Biology subjects

Salo, M. H.

Publications and source records attributed to Salo, M. H..

3 recordsLinked to original sources

bioRxiv2025

Stereospecific GPG acylation by CLN8 drives BMP biosynthesis and its loss leads to Batten disease

Loss-of-function mutations in the endoplasmic reticulum membrane protein CLN8 cause Batten disease, a neurodegenerative lysosomal storage disorder1. Together with the lysosomal enzyme CLN5, CLN8 mediates the biosynthesis of bis(monoacylglycero)phosphate (BMP), a phospholipid essential for lysosomal function and distinguished by its unique S,S stereochemistry2,3. However, the role of CLN8 in BMP synthesis has remained unclear. Here we establish that CLN8 is a glycerophosphoglycerol (GPG) acyltransferase that catalyses the stereospecific acylation of S,S-GPG to produce S,S-lysophosphatidylglycerol (LPG), the CLN5 substrate in BMP synthesis. Using cryo-electron microscopy, we resolve structures of the CLN8 homodimer in apo and substrate-bound states at 2.7 [A] resolution, revealing the active site architecture and a ping-pong acyl transfer mechanism. Batten disease-causing missense mutations impair CLN8 enzymatic activity in vitro and reduce BMP levels in a Cln8R24G knock- in mouse, whereas the Cln8mnd mouse frameshift mutation causes complete loss of BMP in vivo. Exogenous S,S-LPG, but not the R,S stereoisomer, restored BMP synthesis in CLN8- deficient cells and mice, and improved neurological phenotypes in cln8 mutant zebrafish. Together, these findings define the enzymatic function of CLN8, elucidate the biochemical basis of CLN8 Batten disease, and establish a proof-of-concept for treating it through stereospecific BMP precursor supplementation.

biochemistry↗

bioRxiv2025

Novel Cln8 p.R24G mouse line replicates major clinical features of Northern epilepsy

RationaleNorthern epilepsy belongs to a group of genetically diverse lysosomal storage diseases, the neuronal ceroid lipofuscinoses (NCLs). A characteristic feature of NCL pathology is the accumulation of autofluorescent ceroid lipofuscin in the central nervous system. Northern epilepsy is a late-infantile-onset disease. Patients develop normally until 5-10 years old, when they first present with general tonic-clonic seizures, followed by progressive cognitive impairment and a decline in motor skills. Northern epilepsy is caused by a missense variant in CLN8, causing a p.R24G amino acid substitution. CLN8 deficiency has been studied traditionally using motor neuron degeneration (mnd) mice, which carry a spontaneous frame shift variant in the murine orthologue Cln8, which is not known to exist in humans. MethodsWe have generated the first Cln8 p.R24G mouse model (Cln8R24G) using CRISPR/Cas9. Phenotyping analysis of the mice was conducted using behavioral and histopathological studies focusing on the brain and retina. ResultsAt birth, Cln8R24G KI mice were viable and asymptomatic. As the mice aged, a progressive accumulation of autofluorescent ceroid lipofuscin containing the mitochondrial ATP synthase subunit C was evident in different brain regions and retinal layers. Health monitoring revealed that mutant mice developed progressive but mild motor symptoms around 7 months of age. Spontaneous epileptic seizures, like those observed in Northern epilepsy patients, were detected and recorded. An increase in FosB staining intensity, reflecting neuronal hyperactivity, was observed in hippocampal CA1-CA3 pyramidal and dentate granule cells and correlated well with the intensity of seizure activity. Neuroinflammation was evident at 4 months and increased dramatically with age, mainly in the thalamic VPN/VPL nuclei and moderately in the cortex. Neurodegeneration was most prominent in the VPN/VPL thalamic nuclei. ConclusionsWe have generated the Cln8R24G mouse model that genocopies, for the first time, the pathogenic CLN8 variant present in patients with Northern epilepsy. These mice phenocopy major clinical features of the human disease, including mild motor impairment and, unlike the mnd mice, spontaneous generalized tonic-clonic seizures. We hypothesize that our mouse model will open new possibilities for developing and testing targeted treatment options for Northern epilepsy and, more broadly, for early-onset neurodegenerative disorders associated with epilepsy.

neuroscience↗

bioRxiv2024

FINCA disease mouse model exhibits altered behaviour and immune response

Fibrosis, neurodegeneration and cerebral angiomatosis (FINCA) is a childhood-onset multi-organ neurodevelopmental disorder associated with multi-organ manifestations and recurrent infections. The disease is caused by variants in NHLRC2 initiating a cascade of unknown pathological events. Previously, we have demonstrated that despite the significant decrease at the molecular level, the compound heterozygosity of knock out and p.Asp148Tyr alleles in NHLRC2 does not lead to a severe phenotype in mice. Here, we analysed the behavioural and immunological phenotype of the FINCA mice and studied the molecular pathways affected by p.Asp148Tyr in NHLRC2 using mouse and human-derived cell culture models. The FINCA mice displayed a mild hyperactivity and deficient early immune response when challenged with LPS leading to altered cytokine responses, including IFN{gamma}, IL-12, and TNF. By comparing gene expression and putative interaction partners affected by p.Asp148Tyr, we identified Rho GTPase signalling as the common pathway. Altogether, these results establish a multi-dimensional impact of the p.Asp148Tyr variant in NHLRC2. Knowledge of the molecular pathways affected by NHLRC2 and the natural course of FINCA disease progression are instrumental for the development of effective therapeutics. Summary statementFINCA is a paediatric neurodevelopmental and multi-organ disorder caused by variants in NHLRC2. Here, mild hyperactivity in connection with altered early immune response is described in the FINCA mouse model.

neuroscience↗