Biology subjects

Zeitz, M. J.

Publications and source records attributed to Zeitz, M. J..

3 recordsLinked to original sources

bioRxiv2025

An inducible genetic model of chronic hypoxic signaling in cardiomyocytes precipitates severe cardiomyopathy and remodeling.

Cardiovascular disease remains the leading cause of death globally, underscoring the need for physiologically relevant models to investigate mechanisms of heart failure and arrhythmia. Chronic activation of hypoxic signaling pathways, particularly via the hypoxia-inducible factor (HIF) axis, is a key contributor to cardiac remodeling under stress. A major regulator of HIF signaling is the von Hippel-Lindau tumor suppressor (VHL) which, under normoxic conditions, targets HIF for proteasomal degradation. Loss of VHL results in HIF accumulation and persistent hypoxic signaling, but constitutive cardiomyocyte-specific Vhl knockout models are confounded by developmental effects and early mortality. Here, we develop and characterize an inducible, cardiomyocyte-specific Vhl knockout mouse model as a non-invasive and temporally controlled system to study chronic hypoxic stress and its contribution to cardiac remodeling and disease. VhlLoxP/LoxP;MHC-MerCreMer+/- mice were administered tamoxifen to induce Vhl deletion in adult cardiomyocytes. Within 5-7 days post-induction, mice displayed reduced ejection fraction, increased cardiac diameter, and elevated expression of cardiac stress markers. Transcriptomic and protein analyses revealed downregulation of key genes involved in cardiac structure and electrophysiology, including Gja1 (Cx43), Cdh2 (N-cadherin), Cacna1c (CaV1.2), and Kcnq1. Importantly, these changes preceded overt cardiac remodeling, as confirmed in an abbreviated tamoxifen protocol. This inducible Vhl knockout model recapitulates hallmark features of dilated cardiomyopathy and highlights a subset of cardiac structural and ion channel genes as sensitive early responders to chronic hypoxic stress. This platform enables mechanistic dissection of disease onset and progression in ischemic heart disease and serves as a well-controlled and reproducible model for evaluating novel therapeutic strategies.

pathology↗

bioRxiv2024

Astrocytic connexin43 phosphorylation contributes to seizure susceptibility after mild Traumatic Brain Injury

Astrocytes play a crucial role in maintaining brain homeostasis through functional gap junctions (GJs) primarily formed by connexin43 (Cx43) in the cortical gray matter. These GJs facilitate electrical and metabolic coupling between astrocytes, allowing the passage of ions, glucose, and metabolites. Dysregulation of Cx43 has been implicated in various pathologies, including traumatic brain injury (TBI) and acquired epilepsy. After mild TBI/concussion, we previously identified a subset of atypical astrocytes, which are correlated with the development of spontaneous seizures. These astrocytes exhibit reduced Cx43 expression and coupling. However, atypical astrocytes represent a relatively small subset of astrocytes within the cortical gray matter and previous studies suggest an overall increase of Cx43 protein after TBI. Additionally, Cx43 also has non-junctional and channel-independent functions, which include hemichannel communication with the extracellular milieu, cell adhesion, protein trafficking, protein-protein interactions, and intracellular signaling. In the present study, we set out to determine how mild TBI initiates alterations to Cx43 protein expression and localization, how they may be regulated, and whether they contribute to seizure susceptibility. We demonstrate remarkable heterogeneity of Cx43 protein levels from astrocyte to astrocyte. In accordance with our previous findings, a subset of astrocytes lost Cx43 expression, yet total cortical Cx43 protein increased. At the subcellular level, junctional Cx43 protein levels remained stable, while hemichannels and/or cytoplasmic Cx43 were increased. Phosphorylation of Cx43 at serine 368, a key regulatory site influencing GJ assembly and function, increased after mild TBI. Critically, Cx43S368A mutant mice, lacking this phosphorylation, exhibited reduced susceptibility to pentylenetetrazol-induced seizures. These findings suggest that TBI-induced Cx43 phosphorylation enhances seizure susceptibility, while inhibiting this modification presents a potential therapeutic avenue for mitigating neuronal hyperexcitability and seizure development. Significance statementConnexin43 (Cx43) is the main protein comprising astrocyte gap junctions which mediate astrocyte coupling into cellular networks, but it also has other non-junctional functions. Many pathologies present with altered Cx43 regulation. In this study, we assessed Cx43 alterations after mild traumatic brain injury (TBI) in a mouse model. We found that while some astrocytes lost Cx43 expression, other astrocytes had increased cytoplasmic and hemichannel Cx43. This increase correlated with an increase in phosphorylated Cx43 at serine 368. Cx43S368A mutant mice, lacking this phosphorylation, exhibited reduced susceptibility to seizures induced by pentylenetetrazol (PTZ). These findings suggest that TBI-induced Cx43 phosphorylation enhances seizure susceptibility.

neuroscience↗

bioRxiv2022

Acute adenoviral cardiac infection elicits an arrhythmogenic substrate prior to inflammatory myocardial remodeling and myocarditis

BackgroundViral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases, and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate prior to significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species-specificity, models of infection are lacking and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse Adenovirus Type-3 (MAdV-3) was previously reported as cardiotropic, yet has not been utilized to understand mechanisms of cardiac infection and pathology. MethodsWe have developed MAdV-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart prior to an appreciable immune response or gross cardiomyopathy. ResultsOptical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against MAdV-3 induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of MAdV-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 (HAdV-5) increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data. ConclusionsTogether, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

pathology↗