Transforming growth factor-β regulation of proteoglycan synthesis in vascular smooth muscle: Contribution to lipid binding and accelerated atherosclerosis in diabetes

Atherosclerosis is accelerated in the setting of diabetes, but the factors driving this phenomenon remain elusive. Hyperglycemia leads to elevated levels of transforming growth factor (TGF)-beta and TGF-beta has been implicated as a factor in atherosclerosis. Given the established association between hyperglycemia and elevated TGF-beta, it is plausible that elevated TGF-beta levels in diabetes play a pathogenic role in the development of accelerated atherosclerosis. TGF-beta is a potent regulator of extracellular matrix synthesis, including many actions on proteoglycan synthesis that lead to increased binding to low-density lipoprotein and therefore potentially increased lipid retention in the vessel wall and accelerated atherosclerosis. TGF-beta signals through the canonical TGF-beta receptor I-mediated phosphorylation of Smad transcription factors and TGF-beta signaling is also known to involve, positively and negatively, interactions with the mitogen-activated protein kinase pathways. The focus of the present review is on the effects of TGF-beta on proteoglycan synthesis in vascular smooth muscle and particularly the signaling pathways through which TGF-beta exerts its effects, because those pathways may be therapeutic targets for the prevention of pathological modifications in the proteoglycan component of the vessel wall in the vascular diseases of diabetes.