A SUMO4 initiator codon variant in amyotrophic lateral sclerosis reduces SUMO4 expression and alters stress granule dynamics

Abstract

Background Recent evidence points toward a role of the small ubiquitin-like modifier (SUMO) system, including SUMO4, in protecting from stress insults and neurodegeneration, such as the progressive motor neuron disease amyotrophic lateral sclerosis (ALS), e.g., by regulating stress granule (SG) dynamics. Here, we investigated whether SUMO4 variants play a role in ALS pathogenesis. Methods Whole-exome or targeted SUMO4 sequencing was done in 222 unrelated European ALS patients. The consequences of the identified initiator codon variant were analyzed at the mRNA, protein and cellular level. SUMO4 expression was quantified in human tissues. All patients were subjected to clinical, electrophysiological, and neuroradiological characterization. Results A rare heterozygous SUMO4 variant, i.e., SUMO4:c.2T>C p.Met1?, was detected in four of 222 (1.8%) ALS patients, significantly more frequently than in two control cohorts (0.3% each). SUMO4 mRNA and protein expression was diminished in whole blood or fibroblasts of a SUMO4 variant carrier versus controls. Pertinent stress factors, i.e., head trauma or cancer (treated by radiochemotherapy), were significantly more frequent in SUMO4 variant carrier versus non-carrier ALS patients. The mean number of SGs per cell was significantly higher in fibroblasts of a SUMO4 variant carrier compared to controls at baseline, upon oxidative stress, and after recovery, and SUMOylation of ALS-associated valosin-containing protein by SUMO4 was decreased. SUMO4 mRNA expression was highest in brain of all human tissues analyzed. Conclusions Our results are consistent with SUMO4 haploinsufficiency as a contributor to ALS pathogenesis impacting SG dynamics and possibly acting in conjunction with environmental oxidative stress-related factors.

Characterizing the differential distribution and targets of Sumo paralogs in the mouse brain

“…in neuronal development or learning and memory(Ripamonti et al, 2020). Furthermore, SUMOylation has been linked with various brain disorders, including Autism Spectrum Disorder, Epilepsy, Schizophrenia, and neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and Amyotrophic Lateral Sclerosis (Bernstock et al, 2018; Krumova and Weishaupt, 2013; Osmanovic et al, 2022; Rousseaux et al, 2016). However, despite a clear connection with neuronal function and dysfunction, SUMOylation has remained enigmatic due to technical challenges and limitations for studying this modification (Daniel et al, 2017).…”

A New Phase of Networking: The Molecular Composition and Regulatory Dynamics of Mammalian Stress Granules

“…Like ubiquitination, this modification is important for regulating SG disassembly, especially in relation to ALS genetic contexts. For example, SUMO4 mutations identified in ALS patients cause decreased SUMO4 mRNA and protein expression and are associated with significantly more SGs per patient fibroblast in response to oxidative stress . These mutations also resulted in reduced SUMOylation of the ALS-associated protein VCP, suggesting a possible causative link, as SUMOylation was previously shown to direct VCP recruitment to SGs, where it serves a key role in SG disassembly .…”

“…For example, SUMO4 mutations identified in ALS patients cause decreased SUMO4 mRNA and protein expression and are associated with significantly more SGs per patient fibroblast in response to oxidative stress. 205 These mutations also resulted in reduced SUMOylation of the ALS-associated protein VCP, suggesting a possible causative link, as SUMOylation was previously shown to direct VCP recruitment to SGs, where it serves a key role in SG disassembly. 206 In fact, mutations aimed at obstructing SUMO attachment to VCP directly impaired the disassembly of SGs.…”

Update on recent advances in amyotrophic lateral sclerosis

“…A loss-of-function mechanism has also been associated with the DnaJ heat shock protein family member C7 (DNAJC7), which has been identified as a genetic risk factor for ALS according to a large-scale WES study [50]. Indeed, a functional study has recently shown reduced protein levels in ALS patients carrying a p.R156X variant, suggesting a role of DNAJC7 in the regulation of protein misfolding, which is a major molecular pathology in ALS, through its interaction with HSP90 and HSP70 [51].…”