The establishment of human induced pluripotent stem cells (hiPSCs) has enabled the production of in vitro, patient-specific cell models of human disease. In vitro recreation of disease pathology from patient-derived hiPSCs depends on efficient differentiation protocols producing relevant adult cell types. However, myogenic differentiation of hiPSCs has faced obstacles, namely, low efficiency and/or poor reproducibility. Here, we report the rapid, efficient, and reproducible differentiation of hiPSCs into mature myocytes. We demonstrated that inducible expression of myogenic differentiation1 (MYOD1) in immature hiPSCs for at least 5 days drives cells along the myogenic lineage, with efficiencies reaching 70–90%. Myogenic differentiation driven by MYOD1 occurred even in immature, almost completely undifferentiated hiPSCs, without mesodermal transition. Myocytes induced in this manner reach maturity within 2 weeks of differentiation as assessed by marker gene expression and functional properties, including in vitro and in vivo cell fusion and twitching in response to electrical stimulation. Miyoshi Myopathy (MM) is a congenital distal myopathy caused by defective muscle membrane repair due to mutations in DYSFERLIN. Using our induced differentiation technique, we successfully recreated the pathological condition of MM in vitro, demonstrating defective membrane repair in hiPSC-derived myotubes from an MM patient and phenotypic rescue by expression of full-length DYSFERLIN (DYSF). These findings not only facilitate the pathological investigation of MM, but could potentially be applied in modeling of other human muscular diseases by using patient-derived hiPSCs.

Background While increasing coverage of effective vaccines against coronavirus disease 2019 (COVID-19), emergent variants raise concerns about breakthrough infection. Data are limited, however, whether breakthrough infection during the epidemic of the variant is ascribed to insufficient vaccine-induced immunogenicity. Methods We described incident COVID-19 in relation to the vaccination program among workers of a referral hospital in Tokyo. During the predominantly Delta epidemic, we followed 2,415 fully vaccinated staff (BNT162b2) for breakthrough infection and selected three matched controls. We measured post-vaccination neutralizing antibodies against the wild-type, Alpha (B.1.1.7), and Delta (B.1.617.2) strains using live viruses and anti-spike antibodies using quantitative assays, and compared them using the generalized estimating equation model between the two groups. Results No COVID-19 cases occurred 1–2 months after the vaccination program during the fourth epidemic wave in Japan, dominated by the Alpha variant, while 22 cases emerged 2–4 months after the vaccination program during the fifth wave, dominated by the Delta variant. In the vaccinated cohort, all 17 cases of breakthrough infection were mild or asymptomatic and had returned to work early. There was no measurable difference between cases and controls in post-vaccination neutralizing antibody titers against the wild-type, Alpha, and Delta, and anti-spike antibody titers, while neutralizing titers against the variants were considerably lower than those against the wild-type. Conclusions Post-vaccination neutralizing antibody titers were not decreased among patients with breakthrough infection relative to their controls under the Delta variant rampage. The result points to the importance of infection control measures in the post-vaccination era, irrespective of immunogenicity profile.

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Excessive fructose intake is a risk factor for gut symptoms in patients with inflammatory bowel disease, however, its effect on the intestinal tract has not been evaluated previously. The present study investigated the impact of a high-fructose diet (HFd) on intestinal barrier function in mice with experimental colitis. c57/BL6 mice were provided with either a HFd or control diet and either plain drinking water or water containing 1% dextran sulfate sodium (dSS) for 2 weeks. The disease activity index (dAI), pathological scores and expression of inflammatory cytokines were compared among the groups, and the proportions of fecal bacteria in the colon were analyzed. The body weight and colon length were significantly decreased, and the DAI and pathological scores were significantly increased in the DSS/HFD-treated mice compared with the non-dSS-treated and control diet mice. Regarding the expression of inflammatory cytokines, the levels of interleukin (IL)-6, IL-1β and tumor necrosis factor-α were significantly increased, and the expression of the tight junction protein occludin was significantly decreased in the dSS/HFd-treated mice. The total bacterial count was increased in the HFd mice. Taken together, these results indicate that an HFd resulted in the deterioration of intestinal barrier function and increased susceptibility to dSS-induced colitis.