Evidence for telomerase activation in VSMCs exposed to hyperglycemic and hyperhomocysteinemic conditions

While diabetes and homocysteinemia have been demonstrated to be independent risk factors for progression of vascular disease, the activation of telomerase has not been linked to the potent effects of high levels of homocysteine (Hcy) and glucose on vascular smooth muscle cells (VSMC). We examined the proliferative response of VSMCs, resulting from hyperglycemia and hyperhomocysteinemia and their effects on telomerase activity.

Primary cultures of VSMC from human aorta and arteries were used in this experiment from 3rd -5th passages. Hcy or/and glucose were added to the cell culture media in doses equivalent to plasma levels of Hcy in patients with moderate, high homocysteinemia, or physiologically high concentrations of glucose as seen in diabetics. The modified telomeric repeat amplification protocol was used for telomerase activity assay. Cytotoxicity, viability, proliferation, protein phosphorylation, were determined in cultures treated and not treated with Hcy and glucose.

The mitogenic effect of Hcy and glucose on VSMC, independently and together, was observed at 48 hours after treatment. The viable cell numbers were significantly increased at doses comparable to plasma levels of Hcy in hyperhomocysteinemia, as compared to untreated cultures (p < 0.01). Cells exposed to high levels of glucose also exhibited an increased proliferation response (p = 0.01). Telomerase activity was detected in all sets of VSMC cultures exposed to high levels of glucose or/and Hcy (p < 0.01). However, a significant difference was not observed in telomerase activity, when high Hcy or high glucose was used alone or in concert. Significant dual phosphorylation of p38 MAPK was observed in treated cultures but it did not correlate with the telomerase activity detected.

These data establish a link with telomerase activation and the mitogenic effect of hyperhomocysteinemia and hyperglycemia.