Increased phosphorylation of focal adhesion kinase in diabetic rat kidney glomeruli

Abstract

Altered extracellular matrix production by the glomerular mesangium is a feature of diabetes mellitus. Matrix proteins, including fibronectin, via interaction with cell-surface receptors (the integrins) may activate intracellular pathways such as prostaglandin production, shown previously to be stimulated by addition of fibronectin to glomerular cores. However, the signalling pathways involved are unclear. An intracellular tyrosine kinase (focal adhesion kinase), associated with focal adhesions, is known to be phosphorylated after interaction with matrix proteins. We now show for the first time, in glomeruli from diabetic rats, that focal adhesion kinase has increased phosphorylation on tyrosine, when compared with non-diabetic control rats. This phosphorylation was labile and disappeared with extended time of sample preparation or digestion of glomeruli to glomerular cores. Cultured mesangial cells, from non-diabetic rats, plated onto fibronectin also showed increased tyrosine phosphorylation of focal adhesion kinase accompanied by a twofold increase in prostaglandin production. However, it may not be possible to replicate fully the diabetic ¿state¿ in vitro merely by use of raised glucose concentrations, as these conditions (for 3 weeks) resulted in decreased focal adhesion kinase phosphorylation, despite increased fibronectin and prostaglandin levels. A role for increased focal adhesion kinase phosphorylation in kidney glomeruli isolated from diabetic rats, and any linkage to intracellular signalling pathways remains to be determined.

FAK contributes to proteinuria in hypercholesterolaemic rats and modulates podocyte F‐actin re‐organization via activating p38 in response to ox‐LDL

“…Focal adhesion kinase is a 125-kD non-receptor protein-tyrosine kinase and has been implicated in diverse cellular events involving cell motility and proliferation via its auto-phosphorylation at tyrosine 397, which thereby triggers the phosphorylation of other tyrosine residues and initiates downstream signals such as paxillin and PI3K [8,9]. Focal adhesion kinase hyper-phosphorylation was found in several glomerular diseases such as lupus nephritis and anti-GBM disease [10,11]. Sustained activation of FAK was also involved in ox-LDL-stimulated impairment of mouse macrophage migration in vitro [12].…”

“…Hyper-phosphorylation of FAK was found in glomerular diseases such as lupus nephritis and anti-glomerular basement membrane (anti-GBM) disease [9,10]. In diabetic rats, boosted tyrosine phosphorylation of FAK was present in renal glomeruli, with unchanged total FAK expression and unregulated integrin b1 expression [11]. Notably, CD36-dependent sustained activation of FAK was revealed in ox-LDL-stimulated mouse macrophages in vitro, suggesting that FAK was a potential participant in lipid metabolism [12].…”