Aberrant localization of β1 integrin in podocyte cytoplasm of primary FSGS with cellular lesion

Podocyte detachment is a major trigger in pathogenesis of focal segmental glomerulosclerosis (FSGS). Detachment via β1 integrin (ITGB1) endocytosis, associated with endothelial cell injury, has been reported in animal models but remains unknown in human kidneys. The objectives of our study were to examine the difference in ITGB1 dynamics between primary FSGS and minimal change nephrotic syndrome (MCNS), among variants of FSGS, as well as between the presence or absence of cellular lesions (CEL-L) in human kidneys, and to elucidate the pathogenesis of FSGS. Thirty-one patients with primary FSGS and 14 with MCNS were recruited. FSGS cases were categorized into two groups: those with CEL-L, defined by segmental endocapillary hypercellularity occluding lumina, and those without CEL-L. The podocyte cytoplasmic ITGB1 levels, ITGB1 expression, and degrees of podocyte detachment and subendothelial widening were compared between FSGS and MCNS, FSGS variants, and FSGS groups with and without CEL-L (CEL-L( +)/CEL-L( -)). ITGB1 distribution in podocyte cytoplasm was significantly greater in CEL-L( +) group than that in MCNS and CEL-L( -) groups. ITGB1 expression was similar in CEL-L( +) and MCNS, but lower in CEL-L( -) compared with others. Podocyte detachment levels were comparable in CEL-L( +) and CEL-L( -) groups, both exhibiting significantly higher detachment than the MCNS group. Subendothelial widening was significantly greater in CEL-L( +) compared with CEL-L( -) and MCNS groups. The findings of this study imply the existence of distinct pathological mechanisms associated with ITGB1 dynamics between CEL-L( +) and CEL-L( -) groups, and suggest a potential role of endothelial cell injury in the pathogenesis of cellular lesions in FSGS.