Macrophages contribute to the development of renal fibrosis following ischaemia/reperfusion-induced acute kidney injury

Background. Ischaemia/reperfusion is a major cause of acute kidney injury and can result in poor long-term graft function. Although most of the patients with acute kidney injury recover their renal function, significant portion of patients suffer from progressive deterioration of renal function. A persistent inflammatory response might be associated with long-term changes following acute ischaemia/reperfusion. Macrophages are known to infiltrate into tubulointersitium in animal models of chronic kidney disease. However, the role of macrophages in long-term changes after ischaemia/reperfusion remains unknown. We aimed to investigate the role of macrophages on the development of tubulointerstitial fibrosis and functional impairment following acute ischaemia/reperfusion injury by depleting macrophages with liposome clodronate. Methods. Male Sprague-Dawley rats underwent right nephrectomy and clamping of left renal vascular pedicle or sham operation. Liposome clodronate or phosphate buffered saline was administered for 8 weeks. Biochemical and histological renal damage and gene expression of various cytokines were assessed at 4 and 8 weeks after ischaemia/reperfusion. Results. Ischaemic/reperfusion injury resulted in persistent inflammation and tubulointerstital fibrosis with decreased creatinine clearance and increased urinary albumin excretion at 4 and 8 weeks. Macrophage depletion attenuated those changes. This beneficial effect was accompanied with a decrease in gene expression of inflammatory and profibrotic cytokines. Conclusions. These results suggest that macrophages play an important role in mediating persistent inflammation and fibrosis after ischaemia/reperfusion leading to a development of chronic kidney disease. Strategies targeting macrophage infiltration or activation can be useful in the prevention of development of chronic kidney disease following ischaemic injury.