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Background: Although several factors, such as sex and body schema, contribute to gait function, factors for gait dysfunction in Parkinson's disease (PD) have not been elucidated. Postural verticality, a higher-order neural mechanism of gait, is involved in generation of a gait program in healthy individuals; however, its role in patients with PD is unclear. Although subjective postural vertical (SPV), which denotes cognitive information about posture with verticality as the reference axis, is anteriorly and laterally shifted in patients with PD, the presence of sex-related differences in SPV and effect of SPV on gait function remain unclear. Since SPV affects the degree of flexion and lateral bending posture and long-term prognosis of PD, factors affecting SPV in patients with PD should be clarified to improve gait function., Research Question: Is vertical perception of posture (i.e., SPV) related to gait function in patients with PD? Are there any sex-related differences?, Methods: The gait and SPV were evaluated in 59 adult outpatients with PD (31 men and 28 women) using five gait (step length, walking speed, coefficient of variation of step time [step CV], cadence, and mean gait acceleration [acceleration]) and two SPV (SPV in the sagittal and coronal planes) assessments and compared between the sexes., Results: No sex-related differences were observed in the SPV in patients with PD. The SPV and gait assessments demonstrated no association in men. Walking speed and SPV in the sagittal plane (p = 0.029), and step CV and SPV in the coronal (p = 0.018) and sagittal planes (p = 0.032) were correlated in women., Significance: Although no sex-related differences in the SPV were observed, our results demonstrated that the SPV is involved in gait function in women but not in men with PD., Competing Interests: Declaration of Competing Interest This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A nonvolatile optical phase shifter is a critical component for enabling the fabrication of programmable photonic integrated circuits on a Si photonics platform, facilitating communication, computing, and sensing. Although ferroelectric materials such as BaTiO 3 offer nonvolatile optical phase shift capabilities, their compatibility with complementary metal-oxide-semiconductor fabs is limited. Hf 0.5 Zr 0.5 O 2 is an emerging ferroelectric material, which exhibits complementary metal-oxide-semiconductor compatibility. Although extensively studied for ferroelectric transistors and memories, its application to photonics remains relatively unexplored. Here, we show the optical phase shift induced by ferroelectric Hf 0.5 Zr 0.5 O 2 . We observed a negative change in refractive index at a 1.55 μm wavelength in a pristine device regardless of the direction of the applied electric field. The nonvolatile phase shift was only observed once in a pristine device. This non-reversible phase shift can be attributed to the spontaneous polarization within the Hf 0.5 Zr 0.5 O 2 film along the external electric field., (© 2024. The Author(s).)

Fast-twitch muscles are less susceptible to disuse atrophy, activate the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway, and increase protein synthesis under prolonged muscle disuse conditions. However, the mechanism underlying prolonged muscle disuse-induced mTORC1 signaling activation remains unclear. The mevalonate pathway activates the mTORC1 signaling pathway via the prenylation and activation of Ras homolog enriched in brain (Rheb). Therefore, we investigated the effects of hindlimb unloading (HU) for 14 days on the mevalonate and mTORC1 signaling pathways in the plantaris muscle, a fast-twitch muscle, in adult male rats. Rats were divided into HU and control groups. The plantaris muscles of both groups were harvested after the treatment period, and the expression and phosphorylation levels of metabolic and intracellular signaling proteins were analyzed using Western blotting. We found that HU increased the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme of the mevalonate pathway, and activated the mTORC1 signaling pathway without activating AKT, an upstream activator of mTORC1. Furthermore, HU increased prenylated Rheb. Collectively, these findings suggest that the activated mevalonate pathway may be involved in the activation of the Rheb/mTORC1 signaling pathway without AKT activation in fast-twitch muscles under prolonged disuse conditions., (© 2024 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

This study developed advanced ceramic materials with both healing and decomposition functions using a metastable product generated under superheated steam. The developed composite material comprises ZrC particles dispersed in a yttria-stabilized zirconia (YSZ) matrix. After introducing a surface crack of approximately 120 μm on the composite specimen, it showed a complete strength recovery rate after one hour of heat treatment under superheated steam at 400 °C, while it exhibited a decomposition behavior after one hour of heat treatment in air at 400 °C. The XRD analysis of the heat-treated specimens showed that the final product was monoclinic ZrO 2 under both steam and air conditions. In other words, full strength recovery in superheated steam was achieved by a chain reaction involving metastable intermediate products derived from H 2 O, unlike the reaction in air.

Aim: To understand the real-world use of abemaciclib in Japanese patients with early breast cancer (EBC). Methods: This retrospective observational study was conducted using a Japanese administrative claims database in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative EBC who received abemaciclib adjuvant therapy from December 2021-March 2023. Patient characteristics and treatment patterns were summarized. Results: Among 374 patients, 38.2, 51.6 and 63.4% patients received neoadjuvant chemotherapy, adjuvant chemotherapy and radiotherapy, respectively; 13.1% were chemotherapy naive. Tamoxifen (37.7%), letrozole (35.6%), anastrozole (24.3%) were the commonly prescribed concomitant adjuvant endocrine therapies. Abemaciclib dose reductions were observed in 42.0% patients. Conclusion: Use of abemaciclib for treatment of high-risk EBC was described, which could help inform patient selection and treatment patterns.

Introduction: Lumbar spondylolysis is the most common underlying cause of lower back pain (LBP) in young athletes. Conservative treatment methods are often used to reduce pain and promote healing. Several parameters may affect the duration of conservative treatment, such as the time to return to play (RTP), patient behavior, and physical parameters; however, no study has comprehensively assessed the factors that affect the time to RTP., Objectives: This study aimed to determine the factors associated with the time required for RTP among young athletes with early-stage spondylolysis receiving conservative treatment using structural equation modeling (SEM)., Methods: In this retrospective case series, 137 young athletes (128 males and 9 females, aged 9-18 years) with early-stage lumbar spondylolysis were enrolled. All patients were examined using plain radiography and magnetic resonance imaging and treated conservatively (sports cessation, wearing a corset, therapeutic exercises, and low-intensity pulsed ultrasound radiation). SEM was used to investigate the factors affecting the time to RTP in these patients., Results: The final model included the following factors: spondylolysis laterality, symptom duration, lower-extremity flexibility, treatment interval, patient adherence, and residual LBP. SEM revealed that patient adherence to physician orders (p < 0.01), treatment interval (p < 0.001), and spondylolysis laterality (p < 0.001) contributed directly to shortened RTP., Conclusion: Patient adherence is essential for reducing the time to RTP among young athletes receiving conservative treatment for early-stage spondylolysis., Competing Interests: Declaration of competing interest The authors declare no potential conflicts of interest with respect to the research, authorship, or publication of this article., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Controlling the chemical reaction rate concerning degradation and repair is found to be important to design advanced self-healing ceramics. The recovery and degradation behaviors of strength and stiffness were investigated by exposing aqueous solutions of different pH and calcium ion concentrations to the introduced crack on typical self-healing ceramics dispersed with alumina cement as a self-healing agent. The chemical reaction of cement undergoes the following three stages: dissolution of components such as calcium ions, formation of a gel, and formation of final products. Experimental and thermodynamic assessments revealed that even under conditions where the final products are identical (thermodynamic equilibrium), kinetic effects (excessive dissolution of components or insufficient crystal formation) result in strength degradation rather than repair. It was also suggested that the repair function could be enhanced by controlling the nucleation site of the crystals.

We designed a mesoscopic dielectric cuboid antenna connected to a flangeless WR-3.4 open-ended waveguide, and the antenna characteristics at 300 GHz were examined through simulations and experiments. Simulations confirmed that the flangeless design eliminated the flange-induced ripples in the radiation pattern, whose shape varied with frequency, and that the antenna operated in the full bandwidth of the WR-3.4 waveguide (220-330 GHz). Prototypes were then fabricated based on the simulation findings. A prototype with an antenna aperture area of 1.5 mm [Formula: see text] 1.5 mm and an antenna length of 2.35 mm exhibited an antenna gain of 17.2 dBi at 300 GHz and a voltage standing wave ratio of less than 1.5 throughout the WR-3.4 waveguide bandwidth. The level of the side lobes at about [Formula: see text] degrees in the E-plane pattern was approximately [Formula: see text] dB that of the main lobe. Therefore, the proposed antenna, connected to a flangeless waveguide, is a promising antenna for use in future short-range high-speed terahertz wireless applications such as kiosk downloads and board-to-board communication., (© 2023. Springer Nature Limited.)

This Letter demonstrates a high-speed fiber-terahertz-fiber system in the 355-GHz band using stable optical frequency comb generation and a photonics-enabled receiver. At the transmitter, a single dual-drive Mach-Zehnder modulator is employed to generate a frequency comb by driving the modulator under an optimal condition. At the antenna site, a photonics-enabled receiver consisting of an optical local oscillator signal generator, a frequency doubler, and an electronic mixer is used to downconvert the terahertz-wave signal to the microwave band. Simple intensity modulation and a direct detection method are used for transmitting the downconverted signal to the receiver over the second fiber link. To demonstrate the proof of concept, we transmitted a 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing signal over a system consisting of two radio-over-fiber links and a 4 m wireless link in the 355-GHz band and achieved a line rate of 60 Gb/s. We also successfully transmitted a 16-QAM subcarrier multiplexing single-carrier signal over the system and achieved a capacity of 50 Gb/s. The proposed system can facilitate the deployment of ultra-dense small cells in high-frequency bands in beyond-5G networks.

This study aimed to evaluate the mechanism of progression involved in knee osteoarthritis (OA). We used the computed tomography-based finite element method (CT-FEM) of quantitative X-ray CT imaging to calculate and create a model of the load response phase, wherein the greatest burden is placed on the knee joint while walking. Weight gain was simulated by asking a male individual with a normal gait to carry sandbags on both shoulders. We developed a CT-FEM model that incorporated walking characteristics of individuals. Upon simulating changes owing to a weight gain of approximately 20%, the equivalent stress increased extensively in both medial and lower leg aspects of the femur and increased medio-posteriorly by approximately 230%. As the varus angle increased, stress on the surface of the femoral cartilage did not change significantly. However, the equivalent stress on the surface of the subchondral femur was distributed over a wider area, increasing by approximately 170% in the medio-posterior direction. The range of equivalent stress affecting the lower-leg end of the knee joint widened, and stress on the posterior medial side also increased significantly. It was reconfirmed that weight gain and varus enhancement increase knee-joint stress and cause the progression of OA.

Muscle fiber composition is associated with physical performance, with endurance athletes having a high proportion of slow-twitch muscle fibers compared to power athletes. Approximately 45% of muscle fiber composition is heritable, however, single nucleotide polymorphisms (SNP) underlying inter-individual differences in muscle fiber types remain largely unknown. Based on three whole genome SNP datasets, we have shown that the rs236448 A allele located near the cyclin-dependent kinase inhibitor 1A (CDKN1A) gene was associated with an increased proportion of slow-twitch muscle fibers in Russian (n = 151; p = 0.039), Finnish (n = 287; p = 0.03), and Japanese (n = 207; p = 0.008) cohorts (meta-analysis: p = 7.9 × 10−5. Furthermore, the frequency of the rs236448 A allele was significantly higher in Russian (p = 0.045) and Japanese (p = 0.038) elite endurance athletes compared to ethnically matched power athletes. On the contrary, the C allele was associated with a greater proportion of fast-twitch muscle fibers and a predisposition to power sports. CDKN1A participates in cell cycle regulation and is suppressed by the miR-208b, which has a prominent role in the activation of the slow myofiber gene program. Bioinformatic analysis revealed that the rs236448 C allele was associated with increased CDKN1A expression in whole blood (p = 8.5 × 10−15) and with greater appendicular lean mass (p = 1.2 × 10−5), whereas the A allele was associated with longer durations of exercise (p = 0.044) reported amongst the UK Biobank cohort. Furthermore, the expression of CDKN1A increased in response to strength (p < 0.0001) or sprint (p = 0.00035) training. Accordingly, we found that CDKN1A expression is significantly (p = 0.002) higher in the m. vastus lateralis of strength athletes compared to endurance athletes and is positively correlated with the percentage of fast-twitch muscle fibers (p = 0.018). In conclusion, our data suggest that the CDKN1A rs236448 SNP may be implicated in the determination of muscle fiber composition and may affect athletic performance.

Chronic inflammation is considered as an etiology of obesity and type 2 diabetes. Brown adipose tissue (BAT) of obese animals shows increased inflammation. Regular exercise has anti-inflammatory effects; however, the effects of exercise training on BAT inflammation in obese animals remain unclear. Thus, this study aimed to investigate the effects of exercise training on inflammation-related signaling in the BAT of obese and diabetic rats. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an obese/diabetic rodent model, were randomly divided into either sedentary ( n  = 11) or exercise training ( n  = 8) groups. Long-Evans Tokushima Otsuka (LETO; n  = 9) rats were used as the nondiabetic sedentary controls. Exercise training using a treadmill was conducted 4 days per week for 20 weeks, starting at 5 weeks old. As a result, exercise training attenuated the phosphorylation levels of p65 and mitogen-activated protein kinases in the BAT of OLETF rats, concurrently with the improvement of obesity and systemic glucose tolerance. Moreover, exercise training decreased oxidative stress and increased the antioxidant and anti-inflammatory protein levels in the BAT. Conversely, exercise training did not alter the expression levels of uncoupling protein-1 and oxidative phosphorylation-related proteins in the BAT, which were lower in the OLETF rats than the LETO rats. In conclusion, our data suggest that exercise training prevents the activation of inflammatory signaling in the BAT of obese/diabetic rats., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Authors.)

This Letter demonstrates the transmission of fifth-generation new radio (5G NR) millimeter-wave signals over a seamless fiber-terahertz-wave mobile fronthaul system in the 350 GHz band for an ultra-dense small cell network. The system utilizes a simple optical heterodyne method at the transmitter and direct detection at the receiver. As a proof-of-concept demonstration, we successfully transmitted 256- and 64-quadrature amplitude modulation 5G-NR-compliant signals at 24.2 and 38 GHz over a seamless fiber-terahertz system in the 350 GHz band. The proposed system can provide a simple solution to facilitate the deployment of ultra-dense small cells in high-frequency bands in 5G networks and beyond.

Quantum well intermixing (QWI) on a III-V-on-insulator (III-V-OI) substrate is presented for active-passive integration. Shallow implantation at a high temperature, which is essential for QWI on a III-V-OI substrate, is accomplished by phosphorus molecule ion implantation. As a result, the bandgap wavelength of multi-quantum wells (MQWs) on a III-V-OI substrate is successfully tuned by approximately 80 nm, enabling the monolithic integration of electro-absorption modulators and waveguide photodetectors using a lateral p-i-n junction formed along the InP/MQW/InP rib waveguide. Owing to the III-V-OI structure and the rib waveguide structure, the parasitic capacitance per unit length can be reduced to 0.11 fF/µm, which is suitable for high-speed and low-power modulators and photodetectors. The presented QWI can extend the possibility of a III-V complementary metal-oxide-semiconductor (CMOS) photonics platform for large-scale photonic integrated circuits.

Purpose: Selpercatinib is a highly selective, potent, rearranged during transfection(RET)inhibitor. A global, multicenter, open-label, phase 1/2 study of selpercatinib(LIBRETTO-001, NCT03157128)has been ongoing since 2017. We evaluated the data of Japanese patients with RET fusion-positive non-small cell lung cancer(NSCLC)using 30 March 2020 cut-off data., Methods: Phase 2 of LIBRETTO-001 started after confirming the safety of the recommended phase 2 dose(160 mg bid, orally, 28-day cycles)in Japanese. The primary endpoint was the independently assessed objective response rate(RECIST v1.1)., Results: Japanese NSCLC patients, including 44 patients in cohort 1 who had previously received platinum-based(or other)chemotherapy, programmed cell death-1/programmed death-ligand 1 immunotherapy, or both, and four previously untreated patients in cohort 2, were analyzed. The objective response rate was 55.3%(95% confidence interval: 38.3, 71.4; one confirmed complete response, 20 confirmed partial responses)in 38 evaluable patients in cohort 1 who could be followed for ≥2 post-baseline scans. The only evaluable patient in cohort 2 had no response. The most frequent treatment- emergent adverse events were increased alanine aminotransferase, increased aspartate aminotransferase, and diarrhea., Conclusions: Selpercatinib appeared to be effective in Japanese patients with RET fusion-positive NSCLC, and the safety profile was not substantially different from published results.

Background: Focusing on compression fractures of bone by finite elements, we evaluated bone strength based on the computed tomography-based finite element method. However, the exposure dose is an issue. We aimed to investigate the quantity of reduction of the radiation dose with respect to the reference dose by comparing the calculation results of compression fractures of the vertebral body using experimental data obtained from the spine of a pig., Methods: Computed tomography images of a self-made phantom that enclosed the lower lumbar vertebra of edible wild pigs were obtained under baseline-dose conditions using various lower tube currents. Images obtained under reference-dose conditions were reconstructed using the filtered back-projection method, whereas images obtained under low-dose conditions were reconstructed using both the filtered back-projection method and the iterative reconstruction method. Computer simulations involving the creation of finite element models using all images were implemented for the compression load calculation for vertebral body parts. Based on the calculated results, images of the low-dose and reference-dose conditions were compared., Results: Using pigs' lower lumbar vertebrae, finite element model analysis of low-dose X-ray computed tomography images showed that equivalent results can be obtained with a dose of approximately 40% of the standard radiographic reference doses. As for the compression stress intensity, the same results as those under reference-dose conditions were obtained using the iterative reconstruction method in combination with computed tomography-based finite element method., Conclusions: The combination of the iterative reconstruction method with the computed tomography-based finite element method is an effective image reconstruction method for achieving dose reduction., Competing Interests: Declaration of competing interest None., (Copyright © 2021 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.)

Background: This study evaluated the safety and effectiveness of ramucirumab and docetaxel for non-small cell lung cancer (NSCLC) in real-world settings., Research Design and Methods: This single-arm, prospective, multicenter, non-interventional, post-marketing study was conducted in Japan between August 2016 and January 2020. Patients diagnosed with unresectable advanced/recurrent NSCLC were eligible for study inclusion. Data on adverse events (AEs) and survival were collected electronically., Results: Of 401 enrolled patients, 398 were eligible for study inclusion. Most patients were male (68.6%) with a median age of 67.0 years. Patients were predominantly diagnosed with adenocarcinoma (78.1%) or squamous cell carcinoma (16.6%); 46.2% received prior treatment with bevacizumab and 38.7% with immune-checkpoint inhibitors. AEs (any grade) were observed in 323 patients (81.2%; grade ≥ 3: n = 174, 43.7%). The most common AEs (any grade) were malaise (14.3%), decreased appetite (13.0%), and neutrophil count decrease (11.6%). At 12 months from treatment commencement, 93.2% of patients had discontinued, mostly due to progressive disease (53.4%) or AEs (28.3%). The 12-month survival rate was 56.7% (95% confidence interval: 51.5 - 61.8)., Conclusions: Data from real-world settings demonstrate ramucirumab and docetaxel treatment appears to be tolerable and effective in Japanese patients regardless of patient baseline characteristics and prior treatment.

We demonstrate terahertz (THz) wave generation by wavelength conversion in a ridge-type/bulk periodically poled lithium niobate (RT-/bulk-PPLN) under almost the same experimental conditions. When using the RT-PPLN, the ridge structure works as a slab waveguide for the incident pump beam (wavelength: ∼1 μm), and the generated THz wave (∼200 μm) was emitted uniformly from the entire side surface of the crystal. The RT-PPLN has a much higher conversion efficiency from the pumping beam to the THz wave than the bulk-PPLN, and the ratio improved several ten times compared with those of previous studies.

Human skeletal muscle fiber is heterogenous due to its diversity of slow- and fast-twitch fibers. In human, slow-twitched fiber gene expression is correlated to MOTS-c, a mitochondria-derived peptide that has been characterized as an exercise mimetic. Within the MOTS-c open reading frame, there is an East Asian-specific m.1382A>C polymorphism (rs111033358) that changes the 14th amino acid of MOTS-c (i.e., K14Q), a variant of MOTS-c that has less biological activity. Here, we examined the influence of the m.1382A>C polymorphism causing MOTS-c K14Q on skeletal muscle fiber composition and physical performance. The myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIa, and MHC-IIx) as an indicator of muscle fiber composition were assessed in 211 Japanese healthy individuals (102 men and 109 women). Muscular strength was measured in 86 physically active young Japanese men by using an isokinetic dynamometer. The allele frequency of the m.1382A>C polymorphism was assessed in 721 Japanese athletes and 873 ethnicity-matched controls. The m.1382A>C polymorphism genotype was analyzed by TaqMan SNP Genotyping Assay. Individuals with the C allele of the m.1382A>C exhibited a higher proportion of MHC-IIx, an index of fast-twitched fiber, than the A allele carriers. Men with the C allele of m.1382A>C exhibited significantly higher peak torques of leg flexion and extension. Furthermore, the C allele frequency was higher in the order of sprint/power athletes (6.5%), controls (5.1%), and endurance athletes (2.9%). Additionally, young male mice were injected with the MOTS-c neutralizing antibody once a week for four weeks to mimic the C allele of the m.1382A>C and assessed for protein expression levels of MHC-fast and MHC-slow. Mice injected with MOTS-c neutralizing antibody showed a higher expression of MHC-fast than the control mice. These results suggest that the C allele of the East Asian-specific m.1382A>C polymorphism leads to the MOTS-c K14Q contributes to the sprint/power performance through regulating skeletal muscle fiber composition., (Copyright © 2021. Published by Elsevier B.V.)

The demand for high-speed and highly efficient optical communication techniques has been rapidly growing due to the ever-increasing volume of data traffic. As well as the digital coherent communication used for core and metro networks, intensity modulation and direct detection (IM-DD) are still promising schemes in intra/inter data centers thanks to their low latency, high reliability, and good cost performance. In this work, we study a microresonator-based frequency comb as a potential light source for future IM-DD optical systems where applications may include replacing individual stabilized lasers with a continuous laser driven microresonator. Regarding comb line powers and spectral intervals, we compare a modulation instability comb and a soliton microcomb and provide a quantitative analysis with regard to telecom applications. Our experimental demonstration achieved a forward error correction (FEC) free operation of bit-error rate (BER) <10 -9 with a 1.45 Tbps capacity using a total of 145 lines over the entire C-band and revealed the possibility of soliton microcomb-based ultra-dense wavelength division multiplexing (WDM) with a simple, cost-effective IM-DD scheme, with a view to future practical use in data centers.

The specific human epidermal growth factor receptor 2 (HER2)-targeting monoclonal antibody trastuzumab shows considerable clinical efficacy in patients with HER2-overexpressing breast cancer. However, about 20% of patients who receive trastuzumab in the adjuvant setting relapse, and approximately half of patients with metastatic HER2-positive breast cancer develop resistance to trastuzumab within 1 year. Although the mechanism of trastuzumab resistance has been explored broadly, whether and how angiogenesis participates in trastuzumab resistance is unclear. Here, we examined the association between angiogenesis and trastuzumab resistance by using a trastuzumab-resistant cell line (SKBR3-TR). Compared with that from the parental trastuzumab-sensitive SKBR3 cells, the culture supernatant from SKBR3-TR cells significantly increased the sprouting of endothelial cells. To identify intercellular features that contribute to the induction of endothelial tube formation, proteomics revealed that α-crystallin B chain (αB-crystallin) was upregulated in SKBR3-TR cells. Moreover, silencing of αB-crystallin significantly repressed SKBR3-TR-induced tube formation, and knockdown of αB-crystallin in SKBR3-TR cells suppressed the activation of mechanistic target of rapamycin (mTOR) in endothelial cells. In addition, treatment with rapamycin, an inhibitor of mTOR, reversed the SKBR3-TR-induced promotion of tube formation. In summary, αB-crystallin enhanced the ability of SKBR3-TR cells to activate mTOR in endothelial cells and thus promote angiogenesis., Competing Interests: Declaration of competing interest All authors have no conflicts of interest., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Human muscle fiber composition is heterogeneous and mainly determined by genetic factors. A previous study reported that experimentally induced iron deficiency in rats increases the proportion of fast-twitch muscle fibers. Iron status has been reported to be affected by genetic factors. As the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms are strongly associated with iron status in humans, we hypothesized that the genotype score (GS) based on these polymorphisms could be associated with the muscle fiber composition in humans. Herein, we examined 214 Japanese individuals, comprising of 107 men and 107 women, for possible associations of the GS for iron status with the proportion of myosin heavy chain (MHC) isoforms (I, IIa, and IIx) as markers of muscle fiber composition. No statistically significant correlations were found between the GS for iron status and the proportion of MHC isoforms in all participants. When the participants were stratified based on sex, women showed positive and negative correlations of the GS with MHC-IIa (age-adjusted p = 0.020) and MHC-IIx (age-adjusted p = 0.011), respectively. In contrast, no correlation was found in men. In women, a 1-point increase in the GS was associated with 2.42% higher MHC-IIa level and 2.72% lower MHC-IIx level. Our results suggest that the GS based on the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms for iron status is associated with muscle fiber composition in women.