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Myocardial infarction (MI) is a leading cause of death globally. Following MI, the heart undergoes remodeling leading to heart failure. The Hippo pathway is a major regulator of cell growth and survival in cardiomyocytes. Here, we show that serotonin receptor 2B (5-HT2B) regulates the Hippo pathway in cardiomyocytes and modulates heart remodeling following MI. 5-HT2B expression significantly enhanced the Hippo pathway effector Yes-associated protein (YAP) activity resulting in increased cardiomyocyte proliferation and decreased apoptosis. However, transgenic mice overexpressing 5-HT2B in cardiomyocytes had a lower survival rate post-MI. Conversely, modified mRNA (modRNA)-mediated transient 5-HT2B expression in the heart was sufficient to inhibit post-MI remodeling. Pharmacological screening of serotonergic compounds identified SB204741 as a modulator of the Hippo/YAP pathway in cardiomyocytes. SB204741 has been shown to protect the heart from adverse remodeling post-MI. Our findings identify 5-HT2B as a regulator of the Hippo pathway that can be targeted to improve cardiac phenotype following MI. Highlights•Serotonin receptor 2B (5HT2B) regulates the Hippo pathway and activates YAP in cardiomyocytes•5HT2B promotes cardiomyocyte proliferation and survival in vitro•Transgenic overexpression of 5HT2B exacerbates hypertrophic remodeling following MI•modRNA delivery of exogenous 5HT2B was partially protective against MI-induced remodeling Biochemical mechanism; Human metabolism; Molecular network

Background: The pathology of Alzheimer’s Disease (AD) is characterized by aggregates of amyloid beta (Aβ) peptides and neurofibrillary tau tangles. Increased blood-brain barrier (BBB) permeability and reduced Aβ clearance, which signal neurovascular dysfunction, have also been proposed as early markers of AD. Despite intense scrutiny, the mechanisms of AD remain elusive and novel treatments that address core symptoms of dementia are limited. New alternative methods (NAMs) aim to develop in-vitro translational models that recapitulate human pathology more accurately than previous models and could contribute to the development of new therapies. Methods: Here, we developed a NAM model of the cortical neurovascular unit (NVU) using brain cells derived from human induced pluripotent stem cells (hiPSCs) from a patient with AD and a healthy individual. Differentiated neurons, astrocytes, pericytes, microglia, and brain-like microvascular endothelial cells were cultured in a microphysiological system to create a brain-chip model to evaluate NVU-related endpoints. Results: Compared to control, AD brain-chips had reduced claudin-5 and ZO-1 expression and increased paracellular permeability. AD brain-chips also had decreased activity of the efflux transporter P-glycoprotein (P-gp), but its expression was unchanged. In AD brain-chips, levels of Aβ42, total tau, and p-tau 181 were decreased in protein lysates from the brain channel, while levels of total tau and p-tau 181 were increased in protein lysates from the vascular channel. Finally, AD brain-chips had increased levels of the proinflammatory markers IL-6 and MCP-1 in effluent from both brain and vascular channels. Conclusion: In this brain-chip model, we showed Aβ-independent NVU dysfunction that was related to neuroinflammation and vascular tau accumulation. This study demonstrates the utility of the brain-chip model to evaluate changes in NVU functions induced by AD-like pathology and highlights donor-specific responses associated with the use of hiPSC-derived models.

TAR DNA-binding protein 43 (TDP-43) dysfunction is a hallmark of several neurodegenerative diseases, including frontotemporal dementia, amyotrophic lateral sclerosis, and Alzheimer’s disease. Although cryptic exon inclusion is a well-characterized consequence of TDP-43 loss of function, emerging evidence reveals broader roles in RNA metabolism, notably in the regulation of alternative polyadenylation (APA) of disease-relevant transcripts. In the present study, we examined 3′ untranslated region lengthening events in the brains of individuals with frontotemporal lobar degeneration with TDP-43 pathology (FTLD-TDP), focusing on the functional impact of APA dysregulation. To investigate whether TDP-43-mediated APA events occur in the postmortem brain, we measured the 3′ untranslated region length of the retromer component vacuolar protein sorting 35 (VPS35) and the ETS transcription factor (ELK1) in the frontal cortex of a large cohort of FTLD-TDP patients and of healthy controls, and evaluated if these APA events are associated with FTLD-TDP clinical characteristic, markers of TDP-43 pathology [e.g., hyperphosphorylated TDP-43 and cryptic stathmin-2 RNA], or the expression of VPS35 and VPS29 proteins, the latter being essential to the retromer complex. We identified robust 3′ untranslated region lengthening of VPS35 and ELK1 in FTLD-TDP, which strongly associated with markers of TDP-43 pathology, and ELK1 APA also associated with an earlier age of disease onset. Functionally, VPS35 APA was associated with reduced VPS35 and VPS29 protein expression, and lower VPS35 levels were associated with increased hyperphosphorylated TDP-43 and cryptic stathmin-2 RNA. Together, these data implicate APA dysregulation as a critical downstream consequence of TDP-43 dysfunction and suggest that TDP-43 loss may contribute to retromer impairment through APA-mediated repression of retromer subunits. Recent work has shown that TDP-43 loss in frontotemporal dementia (FTD) induces changes in alternative polyadenylation, but the functional consequences of this are unclear. This study reports that 3′UTR lengthening of VPS35 in FTD patient brain samples correlates with reduced VPS35 and VPS29 protein levels, suggesting that TDP-43 loss induces retromer dysfunction.