In vitro silencing of the insulin receptor attenuates cellular accumulation of fibronectin in renal mesangial cells

InsR silencing induced a unique phenotype of reduced fibronectin (FN) accumulation in renal glomerular MCs. Transcription level of FN was not significantly changed in the InsR silenced cells, suggesting the phenotype switching was caused by post-transcriptional modification. The decreased expression of InsR was associated with enhanced activity of insulin-like growth factor-1 receptor (IGF-1R)/PI3K/Akt signaling pathway which contributed in part to the attenuation of cellular FN accumulation. Formation of IGF-1R homodimer was increased in the InsR silenced cells. The InsR silenced cells also showed increased sensitivity to exogenous IGF-1, and increased PI3K activity was reversed significantly by incubating cells with IGF-1R specific antagonist, AG538. PI3K/Akt dependent activation of cAMP responsive element-binding protein (CREB)-1 induced expression of matrix metalloproteinase (MMP)-9 and suppressing MMP activity by doxycycline partially reversed FN accumulation in the InsR silenced cells.The effects of InsR silencing on cellular FN accumulation in vitro are, at least partially, mediated by increased degradation of FN by MMPs which is induced by enhanced signaling sequence of IGF-1R/PI3K/Akt/CREB-1.One of the common local pathologic changes of glomerulonephropathy is accumulation of extracellular matrix (ECM) components, including fibronectin (FN), which results in glomerulosclerosis. Although the mechanisms responsible for the ECM protein deposition are still inconclusive, the role of renal glomerular mesangial cells (MCs) in this sclerotic change has been gathering increasing attentions. Glomerular mesangium is an area which shows the most prominent ECM accumulations in diseased kidney. And the resulting glomerular fibrosis has been recognized as the major degenerative event in glomerulonephropathies regardless of their etiologies [1-3]. MCs are specialized pericytes located among the mesangium area within the renal corpuscle of the kidney [4]. ECM protein depos