Glomerular basement membrane
Laminin-521 is the major laminin expressed in the mature glomerular basement membrane (GBM). However, during glomerulogenesis there are developmental transitions in laminin trimer deposition. Initially the GBM contains laminin-111, laminin-411 and laminin-511. By the capillary loop stage during GMB maturation, laminin-111 is eliminated from the GBM and the beta 2 chain begins to accumulate while the beta 1 chain is down regulated (Miner et al., 1994; Miner et al., 1997; Miner et al., 1998). At maturity, only laminin-521 is detected in the GBM (Miner, 2012).
The a-5 chain laminins (laminin-521 and laminin-511) binds predominantly to the integrin α3β1 receptor on the basal surface of podocytes. The binding of laminin-521 and/or laminin-511 to this integrin is essential for the formation of the typical glomerular capillary loop structure. Lack of binding to the α3β1 receptor results in severe kidney glomerular defects during development (Kikkawa et al., 2003).
Mesangial cells produce laminin-421 and organize glomerular capillaries by binding the laminin α-5 via α3β1 integrin and Lutheran receptor (Kikkawa et al., 2003). Thus, mesangial cells are important for the development and reparation of microvasculature and glomerulogenesis in general (Abrass, 2010).