Intracellular Ca2+ regulating proteins in vascular smooth muscle cells are altered with type 1 diabetes due to the direct effects of hyperglycemia

Abstract

BackgroundDiminished calcium (Ca2+) transients in response to physiological agonists have been reported in vascular smooth muscle cells (VSMCs) from diabetic animals. However, the mechanism responsible was unclear.Methodology/Principal FindingsVSMCs from autoimmune type 1 Diabetes Resistant Bio-Breeding (DR-BB) rats and streptozotocin-induced rats were examined for levels and distribution of inositol trisphosphate receptors (IP3R) and the SR Ca2+ pumps (SERCA 2 and 3). Generally, a decrease in IP3R levels and dramatic increase in ryanodine receptor (RyR) levels were noted in the aortic samples from diabetic animals. Redistribution of the specific IP3R subtypes was dependent on the rat model. SERCA 2 was redistributed to a peri-nuclear pattern that was more prominent in the DR-BB diabetic rat aorta than the STZ diabetic rat. The free intracellular Ca2+ in freshly dispersed VSMCs from control and diabetic animals was monitored using ratiometric Ca2+ sensitive fluorophores viewed by confocal microscopy. In control VSMCs, basal fluorescence levels were significantly higher in the nucleus relative to the cytoplasm, while in diabetic VSMCs they were essentially the same. Vasopressin induced a predictable increase in free intracellular Ca2+ in the VSMCs from control rats with a prolonged and significantly blunted response in the diabetic VSMCs. A slow rise in free intracellular Ca2+ in response to thapsigargin, a specific blocker of SERCA was seen in the control VSMCs but was significantly delayed and prolonged in cells from diabetic rats. To determine whether the changes were due to the direct effects of hyperglycemica, experiments were repeated using cultured rat aortic smooth muscle cells (A7r5) grown in hyperglycemic and control conditions. In general, they demonstrated the same changes in protein levels and distribution as well as the blunted Ca2+ responses to vasopressin and thapsigargin as noted in the cells from diabetic animals.Conclusions/SignificanceThis work demonstrates that the previously-reported reduced Ca2+ signaling in VSMCs from diabetic animals is related to decreases and/or redistribution in the IP3R Ca2+ channels and SERCA proteins. These changes can be duplicated in culture with high glucose levels.

Contribution of Different Mechanisms to Pancreatic Beta-cell Hyper-secretion in Non-obese Diabetic (NOD) Mice during Pre-diabetes

“…We also find that beta-cells from db/db mice also exhibit significant reductions in both SERCA2 and SERCA3 expression (data not shown). Moreover, SERCA function is also impaired in diabetic cardiomyocytes (39), skeletal muscle (40), smooth muscle cells (41), platelets (42), and neurons (43). Therefore, we propose that down-regulation of the SERCA pump is a hallmark of prediabetic stage.…”

Endoplasmic-Reticulum Calcium Depletion and Disease

“…Sp1 and YY1, transcription factors controlling SPCA1 transcription (Kawada et al 2005), become more active in high glucose (Han and Kudlow 1997). The expression of IP 3 R and RyR decreases Searls et al 2010).…”

“…Insulin also inhibits SERCA via enhanced nitrotyrosine formation (Kobayashi et al 2007). SERCA2 is also redistributed to a peri-nuclear pattern (Searls et al 2010). The subsequently decreased [Ca 2þ ] ER stimulates plasma-membrane Ca 2þ influx and induces migration of the smooth-muscle cell, which contributes to neointimal hyperplasia and atherosclerosis (Tong et al 2008).…”

The Exercise-Induced Improvement in hyperglycemia is Mediated by DHT Produced in the Skeletal Muscle of Zucker Diabetic Fatty Rats

“…The inhibitor (2 mg/kg) was dissolved into sesame oil and 200 μl was loaded into the pump. Then, the pump was inserted subcutaneously, and the skin closed with wound clips [18]. To avoid the effect of acute exercise, forty eight hours after the last exercise session [15], blood was taken from the tail vein to assess fasting glucose levels, and the soleus and gastrocnemius muscles were quickly removed, weighed, rinsed in ice-cold saline, and frozen in liquid nitrogen.…”