Background:
Vascular BK channel, composed of the large conductance Ca
2+
-activated K
+
channel αsubunit and the large conductance Ca
2+
-activated K
+
channel β1 subunits, is a key determinant of coronary vasorelaxation and its function is impaired in diabetic vessels. However, our knowledge of diabetic BK channel dysregulation is incomplete. The Sorbin homology and Sorbs2 (SH3 [Src homology 3] domain-containing protein 2) are ubiquitously expressed in arteries, but its role in vascular pathophysiology is unknown.
Methods:
The role of Sorbs2 in regulating vascular BK channel activity was determined using patch-clamp recordings, molecular biological techniques, and in silico analysis.
Results:
Sorbs2 is not only a cytoskeletal protein but also an RNA-binding protein that binds to BK channel proteins and the
Kcnma1
(encoding the large conductance Ca
2+
-activated K
+
channel αsubunit) mRNA, regulating BK channel expression and function in coronary smooth muscle cells. Molecular biological studies reveal that the SH3 domain of Sorbs2 is necessary for Sorbs2 interaction with the large conductance Ca
2+
-activated K
+
channel αsubunit, while both the SH3 and Sorbin homology domains of Sorbs2 interact with the large conductance Ca
2+
-activated K
+
channel β1 subunit. Deletion of the SH3 or Sorbin homology domains abolishes the Sorbs2 effect on the large conductance Ca
2+
-activated K
+
channel αsubunit/the large conductance Ca
2+
-activated K
+
channel β1 subunit current density. Additionally,
Sorbs2
is a target gene of the Nrf2 (nuclear factor erythroid-2-related factor 2), which binds to the promoter of
Sorbs2
and regulates Sorbs2 expression in coronary smooth muscle cells. In vivo studies demonstrate that
Sorbs2
knockout mice at 4 months of age display a significant decrease in BK channel expression and function, accompanied by impaired BK channel Ca
2+
-sensitivity and BK channel-mediated vasodilation in coronary arteries, without altering their body weights and blood glucose levels. Importantly, Sorbs2 expression is significantly downregulated in the coronary arteries of db/db type 2 diabetic mice.
Conclusions:
Sorbs2, a downstream target of Nrf2, plays an important role in regulating BK channel expression and function in vascular smooth muscle cells. Vascular Sorbs2 is downregulated in diabetes. Genetic knockout of
Sorbs2
manifests coronary BK channelopathy and vasculopathy observed in diabetic mice, independent of obesity and glucotoxicity.