Macrophages Can Drive Sympathetic Excitability in the Early Stages of Hypertension

Abstract

Hypertension is a major health burden worldwide with many cases resistant to current treatments. Hyperactivity of the sympathetic nervous contributes to the etiology and progression of the disease, where emerging evidence suggests that inflammation may underpin the development of sympathetic dysautonomia. This study examined whether macrophages could drive the sympathetic phenotype in Spontaneously Hypertensive Rats (SHR) before animals develop high pressure. Stellate neurons from wild-type control Wistar rats and SHRs were co-cultured with blood leukocytes from their own strain, and also crossed cultured between strains. The calcium transient response to nicotinic stimulation was recorded using Fura-2 calcium imaging, where SHR neurons had a greater calcium transient compared with Wistar neurons. However, when co-cultured with leukocytes, Wistar neurons began to phenocopy the SHR sympathetic hyperactivity, while the SHR neurons themselves were unaltered. Resident leukocyte populations of the SHR and Wistar stellate ganglia were then compared using flow cytometry, where there was a shift in monocyte-macrophage subset proportions. While classical monocyte-macrophages were predominant in the Wistar, there were relatively more of the non-classical subset in the SHR, which have been implicated in pro-inflammatory roles in a number of diseases. When bone marrow-derived macrophages (BMDMs) were co-cultured with stellate neurons, they made Wistar neurons recapitulate the SHR nicotinic stimulated calcium transient. Wistar BMDMs however, had no effect on SHR neurons, even though SHR BMDMs increased SHR neuron responsiveness further above their hyper-responsive state. Taken together, these findings show that macrophages can be potent enhancers of sympathetic neuronal calcium responsiveness, and thus could conceivably play a role in peripheral sympathetic hyperactivity observed in the early stages of hypertension.

Abnormal Cyclic Nucleotide Signaling at the Outer Mitochondrial Membrane In Sympathetic Neurons During the Early Stages of Hypertension

“…These observations are consistent with the previous reports showing PDE2A isoforms have distinct subcellular locations in ventricular myocytes 28 and in HEK cells. 13 To clarify whether these isoforms are differentially expressed in SHR SNs as compared with normal SNs, quantitative RT-PCR analysis of PDE2A1-3 mRNA levels in stellate ganglia tissue of 4-week Wistar rats and SHRs was performed. Only mRNA expression for PDE2A2 in SHR neurons showed significant enhancement (n=6 in each group, * P <0.05; Figure 3 B) when compared with neurons from normotensive Wistar rats.…”

“…hyperactivity may result in a number of additional pathological consequences such as cardiac hypertrophy, 10 arrhythmia, 11 vascular dysfunction, 12 and inflammation. 13 Recently, focus has shifted to a more dominant role being played by the sympathetic nervous system in the etiology of hypertension. 14,15 Cross-culture experiments have established that diseased sympathetic neurons from prehypertensive rats are powerful drivers of myocyte function, with evidence showing that healthy sympathetic neurons are able to rescue adrenergic function in diseased cardiomyocytes.…”

Healthy cardiac myocytes can decrease sympathetic hyperexcitability in the early stages of hypertension

“…In the early stages of hypertension in the SHR, the heightened sympathetic responsiveness may result from down-regulation of M-current that restricts neural firing ( Davis et al, 2020 ), local inflammation associated with macrophages ( Neely et al, 2022 ), increased activity of Cav 2.2 ( Larsen et al, 2016a ), impaired NO-cGMP signaling ( Li et al, 2007 ), and abnormal regulation of mitochondrial phosphodiesterases ( Li et al, 2022 ). These responses are linked to greater intracellular calcium (Ca 2+ ) transients ( Li et al, 2012 ; Neely et al, 2022 ) and facilitated exocytosis of classical transmitters ( Lu et al, 2015 ) and neuropeptides ( Herring et al, 2008 ). Combined with a slow re-uptake of norepinephrine by the noradrenaline-transporter (NET) ( Shanks et al, 2013 ), the post-ganglionic pre-synaptic neuron appears to be a powerful driver of myocyte function.…”

“…In the early stages of hypertension in the SHR, the heightened sympathetic responsiveness may result from downregulation of M-current that restricts neural firing (Davis et al, 2020), local inflammation associated with macrophages (Neely et al, 2022), increased activity of Cav 2 . 2 (Larsen et al, 2016a), impaired NO-cGMP signaling (Li et al, 2007), and abnormal regulation of mitochondrial phosphodiesterases (Li et al, 2022).…”

“…2 (Larsen et al, 2016a), impaired NO-cGMP signaling (Li et al, 2007), and abnormal regulation of mitochondrial phosphodiesterases (Li et al, 2022). These responses are linked to greater intracellular calcium (Ca 2+ ) transients (Li et al, 2012;Neely et al, 2022) and facilitated exocytosis of classical transmitters (Lu et al, 2015) and neuropeptides (Herring et al, 2008). Combined with a slow re-uptake of norepinephrine by the noradrenaline-transporter (NET) (Shanks et al, 2013), the post-ganglionic pre-synaptic neuron appears to be a powerful driver of myocyte function.…”