Exercise Ameliorates Disruption of the Dystrophin-Associated Glycoprotein Complex and Fibrosis in the Aging Rat Heart

The dystrophin-glycoprotein complex (DGC) is localized and integrated into the cell membrane. The DGC provides a mechanical link between the cellular cytoskeleton and the extracellular matrix (ECM). In cardiac muscle, disruption of DGC might be involved in mediating cardiac remodeling that occurs with aging, cardiomyopathy, and heart failure through transforming growth factor-beta (TGF-ß). Decorin is a small leucine-rich proteoglycan closely related to the DGC component that binds to collagen. Decorin reduces fibrosis via inhibition of TGF-ß and myofibroblast formation. PURPOSE: To test the hypothesis that exercise training (ET) would alleviate age-related disruption of localization in DGC proteins (dystrophin, α-syntrophin, and β-sarcoglycan), and ET will upregulate decorin. METHODS: Young (3 mo.) and old (31 mo.) FBNF1 rats were assigned into sedentary (YS, OS) and exercise (YE, OE) groups (n=10/group), with ET rats training on a treadmill 45 min/d, 5 d/wk for 12 wk. Hearts were extracted, weighted, and dissected into the left ventricle (LV), septum, and right ventricle. LV and septa samples were homogenized, and protein expression was detected using western immunoblotting. Histology (H&E staining) and immunofluorescence were conducted to examine morphological changes and localization of DGC proteins, decorin, α-SMA, and TGF-ß. Aging and exercise comparisons were made using two-way ANOVA for repeated measure with Fisher’s LSD post hoc test (p\u3c.05). RESULTS: Dystrophin, α-syntrophin, and β-sarcoglycan in LV were delocalized from the membrane with aging, particularly in fibrotic areas, which was normalized by ET. LVs from old rats displayed higher TGF-β-positive staining and protein abundance (+94.5%,p\u3c.05), while TGF-β localization and protein levels were suppressed in OE vs. OS, (-27.5%, p\u3c.05). α-SMA localization was significantly elevated with age (+77.3%, p\u3c.05), but reducedin old hearts with ET (-27.5%, p\u3c.05). Furthermore, collagen type 1 signal intensity was higher in OS (+43.7%, p\u3c.05), and was significantly ameliorated with ET (-27.6%, p\u3c.05). CONCLUSIONS: Our findings indicate that exercise training provides significant protection against fibrosis, myofibroblast activation, and elevation of TGF-ß associated with upregulation of decorin and protection of DGC structure

Nox2 Inhibition Regulates Stress Response and Mitigates Skeletal Muscle Fiber Atrophy during Simulated Microgravity

Insufficient stress response and elevated oxidative stress can contribute to skeletal muscle atrophy during mechanical unloading (e.g., spaceflight and bedrest). Perturbations in heat shock proteins (e.g., HSP70), antioxidant enzymes, and sarcolemmal neuronal nitric oxidase synthase (nNOS) have been linked to unloading-induced atrophy. We recently discovered that the sarcolemmal NADPH oxidase-2 complex (Nox2) is elevated during unloading, downstream of angiotensin II receptor 1, and concomitant with atrophy. Here, we hypothesized that peptidyl inhibition of Nox2 would attenuate disruption of HSP70, MnSOD, and sarcolemmal nNOS during unloading, and thus muscle fiber atrophy. F344 rats were divided into control (CON), hindlimb unloaded (HU), and hindlimb unloaded +7.5 mg/kg/day gp91ds-tat (HUG) groups. Unloading-induced elevation of the Nox2 subunit p67phox-positive staining was mitigated by gp91ds-tat. HSP70 protein abundance was significantly lower in HU muscles, but not HUG. MnSOD decreased with unloading; however, MnSOD was not rescued by gp91ds-tat. In contrast, Nox2 inhibition protected against unloading suppression of the antioxidant transcription factor Nrf2. nNOS bioactivity was reduced by HU, an effect abrogated by Nox2 inhibition. Unloading-induced soleus fiber atrophy was significantly attenuated by gp91ds-tat. These data establish a causal role for Nox2 in unloading-induced muscle atrophy, linked to preservation of HSP70, Nrf2, and sarcolemmal nNOS

Mediation of the Translocation of nNOSμ During Unloading-Induced Atrophy of Skeletal Muscle via NOX2 Inhibition

Mechanical unloading results in detachment of the mu-splice variant of neuronal nitric oxidase synthase (nNOSμ) from the dystrophin-glycoprotein complex and sarcolemma and translocation to the cytosol. We recently found that reactive oxygen species (ROS) play a role in nNOSμ translocation during unloading and muscle atrophy. NOX2, an isoform of NADPH oxidase and source of ROS, may play a causal role in nNOSμ translocation. The purpose of the study was to determine the effectiveness of NOX2 peptidyl inhibition in reducing the translocation of nNOSμ from the sarcolemma and subsequently soleus CSA. Adult male Fisher 344 rats were randomly assigned to one of three groups: CON (control), HU-S (hind limb unloaded with gp91ds-tat scramble) and HU-G (hind limb unloaded with gp91ds-tat). The hind limb unloading period was 7 days. Mean body weights for CON (353.26 g ± 15.47), HU-S (305.14 g ± 18.18) and HU-G (306.34 g ± 16.84) at the beginning of the experiment were not significantly different. Muscle mass/body mass ratio for the gastrocnemius complex (gastrocnemius, plantaris and soleus) was significantly reduced in HU-S rats (10.08 mg/g ± 0.24) but was maintained in HU-G rats (10.88 mg/g ± 0.47). SMASH analysis revealed that average soleus CSA in HU-G rats (3293.08 μm2 ± 46.82) decreased significantly less than HU-S rats (2606.66 μm2 ± 33.46) compared with ambulatory controls (p \u3e 0.0001). Immunofluorescence and staining of nNOS activity with NADPH Diaphorase of soleus tissue showed considerable loss of sarcolemmal nNOSμ in the HU-S group while the HU-G group revealed substantial maintenance of nNOSμ at the sarcolemma. The results of this study suggest that NOX2 inhibition via gp91ds-tat is effective in reducing the translocation of nNOSμ from the sarcolemma to the cytosol and maintaining CSA of the soleus with mechanical unloading via the inhibition of NOX2

The LHS 1678 system : two earth-sized transiting planets and an astrometric companion orbiting an M dwarf near the convective boundary at 20 pc

Funding: The MEarth Team gratefully acknowledges funding from the David and Lucile Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based upon work supported by the National Science Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award), and AST-1616624, and upon work supported by the National Aeronautics and Space Administration under Grant No. 80NSSC18K0476 issued through the XRP Program. This work is made possible by a grant from the John Templeton Foundation. N. A.-D. acknowledges the support of FONDECYT project 3180063. TD acknowledges support from MIT’s Kavli Institute as a Kavli postdoctoral fellow. KH acknowledges support from STFC grant ST/R000824/1. E.A.G. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, the Brinson Foundation, and the Moore Foundation; The material is based upon work supported by NASA under award number 80GSFC21M0002. This work was supported by the lead author’s appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASAWe present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright (VJ = 12.5, Ks = 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04 R⊕ and 0.98 ± 0.06 R⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M⊕ and 1.4 M⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1 R⊕ in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung–Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.Publisher PDFPeer reviewe

Two Warm Super-Earths Transiting the Nearby M Dwarf TOI-2095

We report the detection and validation of two planets orbiting TOI-2095 (TIC 235678745). The host star is a 3700K M1V dwarf with a high proper motion. The star lies at a distance of 42 pc in a sparsely populated portion of the sky and is bright in the infrared (K=9). With data from 24 Sectors of observation during TESS's Cycles 2 and 4, TOI-2095 exhibits two sets of transits associated with super-Earth-sized planets. The planets have orbital periods of 17.7 days and 28.2 days and radii of 1.30 and 1.39 Earth radii, respectively. Archival data, preliminary follow-up observations, and vetting analyses support the planetary interpretation of the detected transit signals. The pair of planets have estimated equilibrium temperatures of approximately 400 K, with stellar insolations of 3.23 and 1.73 times that of Earth, placing them in the Venus zone. The planets also lie in a radius regime signaling the transition between rock-dominated and volatile-rich compositions. They are thus prime targets for follow-up mass measurements to better understand the properties of warm, transition radius planets. The relatively long orbital periods of these two planets provide crucial data that can help shed light on the processes that shape the composition of small planets orbiting M dwarfs.Comment: Submitted to AAS Journal

The LHS 1678 System: Two Earth-sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc

We present the Transiting Exoplanet Survey Satellite (TESS) discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright (V J = 12.5, K s = 8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70 ± 0.04 R ⊕ and 0.98 ± 0.06 R ⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M ⊕ and 1.4 M ⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1 R ⊕ in a 4.97 day orbit is also identified in multicycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung-Russell diagram. This gap is tied to the transition from partially to fully convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars

Muscular dystrophy-dystroglycanopathy in a family of Labrador retrievers with a LARGE1 mutation

Alpha-dystroglycan (αDG) is a highly glycosylated cell surface protein with a significant role in cell-to-extracellular matrix interactions in muscle. αDG interaction with extracellular ligands relies on the activity of the LARGE1 glycosyltransferase that synthesizes and extends the heteropolysaccharide matriglycan. Abnormalities in αDG glycosylation and formation of matriglycan are the pathogenic mechanisms for the dystroglycanopathies, a group of congenital muscular dystrophies. Muscle biopsies were evaluated from related 6-week-old Labrador retriever puppies with poor suckling, small stature compared to normal litter mates, bow-legged stance and markedly elevated creatine kinase activities. A dystrophic phenotype with marked degeneration and regeneration, multifocal mononuclear cell infiltration and endomysial fibrosis was identified on muscle cryosections. Single nucleotide polymorphism (SNP) array genotyping data on the family members identified three regions of homozygosity in 4 cases relative to 8 controls. Analysis of whole genome sequence data from one of the cases identified a stop codon mutation in the LARGE1 gene that truncates 40% of the protein. Immunofluorescent staining and western blotting demonstrated the absence of matriglycan in skeletal muscle and heart from affected dogs. Compared to control, LARGE enzyme activity was not detected. This is the first report of a dystroglycanopathy in dogs