Abstract
Focal segmental glomerulosclerosis (FSGS) is a common cause of proteinuria and nephrotic syndrome leading to end stage renal disease (ESRD). There are two types of FSGS, primary (idiopathic) and secondary forms. Secondary FSGS shows less severe clinical features compared to those of the primary one. However, secondary FSGS has an important clinical significance because a variety of renal diseases progress to ESRD thorough the form of secondary FSGS. The defining feature of FSGS is proteinuria. The key event of FSGS is podocyte injury which is caused by multiple factors. Unanswered questions about how these factors act on podocytes to cause secondary FSGS are various and ill-defined. In this review, we provide brief overview and new insights into FSGS, podocyte injury, and their potential linkage suggesting clues to answer for treatment of the disease.
Highlights
Focal segmental glomerulosclerosis (FSGS) is considered as a group of clinicopathological syndromes sharing a common histologic lesion characterized by focal and segmental scarring in glomerulus
A novel concept and the essential steps of glomerulosclerosis were suggested as follows: (1) increased glomerular capillary pressure and filtration flow through podocyte slits, (2) foot process effacement as an adaptive response, (3) podocyte hypertrophy and glomerulomegaly, (4) mismatch between glomerular tuft growth and podocyte hypertrophy, (5) stretching and attenuation of podocyte cell body, (6) pseudocysts formation by hindered flow of filtrates beneath the podocyte that is partially detached on bare areas of glomerular basement membrane (GBM), (7) complete podocyte detachment by enlarged pseudocysts and adhesion to Bowman’s capsule, (8) glomerular tuft’s adhesion to Bowman’s capsule, (9) spreading of filtrates to interstitium out of nephron through adhesion structure, and (10) interstitial proliferation and nephron degeneration [15, 28,29,30]
Secondary FSGS is not a specific disease but a state representing podocyte injury which is mediated by diverse causes including mechanical and/or nonmechanical stresses and genetic mutations
Summary
Focal segmental glomerulosclerosis (FSGS) is considered as a group of clinicopathological syndromes sharing a common histologic lesion characterized by focal and segmental scarring in glomerulus. A variety of factors could cause FSGS, the common pathogenic mechanism is podocyte injury. FSGS and a related disorder, minimal change disease, are so called “podocytopathy” [1] whose primary pathologic feature is effacement of the podocyte foot processes. There are two types of FSGS, primary (idiopathic) and secondary forms. Primary FSGS is a representative disorder presenting nephrotic syndrome and is a major type of primary glomerulonephritis [4] and accounts for 4% of end stage renal disease (ESRD) in the United States [5]. Understanding about secondary FSGS provides clue to how podocyte and glomerulus adapt to renal injury and survive. We review the pathogenic mechanisms underlying secondary FSGS focused on the podocyte injury causing foot process effacement and glomerulosclerosis
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