al-Abed, Y. | Search bioRxiv

bioRxiv2024

Intrinsic diving reflex induces potent antioxidative response by activation of NRF2 signaling

AimsThis study aims to elucidate the underlying mechanisms of diving reflex, a powerful endogenous mechanism supporting underwater mammalian survival. Antioxidative responses, observed in marine mammals, may be contributing factors. Using a multi-organ approach, this study assesses whether acute and chronic diving reflex activate nuclear factor-erythroid-2-related factor 2 (NRF2) signaling pathways, which regulate cellular antioxidant responses. MethodsMale Sprague-Dawley rats (n=38) underwent either a single diving session to elicit acute diving reflex, or daily diving sessions for 4-weeks to produce chronic diving reflex. NRF2 (total, nuclear, phosphorylated), NRF2-downstream genes, and malondialdehyde were assessed via Western blot, immunofluorescence, RT-PCR, and ELISA in brain, lung, kidney, and serum. ResultsDiving reflex increased nuclear NRF2, phosphorylated NRF2, and antioxidative gene expression, in an organ-specific and exposure time-specific manner. Comparing organs, the brain had the highest increase of phosphorylated NRF2 expression, while kidney had the highest degree of nuclear NRF2 expression. Comparing acute and chronic sessions, phosphorylated NRF2 increased the most with chronic diving reflex, but acute diving reflex had the highest antioxidative gene expression. Notably, calcitonin gene-related peptide appears to mediate diving reflex effects on NRF2 activation. ConclusionsAcute and chronic diving reflex activate potent NRF2 signaling in the brain and peripheral organs. Interestingly, acute diving reflex induces higher expression of downstream antioxidative genes compared to chronic diving reflex. This result contradicts previous assumptions requiring chronic exposure to diving for induction of antioxidative effects and implies that the diving reflex has a strong translational potential during preconditioning and postconditioning therapies. Key PointsO_LIDiving reflex activates potent NRF2 signaling via multiple mechanisms, including phosphorylation, nuclear translocation, and KEAP1 downregulation with both acute and chronic exposure. C_LIO_LIDiving reflex activates NRF2 via differential pathways in the brain and other organs; phosphorylated NRF2 increases more in the brain, while nuclear NRF2 increases more in the peripheral organs. C_LIO_LIAcute diving reflex exposure induces a more pronounced antioxidative effect than chronic diving reflex exposure, indicating that the antioxidative response activated by diving reflex is not dependent upon chronic adaptive responses and supports diving reflex as both a preconditioning and postconditioning treatment. C_LI

physiology↗

bioRxiv2023

Ultrasound neuromodulation of an anti-inflammatory pathway at the spleen produces sustained improvement of experimental pulmonary hypertension

BackgroundInflammation is pathogenically implicated in pulmonary arterial hypertension (PAH); however, it has not been adequately targeted therapeutically. We investigated whether neuromodulation of an anti-inflammatory neuroimmune pathway involving the splenic nerve using noninvasive, focused ultrasound stimulation of the spleen (sFUS) can improve experimental pulmonary hypertension (PH). MethodsPH was induced in rats either by SU5416 (20 mg/kg SQ) injection, followed by 21 (or 35) days of hypoxia (SuHx model), or by monocrotaline (60 mg/kg IP) injection (MCT model). Animals were randomized to receive either daily, 12-min-long sessions of sFUS or sham stimulation, for 14 days. Catheterizations, echocardiography, indices of autonomic function, lung and heart histology and immunohistochemistry, spleen flow cytometry and lung single-cell-RNA sequencing were performed after treatment to assess the effects of sFUS. ResultsSplenic denervation right before induction of PH results in a more severe phenotype. In both SuHx and MCT models of PH, sFUS treatment reduces right ventricular (RV) systolic pressure by 25-30% compared to sham therapy, without affecting systemic pressure, and improves RV function and autonomic indices. sFUS reduces wall thickness, apoptosis, and proliferation in small pulmonary arterioles, suppresses CD3+ and CD68+ cell infiltration in lungs and RV fibrosis and hypertrophy and lowers brain natriuretic peptide. Beneficial effects persist for weeks after sFUS discontinuation and are more robust with early and longer treatment. Splenic denervation abolishes sFUS therapeutic benefits. sFUS partially normalizes CD68+ and CD8+ T-cells cell counts in the spleen and downregulates several inflammatory genes and pathways in nonclassical and classical monocytes, and macrophages in the lung. Differentially expressed genes in those cell types are significantly enriched for human PAH-associated genes. ConclusionssFUS causes dose-dependent, sustained improvement of hemodynamic, autonomic, laboratory and pathological manifestations in two models of experimental PH. Mechanistically, sFUS normalizes immune cell populations in the spleen and downregulates inflammatory genes and pathways in the lung, many of which are relevant in human disease.

neuroscience↗