Hepatic steatosis, a reversible state of metabolic dysregulation, can promote the onset of nonalcoholic steatohepatitis (NASH), and its transition is thought to be critical in disease evolution. The association between endoplasmic reticulum (ER) stress response and hepatocyte metabolism disorders prompted us to characterize ER stress-induced hepatic metabolic dysfunction in human induced pluripotent stem cell-derived hepatocytes (hiPSC-Hep), to explore regulatory pathways and validate a phenotypic in vitro model for progression of liver steatosis. We treated hiPSC-Hep with a ratio of unsaturated and saturated fatty acids in the presence of an inducer of ER stress to synergistically promote triglyceride accumulation and dysregulate lipid metabolism. We monitored lipid accumulation by high-content imaging and measured gene regulation by RNA sequencing and reverse transcription quantitative PCR analyses. Our results show that ER stress potentiated intracellular lipid accumulation by 5-fold in hiPSC-Hep in the absence of apoptosis. Transcriptome pathway analysis identified ER stress pathways as the most significantly dysregulated of all pathways affected. Obeticholic acid dose dependently inhibited lipid accumulation and modulated gene expression downstream of the farnesoid X receptor. We were able to identify modulation of hepatic markers and gene pathways known to be involved in steatosis and nonalcoholic fatty liver disease (NAFLD), in support of a hiPSC-Hep disease model that is relevant to clinical data for human NASH. Our results show that the model can serve as a translational discovery platform for the understanding of molecular pathways involved in NAFLD, and can facilitate the identification of novel therapeutic molecules based on high-throughput screening strategies.

Microphysiological systems provide the opportunity to model accelerated changes at the human tissue level in the extreme space environment. Spaceflight-induced muscle atrophy experienced by astronauts shares similar physiological changes to muscle wasting in older adults, known as sarcopenia. These shared attributes provide a rationale for investigating molecular changes in muscle cells exposed to spaceflight that may mimic the underlying pathophysiology of sarcopenia. We report the results from three-dimensional myobundles derived from muscle biopsies from young and older adults, integrated into an autonomous CubeLab™, and flown to the International Space Station (ISS) aboard SpaceX CRS-21 as part of the NIH/NASA funded Tissue Chips in Space program. Global transcriptomic RNA-Seq analyses comparing the myobundles in space and on the ground revealed downregulation of shared transcripts related to myoblast proliferation and muscle differentiation. The analyses also revealed downregulated differentially expressed gene pathways related to muscle metabolism unique to myobundles derived from the older cohort exposed to the space environment compared to ground controls. Gene classes related to inflammatory pathways were downregulated in flight samples cultured from the younger cohort compared to ground controls. Our muscle tissue chip platform provides an approach to studying the cell autonomous effects of spaceflight on muscle cell biology that may not be appreciated on the whole organ or organism level and sets the stage for continued data collection from muscle tissue chip experimentation in microgravity. We also report on the challenges and opportunities for conducting autonomous tissue-on-chip CubeLab^TMpayloads on the ISS.

Microphysiological systems (MPS), also referred to as tissue chips, incorporating 3D skeletal myobundles are a novel approach for physiological and pharmacological studies to uncover new medical treatments for sarcopenia. We characterize a MPS in which engineered skeletal muscle myobundles derived from donor‐specific satellite cells that model aged phenotypes are encapsulated in a perfused tissue chip platform containing platinum electrodes. Our myobundles were derived from CD56⁺ myogenic cells obtained via percutaneous biopsy of the vastus lateralis from adults phenotyped by age and physical activity. Following 17 days differentiation including 5 days of a 3 V, 2 Hz electrical stimulation regime, the myobundles exhibited fused myotube alignment and upregulation of myogenic, myofiber assembly, signaling and contractile genes as demonstrated by gene array profiling and localization of key components of the sarcomere. Our results demonstrate that myobundles derived from the young, active (YA) group showed high intensity immunofluorescent staining of α‐actinin proteins and responded to electrical stimuli with a ~1 μm displacement magnitude compared with non‐stimulated myobundles. Myobundles derived from older sedentary group (OS) did not display a synchronous contraction response. Hypertrophic potential is increased in YA‐derived myobundles in response to stimulation as shown by upregulation of insulin growth factor (IGF‐1), α‐actinin (ACTN3, ACTA1) and fast twitch troponin protein (TNNI2) compared with OS‐derived myobundles. Our MPS mimics disease states of muscle decline and thus provides an aged system and experimental platform to investigate electrical stimulation mimicking exercise regimes and may be adapted to long duration studies of compound efficacy and toxicity for therapeutic evaluation against sarcopenia.

Significance: The particulate guanylyl cyclase A receptor (GC-A), via its endogenous cardiac-derived hormones atrial natriuretic peptide (ANP) and b-type natriuretic peptide (BNP), plays a pivotal role in maintaining intravascular volume, arterial pressure, cardiovascular structure, function, and, more recently, metabolic homeostasis. As such, therapies to potentiate GC-A signaling via peptide augmentation have yielded promising results in clinical trials. A major breakthrough in GC-A therapeutics would be a small molecule that sensitizes the GC-A receptor to endogenous ANP or BNP, which to date does not exist. Here, we report the development of an orally bioavailable, small molecule positive allosteric modulator of GC-A that exhibits therapeutic activity in human hypertension and heart failure ex vivo.

Microgravity accelerates skeletal muscle degeneration, mimicking aspects of aging, yet its effects on muscle cell function remain underexplored. Using a muscle lab-on-chip model onboard the International Space Station (ISS), we examined 3D-bioengineered myobundles derived from young and older adult donors under microgravity. Electrical stimulation applied intermittently to the myobundles revealed reduced contraction magnitude in microgravity and decreased protein levels of myosin heavy chain 7, a main isoform in slow-twitch muscle fibers. Transcriptomic profiling revealed active myogenesis across ground and spaceflight samples, but younger electrically stimulated myobundles displayed enhanced mitochondrial-related gene expression in microgravity, while older and non-electrically stimulated myobundles were less responsive. Comparative analysis between young and older derived myobundles identified 86 muscle-specific age-associated genes altered in microgravity, linked to inflammation, mitochondrial dysfunction, and cellular stress. These findings highlight a unique age-related molecular response in microgravity and underscores electrical stimulation as a potential countermeasure. These insights advance our understanding of muscle aging and degeneration in microgravity, guiding future therapeutic strategies.