Targeting autophagy in autoimmune glomerular diseases

Abstract

Autophagy is a natural process whereby damaged or dying parts of a cell are eliminated and recycled. The term autophagy usually refers to macroautophagy, which is one of three types of autophagy, alongside microautophagy and chaperone-mediated autophagy. Autophagy is activated by adenosine monophosphate-activated protein kinase (AMPK) and inhibited by mammalian target of rapamycin (mTOR) through their interference with Unc-51-like kinase 1 (ULK1). Dysregulated autophagy is deeply involved in autoimmune glomerular diseases. Upregulated autophagy can induce inflammation and activate innate and adaptive immunity. However, autophagy may also exert a protective role on podocytes, enhance endothelial cell function, and preserve proximal tubular epithelial cells during ischemic or endotoxic acute kidney injury (AKI). Hydroxychloroquine (HCQ) can downregulate increased autophagy and is widely used in lupus nephritis. HCQ causes alkalinization, which results in vacuolization of lysosomes and inhibition of their functions. By inhibiting autophagic activity, HCQ may reduce inflammation and innate immunity, inhibit the activation of T cells, restore the T helper 17/T regulator balance, restrict the production of pro-inflammatory cytokines, and modulate co-stimulatory molecules. This reduces the risk of flares, spares the dosage of glucocorticoids, improves lupus activity, and prevents the thrombotic effects of anti-phospholipid antibodies. Recent studies showed that HCQ can also reduce proteinuria in IgA nephropathy (IgAN) and membranous nephropathy (MN). Drugs that improve mitochondrial function or enhance autophagy, such as metformin, sodium-glucose co-transporter 2 (SGLT2) inhibitors or mTOR inhibitors, may exert protective effects on podocytes and reduce proteinuria in MN or focal segmental glomerulosclerosis (FSGS).

Keywords: Autophagy; Glomerulonephritis; Hydroxychloroquine; Lupus nephritis; Podocyte.