TGFB1 and obesity due to melanocortin 4 receptor deficiency: Among the obesity, upregulation of transforming growth factor-β1 (TGF-β1) in the kidney is induced by elevated leptin levels, promoting extracellular matrix accumulation, which leads to glomerular and tubular basement membrane thickening, glomerulosclerosis, and tubulointerstitial fibrosis (21).