Equilibrative nucleoside transporter 3 depletion in β-cells impairs mitochondrial function and promotes apoptosis: Relationship to pigmented hypertrichotic dermatosis with insulin-dependent diabetes

Abstract

Loss of function recessive mutations in the SLC29A3 gene that encodes human equilibrative nucleoside transporter 3 (ENT3) have been identified in patients with pigmented hypertrichotic dermatosis with insulin-dependent diabetes (PHID). ENT3 is a member of the equilibrative nucleoside transporter (ENT) family whose primary function is mediating transport of nucleosides and nucleobases. The aims of this study were to characterise ENT3 expression in islet β-cells and identify the effects of its depletion on β-cell mitochondrial activity and apoptosis. RT-PCR amplification identified ENT3 expression in human and mouse islets and exocrine pancreas, and in MIN6 β-cells. Immunohistochemistry using human and mouse pancreas sections exhibited extensive ENT3 immunostaining of β-cells, which was confirmed by co-staining with an anti-insulin antibody. In addition, exposure of dispersed human islet cells and MIN6 β-cells to MitoTracker and an ENT3 antibody showed co-localisation of ENT3 to β-cell mitochondria. Consistent with this, Western blot analysis confirmed enhanced ENT3 immunoreactivity in β-cell mitochondria-enriched fractions. Furthermore, ENT3 depletion in β-cells increased mitochondrial DNA content and promoted an energy crisis characterised by enhanced ATP-linked respiration and proton leak. Finally, inhibition of ENT3 activity by dypridamole and depletion of ENT3 by siRNA-induced knockdown resulted in increased caspase 3/7 activities in β-cells. These observations demonstrate that ENT3 is predominantly expressed by islet β-cells where it co-localises with mitochondria. Depletion of ENT3 causes mitochondrial dysfunction which is associated with enhanced β-cell apoptosis. Thus, apoptotic loss of islet β-cells may contribute to the occurrence of autoantibody-negative insulin-dependent diabetes in individuals with non-functional ENT3 mutations.

Vesicular nucleotide transporter (VNUT): appearance of an actress on the stage of purinergic signaling

“…Its gene knockdown suppresses depolarization-evoked ATP release from cultured astrocytes [106]. However, ENT3 prefers nucleosides and nucleobases as substrates, which differs from the content of nucleotides stored in ATP-storing organelles, and is mainly localized in mitochondria [107,108]. These findings support the idea that ENT3 is not involved in the vesicular storage of nucleotides.…”

Identification of the Novel Methylated Genes’ Signature to Predict Prognosis in INRG High-Risk Neuroblastomas

“…SLC29A3 encodes a nucleoside transporter which plays a significant role in the cellular uptake of nucleosides and nucleobases. It was previously reported that many diseases were related to RAD51AP1 expression, including autoinflammatory diseases [ 46 ], H syndrome [ 47 ], insulin-dependent diabetes [ 48 ], pigmentary hypertrichosis, autoimmune insulin-dependent diabetes mellitus [ 49 ], and sclerosing bone dysplasias [ 50 ]. Meanwhile, MIMT1 is an MER1 repeat-containing imprinted transcript, which can undergo hypermethylation in the placenta of intrauterine growth-restricted fetuses in cattle [ 51 ], and truncation of exons 3 and 4 of the MIMT1 gene caused intrauterine growth restriction [ 52 ].…”

H syndrome: Clinical, histological and genetic investigation in Tunisian patients

“…Since 2014, 17 patients have been reported. 11,20,[23][24][25][26][27][28][29][30] Molho-Pessach et al 5 emphasized that the finding of several different mutations in a small geographic region implies that H syndrome may be rather common and underdiagnosed owing to the fact that many patients have a very mild clinical presentation. In our context, geographic endogamy is frequent in Tunisia, especially in rural areas where it could reach 90% and familial endogamy or interrelated marriages are profoundly rooted with an estimated rate of 30% of all kind of unions.…”