The pancreatic β-cell has reduced
antioxidant defences making it more susceptible to oxidative stress. In
cystinosis, a lysosomal storage disorder, an altered redox state may contribute to cellular dysfunction. This
rare disease is caused by an abnormal lysosomal
cystine transporter, cystinosin, which causes excessive accumulation of
cystine in the lysosome.
Cystinosis associated kidney damage and dysfunction leads to the
Fanconi syndrome and ultimately
end-stage renal disease. Following kidney transplant,
cystine accumulation in other organs including the pancreas leads to multi-organ dysfunction. In this study, a Ctns gene knockdown model of
cystinosis was developed in the BRIN-BD11 rat clonal pancreatic β-cell line using Ctns-targeting
siRNA. Additionally there was reduced cystinosin expression, while cell
cystine levels were similarly elevated to the cystinotic state. Decreased levels of chronic (24 h) and acute (20 min) nutrient-stimulated insulin secretion were observed. This decrease may be due to depressed
ATP generation particularly from glycolysis. Increased
ATP production and the
ATP/
ADP ratio are essential for insulin secretion. Oxidised
glutathione levels were augmented, resulting in a lower [
glutathione/oxidised
glutathione] redox potential. Additionally, the mitochondrial membrane potential was reduced, apoptosis levels were elevated, as were markers of oxidative stress, including
reactive oxygen species,
superoxide and
hydrogen peroxide. Furthermore, the basal and activated phosphorylated forms of the redox-sensitive
transcription factor NF-κB were increased in cells with silenced Ctns. From this study, the cystinotic-like pancreatic β-cell model demonstrated that the altered oxidative status of the cell, resulted in depressed mitochondrial function and pathways of
ATP production, causing reduced nutrient-stimulated insulin secretion.