Cardiac sympathetic afferent ablation to prevent ventricular arrhythmia complicating acute myocardial infarction by inhibiting activated astrocytes

Mitochondria-targeted sonodynamic modulation of neuroinflammation to protect against myocardial ischemia‒reperfusion injury

Sympathetic hyperactivation and inflammatory responses are the main causes of myocardial ischemia‒reperfusion (I/R) injury and myocardial I/R-related ventricular arrhythmias (VAs). Previous studies have demonstrated that light-emitting diodes (LEDs) could modulate post-I/R neuroinflammation, thus providing protection against myocardial I/R injury. Nevertheless, further applications of LEDs are constrained due to the low penetration depth (<1 cm) and potential phototoxicity. Low-intensity focused ultrasound (LIFU), an emerging noninvasive neuromodulation strategy with deeper penetration depth (∼10 cm), has been confirmed to modulate sympathetic nerve activity and inflammatory responses. Sonodynamic therapy (SDT), which combines LIFU with sonosensitizers, confers additional advantages, including superior therapeutic efficacy, precise localization of neuronal modulation and negligible side effects. Herein, LIFU and SDT were introduced to modulate post-myocardial I/R neuroinflammation to protect against myocardial I/R injury. The results indicated that LIFU and SDT inhibited sympathetic neural activity, suppressed the activation of astrocytes and microglia, and promoted microglial polarization towards the M2 phenotype, thereby attenuating myocardial I/R injury and preventing I/R-related malignant VAs. These insights suggest that LIFU and SDT inspire a noninvasive and efficient neuroinflammatory modulation strategy with great clinical translation potential thus benefiting more patients with myocardial I/R in the future. STATEMENT OF SIGNIFICANCE: Myocardial ischemia-reperfusion (I/R) may cause I/R injury and I/R-induced ventricular arrhythmias. Sympathetic hyperactivation and inflammatory response play an adverse effect in myocardial I/R injury. Previous studies have shown that light emitting diode (LED) can regulate I/R-induced neuroinflammation, thus playing a myocardial protective role. However, due to the low penetration depth and potential phototoxicity of LED, it is difficult to achieve clinical translation. Herein, we introduced sonodynamic modulation of neuroinflammation to protect against myocardial I/R injury, based on mitochondria-targeted nanosonosensitizers (CCNU980 NPs). We demonstrated that sonodynamic modulation could promote microglial autophagy, thereby preventing myocardial I/R injury and I/R-induced ventricular arrhythmias. This is the first example of sonodynamic modulation of myocardial I/R-induced neuroinflammation, providing a novel strategy for clinical translation.

Circulating mitochondria promoted endothelial cGAS-derived neuroinflammation in subfornical organ to aggravate sympathetic overdrive in heart failure mice

BACKGROUND

Sympathoexcitation contributes to myocardial remodeling in heart failure (HF). Increased circulating pro-inflammatory mediators directly act on the Subfornical organ (SFO), the cardiovascular autonomic center, to increase sympathetic outflow. Circulating mitochondria (C-Mito) are the novel discovered mediators for inter-organ communication. Cyclic GMP-AMP synthase (cGAS) is the pro-inflammatory sensor of damaged mitochondria.

OBJECTIVES

This study aimed to assess the sympathoexcitation effect of C-Mito in HF mice via promoting endothelial cGAS-derived neuroinflammation in the SFO.

METHODS

C-Mito were isolated from HF mice established by isoprenaline (0.0125 mg/kg) infusion via osmotic mini-pumps for 2 weeks. Structural and functional analyses of C-Mito were conducted. Pre-stained C-Mito were intravenously injected every day for 2 weeks. Specific cGAS knockdown (cGAS KD) in the SFO endothelial cells (ECs) was achieved via the administration of AAV9-TIE-shRNA (cGAS) into the SFO. The activation of cGAS in the SFO ECs was assessed. The expression of the mitochondrial redox regulator Dihydroorotate dehydrogenase (DHODH) and its interaction with cGAS were also explored. Neuroinflammation and neuronal activation in the SFO were evaluated. Sympathetic activity, myocardial remodeling, and cardiac systolic dysfunction were measured.

RESULTS

C-Mito were successfully isolated, which showed typical structural characteristics of mitochondria with double-membrane and inner crista. Further analysis showed impaired respiratory complexes activities of C-Mito from HF mice (C-MitoHF) accompanied by oxidative damage. C-Mito entered ECs, instead of glial cells and neurons in the SFO of HF mice. C-MitoHF increased the level of ROS and cytosolic free double-strand DNA (dsDNA), and activated cGAS in cultured brain endothelial cells. Furthermore, C-MitoHF highly expressed DHODH, which interacted with cGAS to facilitate endothelial cGAS activation. C-MitoHF aggravated endothelial inflammation, microglial/astroglial activation, and neuronal sensitization in the SFO of HF mice, which could be ameliorated by cGAS KD in the ECs of the SFO. Further analysis showed C-MitoHF failed to exacerbate sympathoexcitation and myocardial sympathetic hyperinnervation in cGAS KD HF mice. C-MitoHF promoted myocardial fibrosis and hypertrophy, and cardiac systolic dysfunction in HF mice, which could be ameliorated by cGAS KD.

CONCLUSION

Collectively, we demonstrated that damaged C-MitoHF highly expressed DHODH, which promoted endothelial cGAS activation in the SFO, hence aggravating the sympathoexcitation and myocardial injury in HF mice, suggesting that C-Mito might be the novel therapeutic target for sympathoexcitation in HF.