, 2000 ). Activation of PKCβ stimulates NOXs with ROS overproduction under hyperglycemic conditions ( Inoguchi et al, 2000 ; Evcimen and King, 2007 ) and is a cause of impaired vascular BK channel function in diabetic vessels ( Figure 3 ; Zhou et al, 2006 ; Lu et al, 2012 ; Zhang et al, 2020 ). In addition to redox-mediated modification of BK-α, it has been shown that PKC-induced serine phosphorylation at 695 (S695) and 1151 (S1151) in the C-terminus of BK-α inhibits BK channel current density by 50%, and S1151 phosphorylation by PKC also abolishes BK-α activation by protein kinase A (PKA) and protein kinase G (PKG; Zhou et al, 2001 , 2010 ).…”

“…We found that the N-terminus of BK-β1 and the coiled-coil region of MuRF1 are necessary for BK-β1 and MuRF1 interaction ( Yi et al, 2014 ). Importantly, the protein expressions of FBXO-9, FBXO-32, and MuRF1 are unregulated in the arteries of STZ-induced T1DM animals and in primary human coronary arterial SMCs cultured with high glucose ( Zhang et al, 2010a , 2020 ; Lu et al, 2012 ; Yi et al, 2014 ). Such upregulation of FBXO expression is mediated through the suppression of PI3K/AKT-dependent phosphorylation in FOXO-3a, thereby promoting FOXO-3a nuclear translocation and binding to the consensus sequence [GTAAA(C/T)A] in the promoter of Fbxo gene, activating its transcription ( Furuyama et al, 2000 ).…”