podocyte

Podocytes are terminally differentiated epithelial cells that line the outer aspect of the glomerular basement membrane (GBM), forming the visceral layer of Bowman's capsule. Their interdigitating foot processes (pedicels) create filtration slits bridged by slit diaphragms, composed of proteins like nephrin, podocin, and CD2AP, which are critical for size- and charge-selective filtration of plasma. Along with the fenestrated endothelium and GBM, podocytes form the three-layered glomerular filtration barrier.

Podocyte injury leads to 'foot process effacement' (flattening and fusion of foot processes), seen classically on electron microscopy in minimal change disease and as part of the pathology in focal segmental glomerulosclerosis (FSGS), membranous nephropathy, and diabetic nephropathy. This effacement results in loss of the filtration barrier's integrity, causing heavy proteinuria—hallmark of nephrotic syndrome (>3.5 g/day proteinuria, hypoalbuminemia, edema, hyperlipidemia).

Genetic mutations in podocyte proteins (e.g., NPHS1 encoding nephrin, NPHS2 encoding podocin) cause congenital nephrotic syndrome. Podocytes have limited regenerative capacity because they are terminally differentiated and largely unable to proliferate, which explains why podocyte loss (podocytopenia) correlates with progressive glomerulosclerosis and chronic kidney disease.

Clinically relevant diseases: Minimal change disease (podocyte effacement without immune complex deposition, respond to steroids), FSGS (segmental scarring with podocyte injury), diabetic nephropathy (podocyte loss due to hyperglycemia-induced injury, contributing to Kimmelstiel-Wilson nodules), and congenital nephrotic syndrome (Finnish type, NPHS1 mutation).