Mitochondrial distribution violation and nuclear indentations in neurons differentiated from iPSCs of Huntington's disease patients.

AIM: Huntington's disease (HD) is an inherited disease caused by an expansion of cytosine-adenine-guanine (CAG) repeats in the huntingtin gene (HTT) that ultimately leads to neurodegeneration. To study the molecular basis of this disease, induced pluripotent stem cells (iPSCs) generated from patients' fibroblasts were used to investigate axonal mitochondrial trafficking and the nature of nuclear indentations. METHODS: Pathological and control iPSCs generated from patients with a low number of repeats were differentiated in striatal neurons of the brain. Mitochondrial density was measured along the axon using tubulin beta 3 co-staining in pathological and control neurons. To investigate the connection of nuclear roundness with calcium dysregulation, several calcium inhibitors were used. Proteasome system inhibition was applied to mimic premature neuronal ageing. RESULTS: We found that the mitochondrial density was approximately 7.6 ± 0.2 in neurites in control neurons but was only 5.3 ± 0.2 in mutant neurons with 40-44 CAG repeats (p-value <0.005). Neuronal ageing induced by proteasome inhibitor MG132 significantly decreased the mitochondrial density by 15% and 25% in control and mutant neurons to 6.5 ± 0.1 (p-value < 0.005) and 4.0 ± 0.3 (p-value < 0.005), respectively. Thus, for the first time, an impairment of mitochondrial trafficking in pathological neurons with endogenous mutant huntingtin was demonstrated. We found that inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), the ryanodine-receptor (RyR) or the inositol 1,4,5-trisphosphate receptor (IP3R) by specific inhibitors did not specifically affect the nuclear roundness or survival of pathological neurons differentiated from patient iPSCs. Therefore, nuclear calcium homeostasis is not directly associated with HD pathology. CONCLUSION: Identifying HD iPSCs and differentiating from them neurons provide a unique system for modelling the disease in vitro. Impairments of mitochondrial trafficking and nuclear roundness manifest long before the disease onset, while premature neuronal ageing enhances differences in mitochondrial distribution.

Manifestation of Huntington's disease pathology in human induced pluripotent stem cell-derived neurons.

BACKGROUND: Huntington's disease (HD) is an incurable hereditary neurodegenerative disorder, which manifests itself as a loss of GABAergic medium spiny (GABA MS) neurons in the striatum and caused by an expansion of the CAG repeat in exon 1 of the huntingtin gene. There is no cure for HD, existing pharmaceutical can only relieve its symptoms. RESULTS: Here, induced pluripotent stem cells were established from patients with low CAG repeat expansion in the huntingtin gene, and were then efficiently differentiated into GABA MS-like neurons (GMSLNs) under defined culture conditions. The generated HD GMSLNs recapitulated disease pathology in vitro, as evidenced by mutant huntingtin protein aggregation, increased number of lysosomes/autophagosomes, nuclear indentations, and enhanced neuronal death during cell aging. Moreover, store-operated channel (SOC) currents were detected in the differentiated neurons, and enhanced calcium entry was reproducibly demonstrated in all HD GMSLNs genotypes. Additionally, the quinazoline derivative, EVP4593, reduced the number of lysosomes/autophagosomes and SOC currents in HD GMSLNs and exerted neuroprotective effects during cell aging. CONCLUSIONS: Our data is the first to demonstrate the direct link of nuclear morphology and SOC calcium deregulation to mutant huntingtin protein expression in iPSCs-derived neurons with disease-mimetic hallmarks, providing a valuable tool for identification of candidate anti-HD drugs. Our experiments demonstrated that EVP4593 may be a promising anti-HD drug.

Cultivation and differentiation change nuclear localization of chromosome centromeres in human mesenchymal stem cells.

Chromosome arrangement in the interphase nucleus is not accidental. Strong evidences support that nuclear localization is an important mechanism of epigenetic regulation of gene expression. The purpose of this research was to identify differences in the localization of centromeres of chromosomes 6, 12, 18 and X in human mesenchymal stem cells depending on differentiation and cultivating time. We analyzed centromere positions in more than 4000 nuclei in 19 mesenchymal stem cell cultures before and after prolonged cultivation and after differentiation into osteogenic and adipogenic directions. We found a centromere reposition of HSAX at late passages and after differentiation in osteogenic direction as well as of HSA12 and HSA18 after adipogenic differentiation. The observed changes of the nuclear structure are new nuclear characteristics of the studied cells which may reflect regulatory changes of gene expression during the studied processes.