Two Types of Mouse Models for Sarcopenia Research: Senescence Acceleration and Genetic Modification Models

Sarcopenia leads to loss of skeletal muscle mass, quality, and strength due to aging; it was recently given a disease code (International Classification of Diseases, Tenth Revision, Clinical Modification, M62.84). As a result, in recent years, sarcopenia-related research has increased. In addition, various studies seeking to prevent and treat sarcopenia by identifying the various mechanisms related to the reduction of skeletal muscle properties have been conducted. Previous studies have identified muscle synthesis and breakdown; investigating them has generated evidence for preventing and treating sarcopenia. Mouse models are still the most useful ones for determining mechanisms underlying sarcopenia through correlations and interventions involving specific genes and their phenotypes. Mouse models used to study sarcopenia often induce muscle atrophy by hindlimb unloading, denervation, or immobilization. Though it is less frequently used, the senescence-accelerated mouse can also be useful for sarcopenia research. Herein, we discuss cases where senescence-accelerated and genetically engineered mouse models were used in sarcopenia research and different perspectives to use them.

Two Types of Mouse Models for Sarcopenia Research: Senescence Acceleration and Genetic Modification Models

Sarcopenia leads to loss of skeletal muscle mass, quality, and strength due to aging; it was recently given a disease code (International Classification of Diseases, Tenth Revision, Clinical Modification, M62.84). As a result, in recent years, sarcopenia-related research has increased. In addition, various studies seeking to prevent and treat sarcopenia by identifying the various mechanisms related to the reduction of skeletal muscle properties have been conducted. Previous studies have identified muscle synthesis and breakdown; investigating them has generated evidence for preventing and treating sarcopenia. Mouse models are still the most useful ones for determining mechanisms underlying sarcopenia through correlations and interventions involving specific genes and their phenotypes. Mouse models used to study sarcopenia often induce muscle atrophy by hindlimb unloading, denervation, or immobilization. Though it is less frequently used, the senescence-accelerated mouse can also be useful for sarcopenia research. Herein, we discuss cases where senescence-accelerated and genetically engineered mouse models were used in sarcopenia research and different perspectives to use them.

Rodent Model of Muscular Atrophy for Sarcopenia Study

The hallmark symptom of sarcopenia is the loss of muscle mass and strength without the loss of overall body weight. Sarcopenia patients are likely to have worse clinical outcomes and higher mortality than do healthy individuals. The sarcopenia population shows an annual increase of ~0.8% in the population after age 50, and the prevalence rate is rapidly increasing with the recent worldwide aging trend. Based on International Classification of Diseases, Tenth Revision, a global classification of disease published by the World Health Organization, issued the disease code (M62.84) given to sarcopenia in 2016. Therefore, it is expected that the study of sarcopenia will be further activated based on the classification of disease codes in the aging society. Several epidemiological studies and meta-analyses have looked at the correlation between the prevalence of sarcopenia and several environmental factors. In addition, studies using cell lines and rodents have been done to understand the biological mechanism of sarcopenia. Laboratory rodent models are widely applicable in sarcopenia studies because of the advantages of time savings, cost saving, and various analytical applications that could not be used for human subjects. The rodent models that can be applied to the sarcopenia research are diverse, but a simple and fast method that can cause atrophy or aging is preferred. Therefore, we will introduce various methods of inducing muscular atrophy in rodent models to be applied to the study of sarcopenia.

Osteoclasts in the Inflammatory Arthritis: Implications for Pathologic Osteolysis

The enhanced differentiation and activation of osteoclasts (OCs) in the inflammatory arthritis such as rheumatoid arthritis (RA) and gout causes not only local bone erosion, but also systemic osteoporosis, leading to functional disabilities and morbidity. The induction and amplification of NFATc1, a master regulator of OC differentiation, is mainly regulated by receptor activator of NF-κB (RANK) ligand-RANK and calcium signaling which are amplified in the inflammatory milieu, as well as by inflammatory cytokines such as TNFα, IL-1β and IL-6. Moreover, the predominance of CD4+ T cell subsets, which varies depending on the condition of inflammatory diseases, can determine the fate of OC differentiation. Anti-citrullinated peptide antibodies which are critical in the pathogenesis of RA can bind to the citrullinated vimentin on the surface of OC precursors, and in turn promote OC differentiation and function via IL-8. In addition to adaptive immunity, the activation of innate immune system including the nucleotide oligomerization domain leucine rich repeat with a pyrin domain 3 inflammasome and TLRs can regulate OC maturation. The emerging perspectives about the diverse and close interactions between the immune cells and OCs in inflammatory milieu can have a significant impact on the future direction of drug development.

DICAM-mediated Inhibition of Type 1 Interferon System during Macrophage Differentiation of THP-1 Cells

OBJECTIVE: We have previously shown that DICAM inhibits LPS-mediated macrophage differentiation. However, less is known about the exact action mechanisms of DICAM on the macrophage function and differentiation. METHODS: To induce differentiation into a resting M0 macrophage, THP-1 cells were cultured with 100 nM PMA for 24 h, and then rested for 3 days. THP-1 cells were infected with 50 moi of control LacZ- or DICAM-containing adenovirus. The RNA expression profile associated with DICAM during THP-1 differentiation was analyzed with a microarray chip and in silico analysis with Ingenuity Pathway Analysis (IPA) program. RESULTS: A disease and function analysis of the microarray data in DICAM-overexpressed THP-1 cells revealed a suppression in the expression of multiple genes involved in the response of myeloid cells and phagocytes, and an increase of genes associated with apoptosis of fibroblast cell-line, and viral infection and replication. The canonical pathway analysis also showed the most prominent changes of signaling pathways that involve inflammation responses. An upstream regulator analysis identifyingmolecules upstream of the genes that potentially explain the observed expression changes revealed that IRF7 and the genes in type 1 interferon system, such as IFNA2 and IFNAR,was significantly attenuated by DICAM. A mechanistic network analysis confirmed a direct causal association between IRF7 and type 1 interferon system. A real-time RT-PCR analysis validating the microarray data verified the significant suppression of IRFs, IFNA2, and IFNB1. CONCLUSION: These results suggest that DICAM can be a critical regulator of type 1 interferon system, which is an essential mediator in the process of intracellular infection and systemic lupus erythematosus.

DICAM Inhibits Activation of Macrophage by Lipopolysaccharide

OBJECTIVE: DICAM, a dual Ig domain containing adhesion molecule, is involved in cell-cell adhesion through direct interaction with alphavbeta3 integrin. In our previous study showing the inhibitory role of DICAM in osteoclast differentiation, we found that DICAM also has a suppressive role in macrophage, the precursor cell of osteoclast. The role of DICAM in macrophage activation at the inflammatory milieu, however, remains obscure. METHODS: Expression pattern of DICAM by inflammatory cytokines and lipopolysaccharide (LPS) was studied with RAW264.7, a murine macrophage cell line. To study the role of DICAM on macrophage activation, we stably transduced DICAM, or empty vector, into RAW264.7, and then compared the LPS-mediated activation such as spreading and TNF-alpha production. RESULTS: DICAM was abundantly expressed in the synovial tissue of collagen-induced arthritis. When we assessed the expression of DICAM in RAW264.7 cells by mediators of inflammation, inflammatory cytokines, such as TNF-alpha, IL-1beta, and IFN-gamma, and M-CSF increased the expression of DICAM; however, LPS decreased. Functionally, DICAM that stably transduced-RAW264.7 cells showed attenuation of LPS-mediated macrophage activation including spreading and TNF-alpha production. DICAM decreased the phosphorylation of JNK MAP kinase by M-CSF and LPS stimulation, which was corroborated by a decrease in the expression of ITAM-associated receptors including Trem2, Pira1, and Oscar. Finally, a recombinant ectodomain of DICAM suppressed LPS-induced activation of RAW264.7 cells. CONCLUSION: These results indicate that DICAM acts as a negative regulator of LPS-mediated macrophage activation.

Effect of Ultraviolet Irradiation on Bone Metabolism: Serologic & Radiological Study in Mouse / 대한정형외과연구학회지

PURPOSE: The purpose of this study was to investigate the effects of low energy-ultraviolet B (UVB) irradiation on bone metabolism and turnover in mice. MATERIALS AND METHODS: Five-week old C57BL/6 mice were randomly allocated into two groups. Control group (n=35) was not exposed to UVB and experimental group (n=35) was exposed to low energy-UVB for 30 min a day during 7 days. Serological and radiological examination was performed at 0, 1, 2, 4, 8 week(s) of each group (n=7). RESULTS: Analysis of biochemical bone markers revealed that alkaline phosphatase (ALP) was detected higher in the UVB group compared to control group. Serum level of osteocalcin was higher in UVB group at 1st week after UVB irradiation (p=0.031). The mean value of Vitamin D was significantly higher in UVB group than control group (p=0.032). Bone mineral density (BMD) from both 5th lumbar spine (p=0.124) and femur (p=0.862) showed higher in UVB group than control group from two weeks after irradiation, but they were not statistically significant. CONCLUSION: Our study with radiological bone mineral density and serological tests for biochemical bone turnover markers revealed that ultraviolet irradiation contributed positive effect on bone formation.