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Abstract
Background: Physical frailty in older individuals is characterized by subjective symptoms of fatigue and exercise intolerance (EI). Objective abnormalities in skeletal muscle (SM) mitochondrial high-energy phosphate (HEP) metabolism contribute to EI in inherited myopathies, but their presence or link to EI in the frail older adult is unknown. Methods: Three groups of ambulatory, community-dwelling adults with no history of significant coronary disease were studied: frail, older individuals (FO, 81±2.7 years, mean±SEM), non-frail, older individuals (NFO, 79±2.0 years), and healthy middle-aged controls (CONT, 51±2.1 years). Lower extremity SM HEP levels and mitochondrial function were measured with 31P magnetic resonance (MR) techniques during graded, multistage plantar flexion exercise (PFE). EI was quantified by six-minute walk and peak oxygen consumption during cardiopulmonary testing (peak-VO2). Results: During graded exercise, frail older (FO), non-frail older (NFO), and healthy middle-aged individuals all fatigued at similar SM HEP levels measured by 31P MR. However, FO fatigued fastest with several-fold higher rates of PFE-induced HEP decline, which correlated closely with shorter exercise duration in the MR scanner and with six-minute walk distance and lower peak oxygen consumption on cardiopulmonary testing (p<0.001 for all). SM mitochondrial oxidative capacity was lower in older individuals and correlated with rapid HEP decline but less closely with EI. Conclusions: Several-fold faster skeletal muscle energetic decline during exercise occurs in frail older individuals and correlates closely with multiple measures of EI. Rapid energetic decline represents an objective, functional measure of SM metabolic changes and a potential new target for mitigating frailty-associated physical limitations.
Authors
Sabra C. Lewsey, Kilian Weiss, Michael Schär, Yi Zhang, Paul A. Bottomley, T. Jake Samuel, Qian-Li Xue, Angela Steinberg, Jeremy Walston, Gary Gerstenblith, Robert G. Weiss
Abstract
Background: Patients infected with SARS-CoV-2 differ in the severity of disease. We hypothesized that characteristics of SARS-CoV-2 specific immunity correlate with disease severity. Methods: In this study, SARS-CoV-2 specific T-cells and antibodies were characterized in uninfected controls and patients with different COVID-19 related disease severity. SARS-CoV-2 specific T-cells were flow-cytometrically quantified after stimulation with SARS-CoV-2 peptide pools and analyzed for expression of cytokines (IFNγ, IL-2 and TNFα) and markers for activation, proliferation and functional anergy. SARS-CoV-2 specific IgG and IgA antibodies were quantified using ELISA. Moreover, global characteristics of lymphocyte subpopulations were compared between patient groups and uninfected controls Results: Despite severe lymphopenia affecting all major lymphocyte subpopulations, patients with severe disease mounted significantly higher levels of SARS-CoV-2 specific T-cells as compared to convalescent individuals. SARS-CoV-2 specific CD4 T-cells dominated over CD8 T-cells and closely correlated with the number of plasmablasts and SARS-CoV-2 specific IgA- and IgG-levels. Unlike in convalescents, SARS-CoV-2 specific T-cells in patients with severe disease showed marked alterations in phenotypical and functional properties, which also extended to CD4 and CD8 T-cells in general. Conclusion: Given the strong induction of specific immunity to control viral replication in patients with severe disease, the functionally altered characteristics may result from the need for contraction of specific and general immunity to counteract excessive immunopathology in the lung. Trial registration: n.a. Funding: The study was supported by institutional funds by M.S., and in part by grants of Saarland University (to M.S. and. R.B), the State of Saarland, and the Dr. Rolf M. Schwiete Stiftung to R.B.
Authors
David Schub, Verena Klemis, Sophie Schneitler, Janine Mihm, Philipp M. Lepper, Heinrike Wilkens, Robert Bals, Hermann Eichler, Barbara C. Gärtner, Sören L. Becker, Urban Sester, Martina Sester, Tina Schmidt
Abstract
A critical response to lysosomal membrane permeabilization (LMP) is the clearance of damaged lysosomes through a selective form of macroautophagy known as lysophagy. Although regulators of this process are emerging, whether organ and cell specific components contribute to the control of lysophagy remains incompletely understood. Here, we examine LMP and lysophagy in Niemann-Pick type C disease (NPC), an autosomal recessive disorder characterized by the accumulation of unesterified cholesterol within late endosomes and lysosomes, leading to neurodegeneration and early death. We demonstrate that NPC patient fibroblasts show enhanced sensitivity to lysosomal damage as a consequence of lipid storage. Moreover, we describe a role for the glycan binding F-box protein Fbxo2 in CNS lysophagy. Fbxo2 functions as a component of the SCF ubiquitin ligase complex. Loss of Fbxo2 in mouse primary cortical cultures delays clearance of damaged lysosomes and decreases viability following lysosomal damage. Moreover, Fbxo2 deficiency in a mouse model of NPC exacerbates deficits in motor function, enhances neurodegeneration, and reduces survival. Collectively, our data identify a role for Fbxo2 in CNS lysophagy and establish its functional importance in NPC.
Authors
Elaine A. Liu, Mark L. Schultz, Chisaki Mochida, Chan Chung, Henry L. Paulson, Andrew P. Lieberman
Abstract
Dilated cardiomyopathy (DCM) is often associated with sarcomere protein mutations that confer reduced myofilament tension-generating capacity. We demonstrate that cardiac twitch tension-time integrals can be targeted and tuned to prevent DCM remodeling in hearts with contractile dysfunction. We employ a transgenic murine model of DCM caused by the D230N tropomyosin (Tm) mutation and design a sarcomere-based intervention specifically targeting the twitch tension-time integral of D230N-Tm hearts using multiscale computational models of intra- and inter-molecular interactions in the thin filament and cell-level contractile simulations. Our models predict that increasing the calcium-sensitivity of thin filament activation using the cardiac troponin C (cTnC) variant L48Q can sufficiently augment twitch tension-time integrals of D230N-Tm hearts. Indeed, cardiac muscle isolated from double-transgenic (DTG) hearts expressing D230N Tm and L48Q cTnC have increased calcium-sensitivity of tension development and increased twitch tension-time integrals compared to preparations from hearts with D230N Tm alone. Longitudinal echocardiographic measurements revealed that DTG hearts retain normal cardiac morphology and function, while D230N-Tm hearts develop progressive DCM. We present a computational and experimental framework for targeting molecular mechanisms governing the twitch tension of cardiomyopathic hearts to counteract putative mechanical drivers of adverse remodeling, and open new possibilities for tension-based treatments of genetic cardiomyopathies.
Authors
Joseph D. Powers, Kristina B. Kooiker, Allison B. Mason, Abigail E. Teitgen, Galina V. Flint, Jil C. Tardiff, Steven D. Schwartz, Andrew D. McCulloch, Michael Regnier, Jennifer Davis, Farid Moussavi-Harami
Abstract
Impaired tolerance to innocuous particles during allergic asthma has been linked to the increased plasticity of FoxP3+ regulatory T (Treg) cells, reprogramming into pathogenic effector cells, thus exacerbating airway disease. Failure in tolerance is suggested to be driven by TH2 inflammatory signals. The canonical IL-4Rα-signalling, an essential driver of TH2-type airway responses to allergens was investigated on its in vivo role on the regulatory function of FoxP3+ Tregs in allergic asthma. We used transgenic Foxp3creIL-4rα-/lox and littermate control mice to investigate the role of IL-4/IL-13 signalling via T regs in a house dust mite (HDM)-induced allergic airway disease. We sensitised mice intratracheally on day 0 and challenged them on day 6-10 and analysed airway hyperresponsiveness (AHR), airway inflammation, mucus production and cellular profile on day 14. In the absence of IL-4Rα responsiveness on FoxP3+ Tregs, there was an exacerbated AHR and airway inflammation in HDM-sensitised mice. Interestingly, a reduced induction of FoxP3+ Tregs accompanied increased IL-33 “alarmin” production and innate lymphoid cells type 2 (ILC2) activation in the lung exacerbating airway hyperreactivity and lung eosinophilia. We conclude that IL-4Rα unresponsive FoxP3+ T regulatory cells results in exaggerated innate TH2-type, IL-33-dependent airway inflammation and a break in tolerance during allergic asthma.
Authors
Jermaine Khumalo, Frank Kirstein, Sabelo Hadebe, Frank Brombacher
Abstract
Ischemia-reperfusion-induced edema (IRE) one of the most significant causes of mortality after lung transplantation can be mimicked ex-vivo in isolated perfused mouse lungs (IPL). Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel studied in endothelium, while its role in the lung epithelium remains elusive. Here we show enhanced IRE in TRPV4-deficient (TRPV4–/–) IPL compared to wild-type (WT) controls, indicating a protective role of TRPV4 to maintain the alveolar epithelial barrier. By immunohistochemistry, mRNA profiling and electrophysiological characterization, we detected TRPV4 in bronchial epithelium, alveolar type I (ATI) and alveolar type II (ATII) cells. Genetic ablation of TRPV4 resulted in reduced expression of the water conducting aquaporin-5 (AQP-5) channel in ATI cells. Migration of TRPV4–/– ATI cells was reduced and cell barrier function was impaired. Analysis of isolated primary TRPV4-deficient ATII cells revealed a reduced expression of surfactant protein C (SP-C) and the TRPV4 activator GSK1016790A induced increases in current densities only in WT ATII cells. Moreover, TRPV4–/– lungs of adult mice developed significantly larger mean chord lengths and altered lung function compared to WT lungs. Therefore, our data discover essential functions of TRPV4 channels in alveolar epithelial cells and in the protection from edema formation.
Authors
Jonas Weber, Suhasini Rajan, Christian Schremmer, Yu-Kai Chao, Gabriela Krasteva-Christ, Martina Kannler, Ali Önder Yildirim, Monika Brosien, Johann Schredelseker, Norbert Weissmann, Christian Grimm, Thomas Gudermann, Alexander Dietrich
Abstract
Background: Left atrial (LA) and left ventricular (LV) remodeling are associated with atrial fibrillation (AF). The prospective associations of impairment in cardiac mechanical function, as assessed by speckle-tracking echocardiography, with incident AF are less clear. Methods: In the Cardiovascular Health Study, a community-based cohort of older adults, participants free of AF with echocardiograms of adequate quality for speckle-tracking were included. We evaluated the associations of indices of cardiac mechanics (LA reservoir strain, LV longitudinal strain, and LV early diastolic strain rate) with incident AF. Results: Of 4,341 participants with strain imaging, participants with lower LA reservoir strain were older, had more cardiometabolic risk factors, and had lower renal function at baseline. Over median follow-up of 10 years, 497 (11.4%) participants developed AF. Compared with the highest quartile of LA reservoir strain, the lowest quartile of LA reservoir strain was associated with higher risk of AF after covariate adjustment, including LA volume and LV longitudinal strain (HR: 1.80, 95% CI: 1.31-2.45, P <0.001). The association of LA reservoir strain and AF was stronger in subgroups with higher blood pressure, NT-proBNP, and LA volumes. There were no associations of LV longitudinal strain and LV early diastolic strain rate with incident AF after adjustment for LA reservoir strain. Conclusion: Lower LA reservoir strain was associated with incident AF, independent of LV mechanics, and with stronger associations in high-risk subgroups. These findings suggest that mechanical dysfunction of the LA precedes the development of AF. Therapies targeting LA mechanical dysfunction may prevent progression to AF.
Authors
Ravi B. Patel, Joseph A. Delaney, Mo Hu, Harnish Patel, Jeanette Y. Cheng, John Gottdiener, Jorge R. Kizer, Gregory M. Marcus, Mintu P. Turakhia, Rajat Deo, Susan R. Heckbert, Bruce M. Psaty, Sanjiv J. Shah
Abstract
In the aging population, lower urinary tract (LUT) dysfunction is common and often leads to storage and voiding difficulties classified into overlapping symptom syndromes. Despite prevalence and consequences of these syndromes, LUT disorders continue to be undertreated simply because there are few therapeutic options. LUT function and structure were assessed in aged (>25 months) male and female Fischer 344 rats randomized to oral treatment with a purine nucleoside phosphorylase (PNPase inhibitor) 8-aminoguanine (8-AG) for 6 weeks or vehicle. The bladders of aged rats exhibited multiple abnormalities: tactile insensitivity, vascular remodeling, reduced collagen-fiber tortuosity, increased bladder stiffness, abnormal smooth muscle morphology, swelling of mitochondria and increases in uro-damaging purine metabolites. Treatment of aged rats with 8-AG restored all evaluated histological, ultrastructural and physiological abnormalities toward that of a younger state. 8-AG, is an effective treatment that ameliorates key age-related structural and physiologic bladder abnormalities. Because PNPase inhibition blocks metabolism of inosine to hypoxanthine and guanosine to guanine, likely uro-protective effects of 8-AG are mediated by increased bladder levels of uro-protective inosine and guanosine and reductions in uro-damaging hypoxanthine and xanthine. These findings demonstrate 8-AG has translational potential for treating age-associated LUT dysfunctions and resultant syndromes in humans.
Authors
Lori A. Birder, Amanda Wolf-Johnston, Alan J. Wein, Fangzhou Cheng, Mara Grove-Sullivan, Anthony J. Kanai, Alan M. Watson, Donna Stolz, Simon C. Watkins, Anne M. Robertson, Diane Newman, Roger R. Dmochowski, Edwin K. Jackson
Abstract
Focal adhesion kinase (FAK) is an important mediator of extracellular matrix-integrin mechano-signal transduction that regulates cell motility, survival, and proliferation. As such, FAK is being investigated as a potential therapeutic target for malignant and fibrotic diseases, and numerous clinical trials of FAK inhibitors are underway. The function of FAK in non-malignant non-motile epithelial cells is not well understood. We previously showed that hepatocytes demonstrated activated FAK near stiff collagen tracts in fibrotic liver. In this study, we examined the role of liver epithelial FAK by inducing fibrotic liver disease in mice with liver epithelial FAK deficiency. We found that mice that lack FAK in liver epithelial cells develop more severe liver injury and worse fibrosis as compared to controls. Increased fibrosis in liver epithelial FAK-deficient mice is linked to the activation of several pro-fibrotic pathways, including the hedgehog-smoothened pathway. FAK-deficient hepatocytes produce increased Indian hedgehog in a manner dependent on matrix stiffness. Furthermore, expression of the hedgehog receptor, smoothened, is increased in macrophages and biliary cells of hepatocyte-specific FAK-deficient fibrotic liver. These results indicate that liver epithelial FAK has important regulatory roles in the response to liver injury and progression of fibrosis.
Authors
Yun Weng, Tyler J. Lieberthal, Vivian X. Zhou, Maya Lopez-Ichikawa, Manuel Armas-Phan, Tristan K. Bond, Miya C. Yoshida, Won-Tak Choi, Tammy T. Chang
Abstract
Protein phosphatase 2A is a ubiquitously expressed serine/threonine phosphatase which comprises a scaffold, a catalytic and multiple regulatory subunits and has been shown to be important in the expression of autoimmunity. We considered that a distinct subunit may account for the decreased production of interleukin-2 (IL-2) in people and mice with systemic autoimmunity. We show that the regulatory subunit PPP2R2D is increased in T cells from people with systemic lupus erythematosus and regulates IL-2 production. Mice lacking PPP2R2D only in T cells produce more IL-2 because the IL-2 gene and genes coding for IL-2 enhancing transcription factors remain open and the levels of the enhancer phosphorylated CREB are high. Mice with T cell-specific PPP2R2D deficiency display less systemic autoimmunity when exposed to a TLR7 stimulator. While genes related to regulatory T cell function do not change in the absence of PPP2R2D, regulatory T cells exhibit high suppressive function in vitro and in vivo. Because the ubiquitous expression of protein phosphatase 2A cannot permit systemic therapeutic manipulation, the identification of regulatory subunits able to control specific T cell functions opens the way for the development of novel, function-specific drugs.
Authors
Wenliang Pan, Amir Sharabi, Andrew P. Ferretti, Yinfeng Zhang, Catalina Burbano, Nobuya Yoshida, Maria G. Tsokos, George C. Tsokos
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