Enhanced Neuropeptide Y Synthesis During Intermittent Hypoxia in the Rat Adrenal Medulla: Role of Reactive Oxygen Species–Dependent Alterations in Precursor Peptide Processing

Abstract

Intermittent hypoxia (IH) associated with recurrent apneas often leads to cardiovascular abnormalities. Previously, we showed that IH treatment elevates blood pressure and increases plasma catecholamines (CAs) in rats via reactive oxygen species (ROS)-dependent enhanced synthesis and secretion from the adrenal medulla (AM). Neuropeptide Y (NPY), a sympathetic neurotransmitter that colocalizes with CA in the AM, has been implicated in blood pressure regulation during persistent stress. Here, we investigated whether IH facilitates NPY synthesis in the rat AM and assessed the role of ROS signaling. IH increased NPY-like immunoreactivity in many dopamine-β-hydroxylase-expressing chromaffin cells with a parallel increase in preproNPY mRNA and protein. IH increased the activities of proNPY-processing enzymes, which were due, in part, to elevated protein expression and increased proteolytic processing. IH increased ROS generation, and antioxidants reversed IH-induced increases in ROS, preproNPY, and its processing to bioactive NPY in the AM. IH treatment increased blood pressure and antioxidants and inhibition of NPY amidation prevented this response. These findings suggest that IH-induced elevation in NPY expression in the rat AM is mediated by ROS-dependent augmentation of preproNPY mRNA expression and proNPY-processing enzyme activities and contributes to IH-induced elevation of blood pressure.

Role of oxidative stress‐induced endothelin‐converting enzyme activity in the alteration of carotid body function by chronic intermittent hypoxia

“…Given that CIH increases ROS levels in the carotid body (Peng et al 2003), these findings demonstrate that ROS‐dependent activation of ECE contributes to CIH‐induced ET‐1 upregulation in the rat carotid body. These observations are reminiscent of an earlier report showing that CIH‐induced upregulation of neuropeptide Y in the rat adrenal medulla is also mediated by ROS‐dependent activation of processing of neuropeptide Y from its precursor protein (Raghuraman et al 2011). The mechanism(s) by which ROS activates ECE, however, requires further investigation, which is beyond the scope of the present study.…”

NADPH Oxidase-Derived H2O2Contributes to Angiotensin II-Induced Aldosterone Synthesis in Human and Rat Adrenal Cortical Cells

“…Real-time PCR was performed using a MiniOpticon system (Bio-Rad) with SYBR GreenER two-step quantitative RT-PCR kit (Invitrogen) as previously described (32). The primer sequences used for real-time PCR analysis of 18S, CYP11B2, Nox1, Nox2, Nox4, Nox5, and Duox1 in human and rat adrenal cortical cells are shown in Supplementary Table S1.…”

“…Adrenal cortical slices were homogenized, and MDA levels in the homogenates were determined as a measure of lipid oxidation as previously described (32) and expressed as nanomoles per milligram of protein.…”

Hypoxia. 3. Hypoxia and neurotransmitter synthesis

“…It has been suggested that CH-evoked changes in NPY-like immunoreactivity in the carotid body and specific brain regions may contribute to adaptative mechanisms involving morphological changes in carotid bodies and alterations in sympathetic control and neuroendocrine function, respectively (92). IH (15 s paradigm) augmented NPY-like immunoreactivity in the rat brainstem (105) and markedly upregulated NPY expression in DBH-expressing adrenal chromaffin cells (96). IH-induced increase in NPY in the adrenal medulla was associated with ROS-dependent upregulation of prepro-NPY mRNA and protein as well as increased prepro-NPY processing.…”