Progressive Renal Disease: Fibroblasts, Extracellular Matrix, and Integrins

Abstract

Progressive renal disease is characterized by expansion of the tubulo-interstitium and accumulation of extracellular matrix within this tissue compartment. Interstitial fibroblasts are the primary producers of the interstitial matrix, and in the evolution of tubulo-interstitial fibrosis these cells undergo changes, namely increased proliferation, differentiation to myofibroblasts, and altered extracellular matrix metabolism, all of which, in other cell types, have been shown to be regulated by the major family of extracellular matrix receptors, the integrins. In the normal kidney, interstitial fibroblasts express α₁, α₄, α₅, and β₁ integrins, and fibrosis is associated with increased expression of α₁, α₂, α₅, α_v, and β₁ integrins. In particular, α₅, β₁, and α_v are suggested to be linked with the fibrotic process. In vitro, renal fibroblasts express a similar range of integrins, and ligation of selected receptors is associated with specific functions. Ligation of α₆ stimulates proliferation, while α₅ promotes expression of myofibroblastic phenotype, and β₁ integrin has been implicated in cell contraction. Recent studies suggest that renal fibroblasts also express the non-integrin matrix receptors, discoidin domain receptors, and that changes in activation of these receptors may be associated with fibrogenic events. Thus the current, albeit limited, data suggest an important role for receptors for extracellular matrix molecules in the pathogenesis of progressive renal fibrosis.