Activation of Orexin System Stimulates CaMKII Expression.

Yuanyuan Fan,Enshe Jiang,Zhiying Shan,Huanjia Gao,Chunxiu Yu,Jeremy Bigalke,Qinghui Chen,Bojun Chen

doi:10.3389/fphys.2021.698185

Abstract

Hyperactivity of the orexin system within the paraventricular nucleus (PVN) has been shown to contribute to increased sympathetic nerve activity (SNA) and blood pressure (BP) in rodent animals. However, the underlying molecular mechanisms remain unclear. Here, we test the hypothesis that orexin system activation stimulates calcium/calmodulin-dependent kinase II (CaMKII) expression and activation, and stimulation of CaMKII expressing PVN neurons increases SNA and BP. Real-time PCR and/or western blot were carried out to test the effect of orexin-A administration on CaMKII expression in the PVN of normal Sprague Dawley (SD) rats and orexin receptor 1 (OX1R) expressing PC12 cells. Immunostaining was performed to assess OX1R cellular localization in the PVN of SD rats as well as orexin-A treatment on CaMKII activation in cultured hypothalamic neurons. In vivo sympathetic nerve recordings were employed to test the impact of optogenetic stimulation of CaMKII-expressing PVN neurons on the renal SNA (RSNA) and BP. The results showed that intracerebroventricular injection of orexin-A into the SD rat increases mRNA expression of CaMKII subunits in the PVN. In addition, Orexin-A treatment increases CaMKII expression and its phosphorylation in OX1R-expressing PC12 cells. Furthermore, Orexin-A treatment increases CaMKII activation in cultured hypothalamic neurons from neonatal SD rats. Finally, optogenetic excitation of PVN CaMKII-expressing neurons results in robust increases in RSNA and BP in SD rats. Our results suggest that increased orexin system activity activates CaMKII expression in cardiovascular relevant regions, and this may be relevant to the downstream cardiovascular effects of CaMKII.

Highlights

Orexin-A and orexin-B are neuronal peptides processed from the same precursor, prepro-orexin, which is produced by a small number of neurons located in the lateral hypothalamus (Meister and Hakansson, 1998; Sakurai et al, 1998)
Intracerebroventricular injection of orexin-A into the Sprague Dawley (SD) rats resulted in significant increases in the mRNA expression of CaMKIIa (1.5-fold) and CaMKIIb (1.3-fold) compared to control saline injection rats (Figure 1)
This study is the first to investigate the contribution of the orexin system on the regulation of calmodulin-dependent kinase II (CaMKII), a key protein kinase involved in multiple functions including cardiovascular function and blood pressure (BP) regulation (Mohler and Hund, 2011; Prasad et al, 2015)

Summary

Introduction

Orexin-A and orexin-B are neuronal peptides processed from the same precursor, prepro-orexin, which is produced by a small number of neurons located in the lateral hypothalamus (Meister and Hakansson, 1998; Sakurai et al, 1998). Orexin-A is only produced by a limited number of neurons within the lateral hypothalamic area, orexin receptors innervate a vast number of brain and spinal cord structures (Antunes et al, 2001), resulting in far-reaching influences of the sequestered orexin-producing neurons. Through their axonal synapses with their receptor-expressing neurons, they convey signals to postsynaptic neurons, effectively regulating their activities

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