Activation of the transcription factor EB rescues lysosomal abnormalities in cystinotic kidney cells

Abstract

Nephropathic cystinosis is a rare autosomal recessive lysosomal storage disease characterized by accumulation of cystine into lysosomes secondary to mutations in the cystine lysosomal transporter, cystinosin. The defect initially causes proximal tubular dysfunction (Fanconi syndrome) which in time progresses to end-stage renal disease. Cystinotic patients treated with the cystine-depleting agent, cysteamine, have improved life expectancy, delayed progression to chronic renal failure, but persistence of Fanconi syndrome. Here, we have investigated the role of the transcription factor EB (TFEB), a master regulator of the autophagy-lysosomal pathway, in conditionally immortalized proximal tubular epithelial cells derived from the urine of a healthy volunteer or a cystinotic patient. Lack of cystinosin reduced TFEB expression and induced TFEB nuclear translocation. Stimulation of endogenous TFEB activity by genistein, or overexpression of exogenous TFEB lowered cystine levels within 24 hours in cystinotic cells. Overexpression of TFEB also stimulated delayed endocytic cargo processing within 24 hours. Rescue of other abnormalities of the lysosomal compartment was observed but required prolonged expression of TFEB. These abnormalities could not be corrected with cysteamine. Thus, these data show that the consequences of cystinosin deficiency are not restricted to cystine accumulation and support the role of TFEB as a therapeutic target for the treatment of lysosomal storage diseases, in particular of cystinosis.

The renal Fanconi syndrome in cystinosis: pathogenic insights and therapeutic perspectives

“…Conditionally immortalized PTCs derived from the urine of a patient with cystinosis showed persistent nuclear translocation of TFEB, indicating stimulation of lysosomal clearance. Prolonged overexpression of exogenous TFEB or its pharmacological activation by genistein lowered cystine levels and corrected cellular alterations in endocytic trafficking and rescued deficits that could not be corrected by cysteamine, demonstrating again that the absence of cystinosin affects lysosomal signalling and pointing to the potential benefits of pharmacological intervention targeting TFEB 145 .…”

“…This factor is silenced by mTOR-dependent phosphorylation, which causes it to become trapped in the cytosol, and is in turn activated by Ca 2+ -dependent dephosphorylation, which enables its nuclear translocation. Expression of TFEB mRNA and protein is impaired in PTCs deficient in cystinosin 145 . Conditionally immortalized PTCs derived from the urine of a patient with cystinosis showed persistent nuclear translocation of TFEB, indicating stimulation of lysosomal clearance.…”

TFEB at a glance

“…Overexpression of TFEB in cellular and mouse models of several LSDs, including multiple sulfatase deficiency, mucopolysaccharidosis type IIIA, Batten disease, Pompe disease, Gaucher disease, Tay-Sachs disease and cystinosis, have been shown to be beneficial in reducing substrate accumulation; such overexpression also improved overall autophagy and lysosomal function, and ameliorated the severity of cellular and tissue phenotypes Rega et al, 2016;Song et al, 2013;Spampanato et al, 2013). Although the mechanism by which TFEB reduces lysosomal storage and overcomes lysosomal malfunction in LSDs is not fully understood, it is likely that induction of lysosomal exocytosis and secretion of the undigested material plays a major beneficial role .…”

First Successful Conception Induced by a Male Cystinosis Patient

“…However, in this case, the patient had clear signs of primary hypogonadism, sufficient to explain his infertility. As several studies demonstrated recently that cystinosin is involved in numerous cellular processes, one can argue whether merely the lysosomal cystine accumulation should be considered as the only pathophysiological mechanism involved in infertility (Raggi et al 2014;Giade Chevronnay et al 2015;Ivanova et al 2015Ivanova et al , 2016Rega et al 2016). In this regard, it is of note that the cystinosin-LKG isoform, of which its localization is not limited to the lysosomal membrane, has the highest expression in the testes compared to other organs (Taranta et al 2008).…”