Regulation of eicosanoid signaling lipids to improve skeletal muscle function and increase healthspan during aging

ABSTRACT COVID-19 symptom severity is directly linked to age as well as other comorbidities such as diabetes, poor respiratory function, and cardiovascular disease. As of September 22, approximately 7.0 million cases of COVID- 19 have been reported in the US, and the overall cumulative COVID-19 hospitalization rate is high, with individuals over age 65 twelve times as likely as those under 40 to be hospitalized for COVID-19. While in the hospital, many COVID-19 patients require respiratory support from a ventilator. Although many patients survive COVID-19, recovery is prolonged due to diaphragm muscle weakness and some never completely recover due to ventilator-induced diaphragm dysfunction (VIDD), a condition that reduces the ability of a patient to be weaned to independent breathing. VIDD risk and severity increase in elderly COVID-19 patients who are particularly susceptible because they spend weeks, as opposed to days, immobilized and on mechanical ventilation. There is currently no treatment for VIDD. This project proposes to acquire preclinical data in support of a therapy for VIDD that utilizes a promising new small molecule that acts by a mechanism different from previously tested therapeutics developed to treat VIDD. Our preliminary data suggest that Prostaglandin E2 (PGE2), the target of our drug, acts on both muscle stem cells (MuSCs) to augment their proliferation and regenerative function, and on mature myofibers to improve strength, particularly in the elderly. We hypothesize that PGE2/EP4 signaling will act in aged diaphragm muscles as in aged limb muscles and can be modulated to improve diaphragm muscle function. Specifically, we aim to (i) demonstrate that PGE2 augments the proliferative and regenerative function of MuSCs isolated from human diaphragm biopsies obtained 4 hr after patients are put on a ventilator and (ii) assess the efficacy of our drug in enhancing MuSC function and promoting myofiber hypertrophy to counter diaphragm atrophy in a rodent model of VIDD. Toward these goals, we will utilize human diaphragm biopsies obtained from young (< 40yr) and elderly (> 65yr) patients at the time of cardiothoracic surgery and perform both functional assays of PGE2 treated human MuSC regenerative capacity in culture and following transplantation into immunodeficient mice. We will also assess in human diaphragm if the rapid atrophy induced by a ventilator leads to a decline in PGE2 levels and disruption of TGF-beta, cAMP/CREB, and AKT/FOXO signaling pathways. Finally, we will determine if PGE2 elevation via our therapeutic improves diaphragm function and regenerative capacity in the context of mechanical ventilation in a well-established rodent model of VIDD, which causes diaphragm atrophy and reduced contractile force. The project is a preclinical collaboration between Stanford faculty, Dr. Helen Blau, who characterized a novel small molecule drug as a potential therapeutic for sarcopenia, and Dr. Joseph Shrager, a prominent cardiothoracic surgeon who has carried out VIDD clinical trials. Our drug, if proven effective, may allow earlier weaning from ventilators of COVID-19 patients and significantly improve COVID-19 outcomes, particularly for elderly patients.