Project description:Women’s aging is characterized by menopausal loss of ovarian function, which has been suggested as a contributing factor to aging-related muscle deterioration and predisposes to the metabolic dysfunctions. However, the underlying molecular mechanisms have remained unknown. To identify mechanisms, we utilized muscle samples from 24 pre- and postmenopausal women, established proteome-wide profiles and identified upstream regulators and downstream cellular pathways associated with the differences in age, menopausal status and use of hormone replacement therapy (HRT). None of the premenopausal women used hormonal medication while the postmenopausal women were monozygotic twin-sister pairs who were either current HRT users or had never used HRT. The proteomic analyses resulted in the quantification of 762 muscle proteins of which 158 were for the first time associated with female muscle aging. The Ingenuity Pathway Analysis pinpointed 17β-estradiol as a potential upstream regulator of the observed differences in the major downstream pathways including dysregulated cell death and glycolysis pathways. The results increase knowledge on the factors related to skeletal muscle signaling and aging. This is of importance, since the role of female sex hormones in the regulation of muscle cell signaling has been under appreciated and scarcely studied as compared to vast amount of data on male sex hormones and skeletal muscle. Our results clearly demonstrate the also female sex hormones and HRT should be considered as potential active players and an intervention targets to promote women’s muscular health.
Project description:As global life expectancy continues to climb, maintaining skeletal muscle function is increasingly essential to ensure a good life quality for aging populations. Calorie restriction (CR) is the most potent and reproducible intervention to extend health and lifespan, but is largely unachievable in humans. Therefore, identification of “CR mimetics” has received much attention. Since CR targets nutrient-sensing pathways centering on mTORC1, rapamycin, the allosteric inhibitor of mTORC1, has been proposed as a potential CR mimetic and counteracts age-related muscle loss. Therefore, we tested whether rapamycin acts via similar mechanisms as CR to slow muscle aging. Contrary to our prediction, long-term CR and rapamycin-treated geriatric mice display distinct skeletal muscle gene expression profiles despite both conferring benefits to aging skeletal muscle. Furthermore, CR improved muscle integrity in a mouse with nutrient-insensitive sustained muscle mTORC1 activity and rapamycin provided additive benefits to CR in aging mouse muscles. Therefore, RM and CR exert distinct, compounding effects in aging skeletal muscle, opening the possibility of parallel interventions to counteract muscle aging.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.