HSPG2

Perlecan is a massive heparan sulfate proteoglycan (468 kDa, 4391 amino acids) that functions as a critical structural organizer and signaling hub of basement membranes throughout the body. The protein contains five structurally distinct domains that enable diverse functions through interactions with extracellular matrix components (laminin, type IV collagen, nidogens, fibrillin-1) and cell surface receptors. Heparan sulfate chains attached primarily to domain I (at serines 65, 71, 76) and domain V create high negative charge density essential for basement membrane hydration and charge-based filtration, particularly in the glomerular basement membrane. These heparan sulfate chains sequester and present growth factors (FGF-2, FGF-18, VEGF, BMP, PDGF) to their cognate receptors, forming ternary complexes that activate downstream signaling cascades regulating cell proliferation, differentiation, and angiogenesis. Domain III binds FGF-18 and PDGF through its core protein. Perlecan plays essential roles in growth plate development and endochondral ossification by modulating FGF receptor signaling and enabling vascular invasion required for bone formation. At neuromuscular junctions, perlecan localizes acetylcholinesterase and maintains synaptic stability. Proteolytic cleavage by cathepsin L and BMP1-tolloid metalloproteinases generates endorepellin (domain V fragment) and LG3 peptide, which exhibit anti-angiogenic activity opposing the pro-angiogenic function of full-length perlecan through dual antagonism of VEGFR2 and α2β1 integrin. Loss-of-function mutations cause dyssegmental dysplasia (Silverman-Handmaker type, typically perinatally lethal), while hypomorphic mutations cause Schwartz-Jampel syndrome characterized by chondrodysplasia and myotonia.

Disorders

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