p62/SQSTM1 prominently accumulates in renal proximal tubules in nephropathic cystinosis.
BACKGROUND
Nephropathic cystinosis, a lysosomal storage disorder, is associated with generalized proximal tubular dysfunction and progressive renal failure. The underlying molecular and cellular mechanisms leading to renal tubular injury remain largely unknown. Abnormal induction of autophagy has been shown in cystinosis. We have studied the autophagic flux in cystinosis by evaluating autophagy-specific substrates.


METHODS
LC3 and p62 expression was evaluated by (1) immunohistochemistry performed on kidney biopsies obtained from four nephropathic cystinosis patients, four patients with renal injury due to causes other than cystinosis, and four normal kidney tissues and (2) fluorescence imaging in cultured renal proximal tubular epithelial (RPTE) cells obtained from four nephropathic cystinosis patients and two lots of normal primary RPTE cells, both in basal and starvation conditions. p62 expression was also corroborated by western blot analysis in RPTE cells.


RESULTS
There was a significant buildup of p62 protein in patients with nephropathic cystinosis, specifically in the proximal tubules in kidney biopsies and RPTE cells (p = 0.0004), and the accumulation was further enhanced upon starvation. Cystinotic RPTE cells exhibited a significant co-localization of p62 with LC3.


CONCLUSIONS
Our findings indicate a potential block in the autophagic flux in cystinosis, thus providing key insights into the underlying mechanisms of tubular injury in cystinosis.
California Pacific Medical Center Research Institute, 475 Brannan Street, Ste 220, San Francisco, CA, 94107, USA. poonam@cpmcri.org.
Poonam
P
Sansanwal
California Pacific Medical Center Research Institute, 475 Brannan Street, Ste 220, San Francisco, CA, 94107, USA. sarwalm@cpmcri.org.
Minnie M
MM
Sarwal
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000293:Adolescent; D001343:Autophagy; D001706:Biopsy; D015153:Blotting, Western; D016022:Case-Control Studies; D002478:Cells, Cultured; D002648:Child; D003554:Cystinosis / Q000378:metabolism* / Q000473:pathology; D004847:Epithelial Cells / Q000378:metabolism; D005198:Fanconi Syndrome / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000473:pathology; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009404:Nephrotic Syndrome / Q000378:metabolism* / Q000473:pathology; D000071456:Sequestosome-1 Protein; D015854:Up-Regulation
D048868:Adaptor Proteins, Signal Transducing; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein