SPARC and the kidney glomerulus: Matricellular proteins exhibit diverse functions under normal and pathological conditions

In the last decade, numerous studies have emphasized the important function s that matricellular proteins subserve during angiogenesis, wound healing, and the maintenance of organ and tissue integrity. Matricellular proteins a re defined as a group of secreted regulatory macromolecules that are not st ructural components of the extracellular matrix (ECM) but rather mediate in teractions between the ECM and cells. One of these matricellular proteins, termed SPARC (secreted protein acidic and rich in cysteine), is produced du ring the produced during the process of wound healing and is prominent in s everal types of injury. An excessive deposition of glomerular matrix and an elevated proliferation of certain glomerular cells characterize a variety of kidney diseases. The proliferation of these cells is associated typicall y with the remodeling process that occurs after kidney injury, and is, at l east in part, modulated by the altered expression of ECM, various growth fa ctors, and the elevated production of matricellular proteins (e.g. SPARC). The secretion of one or more of the matricellular proteins can lead to expa nsion of the glomerular basement membrane, infiltration of immunocompetent cells, and, in some cases, to a reversal of the pathological condition. How ever, these proteins can lead to expansion of the glomerular basement membr ane, infiltration of immunocompetent cells, and, in some cases. to a revers al of the pathological condition. However, these proteins can also contribu te collectively to renal fibrosis, glomerulosclerosis, glomerulonephritis, and the eventual loss of renal function. The purpose of this review is to e valuate the multiple functions of SPARC in the kidney glomerulus under norm al and pathological conditions.