Urine-Derived Stem Cells Express 571 Neuromuscular Disorders Causing Genes, Making Them a Potential in vitro Model for Rare Genetic Diseases

ATM knock out alters calcium signalling and augments contraction in skeletal muscle cells differentiated from human urine-derived stem cells

Ataxia-telangiectasia (A-T) is a rare neurodegenerative disorder caused by the deficiency of the serine/threonine kinase ataxia telangiectasia mutated (ATM) protein, whose loss of function leads to altered cell cycle, apoptosis, oxidative stress balance and DNA repair after damage. The clinical manifestations are multisystemic, among them cerebellar degeneration and muscular ataxia. The molecular mechanism by which ATM loss leads to A-T is still uncertain and, currently only symptomatic treatments are available. In this study, we generated a functional skeletal muscle cell model that recapitulates A-T and highlights the role of ATM in calcium signalling and muscle contraction. To this aim, by using CRISPR/Cas9 technology, we knocked out the ATM protein in urine-derived stem cells (USCs) from healthy donors. The resulting USCs-ATM-KO maintained stemness but showed G2/S cell cycle progression and an inability to repair DNA after UV damage. Moreover, they showed increased cytosolic calcium release after ATP stimulation to the detriment of the mitochondria. The alterations of calcium homoeostasis were maintained after differentiation of USCs-ATM-KO into skeletal muscle cells (USC-SkMCs) and correlated with impaired cell contraction. Indeed, USC-SkMCs-ATM-KO contraction kinetics were dramatically accelerated compared to control cells. These results highlight the relevant function of ATM in skeletal muscle, which is not only dependent on a non-functional neuronal communication, paving the way for future studies on a muscular interpretation of A-T ataxia.

A Novel Synonymous Variant in SQSTM1 Causes Neurodegeneration With Ataxia, Dystonia, and Gaze Palsy Revealed by Urine-Derived Cells-Based Functional Analysis

BACKGROUND

Heterozygous variants of sequestosome-1 gene (SQSTM1) have been reported in patients with various neurological disorders, whereas biallelic pathogenic variants of SQSTM1 can cause child-onset and multisystem neurodegeneration, including cerebellar ataxia, dystonia, and vertical gaze palsy (NADGP). Here, we describe two cases of NADGP in a Japanese family.

METHODS

We performed clinical and genetic laboratory evaluations of the two patients and their healthy parents.

RESULTS

By whole-exome sequencing, we identified compound heterozygous variants in SQSTM1(NM_003900.5): c.1A>G p.(Met1?) in the initial codon, and c.969G>A, located at the 3' end of exon 6, which is novel and seemingly a synonymous but is actually a truncating variant causing aberrant splicing. An SQSTM1 protein expression assay using urine-derived cells (UDCs) demonstrated that both variants (c.1A>G and c.969G>A) were unable to induce normal splicing of premessenger RNA. Cerebellar ataxia is a characteristic manifestation of this disorder; however, brain magnetic resonance imaging studies have not shown significant cerebellar atrophy. Our patients experienced chorea during adolescence.

CONCLUSIONS

Only a few reports have highlighted the presence of chorea; however, our findings suggest that NADGP should be considered as a differential diagnosis of hereditary chorea. This study also demonstrates the utility of UDCs, obtained using noninvasive approaches, in functionally analyzing genetic diseases.

Application of mesenchymal stem cell-derived exosomes from different sources in intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a main cause of lower back pain, leading to psychological and economic burdens to patients. Physical therapy only delays pain in patients but cannot eliminate the cause of IVDD. Surgery is required when the patient cannot tolerate pain or has severe neurological symptoms. Although surgical resection of IVD or decompression of the laminae eliminates the diseased segment, it damages adjacent normal IVD. There is also a risk of re-protrusion after IVD removal. Cell therapy has played a crucial role in the development of regenerative medicine. Cell transplantation promotes regeneration of degenerative tissue. However, owing to the lack of vascular structure in IVD, sufficient nutrients cannot be provided for transplanted mesenchymal stem cells (MSCs). In addition, dead cells release harmful substances that aggravate IVDD. Extracellular vesicles (EVs) have been extensively studied as an emerging therapeutic approach. EVs generated by paracrine MSCs retain the potential of MSCs and serve as carriers to deliver their contents to target cells to regulate target cell activity. Owing to their double-layered membrane structure, EVs have a low immunogenicity and no immune rejection. Therefore, EVs are considered an emerging therapeutic modality in IVDD. However, they are limited by mass production and low loading rates. In this review, the structure of IVD and advantages of EVs are introduced, and the application of MSC-EVs in IVDD is discussed. The current limitations of EVs and future applications are described.