Ischemic cardiac injury regulates sleep through an immune-mediated heart-brain axis - Abstract The brain and heart are vital co-dependent organs and proper inter-organ communication is necessary for health. Brain-heart connectivity occurs through neuronal innervation and vascular supply of immune cells and molecules. This heart-brain axis is calibrated by many factors and one of the most important is sleep. Sleep influences the immune system and heart function through top-down efferent signaling. What is unknown, however, is if the heart or cardiovascular injury influences sleep and the brain’s sleep circuits through bottom-up proprioceptive mechanisms. As described herein, our preliminary data suggest that after ischemic myocardial infarction (MI) monocytes are rapidly recruited to the brain’s superior thalamus by reactive microglia. In the brain, monocytes generate TNF that signals through thalamic glutamatergic neurons to increase sleep. Our data purport that augmented sleep after MI limits cardiac sympathetic input to supports heart healing. Our goal is to document the neuroimmune pathways that regulate sleep after MI and the consequential brain-heart outputs that mediate cardiac recovery. Our specific hypothesis is that after MI microglia recruit TNF-producing monocytes to the thalamus to augment sleep which restricts sympathetic outflow from the brain to the heart and promotes cardiac healing. We will achieve our goal through three independent aims utilizing murine models and advanced tools in neuroscience, immunology, and cardiology. In Aim 1 we will investigate how thalamic neuroinflammation after MI promotes sleep. Using cellular tracking, functional, and reprogramming assays we will document changes in neuroinflammation, monocyte influx, and the blood brain barrier after MI. Telemetric recording and scoring of electroencephalogram (EEG) signals coupled with spectral analysis will quantify increases in sleep pressure, drive, and alterations in micro-architecture after MI. Supported by our preliminary data, microglia- specific deletion of Ccl2 or pharmacological blockade of TNF in the thalamus will link these pathways to sleep regulation post-MI. In Aim 2 we will assess how neuroinflammation after MI limits sympathetic output from the brain to the heart. We will stereotactically deliver anti-TNF compounds to the thalamus or delete Ccl2 from microglia and assess the impact on cardiac sympathetic responses post-MI by quantifying heart sympathetic nerve activity and abundance, catecholamine synthesis, and heart rate variability and arrhythmia by telemetric echocardiogram analysis. Finally, in Aim 3, we will modify sleep after MI and test the outcome on heart healing, inflammation, and sympathetic signaling. Mice will be subjected to sleep fragmentation after MI and cardiac flow cytometry, immunofluorescent imaging, and transcript sequencing will evaluate heart inflammation, fibrosis, and remodeling, while MRI will quantify heart function. Heart sympathetic responses will be evaluated; and we will test the specific hypothesis that sleep modulates cardiac inflammation by altering macrophage Adrβ2 catecholamine signaling. Supported by our multidisciplinary team, our discoveries will identify novel fundamental biology linking the brain, heart, and sleep, and advocate for rigorous sleep management in post-MI clinical care.
