Role of mesenchymal stem cells in proteinuric nephropathy

Abstract

Proteinuria has been recognized as a common feature in many forms of chronic kidney disease (CKD). As traditional medications for proteinuric nephropathy, such as blockade of the renin-angiotensin system (RAS), has only achieved limited clinical success, more effective renoprotective strategies need to be explored. Bone marrow-derived mesenchymal stem/stromal cells (BM-MSCs) have recently shown promise as a therapeutic tool in acute kidney injury (AKI) models. The therapeutic potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) in proteinuric nephropathy models is unknown.

Using a co-culture model of human proximal tubular epithelial cells (PTECs) and BM-MSCs, I first examined the potential effect of BM-MSCs in albumin-induced pro-inflammatory response and epithelial-to-mesenchymal transition (EMT) in PTECs. The unstimulated BM-MSCs exerted moderate suppressive effect on tubular inflammation as only albumin-induced CCL-2 and CCL-5 expression was attenuated in PTECs. When concomitantly stimulated by albumin excess, however, BM-MSCs remarkably suppressed albumin-induced tubular IL-6, IL-8, TNF-α, CCL-2, and CCL-5 expression, suggesting albumin overloaded milieu to be a prerequisite for them to fully exhibit their anti-inflammatory effects. This effect was mediated via deactivation of tubular NF-κB signaling as BM-MSCs prevented the overexpression of p-IκB and nuclear translocation of NF-κB. In addition, albumin-induced tubular EMT, as shown by the loss of E-cadherin and induction of α-SMA, FN-1 and collagen IV in PTECs, was also prevented by BM-MSC co-culture.

To dissect the mechanism of action, I next explored the paracrine factors secreted by BM-MSCs under an albumin-overloaded condition and studied their contribution to the protective effect on tubular inflammation and EMT. Albumin-overloaded BM-MSCs per se overexpressed 34 paracrine factors, of which hepatocyte growth factor (HGF) and TNFα-stimulating gene (TSG)-6 were regulated by P38 and NF-κB signaling. These paracrine factors suppressed both the proinflammatory and profibrotic phenotypes in albumin-induced PTECs. Neutralizing HGF and TSG-6 abolished the anti-inflammatory and anti-EMT effects of BM-MSC co-culture in albumin-induced PTECs, respectively.

Finally, in albumin-overloaded mice, a well established murine model reminiscent of human CKD, treatment with mouse BM-MSCs markedly reduced BUN, tubular CCL-2 and CCL-5 expression, interstitial macrophage, α-SMA and collagen IV accumulation independent of changes in proteinuria, together with upregulated renal cortical expression of HGF. Exogenous BM-MSCs were detected in their kidneys by PKH-26 staining. Collectively, these in vitro and in vivo data suggest a modulatory effect of BM-MSCs on albumin-induced tubular inflammation and fibrosis and underscore a therapeutic potential of BM-MSCs for CKD in the future.