Risk stratification and prognosis prediction using cardiac biomarkers in COVID-19: a single-centre retrospective cohort study.

OBJECTIVE: There is a need for a robust tool to stratify the patient's risk with COVID-19. We assessed the prognostic values of cardiac biomarkers for COVID-19 patients. METHODS: This is a single-centre retrospective cohort study. Consecutive laboratory-confirmed COVID-19 patients admitted to the Kobe City Medical Center General Hospital from July 2020 to September 2021 were included. We obtained cardiac biomarker values from electronic health records and institutional blood banks. We stratified patients with cardiac biomarkers as high-sensitive troponin I (hsTnI), N-terminal pro-B-type natriuretic peptide (NT-proBNP), creatine kinase (CK) and CK myocardial band (CK-MB), using the clinically relevant thresholds. Prespecified primary outcome measure was all-cause death. RESULTS: A total of 917 patients were included. hsTnI, NT-proBNP, CK and CK-MB were associated with the significantly higher cumulative 30-day incidence of all-cause death (hsTnI: <5.0 ng/L group; 4.3%, 5.0 ng/L-99%ile upper reference limit (URL) group; 8.8% and ≥99% ile URL group; 25.2%, p<0.001. NT-proBNP: <125 pg/mL group; 5.3%, 125-900 pg/mL group; 10.5% and ≥900 pg/mL group; 31.9%, p<0.001. CK:

Effect and feasibility of the combination of branched chain amino acid and exercise therapy on muscle mass and echo intensity of muscle in orthopedic patients in a convalescent rehabilitation hospital: A crossover trial.

Background and Aims: This study examined the feasibility of nutritional support combined with exercise intervention for restoring muscle and physical functions in convalescent orthopedic patients. Methods: We used a crossover design in which nutritional support combined with exercise intervention was administered daily during the early (1 month) and late (1 month) cycles with a 1-week washout period. The exercise intervention was performed twice daily for 2 months in the early and late groups. The exercise intervention consisted of one set of muscle strength, stretching, and physical activity exercises for 20 min each. Nutritional interventions were administered immediately after the exercise. A 3.4 g of branched-chain amino acid supplements (BCAAs) or 1.2 g of starch was ingested. We measured the skeletal muscle mass and isometric muscle strength of the limbs and performed balance tests. After the crossover, the BCAA and Placebo groups were compared. Results: The ratio of improvement in the echo intensity of the rectus femoris (RF) was significantly higher in the BCAA group. A comparison of the order of nutritional intervention showed a significant effect on the RF echo intensity in both groups only when BCAAs were administered. Conclusion: This study's results suggest that the proposed combined intervention improves muscle quality and mass in convalescent orthopedic patients.

The CalcR-PKA-Yap1 Axis Is Critical for Maintaining Quiescence in Muscle Stem Cells.

Quiescence is a fundamental property of adult stem cells. Recent evidence indicates that quiescence is not a default state but requires active signaling that prevents accidental or untimely activation of stem cells. The calcitonin receptor (CalcR) is critical for sustaining quiescence in muscle satellite (stem) cells (MuSCs). However, the molecular mechanisms by which CalcR signaling regulates quiescence in MuSCs are enigmatic. Here, we demonstrate that transgenic expression of the catalytic domain of protein kinase A (PKA) restores the quiescence of CalcR-mutant MuSCs and delays MuSC activation. Mechanistically, CalcR-activated PKA phosphorylates Lats1/2, the main effector of Hippo signaling, thereby inhibiting the nuclear accumulation of Yap1, which prevents expression of Hippo-target genes, including cell-cycle-related molecules. Importantly, genetic inactivation of Yap1 in CalcR-mutant MuSCs reinstates quiescence in CalcR-mutant MuSCs, indicating that the CalcR-PKA-Lats1/2-Yap1 axis plays a critical role in sustaining MuSC quiescence.

Sustained expression of HeyL is critical for the proliferation of muscle stem cells in overloaded muscle.

In overloaded and regenerating muscle, the generation of new myonuclei depends on muscle satellite cells (MuSCs). Because MuSC behaviors in these two environments have not been considered separately, MuSC behaviors in overloaded muscle remain unexamined. Here, we show that most MuSCs in overloaded muscle, unlike MuSCs in regenerating muscle, proliferate in the absence of MyoD expression. Mechanistically, MuSCs in overloaded muscle sustain the expression of Heyl, a Notch effector gene, to suppress MyoD expression, which allows effective MuSC proliferation on myofibers and beneath the basal lamina. Although Heyl-knockout mice show no impairment in an injury model, in a hypertrophy model, their muscles harbor fewer new MuSC-derived myonuclei due to increased MyoD expression and diminished proliferation, which ultimately causes blunted hypertrophy. Our results show that sustained HeyL expression is critical for MuSC proliferation specifically in overloaded muscle, and thus indicate that the MuSC-proliferation mechanism differs in overloaded and regenerating muscle.

Cell-autonomous and redundant roles of Hey1 and HeyL in muscle stem cells: HeyL requires Hes1 to bind diverse DNA sites.

The undifferentiated state of muscle stem (satellite) cells (MuSCs) is maintained by the canonical Notch pathway. Although three bHLH transcriptional factors, Hey1, HeyL and Hes1, are considered to be potential effectors of the Notch pathway exerting anti-myogenic effects, neither HeyL nor Hes1 inhibits myogenic differentiation of myogenic cell lines. Furthermore, whether these factors work redundantly or cooperatively is unknown. Here, we showed cell-autonomous functions of Hey1 and HeyL in MuSCs using conditional and genetic null mice. Analysis of cultured MuSCs revealed anti-myogenic activity of both HeyL and Hes1. We found that HeyL forms heterodimeric complexes with Hes1 in living cells. Moreover, our ChIP-seq experiments demonstrated that, compared with HeyL alone, the HeyL-Hes1 heterodimer binds with high affinity to specific sites in the chromatin, including the binding sites of Hey1. Finally, analyses of myogenin promoter activity showed that HeyL and Hes1 act synergistically to suppress myogenic differentiation. Collectively, these results suggest that HeyL and Hey1 function redundantly in MuSCs, and that HeyL requires Hes1 for effective DNA binding and biological activity.

[Homeostasis and Disorder of Musculoskeletal System.Molecular mechanism underlying muscle development and regeneration.]

Skeletal muscle composes 30-40% of our body weight and is formed by multinuclear cells called myofibers. The formation of myofiber depends on the dynamic proliferation, differentiation and fusion of the myogenic progenitors during development. In the adult stage, the skeletal muscle exhibits excellent regeneration ability as well, depended on the muscle stem(satellite)cells that generate and repair myofibers. In this review, we would like to introduce ① the mechanisms of myogenic progenitor-dependent myofiber formation in myogenesis, ② the common fusion mechanism for myogenesis and muscle regeneration, and ③ the current status and prospects for clinical application utilizing satellite cells.

Notch ligands regulate the muscle stem-like state ex vivo but are not sufficient for retaining regenerative capacity.

Myogenic stem cells are a promising avenue for the treatment of muscular disorders. Freshly isolated muscle stem cells have a remarkable engraftment ability in vivo, but their cell number is limited. Current conventional culture conditions do not allow muscle stem cells to expand in vitro with their bona fide engraftment efficiency, requiring the improvement of culture procedures for achieving successful cell-therapy for muscle disorders. Here we expanded mouse muscle stem cells and human myoblasts with Notch ligands, DLL1, DLL4, and JAG1 to activate Notch signaling in vitro and to investigate whether these cells could retain their engraftment efficiency. Notch signaling promotes the expansion of Pax7+MyoD- mouse muscle stem-like cells and inhibits differentiation even after passage in vitro. Treatment with Notch ligands induced the Notch target genes and generated PAX7+MYOD- stem-like cells from human myoblasts previously cultured on conventional culture plates. However, cells treated with Notch ligands exhibit a stem cell-like state in culture, yet their regenerative ability was less than that of freshly isolated cells in vivo and was comparable to that of the control. These unexpected findings suggest that artificial maintenance of Notch signaling alone is insufficient for improving regenerative capacity of mouse and human donor-muscle cells and suggest that combinatorial events are critical to achieve muscle stem cell and myoblast engraftment potential.

Molecular organizations of myofibrils of skeletal muscle studied by atomic force microscopy.

By applying AFM technology, we studied mechanical characteristics of myofibrils of skeletal muscle. The obtained results indicate that (1) the Z-band is the most rigid sarcomere component stabilizing the myofibril structures, (2) various filamentous components are inter-connected in sarcomere with sufficient mechanical strength to support the contractile force, and (3) the molecular structure of the overlap region between actin and myosin filaments is anisotropic. In any case the present studies clearly indicate that the AFM technique is a powerful tool to investigate the mechanical characteristics of sarcomere structure of muscle fiber.