Biology subjects

Young, L. H.

Publications and source records attributed to Young, L. H..

7 recordsLinked to original sources

bioRxiv2025

Transient AMPK activation by nutrient stress of high fat diet preserves cardiac electrophysiological stability and protects against arrhythmias

Sudden cardiac death (SCD) is a major complication of obesity, yet it remains unclear whether early metabolic stress, prior to the onset of overt obesity or structural remodeling, can independently promote arrhythmias. In vitro studies suggest that fatty acids can allosterically stimulate AMP-activated protein kinase (AMPK), a key metabolic sensor known to preserve myocardial viability and mitochondrial function following ischemia-reperfusion (I/R) injury. We hypothesized that AMPK signaling critically modulates the electrophysiological (EP) response to high-fat diet (HFD)-induced metabolic stress. MethodsTo test this, wild-type (WT) and AMPK kinase-dead (AMPK-KD) mice were subjected to an 8-week HFD regimen beginning at 4 weeks of age. Controls remained on normal diet (ND) for the same duration. Arrhythmia susceptibility was assessed ex vivo using rapid pacing and I/R challenge protocols. Changes in the EP substrate were defined by high-resolution optical action potential mapping. Underlying mechanisms were probed using western blotting, confocal and transmission electron microscopy. ResultsHFD-fed wild-type (WT) hearts did not display increased arrhythmia susceptibility in response to either burst pacing or I/R challenge. On the contrary, they exhibited a paradoxical enhancement in post-ischemic EP recovery compared to ND-fed controls. This improvement was associated with increased phosphorylation of canonical AMPK targets, including acetyl-CoA carboxylase (ACC) and raptor, consistent with the activation of a cardioprotective metabolic program. In sharp contrast, AMPK-deficient (AMPK-KD) hearts demonstrated heightened vulnerability to inducible ventricular tachycardia (VT), irrespective of diet. Conduction slowing emerged as an early EP abnormality in these hearts and served as the initial substrate (or first hit) that promoted their increased incidence of non-sustained VT. Notably, this conduction impairment arose in conjunction with an increase (rather than decrease) in Cx43 and Nav1.5 protein expression. Mechanistically, defective conduction in AMPK-KD hearts was linked to impaired autophagic degradation of intercalated disc proteins resulting from reduced phosphorylation of ULK1, a downstream effector of AMPK. Consequently, unphosphorylated Cx43 accumulated at the intercalated disc, likely replacing phosphorylated isoforms (p-Cx43). In addition, AMPK-KD hearts exhibited swollen, fragmented mitochondria and reduced levels of mitochondrial fusion proteins. Upon HFD challenge, this vulnerable mitochondrial substrate generated excessive reactive oxygen species (ROS) coinciding with accelerated repolarization. Together, impaired conduction and action potential shortening promoted VT sustenance in HFD-fed AMPK-deficient hearts. ConclusionsOur findings identify AMPK as a key metabolic regulator that integrates redox balance, mitochondrial integrity, and protein homeostasis to preserve cardiac excitability during early nutrient overload. Loss of AMPK signaling, as occurs with aging and advanced metabolic disease, may therefore represent a pivotal mechanism linking HFD to increased SCD risk.

physiology↗

bioRxiv2025

Two Specialized Intrinsic Cardiac Neuron Types Safeguard Heart Homeostasis and Stress Resilience

The intrinsic cardiac nervous system (ICNS), often referred to as "the little brain on the heart", plays a central role in heart-brain communication and is increasingly recognized as both a contributor to cardiac disorders, including atrial fibrillation, heart failure, and sudden cardiac death, and a growing target for therapeutic intervention. Despite its clinical relevance, the molecular and functional organization of the ICNS remains poorly understood. Using single-cell transcriptomics, high-resolution imaging, and cell-specific genetic tools in mice, we identified two molecularly distinct intrinsic cardiac neuron (ICN) subtypes marked by Npy and Ddah1, each exhibiting unique anatomical innervation patterns. Npy ICNs function as parasympathetic postganglionic neurons essential for maintaining coronary perfusion and cardiac homeostasis during routine physiological activity. In contrast, Ddah1 ICNs are crucial for preserving cardiac electrical stability and preventing sudden death under extreme stress. These findings uncover specialized ICNS pathways that support cardiac homeostasis and resilience, providing a foundation for developing targeted neurocardiac therapies for autonomic dysfunction in human heart disease.

neuroscience↗

bioRxiv2024

PIEZO1 overexpression in hereditary hemorrhagic telangiectasia arteriovenous malformations

BackgroundHereditary hemorrhagic telangiectasia (HHT) is an inherited vascular disorder characterized by arteriovenous malformations (AVMs). Loss-of-function mutations in Activin receptor-like kinase 1 (ALK1) cause type 2 HHT and Alk1 knockout (KO) mice develop AVMs due to overactivation of VEGFR2/PI3K/AKT signaling pathways. However, the full spectrum of signaling alterations in Alk1 mutants remains unknown and means to combat AVM formation in patients are yet to be developed. MethodsSingle-cell RNA sequencing of endothelial-specific Alk1 KO mouse retinas and controls identified a cluster of endothelial cells (ECs) that was unique to Alk1 mutants and that overexpressed fluid shear stress (FSS) signaling signatures including upregulation of the mechanosensitive ion channel PIEZO1. PIEZO1 overexpression was confirmed in human HHT lesions, and genetic and pharmacological PIEZO1 inhibition was tested in Alk1 KO mice, as well as downstream PIEZO1 signaling. ResultsPharmacological PIEZO1 inhibition, and genetic Piezo1 deletion in Alk1-deficient mice effectively mitigated AVM formation. Furthermore, we identified that elevated VEGFR2/AKT, ERK5-p62-KLF4, hypoxia and proliferation signaling were significantly reduced in Alk1-Piezo1 double ECKO mice. ConclusionsPIEZO1 overexpression and signaling is integral to HHT2, and PIEZO1 blockade reduces AVM formation and alleviates cellular and molecular hallmarks of ALK1-deficient cells. This finding provides new insights into the mechanistic underpinnings of ALK1-related vascular diseases and identifies potential therapeutic targets to prevent AVMs.

molecular biology↗

bioRxiv2024

An atypical E3 ligase safeguards the ribosome during nutrient stress

Metabolic stress must be effectively mitigated for the survival of cells and organisms. Ribosomes have emerged as signaling hubs that sense metabolic perturbations and coordinate responses that either restore homeostasis or trigger cell death. As yet, the mechanisms governing these cell fate decisions are not well understood. Here, we report an unexpected role for the atypical E3 ligase HOIL-1 in safeguarding the ribosome. We find HOIL-1 mutations associated with cardiomyopathy broadly sensitize cells to nutrient and translational stress. These signals converge on the ribotoxic stress sentinel ZAK. Mechanistically, mutant HOIL-1 excludes a ribosome quality control E3 ligase from its functional complex and remodels the ribosome ubiquitin landscape. This quality control failure renders glucose starvation ribotoxic, precipitating a ZAK-ATF4-xCT-driven noncanonical cell death. We further show HOIL-1 loss exacerbates cardiac dysfunction under pressure overload. These data reveal an unrecognized ribosome signaling axis and a molecular circuit controlling cell fate during nutrient stress.

cell biology↗

bioRxiv2024

Role of AMPK in Atrial Metabolic Homeostasis and Substrate Preference

Atrial fibrillation is the most common clinical arrhythmia and may be due in part to metabolic stress. Atrial specific deletion of the master metabolic sensor, AMP-activated protein kinase (AMPK), induces atrial remodeling culminating in atrial fibrillation in mice, implicating AMPK signaling in the maintenance of atrial electrical and structural homeostasis. However, atrial substrate preference for mitochondrial oxidation and the role of AMPK in regulating atrial metabolism are unknown. Here, using LC-MS/MS methodology combined with infusions of [13C6]glucose and [13C4]{beta}-hydroxybutyrate in conscious mice, we demonstrate that conditional deletion of atrial AMPK catalytic subunits shifts mitochondrial atrial metabolism away from fatty acid oxidation and towards pyruvate oxidation. LC-MS/MS-based quantification of acyl-CoAs demonstrated decreased atrial tissue content of long-chain fatty acyl-CoAs. Proteomic analysis revealed a broad downregulation of proteins responsible for fatty acid uptake (LPL, CD36, FABP3), acylation and oxidation. Atrial AMPK deletion reduced expression of atrial PGC1- and downstream PGC1-/PPAR/RXR regulated gene transcripts. In contrast, atrial [14C]2-deoxyglucose uptake and GLUT1 expression increased with fasting in mice with AMPK deletion, while the expression of glycolytic enzymes exhibited heterogenous changes. Thus, these results highlight the crucial homeostatic role of AMPK in the atrium, with loss of atrial AMPK leading to downregulation of the PGC1-/PPAR pathway and broad metabolic reprogramming with a loss of fatty acid oxidation, which may contribute to atrial remodeling and arrhythmia.

physiology↗

bioRxiv2023

Differential developmental blueprints of organ-intrinsic nervous systems

The organ-intrinsic nervous system is a major interface between visceral organs and the brain, mediating important sensory and regulatory functions in the body-brain axis and serving as critical local processors for organ homeostasis. Molecularly, anatomically, and functionally, organ-intrinsic neurons are highly specialized for their host organs. However, the underlying mechanism that drives this specialization is largely unknown. Here, we describe the differential strategies utilized to achieve organ-specific organization between the enteric nervous system (ENS)1 and the intrinsic cardiac nervous system (ICNS)2, a neuronal network essential for heart performance but poorly characterized. Integrating high-resolution whole-embryo imaging, single-cell genomics, spatial transcriptomics, proteomics, and bioinformatics, we uncover that unlike the ENS which is highly mobile and colonizes the entire gastrointestinal (GI) tract, the ICNS uses a rich set of extracellular matrix (ECM) genes that match with surrounding heart cells and an intermediate dedicated neuronal progenitor state to stabilize itself for a beads-on-the-necklace organization on heart atria. While ICNS- and ENS-precursors are genetically similar, their differentiation paths are influenced by their host-organs, leading to distinct mature neuron types. Co-culturing ENS-precursors with heart cells shifts their identity towards the ICNS and induces the expression of heart-matching ECM genes. Our cross-organ study thus reveals fundamental principles for the maturation and specialization of organ-intrinsic neurons.

neuroscience↗

bioRxiv2020

Type I Interferon Limits Viral Dissemination-Driven Clinical Heterogeneity in a Native Murine Betacoronavirus Model of COVID-19

Emerging clinical data demonstrates that COVID-19, the disease caused by SARS-CoV2, is a syndrome that variably affects nearly every organ system. Indeed, the clinical heterogeneity of COVID-19 ranges from relatively asymptomatic to severe disease with death resultant from multiple constellations of organ failures. In addition to genetics and host characteristics, it is likely that viral dissemination is a key determinant of disease manifestation. Given the complexity of disease expression, one major limitation in current animal models is the ability to capture this clinical heterogeneity due to technical limitations related to murinizing SARS-CoV2 or humanizing mice to render susceptible to infection. Here we describe a murine model of COVID-19 using respiratory infection with the native mouse betacoronavirus MHV-A59. We find that whereas high viral inoculums uniformly led to hypoxemic respiratory failure and death, lethal dose 50% (LD50) inoculums led to a recapitulation of most hallmark clinical features of COVID-19, including lymphocytopenias, heart and liver damage, and autonomic dysfunction. We find that extrapulmonary manifestations are due to viral metastasis and identify a critical role for type-I but not type-III interferons in preventing systemic viral dissemination. Early, but not late treatment with intrapulmonary type-I interferon, as well as convalescent serum, provided significant protection from lethality by limiting viral dissemination. We thus establish a Biosafety Level II model that may be a useful addition to the current pre-clinical animal models of COVID-19 for understanding disease pathogenesis and facilitating therapeutic development for human translation.

immunology↗