👤 Eric Sulpice

Xeroderma Pigmentosum C is a dermal hereditary disease caused by a mutation in the DNA damage recognition protein XPC that belongs to the Nucleotide excision repair pathway. XPC patients display heightened sensitivity to light and an inability to mend DNA damage caused by UV radiation, resulting in the accumulation of lesions that can transform into mutations and eventually lead to cancer. To address this issue, we conducted a screening of siRNAs targeting human kinases, given their involvement in various DNA repair pathways, aiming to restore normal cellular behavior. We introduced this siRNA library into both normal and XPC patient-derived fibroblasts, followed by UVB exposure to induce DNA damage. We assessed the reversal of the XPC phenotype by measuring reduced photosensitivity and enhanced DNA repair. Among the 1292 kinase-targeting siRNAs screened, twenty-eight showed significant improvement in cellular survival compared to cells transfected with non-targeting siRNA after UV exposure in XPC cells. From these candidates, PIK3C3 and LATS1 were identified as particularly effective, promoting over 20% repair of 6-4 photoproduct (6-4PP) DNA lesions. Specifically targeting the autophagy-related protein PIK3C3 alone demonstrated remarkable photoprotective effects in XPC-affected cells, which were validated in primary XPC patient fibroblasts and CRISPR-Cas9 engineered XPC knockout keratinocytes. PIK3C3 knock down in XP-C cells ameliorated in UVB dose response analysis, decreased apoptosis with no effect on proliferation. More importantly, PIK3C3 knock down was found to induce an increase in UVRAG expression, a previously reported cDNA conveying lower photosensitivity in XP-C cells. Thus, attempts to improve the XPC photosensitive and deficient repair phenotype using PIK3C3 inhibitors could pave a way for new therapeutic approaches delaying or preventing tumor initiation. Show less

The aim of this work was to evaluate reverse cholesterol transport (RCT) in hamster, animal model expressing CETP under a high cholesterol diet (HF) supplemented with Ezetimibe using primary labelled macrophages. We studied three groups of hamsters (n=8/group) for 4 weeks: 1) chow diet group: Chow, 2) High cholesterol diet group: HF and 3) HF group supplemented with 0.01% of ezetimibe: HF+0.01%Ezet. Following intraperitoneal injection of Show less

Impaired adipose tissue insulin signalling is a critical feature of insulin resistance. Here we identify a pathway linking the lipolytic enzyme hormone-sensitive lipase (HSL) to insulin action via the glucose-responsive transcription factor ChREBP and its target, the fatty acid elongase ELOVL6. Genetic inhibition of HSL in human adipocytes and mouse adipose tissue results in enhanced insulin sensitivity and induction of ELOVL6. ELOVL6 promotes an increase in phospholipid oleic acid, which modifies plasma membrane fluidity and enhances insulin signalling. HSL deficiency-mediated effects are suppressed by gene silencing of ChREBP and ELOVL6. Mechanistically, physical interaction between HSL, independent of lipase activity, and the isoform activated by glucose metabolism ChREBPα impairs ChREBPα translocation into the nucleus and induction of ChREBPβ, the isoform with high transcriptional activity that is strongly associated with whole-body insulin sensitivity. Targeting the HSL-ChREBP interaction may allow therapeutic strategies for the restoration of insulin sensitivity. Show less

The use of rat and mouse models limits the translation to humans for developing novel drugs targeting nonalcoholic steatohepatitis (NASH). Obeticholic acid (OCA) illustrates this limitation since its dyslipidemic effect in humans cannot be observed in these rodents. Conversely, Golden Syrian hamsters have a lipoprotein metabolism mimicking human dyslipidemia since it does express the cholesteryl ester transfer protein (CETP). We therefore developed a Diet-Induced NASH (DIN) hamster model and evaluated the impact of OCA. Compared with chow fed controls, hamsters fed for 20 weeks with a free-choice (FC) diet, developed obesity, insulin resistance, dyslipidemia and NASH (microvesicular steatosis, inflammation, hepatocyte ballooning and perisinusoidal to bridging fibrosis). After 20 weeks of diet, FC fed hamsters were treated without or with obeticholic acid (15mg/kg/day) for 5 weeks. Although a non-significant trend towards higher dietary caloric intake was observed, OCA significantly lowered body weight after 5 weeks of treatment. OCA significantly increased CETP activity and LDL-C levels by 20% and 27%, and reduced HDL-C levels by 20%. OCA blunted hepatic gene expression of Cyp7a1 and Cyp8b1 and reduced fecal bile acids mass excretion by 64% (P < 0.05). Hamsters treated with OCA showed a trend towards higher scavenger receptor Class B type I (SR-BI) and lower LDL-receptor hepatic protein expression. OCA reduced NAS score for inflammation (P < 0.01) and total NAS score, although not significantly. Compared to mouse and rat models, the DIN hamster replicates benefits and side effects of OCA as observed in humans, and should be useful for evaluating novel drugs targeting NASH. Show less

Inhibition of dipeptidyl peptidase-4 (DPP-4) activity improves glucose homeostasis through a mode of action related to the stabilization of the active forms of DPP-4-sensitive hormones such as the incretins that enhance glucose-induced insulin secretion. However, the DPP-4 enzyme is highly expressed on the surface of intestinal epithelial cells; hence, the role of intestinal vs. systemic DPP-4 remains unclear. To analyze mechanisms through which the DPP-4 inhibitor sitagliptin regulates glycemia in mice, we administered low oral doses of the DPP-4 inhibitor sitagliptin that selectively reduced DPP-4 activity in the intestine. Glp1r(-/-) and Gipr(-/-) mice were studied and glucagon-like peptide (GLP)-1 receptor (GLP-1R) signaling was blocked by an i.v. infusion of the corresponding receptor antagonist exendin (9-39). The role of the dipeptides His-Ala and Tyr-Ala as DPP-4-generated GLP-1 and glucose-dependent insulinotropic peptide (GIP) degradation products was studied in vivo and in vitro on isolated islets. We demonstrate that very low doses of oral sitagliptin improve glucose tolerance and plasma insulin levels with selective reduction of intestinal but not systemic DPP-4 activity. The glucoregulatory action of sitagliptin was associated with increased vagus nerve activity and was diminished in wild-type mice treated with the GLP-1R antagonist exendin (9-39) and in Glp1r(-/-) and Gipr(-/-) mice. Furthermore, the dipeptides liberated from GLP-1 (His-Ala) and GIP (Tyr-Ala) deteriorated glucose tolerance, reduced insulin, and increased portal glucagon levels. The predominant mechanism through which DPP-4 inhibitors regulate glycemia involves local inhibition of intestinal DPP-4 activity, activation of incretin receptors, reduced liberation of bioactive dipeptides, and activation of the gut-to-pancreas neural axis. Show less