Cusimano, A. | bioRxiv Science

bioRxiv2025

The RNA-binding activity of SACSIN HEPN domain is connected to ARSACS

Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is a neurodegenerative disorder caused by mutations in the SACS gene, though the molecular function of its protein product, SACSIN, remains elusive. Therapeutic strategies for ARSACS are limited, mostly due to the exceptionally large size of SACSIN ([~]520 kDa), which precludes conventional gene therapy and standard molecular delivery methods. Over 200 pathogenic variants, including missense and nonsense mutations, have been identified. Regardless of variant type, patients uniformly exhibit cerebellar ataxia and spasticity. Among them, patients carrying missense mutations within the SACSIN higher eukaryotes and prokaryotes nucleotide-binding (HEPN) domain, suggesting that the alteration of the functional role of SACSIN HEPN domain could be linked to the manifestation of ARSACS symptoms. Here, we provide the first direct evidence that SACSIN HEPN domain binds RNA, corroborating the hypothesis that SACSIN functions as an RNA-binding protein. In silico predictions through the catRAPID algorithm as well as AlphaFold 3 revealed the propensity of SACSIN HEPN domain to specifically interact with RNAs. These interactions were validated both in vitro and in cell studies, confirming that SACSIN HEPN domain binds to RNA transcripts. Overall, our study unveils an unknown molecular function of SACSIN that, if altered, can contribute to the development of ARSACS disease. Therefore, paving the way for innovative therapeutic approaches for ARSACS patients.

molecular biology↗

bioRxiv2020

NUPR1 protects liver from lipotoxic injury by improving the endoplasmic reticulum stress response

Background and AimsNon-alcoholic fatty liver disease and related hepatic syndromes affect up to one third of the adult population. The molecular mechanisms underlying NAFL etiology remain elusive. Nuclear Protein 1 (NUPR1) expression increases upon cell injury in all organs and recently we report its active participation in the activation of the Unfolded Protein Response (UPR). The UPR typically maintains protein homeostasis, but downstream mediators of the pathway regulate metabolic functions, including lipid metabolism. NUPR1 and UPR increase have been reported in obesity and liver pathologies and the goal of this study was to investigate the roles of NUPR1 in this context. MethodsWe used patient-derived liver biopsies and in vitro and in vivo NUPR1 loss of functions models. First, we analysed NUPR1 expression in a cohort of morbidly obese patients (MOPs), with either simple fatty liver (NAFL) or more severe steatohepatitis (NASH). Next, we explored the metabolic roles of NUPR1 in wild type (Nupr1+/+) or Nupr1 knockout mice (Nupr1-/-) fed ad libitum with a high fat diet (HFD) for up to 15 weeks. ResultsNUPR1 expression is inversely correlated to hepatic steatosis progression. We found that NUPR1 participates in the activation of PPAR- signalling via UPR. PPAR- signalling, is involved in the maintenance of fat metabolism and proper lipid homeostasis and energy balance. As PPAR- signalling is controlled by UPR, collectively, these findings suggest a novel function for NUPR1 in protecting liver from metabolic distress by controlling lipid homeostasis, possibly through the UPR. ObjectiveNon-alcoholic fatty liver (NAFL) disease and related hepatic syndromes affect up to one third of the adult population in industrialised and developing countries. However, the molecular mechanisms underlying NAFL etiology remain elusive. Nuclear Protein 1 (NUPR1) expression increases upon cell injury in all organs including the liver. Recently, we report NUPR1 actively participates in activation of the Unfolded Protein Response (UPR). The UPR typically maintains protein homeostasis, but downstream mediators of the pathway regulate metabolic functions, including lipid metabolism. NUPR1 and UPR increase have been reported in obesity and liver pathologies and the goal of this study was to investigate the roles of NUPR1 in this context. DesignWe used patient-derived liver biopsies and in vitro and in vivo NUPR1 loss of functions models. First, we analysed NUPR1 expression in a cohort of morbidly obese patients (MOPs), with either simple fatty liver (NAFL) or more severe steatohepatitis (NASH). Next, we explored the metabolic roles of NUPR1 in wild type (Nupr1+/+) or Nupr1 knockout mice (Nupr1-/-) fed ad libitum with a high fat diet (HFD) for up to 15 weeks. ResultsNUPR1 expression is inversely correlated to hepatic steatosis progression. Mechanistically, we found NUPR1 participates in the activation of PPAR- signalling via UPR. PPAR- signalling, is involved in the maintenance of fat metabolism and proper lipid homeostasis and energy balance. As PPAR- signalling is controlled by UPR, collectively, these findings suggest a novel function for NUPR1 in protecting liver from metabolic distress by controlling lipid homeostasis, possibly through the UPR. ConclusionsAs PPAR- signalling is controlled by UPR, collectively, these findings suggest a novel function for NUPR1 in protecting liver from metabolic distress by controlling lipid homeostasis, possibly through the UPR. Lay summaryNUPR1 is activated during high caloric intake in both mice and patients. Decrease in expression or inhibition of NUPR1 worsens lipid deposition and hepatic damage. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=192 SRC="FIGDIR/small/350652v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@1d370c0org.highwire.dtl.DTLVardef@8f8dc9org.highwire.dtl.DTLVardef@a5aa49org.highwire.dtl.DTLVardef@4eb585_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LINUPR1 protects liver from high caloric intake hepatic damage C_LIO_LIThe function of NUPR1 in this context is to control the lipid homeostasis through the UPR and more specifically through PPAR- signalling. C_LIO_LINUPR1 could be used as a predictive marker for the gravity of NAFL progression. Moreover, as clinical interest is being raised around NUPR1 inhibitors to treat liver and pancreatic cancer, care should be taken in monitoring lipotoxic parameters. C_LI

cell biology↗