Biology subjects

Ylikallio, E.

Publications and source records attributed to Ylikallio, E..

5 recordsLinked to original sources

bioRxiv2024

IP3 receptor depletion in a spontaneous canine model of Charcot-Marie-Tooth disease 1J with amelogenesis imperfecta

Inositol 1,4,5-trisphosphate receptors (IP3R) mediate Ca2+ release from intracellular stores, contributing to complex regulation of numerous physiological responses. The involvement of the three IP3R genes (ITPR1, ITPR2 and ITPR3) in inherited human diseases has started to shed light on the essential roles of each receptor in different human tissues and cell types. Variants in the ITPR3 gene, which encodes IP3R3, have recently been found to cause demyelinating sensorimotor Charcot-Marie-Tooth neuropathy type 1J (CMT1J). In addition to peripheral neuropathy, immunodeficiency and tooth abnormalities are occasionally present. Here, we report the identification of a homozygous nonsense variant in the ITPR3 gene in Lancashire Heeler dogs, presenting with a severe developmental enamel defect and reduced nerve conduction velocity. We studied the primary skin fibroblasts of the affected dogs and observed that the nonsense variant in ITPR3 led to a complete absence of full-length IP3R3 protein. Unexpectedly, the protein levels of IP3R1 and IP3R2 were also markedly decreased, suggesting co-regulation. Functional Ca2+ measurements revealed reduced IP3R-mediated Ca2+ flux upon stimulation of G-protein-coupled-receptors in the affected dog fibroblasts. We were able to rescue the IP3R1 and IP3R2 depletion by proteasome inhibition but not the IP3R3 loss, which was facilitated by nonsense-mediated mRNA decay. These findings highlight the first spontaneous mammalian phenotype caused by a nonsense variant in ITPR3, leading to the loss of IP3R3. The human and canine IP3R3 proteins are highly similar, and our study suggests that the tissue involvement resulting from the receptors dysfunction is also conserved. In summary, IP3R3 is critical for enamel formation and peripheral nerve maintenance. Author summaryWe investigated pet dogs, Lancashire Heelers, with impairments in tooth development and in the nerves that regulate limb muscles. Through genetic studies of the dog pedigree, we found that the phenotypes were caused by a recessively inherited mutation in the ITPR3 gene, which encodes one of three IP3 receptors (IP3R) isoforms (IP3R3 isoform) that are needed for intracellular Ca2+ signaling. Mutated IP3R3 has been recently linked to a human inherited neuropathy called Charcot-Marie-Tooth disease type 1J, which impairs peripheral nerve function and is accompanied by immunodeficiency and abnormal teeth in some individuals. We showed that in the skin cells of the affected dogs, the full-length IP3R3 protein was completely absent, and also the protein levels of the other two IP3R isoforms (IP3R1 and IP3R2) were severely lowered. This led to impaired agonist-induced Ca2+ release and signaling. Our results demonstrate the high conservation between human and canine IP3 receptors and their significance for different tissue systems. The genetic studies now highlight that IP3R3 is vital for peripheral nerve function and enamel development.

genetics↗

bioRxiv2022

Structural insights into Charcot-Marie-Tooth disease-linked mutations in human GDAP1

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral polyneuropathy in humans, and its different subtypes are linked to mutations in dozens of different genes. Mutations in ganglioside-induced differentiation-associated protein 1 (GDAP1) cause two types of CMT, demyelinating CMT4A and axonal CMT2K. The GDAP1-linked CMT genotypes are mainly missense point mutations. Despite clinical profiling and in vivo studies on the mutations, the etiology of GDAP1-linked CMT is poorly understood. Here, we describe the biochemical and structural properties of the Finnish founding CMT2K mutation H123R as well as CMT2K-linked R120W, both of which are autosomal dominant mutations. The disease variant proteins retain close to normal structure and solution behaviour, but both present a large decrease in thermal stability. Using GDAP1 variant crystal structures, we identify a side chain interaction network between helices 3, 6, and 7, which is affected by CMT mutations, as well as a hinge in the long helix 6, which is linked to structural flexibility. Structural analysis of GDAP1 indicates that CMT may arise from disruption of specific intra- and intermolecular interaction networks, leading to alterations in GDAP1 structure and stability, and eventually, insufficient motor and sensory neuron function.

biochemistry↗

bioRxiv2021

Biallelic loss-of-function OBSCN variants predispose individuals to severe, recurrent rhabdomyolysis

Rhabdomyolysis is the acute breakdown of skeletal myofibres in response to an initiating factor, most commonly toxins and over exertion. A variety of genetic disorders predispose to rhabdomyolysis through different pathogenic mechanisms, particularly in patients with recurrent episodes. However, the majority of cases remain without a genetic diagnosis. Here we present six patients who presented with severe and recurrent rhabdomyolysis, usually with onset in the teenage years; other features included a history of myalgia and muscle cramps. We identified ten bi-allelic loss-of-function variants in the gene encoding obscurin (OBSCN) co-segregating with disease. We show reduced expression of OBSCN and loss of obscurin protein in patient muscle. Obscurin is proposed to be involved in SR function and Ca2+ handling. Patient cultured myoblasts appear more susceptible to starvation as evidenced by a greater decreased in SR Ca2+ content compared to control myoblasts. This likely reflects a lower efficiency when pumping Ca2+ back into the SR and/or a decrease in Ca2+ SR storage ability when metabolism is diminished. OSBCN variants have previously been associated with cardiomyopathies. None of the patients presented with a cardiomyopathy and cardiac examinations were normal in all cases in which cardiac function was assessed. There was also no history of cardiomyopathy in first degree relatives, in particular in any of the carrier parents. This cohort is relatively young, thus follow-up studies and the identification of additional cases with bi-allelic null OBSCN variants will further delineate OBSCN-related disease and the clinical course of disease.

genetics↗

bioRxiv2021

Peripheral neuropathy linked mRNA export factor GANP reshapes gene regulation in human motor neurons

Loss-of-function of the mRNA export protein GANP (MCM3AP gene) cause early-onset sensorimotor neuropathy, characterised by axonal degeneration in long peripheral nerves. GANP functions as a scaffold at nuclear pore complexes, contributing to selective nuclear export of mRNAs. Here, we aimed to identify motor neuron specific transcripts that are regulated by GANP and may be limiting for local protein synthesis in motor neuron axons. We compared motor neurons with a gene edited mutation in the Sac3 mRNA binding domain of GANP to isogenic controls. We also examined patient-derived motor neurons. RNA sequencing of motor neurons as well as nuclear and axonal subcompartments showed that mutant GANP had a profound effect on motor neuron transcriptomes, with alterations in nearly 40 percent of all expressed genes and broad changes in splicing. Expression changes in multiple genes critical for neuronal functions, combined with compensatory upregulation of protein synthesis and early-stage metabolic stress genes, indicated that RNA metabolism was abnormal in GANP-deficient motor neurons. Surprisingly, limited evidence was found for large-scale nuclear retention of mRNA. This first study of neuropathy-linked GANP defects in human motor neurons shows that GANP has a wide gene regulatory role in a disease-relevant cell type that requires long-distance mRNA transport.

neuroscience↗

bioRxiv2019

CHCHD10 OR CHCHD2 ARE NOT REQUIRED FOR HUMAN MOTOR NEURON DIFFERENTIATION IN VITRO BUT MODIFY SYNAPTIC TRANSCRIPTOMES

Mitochondrial intermembrane space proteins CHCHD2 and CHCHD10 have roles in diseases affecting motor neurons such as amyotrophic lateral sclerosis, spinal muscular atrophy and axonal neuropathy and in Parkinsons disease, and form a complex of unknown function. Here we address the importance of these two proteins in human motor neurons. We show that gene edited human induced pluripotent stem cells (iPSC) lacking either CHCHD2 or CHCHD10 are viable and can be differentiated into functional motor neurons that fire spontaneous and evoked action potentials. Knockout iPSC and motor neurons sustain mitochondrial ultrastructure and show reciprocal compensatory increases in CHCHD2 or CHCHD10. Knockout motor neurons have largely overlapping transcriptome profiles compared to isogenic control line, in particular for synaptic gene expression. Our results show that absence of CHCHD2 or CHCHD10 does not disrupt functionality, but induces similar modifications in human motor neurons. Thus pathogenic mechanisms may involve loss of synaptic function.

neuroscience↗