Hojun Lee’s research while affiliated with Seoul Women's University and other places

Aging in mammals, including humans, is accompanied by loss of bone and muscular function and mass, characterized by osteoporosis and sarcopenia. Although resistance exercise training (RET) is considered an effective intervention, its effect is blunted in some elderly individuals. Fibroblast growth factor (FGF) and its receptor, FGFR, can modulate bone and muscle quality during aging and physical performance. To elucidate this possibility, the FGFR inhibitor NVP-BGJ398 was administrated to C57BL/6n mice for 8 weeks with or without RET. Treatment with NVP-BGJ398 decreased grip strength, muscular endurance, running capacity and bone quality in the mice. FGFR inhibition elevated bone resorption and relevant gene expression, indicating altered bone formation and resorption. RET attenuated tibial bone resorption, accompanied by changes in the expression of relevant genes. However, RET did not overcome the detrimental effect of NVP-BGJ398 on muscular function. Taken together, these findings provide evidence that FGFR signaling may have a potential role in the maintenance of physical performance and quality of bone and muscles.

This study aimed to examine the distribution and contractile properties of single muscle fiber sex/myosin heavy chain (MHC) type-related differences and to evaluate the correlation of cross-sectional area (CSA) and specific force (SF) in a single muscle fiber. Six young men and six young women were participated in this study. Muscle sample was obtained from vastus lateralis muscle. To examine potential gender differences within each fiber contractile properties (CSA, maximal isometric force, SF, maximal shortening velocity) and relationship between CSA and SF of single fiber using Pearson correlation. After mechanical measurements, single muscle fiber determined MHC isoforms using silver stain. MHC isoform composition did not differ by sex (chi-square=6.978, P=0.073). There were sex-related differences in CSA and maximal isometric force (P<0.05), but no fiber type-related differences (P>0.05). Related to SF and maximal shortening velocity, there were no sex-related differences only fiber type-related differences (P<0.05). However, there were differences in SF between single fiber types in men but not in women. A negative correlation was found between CSA and SF in both men and women (P<0.05). It is suggested that there might be different mechanical properties of cross-bridges according to sex.

Background: Increasing the participation rate in health screenings is a major challenge. In West Virginia, USA, where a statewide, state-funded school-based health screening program has been offered to fifth-grade students and their parents/guardians for nearly 20 years, more than 50% of eligible participants consistently opt-out. Consequently, the purpose of this investigation is to determine a parent/guardian's reasons for deciding whether to participate in a school-based health screening. Methods: A cross-sectional study design was used and a total of 216 parents/guardians of fourth-grade students from 10 elementary schools in the northeast region of West Virginia participated in the study. The survey, based on the theory of planned behavior (TPB), was used to explore a parent/guardian's intentions when opting in or out of a school-based health screening for their child, and included items that represented direct determinants, indirect determinants, and behavioral intentions. Multiple regression analyses were conducted to measure the questionnaire's potential to predict intentions and identify the predictive strength of each direct determinant. Results: Results show that attitude, subjective norms, and perceived behavioral control in the TPB (43%) provided strong evidence for predicting participation intentions. Specifically, attitude (β=0.73, P<0.001) was the strongest predictor of intention, followed by subjective norms (β=-0.17, P<0.01). Conclusion: This study suggests that strategies to facilitate positive attitudes and increase parental awareness of health screening initiatives may influence participation rates within community- and school-based programming.

Physical exercise is increasingly recognized as an important component in the neuroscience related field. What is the targeting of exercise and what accounts for the exercise’s benefits observed in neuroscience? Several types of exercise have been studied in various fields across physiological, psychological, and biochemical experiments of neuroscience. However, more clarity is needed to unveil optimal exercise conditions such as frequency, intensity, type, and time. In this review, we briefly highlight the positive effects of exercise on promoting brain function. Key areas relate to exercise neuroscience are as follow: structural level with synaptic plasticity and neurogenesis, functional level with behavioral development, and molecular level with possible mechanisms that involved in exercise-induced brain plasticity. Overall, we provide the importance of understanding the exercise neuroscience and highlight suggestions for future health research.

Aim We investigated whether exercise‐mediated acquisition of muscle mass and strength would occur in a concurrent manner in older adults. Methods A total of 152 community‐dwelling older adults (young‐old aged 65–74 years, old‐old aged >75 years) were allocated into either 8‐week comprehensive exercise training or the control group. Participants (n = 136) completed all pre‐ and post‐intervention testing visits (young‐old n = 73, old‐old n = 63). Older adults in exercise groups were subjected to a series of programmed elastic band and free exercises twice per week at three to five sets of 15–20 repetitions. Body composition, skeletal muscle mass, knee strength (extensors and flexors) and gait‐related physical function were evaluated as main variables. Results As expected, muscular mass and knee strength (both extensors and flexors) were inversely correlated with age in the old‐old group (all P < 0.001). However, knee extensor strength was the only lower limb component inversely correlated with age in the young‐old group (P < 0.043). Knee extensor strength was significantly increased by exercise training in both the young‐old and old‐old groups (young old P < 0.042, old‐old P < 0.011). Training‐induced muscle hypertrophy was observed only in the young‐old group (P < 0.025). the correlation of knee extensor strength against gait‐related physical function was the greatest, followed by knee flexor strength and muscle mass. Conclusions The present results showed that age‐associated strength decline of the knee extensor occurs earlier compared with the knee flexor during the aging process, and exercise training increases muscular strength without significant changes of muscle mass in older adults aged aged ≥75 years. Geriatr Gerontol Int 2019; ••: ••–••.

PURPOSE Grip strength has been well documented to represent whole body strength. This study was performed to investigate whether absolute and relative grip strength is associated with thigh strength, and thigh-derived single muscle fiber contractile properties. METHODS Twelve healthy young adults (mean age 27.42 years) received needle biopsy on vastus lateralis muscles. Chemically skinned muscle fibers (n=215) were used to analyze single muscle fiber contractile properties (cross sectional area, maximal force, specific force, maximal shortening velocity) and MHC isoform composition. Pearson correlation was tested to identify the relationship between dominant hand grip strength, thigh strength, and thigh-derived single muscle fiber contractile properties. RESULTS The distribution of MHC I was higher in all the subjects compared to MHC II (type I: 57.2%, IIa: 37.2%, IIa/IIx: 2.3%, IIx: 3.3%). Specific force (8.2%) and maximal shortening velocity (74%) in MHC II were greater than those of MHC I. Absolute and relative grip strength normalized by height had a positive correlation with knee extensor isometric (r=.777, r=.75) and isokinetic (r=.632, r=.603) strength. In addition, the positive correlation of knee extensor isometric and isokinetic strength was observed against both CSA and Po in the thigh-derived single muscle fiber. Finally, Absolute and relative grip strength normalized by height were positively correlated with CSA (r=.279, r=.267) and Po (r=.373, r=.351) in MHC II, but not in MHC I. CONCLUSIONS These data suggest that hand grip strength is highly associated with not only whole thigh muscle strength, but also thigh-derived fast single muscle fiber contractile properties (MHC II).

Exercise is regarded as a potent stimulus in modulation of glucose utility and mitochondrial adaptations in skeletal muscle, leading to enhanced metabolic health. As mitochondria play a crucial role in sustaining metabolic homeostasis, and disturbances in mitochondrial function are highly linked with development of metabolic diseases, a comprehensive understanding of exercise-mediated mitochondrial remodeling under the pathophysiological condition of type 2 diabetes is warranted to develop an efficient therapeutic strategy. Although it is evident that the primary etiology of type 2 diabetes is insulin resistance, there is accumulating evidence linking abnormal mitochondrial functional and morphological properties to development of type 2 diabetes. Despite this, the precise molecular and cellular events that underline these phenomena remain uncertain. Mitochondria are highly dynamic subcellular organelles that can change mass and shape as necessary via coordinated processes such as mitochondrial fusion, fission, and biogenesis. Mitochondrial fusion is controlled by proteins, including mitofusin-1, mitofusin-2, and optic atrophy protein 1, while the fission process is mainly modulated by control of fission protein 1 and dynamin-related protein 1. Peroxisome proliferator-activated receptor gamma coactivator-1α acts as a master controller of mitochondrial biogenesis. The present review’s primary aims were to briefly discuss the cellular mechanisms of muscle fiber type-dependent glucose uptake and to highlight emerging evidence linking disturbances in mitochondrial dynamics to development of insulin resistance and type 2 diabetes. The potential for exercise to normalize type 2 diabetes-induced aberrant mitochondrial integrity is also addressed.

Purpose: This study aimed to examine the exercise-mediated musculoskeletal recovery following hindlimb suspension (HS) in order to identify whether bone modeling and muscle hypertrophy would eventuate in a synchronized manner during recovery stage. Methods: To identify whether 2-week HS would be sufficient to induce a significant reduction of physiological indices in both tibia and adjacent hindlimb muscles, a total of 20 rats was randomized into 2-week HS (n = 10) and age-matched control group (n = 10, CON). Another batch of rats were randomly assigned to three different groups to identify recovery intervention effects following suspension: (1) 2-week HS followed by 4-week spontaneous reloading recovery (HRE, n = 7). (2) 2-week HS followed by 4-week progressive resistance ladder climbing exercise (HEX, n = 7). (3) Age-matched control (CON, n = 7). DXA, micro-CT, and ¹⁸F-sodium fluoride (NaF) imaging, and EIA analysis were utilized to measure tibia bone indices. Hindlimb muscle wet weight and grip strength were measured to evaluate muscle mass and strength, respectively. Results: In study 1, bone quality values [bone volume/total volume (BV/TV): -27%, areal bone mineral density (aBMD): -23%, mineral contents: -7.9%, mineral density: –4.1%, and bone density: -38.9%] and skeletal muscle weight (soleus: -46.8%, gastrocnemius: -19.6%, plantaris: -20.8%, TA: -22.8%, and EDL: -9.9%) were significantly lower in HS group compared to CON group. In study 2, micro-CT and DXA-based bone morphology (bone density, BT/TV, and aBMD) were fully recovered in HRE or HEX group. However, suspension-induced dysregulation of bone mineral metabolism was returned to age-matched control group in only HEX group, but not in HRE group. A greater level of biomarkers of bone formation (P1NF) and resorption (CTX-1) was observed in only HRE group compared to CON. The hindlimb skeletal muscle mass was significantly lower in both HRE and HEX groups compared to CON group. Hindlimb grip strength was the greatest in HEX group, followed by CON and HRE groups. Conclusion: Following HS, progressive resistance exercise promotes recovery rates of bone and skeletal muscle strength without a significant increase in muscular mass, suggesting that exercise-induced reacquisition of bone and muscle strength is independent of muscle hypertrophy during early recovery stage.

PURPOSE The purpose of this review was to determine the role of mitochondria in the maintenance of vascular homeostasis and to investigate the benefit of exercise in the regulation of mitochondrial integrity. METHODS In this review, a literature review was performed to summarize the role of mitochondria in the functional maintenance of vasculature and the effect of aerobic exercise training on the mitochondrial quantity- and quality-control. RESULTS Enhancing structural and functional integrity of mitochondria is regarded as a novel therapeutic target for the prevention and the improvement of cardiovascular diseases. Mitochondria have been regarded as the intracellular power plant for the generation of ATP, the molecular resource of intracellular energy transfer. However, the role of mitochondria goes beyond the oxidative phosphorylation in the vasculature. Mitochondrial dysfunction is directly associated with the development of cardiovascular diseases, such as atherosclerosis, hypertension, hyperlipidemia, and diabetes, by enhancing pro-inflammatory, pro-apoptotic, and pro-senescent mechanisms. Regular training of aerobic exercise may contribute to the maintenance of vascular homeostasis by regulating mitochondrial biogenesis, dynamics, and clearance. CONCLUSIONS Mitochondria are the emerging therapeutic target of the aerobic exercise for the maintenance and the improvement of vascular homeostasis.

[Purpose] Myogenic progenitors play a critical role in injury-induced myofiber regeneration. The purpose of this study was to characterize the effects of oleate and L-carnitine on the overall behavior of proliferating myogenic progenitors (myoblasts) and its link to the mitochondrial biogenic process. [Methods] C2C12 myoblasts were cultured either with no treatment, oleate, L-carnitine, or their mixture. Proliferating myoblasts were investigated under a phase-contrast microscope. Myonuclei and myosin heavy chain were stained with DAPI and MF20 antibody, respectively, in differentiated myotubes and visualized under florescence microscopy. Mitochondrial biogenic markers and porin were assessed by qRT-PCR or immunoblotting. [Results] Increased proliferation rate was observed in myoblasts conditioned with oleate or a mixture of oleate and L-carnitine in contrast to that in non-treated (NT) and L-carnitine-treated myoblasts. Myoblast viability was not statistically different among all tested groups. Fusion index and myotube width were greater in oleate- or L-carnitine-conditioned myotubes than those in NT myotubes, with the greatest effect seen in myotubes conditioned with the mixture. The gene expressions of Pgc1-α, Nrf1, and Tfam were the greatest in myotubes conditioned with the mixture, whereas the level of Ncor1 expression was lower compared to those of the other groups. Protein level of porin was the greatest in myotubes conditioned with the mixture, followed by that of individually treated myotubes with oleate and L-carnitine. [Conclusion] These results provide a critical piece of cellular evidence that combined treatment of oleate and L-carnitine could serve as a potential therapeutic strategy to facilitate biological activation of myogenic progenitors.