Impact of AMP-activated protein kinase a1 deficiency on tissue injury following unilateral ureteral obstruction

Abstract

Background AMP-activated protein kinase (Ampk) is a sensor of the cellular energy status and a powerful regulator of metabolism. Activation of Ampk was previously shown to participate in monocyte-to-fibroblast transition and matrix protein production in renal tissue. Thus, the present study explored whether the catalytic Ampka1 isoform participates in the regulation of the renal fibrotic response following unilateral ureteral obstruction (UUO). Methods UUO was induced in gene-targeted mice lacking functional Ampka1 (Ampka1 -/-) and in corresponding wild-type mice (Ampka1 +/+). In the obstructed kidney and, for comparison, in the non-obstructed control kidney, quantitative RT-PCR, Western blotting and immunostaining were employed to determine transcript levels and protein abundance, respectively. Results In Ampka1 +/+ mice, UUO significantly up-regulated the protein abundance of the Ampka1 isoform, but significantly down-regulated the Ampka2 isoform in renal tissue. Phosphorylated Ampka protein levels were significantly increased in obstructed kidney tissue of Ampka1 +/+ mice but not of Ampka1 -/- mice. Renal expression of a-smooth muscle actin was increased following UUO, an effect again less pronounced in Ampka1 -/- mice than in Ampka1 +/+ mice. Histological analysis did not reveal a profound effect of Ampka1 deficiency on collagen 1 protein deposition. UUO significantly increased phosphorylated and total Tgfβ- activated kinase 1 (Tak1) protein, as well as transcript levels of Tak1-downstream targets c-Fos, Il6, Pai1 and Snai1 in Ampka1 +/+ mice, effects again significantly ameliorated in Ampka1 -/- mice. Moreover, Ampka1 deficiency inhibited the UUO-induced mRNA expression of Cd206, a marker of M2 macrophages and of Cxcl16, a pro-fibrotic chemokine associated with myeloid fibroblast formation. The effects of Ampka1 deficiency during UUO were, however, paralleled by increased tubular injury and apoptosis. Conclusions Renal obstruction induces an isoform shift from Ampka2 towards Ampka1, which contributes to the signaling involved in cell survival and fibrosis. Copyright: