PP2A contributes to endothelial death in high glucose: inhibition by benfotiamine

Abstract

Endothelial death is critical in diabetic vascular diseases, but regulating factors have been only partially elucidated. Phosphatases play important regulatory roles in cell metabolism, but have not previously been implicated in hyperglycemia-induced cell death. We investigated the role of the phosphatase, type 2A protein phosphatase (PP2A), in hyperglycemia-induced changes in signaling and death in bovine aortic endothelial cells (BAEC). We explored also the influence of benfotiamine on this phosphatase. Activation of PP2A was assessed in BAEC by the extent of methylation and measurement of activity, and the enzyme was inhibited using selective pharmacological (okadaic acid, sodium fostriecin) and molecular (small interfering RNA) approaches. BAECs cultured in 30 mM glucose significantly increased PP2A methylation and activity, and PP2A inhibitors blocked these abnormalities. PP2A activity was increased also in aorta and retina from diabetic rats. NF-κB activity and cell death in BAEC were significantly increased in 30 mM glucose and inhibited by PP2A inhibition. NF-κB played a role in the hyperglycemia-induced death of BAEC, since blocking its translocation with SN50 also inhibited cell death. Inhibition of PP2A blocked the hyperglycemia-induced dephosphorylation of NF-κB and Bad, thus favoring cell survival. Incubation of benfotiamine with BAEC inhibited the high glucose-induced activation of PP2A and NF-κB and cell death, as well as several other metabolic defects, which likewise were inhibited by inhibitors of PP2A. Activation of PP2A contributes to endothelial cell death in high glucose, and beneficial actions of benfotiamine are due, at least in part, to inhibition of PP2A activation.

Endothelial Cell Autophagy Maintains Shear Stress–Induced Nitric Oxide Generation via Glycolysis-Dependent Purinergic Signaling to Endothelial Nitric Oxide Synthase

“…13–17 Vascular protein phosphatase 2A (PP2A) activity is increased in pathologies associated with suppressed p-eNOS S1177 and compromised endothelial function. 16, 18–20 We observed no evidence that shear stress altered PP2A activation in the absence or presence of Atg3 siRNA.…”

Retinoic acid protects cardiomyocytes from high glucose‐induced apoptosis through inhibition of NF‐κB signaling Pathway

“…Previous studies have shown that PP2A, a family of phosphoserine-and phosphothreonine-specific enzymes, is involved in regulation of the dephosphorylation of IKK and IkBa (Miskolci et al, 2003;Witt et al, 2009). Although previous studies have shown that PP2A is activated by HG in endothelial cells and pancreatic beta-cells (Ravnskjaer et al, 2006;Du et al, 2010), our results showed that PP2A activity was significantly suppressed by HG in cardiomyocytes, as demonstrated by sustained tyrosine phosphorylation of PP2Ac following HG exposure, suggesting that the regulation of PP2A activation by HG may be cell type specific. Inhibition of PP2A activation by okadaic acid, or silencing the expression of PP2Ac in cardiomyocytes, further enhanced HG-induced sustained phosphorylation of IKK/IkBa and subsequent degradation of IkBa.…”

Molecular and Cellular Mechanisms of Cardiovascular Disorders in Diabetes

“…Activation of transketolase by the lipid-soluble thiamine derivative benfotiamine inhibits three of the major hyperglycemia-driven pathways implicated in the pathogenesis of vascular diabetic vascular damage (the DAG-protein kinase C (PKC) pathway, the methylglyoxal-advanced glycation end product (AGE) formation pathway, and the hexosamine pathway) and inhibits hyperglycemia-induced NFκB activation 77 . Transketolase activation by benfotiamine also prevented high glucose-induced arterial endothelial cell death 78 , improved diastolic and systolic function, prevented left ventricular end-diastolic pressure increase and chamber dilatation, improved cardiac perfusion, and reduced cardiomyocyte apoptosis and interstitial fibrosis 79 .…”