Blockage of the lysosome-dependent autophagic pathway contributes to complement membrane attack complex-induced podocyte injury in idiopathic membranous nephropathy

Abstract

Dysregulation of autophagy-mediated podocyte homeostasis is proposed to play a role in idiopathic membranous nephropathy (IMN). In the present study, autophagic activity and lysosomal alterations were investigated in podocytes of IMN patients and in cultured podocytes exposed to sublytic terminal complement complex, C5b-9. C5b-9 upregulated the number of LC3 positive puncta and the expression of p62 in patient podocytes and in C5b-9 injuried podocyte model. The lysosomal turnover of LC3-II was not influenced, although the BECN1 expression level was upregulated after exposure of podocytes to C5b-9. C5b-9 also caused a significant increase in the number of autophagosomes but not autolysosomes, suggesting that C5b-9 impairs the lysosomal degration of autophagosomes. Moreover, C5b-9 exacerbated the apoptosis of podocytes, which could be mimicked by chloroquine treatment, indicating that C5b-9 triggered podocyte injury, at least partially through inhibiting autophagy. Subsequent studies revealed that C5b-9 triggered lysosomal membrane permeabilization, which likely caused the decrease in enzymatic activity, defective acidification of lysosomes, and suppression of DQ-ovalbumin degradation. Taken together, our results suggest that the lysosomal-dependent autophagic pathway is blocked by C5b-9, which may play a key role in podocyte injury during the development of IMN.

Autophagy markers LC3 and p62 accumulate in immune‐mediated necrotizing myopathy

“…In this scenario, autoimmune attack could primarily produce autophagy dysfunction, as suggested in our IMNM samples by C5b‐9 deposits in degenerating myofibers, in which there is also a diffuse accumulation of LC3b. Complement membrane attack complex has been demonstrated to inhibit autophagy and lysosomal degradation, increasing the damage to cultured podocytes in an idiopathic membranous nephropathy model and in human disease . Impaired autophagy may also entail the accumulation of damaged mitochondria, as seen in all 3 anti‐HMGCR + IMNM patients, being an additional death trigger.…”

Advances of the experimental models of idiopathic membranous nephropathy (Review)

“…Some researchers used zymosan to assemble c5b-9 complement complexes, which were developed to interfere with mouse serum to obtain ZaS. Subsequently, ZaS was applied to stimulate podocytes to develop the Mn model in vitro (69)(70)(71) (Fig. 3).…”

Podocyte Lysosome Dysfunction in Chronic Glomerular Diseases

“…Intracellular destruction of endocytic, phagocytic, and autophagic materials is dependent on lysosomes which serve as the major degradative compartments with their digestive function [15][16][17]. Beyond intracellular digestion, lysosomes may mediate cellular signaling in different cells [18][19][20] such as their role in receptor recycling through an endocytic pathway [21] and as a Ca 2+ store importantly participating in the physiological regulation of cell functions or activities in many tissues or cells [19,[22][23][24][25], including podocytes [26][27][28]. In podocytes, normally functioning lysosomes are particularly important for the protection of this terminally differentiated cell type from the challenges of various danger factors [27,[29][30][31].…”

“…Beyond intracellular digestion, lysosomes may mediate cellular signaling in different cells [18][19][20] such as their role in receptor recycling through an endocytic pathway [21] and as a Ca 2+ store importantly participating in the physiological regulation of cell functions or activities in many tissues or cells [19,[22][23][24][25], including podocytes [26][27][28]. In podocytes, normally functioning lysosomes are particularly important for the protection of this terminally differentiated cell type from the challenges of various danger factors [27,[29][30][31]. Recent clinical and experimental studies have indicated that the deficiency or loss of lysosome function in podocytes results in proteinuria, glomerular sclerosis, and dramatically increased susceptibility to different pathological stimuli [32][33][34][35].…”

“…Lysosome contents including cathepsins as the main stimulator of the cell death are released during the destabilization of lysosomal membrane [125]. Recent studies have shown the important role of LMP in podocyte injury under pathological conditions such as idiopathic membranous nephropathy [27] and diabetic nephropathy (DN) [126]. As a dangerous factor elevated during DN, advanced glycation end products (AGEs) have been found to induce LMP in murine podocytes [126].…”