Complexities of the glomerular basement membrane

The glomerular basement membrane (GBM) is a key component of the glomerular capillary wall and is essential for kidney filtration. The major components of the GBM include laminins, type IV collagen, nidogens and heparan sulfate proteoglycans. In addition, the GBM harbours a number of other structural and regulatory components and provides a reservoir for growth factors. New technologies have improved our ability to study the composition and assembly of basement membranes. We now know that the GBM is a complex macromolecular structure that undergoes key transitions during glomerular development. Defects in GBM components are associated with a range of hereditary human diseases such as Alport syndrome, which is caused by defects in the genes COL4A3 , COL4A4 and COL4A5 , and Pierson syndrome, which is caused by variants in LAMB2 . In addition, the GBM is affected by acquired autoimmune disorders and metabolic diseases such as diabetes mellitus. Current treatments for diseases associated with GBM involvement aim to reduce intraglomerular pressure and to treat the underlying cause where possible. As our understanding about the maintenance and turnover of the GBM improves, therapies to replace GBM components or to stimulate GBM repair could translate into new therapies for patients with GBM-associated disease. The glomerular basement membrane (GBM) is essential for kidney filtration. This Review describes how studies of GBM composition and structure have provided insights into GBM assembly, its developmental transitions and its role in glomerular filtration. The authors also discuss GBM-associated diseases and current and potential future treatments for these disorders. Key points The glomerular basement membrane (GBM) is composed of many unique components that are likely to be important for appropriate GBM function. The application of new imaging and proteomics technologies is enabling greater insight into GBM organization in health and disease. The composition of the GBM changes during glomerulogenesis to permit proper development and filtration function. The GBM is a major contributor to the size selectivity of the glomerular filter. Causes of GBM-associated disease include primary genetic defects in basement membrane components and damage secondary to autoimmune and metabolic diseases, leading to abnormal synthesis and/or turnover of GBM proteins. Novel pharmacological and genome-editing approaches might facilitate basement membrane repair and treatment of G