Hypothalamic Oxytocin Neuron Activation Attenuates Intermittent Hypoxia-Induced Hypertension and Cardiac Dysfunction in an Animal Model of Sleep Apnea

Oxytocin Receptor Expression and Activation in Parasympathetic Brainstem Cardiac Vagal Neurons

Autonomic imbalance, particularly reduced activity from brainstem parasympathetic cardiac vagal neurons (CVNs) is a major characteristic of many cardiorespiratory diseases. Therapeutic approaches to selectively increase CVN activity have been limited by lack of identified selective translational targets. Recent work has shown that there is an important excitatory synaptic pathway from oxytocin (OXT) neurons in the paraventricular nucleus of the hypothalamus (PVN) to brainstem CVNs, and that OXT could provide a key selective excitation of CVNs. In clinical studies, intranasal OXT increases parasympathetic cardiac activity, autonomic balance, and reduces obstructive event durations and oxygen desaturations in obstructive sleep apnea patients. However, the mechanisms by which activation of hypothalamic OXT neurons, or intranasal OXT, increases brainstem parasympathetic cardiac activity is poorly understood. CVNs are located in two cholinergic brainstem nuclei: the nucleus ambiguus (NA) and dorsal motor nucleus of the vagus (DMNX). In this study we characterize the co-localization of OXT receptors in CVNs (OXTR), as well as non-CVN cholinergic neurons, located in the NA and DMNX nuclei. Selective chemogenetic excitation of OXTR+ CVNs was performed by expressing DREADDs with a combination of Cre and flp dependent viruses. We found that OXT receptors are highly expressed in CVNs in the DMNX and OXT increases DMNX CVN activity, but the receptors and responses are absent in CVNs in the NA. Selective chemogenetic activation of OXTR+ CVNs in the DMNX evoked a rapid and sustained bradycardia.

Paranodal instability driven by axonal mitochondrial accumulation in ischemic demyelination and cognitive decline

BACKGROUND

Subcortical ischemic demyelination is the primary cause of vascular cognitive impairment in the elderly. However, its underlying mechanisms remain elusive.

METHODS

Using a bilateral common carotid artery stenosis (BACS) mouse model and an in vitro cerebellar slice model treated with low glucose-low oxygen (LGLO), we investigated a novel mechanism of vascular demyelination.

RESULTS

This work identified syntaphilin-mediated docking of mitochondria as the initial event preceding ischemic demyelination. This axonal insult drives paranodal retraction, myelin instability, and subsequent cognitive impairment through excessive oxidation of protein 4.1B by mitochondrial ROS. Syntaphilin knockdown reestablished the balance of mitochondrial axoplasmic transport, reduced axonal ROS burden, and consequently decreased the abnormal oxidation of protein 4.1B, an essential component that secures the Caspr1/contactin-1/NF155 complex tethered to the axonal cytoskeleton βII-Spectrin within paranodes. This ultimately protected the paranodal structure and myelin and improved cognitive function.

CONCLUSIONS

Our findings reveal a distinct pathological characteristic of ischemic demyelination and highlight the therapeutic potential of modulating axonal mitochondrial mobility to stabilize myelin structures and improve vascular cognitive impairment.

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

The role of TRAP1 in regulating mitochondrial dynamics during acute hypoxia-induced brain injury

Brain damage caused by acute hypoxia is associated with the physiological activities of mitochondria. Although mitochondria being dynamically regulated, our comprehensive understanding of the response of specific brain cell types to acute hypoxia remains ambiguous. Tumor necrosis factor receptor-associated protein 1 (TRAP1), a mitochondrial-based molecular chaperone, plays a role in controlling mitochondrial movements. Herein, we demonstrated that acute hypoxia significantly alters mitochondria morphology and functionality in both in vivo and in vitro brain injury experiments. Summary-data-based Mendelian Randomization (SMR) analyses revealed possible causative links between mitochondria-related genes and hypoxia injury. Advancing the protein-protein interaction network and molecular docking further elucidated the associations between TRAP1 and mitochondrial dynamics. Furthermore, it was shown that TRAP1 knockdown levels variably affected the expression of key mitochondrial dynamics proteins (DRP1, FIS1, and MFN1/2) in primary hippocampal neurons, astrocytes, and BV-2 cell, leading to changes in mitochondrial structure and function. Understanding the function of TRAP1 in altering mitochondrial physiological activity during hypoxia-induced acute brain injury could help serve as a potential therapeutic target to mitigate neurological damage.

PPARγ Agonist Rosiglitazone and Antagonist GW9662: Antihypertensive Effects on Chronic Intermittent Hypoxia-Induced Hypertension in Rats

The increased incidence of hypertension associated with obstructive sleep apnea (OSA) presents significant physical, psychological, and economic challenges. Peroxisome proliferator-activated receptor gamma (PPARγ) plays a role in both OSA and hypertension, yet the therapeutic potential of PPARγ agonists and antagonists for OSA-related hypertension remains unexplored. Therefore, we constructed a chronic intermittent hypoxia (CIH)-induced hypertension rat model that mimics the pathogenesis of OSA-related hypertension in humans. The model involved administering PPARγ agonist rosiglitazone (RSG), PPARγ antagonist GW9662, or normal saline, followed by regular monitoring of blood pressure and thoracic aorta analysis using staining and electron microscopy. Intriguingly, our results indicated that both RSG and GW9662 appeared to potently counteract CIH-induced hypertension. In silico study suggested that GW9662's antihypertensive effect might mediated through angiotensin II receptor type 1 (AGTR1). Our findings provide insights into the mechanisms of OSA-related hypertension and propose novel therapeutic targets.

Sex differences in cardiac transcriptomic response to neonatal sleep apnea

Pediatric obstructive sleep apnea poses a significant health risk, with potential long-term consequences on cardiovascular health. This study explores the dichotomous nature of neonatal cardiac response to chronic intermittent hypoxia (CIH) between males and females, aiming to fill a critical knowledge gap in the understanding of sex-specific cardiovascular consequences of sleep apnea in early life. Neonates were exposed to CIH until p28 and underwent comprehensive in vivo physiological assessments, including whole-body plethysmography, treadmill stress-tests, and echocardiography. Results indicated that male CIH rats weighed 13.7% less than age-matched control males (p = 0.0365), while females exhibited a mild yet significant increased respiratory drive during sleep (93.94 ± 0.84 vs. 95.31 ± 0.81;p = 0.02). Transcriptomic analysis of left ventricular tissue revealed a substantial sex-based difference in the cardiac response to CIH, with males demonstrating a more pronounced alteration in gene expression compared to females (5986 vs. 3174 genes). The dysregulated miRNAs in males target metabolic genes, potentially predisposing the heart to altered metabolism and substrate utilization. Furthermore, CIH in males was associated with thinner left ventricular walls and dysregulation of genes involved in the cardiac action potential, possibly predisposing males to CIH-related arrhythmia. These findings emphasize the importance of considering sex-specific responses in understanding the cardiovascular implications of pediatric sleep apnea.

Outcomes of hypothalamic oxytocin neuron-driven cardioprotection after acute myocardial infarction

Altered autonomic balance is a hallmark of numerous cardiovascular diseases, including myocardial infarction (MI). Although device-based vagal stimulation is cardioprotective during chronic disease, a non-invasive approach to selectively stimulate the cardiac parasympathetic system immediately after an infarction does not exist and is desperately needed. Cardiac vagal neurons (CVNs) in the brainstem receive powerful excitation from a population of neurons in the paraventricular nucleus (PVN) of the hypothalamus that co-release oxytocin (OXT) and glutamate to excite CVNs. We tested if chemogenetic activation of PVN-OXT neurons following MI would be cardioprotective. The PVN of neonatal rats was transfected with vectors to selectively express DREADDs within OXT neurons. At 6 weeks of age, an MI was induced and DREADDs were activated with clozapine-N-oxide. Seven days following MI, patch-clamp electrophysiology confirmed the augmented excitatory neurotransmission from PVN-OXT neurons to downstream nuclei critical for parasympathetic activity with treatment (43.7 ± 10 vs 86.9 ± 9 pA; MI vs. treatment), resulting in stark improvements in survival (85% vs. 95%; MI vs. treatment), inflammation, fibrosis assessed by trichrome blue staining, mitochondrial function assessed by Seahorse assays, and reduced incidence of arrhythmias (50% vs. 10% cumulative incidence of ventricular fibrillation; MI vs. treatment). Myocardial transcriptomic analysis provided molecular insight into potential cardioprotective mechanisms, which revealed the preservation of beneficial signaling pathways, including muscarinic receptor activation, in treated animals. These comprehensive results demonstrate that the PVN-OXT network could be a promising therapeutic target to quickly activate beneficial parasympathetic-mediated cellular pathways within the heart during the early stages of infarction.