Glial reactivity and neuronal activation patterns in autonomic brain regions in heart failure with preserved ejection fraction
DOI: Pending DOI
Synopsis
The contribution of central neuroimmune mechanisms to autonomic imbalance in heart failure with preserved ejection fraction (HFpEF) remains unclear. We used an obese/hypertensive mouse model of HFpEF to characterize glial states and neuronal activation across autonomic brain regions. We observe early, transient glial reactivity and neuronal activation in parasympathetic nuclei, whereas these neuroimmune alterations persist in hypothalamic and sympathoexcitatory regions throughout disease progression. These changes occur without changes in total microglial numbers, suggesting phenotypic rather than proliferative remodeling. Our findings support region-specific neuroimmune alterations during HFpEF progression.
Background
Heart failure with preserved ejection fraction (HFpEF) is a leading cause of cardiovascular morbidity and mortality and is strongly associated with obesity, hypertension, metabolic dysfunction, and systemic inflammation1–3. Despite increasing recognition of inflammatory mechanisms in HFpEF, the contribution of central neuroimmune alterations and autonomic dysregulation to disease progression remains insufficiently understood4,5. Experimental and clinical studies suggest that autonomic imbalance, characterized by enhanced sympathetic activity and impaired parasympathetic regulation, contributes to cardiac dysfunction and adverse cardiovascular outcomes in HFpEF6,7. However, whether distinct neuroimmune states emerge across autonomic brain regions during disease development remains unclear. Glial cells, including microglia and astrocytes, dynamically respond to inflammatory and neuronal stress signals through region-specific phenotypic adaptations that may influence autonomic circuits7. We therefore aimed to characterize temporal patterns of glial reactivity and neuronal activation across key autonomic brain regions during HFpEF progression in mice.
Methods
Ten-week-old C57BL/6NJ mice received high-fat diet and L-NAME in drinking water for 8 weeks to induce an obese/hypertensive HFpEF phenotype. Body weight, blood pressure, glucose tolerance, heart rate variability, and echocardiographic parameters were assessed longitudinally. Brain tissue was collected at week 1 (early stage) and week 8 (established stage) following disease induction. Immunohistochemical analyses were performed in autonomic regions implicated in cardiovascular regulation, including the paraventricular nucleus (PVN), nucleus tractus solitarius (NTS), rostral ventrolateral medulla (RVLM), dorsal motor nucleus of the vagus (DMV), nucleus ambiguus (NA), area postrema (AP), and subfornical organ (SFO). Microglial morphology was assessed using Iba-1/CD68 imaging and morphometric analyses including soma size, solidity, and branching complexity. Astrocytic reactivity was assessed using GFAP-positive area fraction and integrated density measurements. Total microglial cell numbers were also quantified. To characterize region-specific microglial phenotypes, MHC-II and CD39 expression were evaluated. Neuronal activation was assessed using c-Fos immunoreactivity. Statistical comparisons were performed using mixed-effects models between HFpEF and control groups (N=5 per group), with p<0.05 considered statistically significant.
Results
At the established disease stage (week 8), mice exhibited increased body weight, elevated blood pressure, impaired glucose tolerance, reduced heart rate variability, and echocardiographic evidence of diastolic dysfunction compared with healthy controls. At week 1 following disease induction, glial reactivity in the PVN, NTS, RVLM, DMV, and NA was characterized by increased microglial soma size, increased solidity, reduced branching complexity, and increased astrocytic reactivity compared with controls (all p<0.05). In addition, neuronal activation was elevated, with an average 14-fold increase in c-Fos+ neurons across autonomic nuclei during this early stage. By week 8, elevated c-Fos expression and glial reactivity persisted predominantly in the PVN, NTS, and RVLM, with c-Fos+ neurons remaining on average 8.5-fold higher than in healthy controls (all p<0.01), whereas the DMV and NA demonstrated resolution of both glial reactivity and neuronal activation. Importantly, no significant differences in total microglial cell numbers were identified between groups. Region-specific microglial phenotypes were additionally identified, with an MHC-II-associated phenotype enriched in the SFO and AP and a CD39-associated phenotype enriched in the PVN, RVLM, and NTS.
Discussion
HFpEF progression is associated with dynamic and region-specific glial and neuronal remodeling across autonomic brain regions. Early transient activation within parasympathetic nuclei followed by persistent activation of hypothalamic and sympathoexcitatory circuits suggests evolving autonomic imbalance during disease progression. Importantly, these alterations occurred without changes in total microglial cell numbers, supporting the concept that functional state transitions rather than microglial expansion underlie neuroimmune remodeling in HFpEF. Distinct region-specific microglial phenotypes were also identified, with MHC-II–high microglia enriched in the circumventricular organs (SFO and AP), potentially reflecting cytokine-driven immune activation within these structures, which are known for sensing circulating inflammatory signals. In contrast, CD39-high microglia were enriched in the PVN, RVLM, and NTS, consistent with altered purinergic signaling within chronically activated autonomic circuits, potentially driven by increased extracellular ATP release from activated neurons, astrocytes, or vessels. These findings suggest pathological glia–neuron interactions that may contribute to dysautonomia and drive cardiac dysfunction in HFpEF, and support future investigation of neuromodulatory and neuroimmune-targeted approaches aimed at restoring autonomic balance in cardiometabolic heart failure.
Disclosures
Nothing to disclose by any authors.
References
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