Impact of Chromogranin A deficiency on catecholamine storage, catecholamine granule morphology and chromaffin cell energy metabolism in vivo

Abstract

Chromogranin A (CgA) is a prohormone and granulogenic factor in neuroendocrine tissues with a regulated secretory pathway. The impact of CgA depletion on secretory granule formation has been previously demonstrated in cell culture. However, studies linking the structural effects of CgA deficiency with secretory performance and cell metabolism in the adrenomedullary chromaffin cells in vivo have not previously been reported. Adrenomedullary content of the secreted adrenal catecholamines norepinephrine (NE) and epinephrine (EPI) was decreased 30–40 % in Chga-KO mice. Quantification of NE and EPI-storing dense core (DC) vesicles (DCV) revealed decreased DCV numbers in chromaffin cells in Chga-KO mice. For both cell types, the DCV diameter in Chga-KO mice was less (100–200 nm) than in WT mice (200–350 nm). The volume density of the vesicle and vesicle number was also lower in Chga-KO mice. Chga-KO mice showed an ~47 % increase in DCV/DC ratio, implying vesicle swelling due to increased osmotically active free catecholamines. Upon challenge with 2 U/kg insulin, there was a diminution in adrenomedullary EPI, no change in NE and a very large increase in the EPI and NE precursor dopamine (DA), consistent with increased catecholamine biosynthesis during prolonged secretion. We found dilated mitochondrial cristae, endoplasmic reticulum and Golgi complex, as well as increased synaptic mitochondria, synaptic vesicles and glycogen granules in Chga-KO mice compared to WT mice, suggesting that decreased granulogenesis and catecholamine storage in CgA-deficient mouse adrenal medulla is compensated by increased VMAT-dependent catecholamine update into storage vesicles, at the expense of enhanced energy expenditure by the chromaffin cell.

CCN6 regulates mitochondrial function

“…Accordingly, transmission electron microscopy (TEM) analysis was performed, following similar procedures to those previously described (Pasqua et al, 2015), to evaluate the mitochondria of both CCN6-siRNAtransfected cells and the corresponding controls. TEM revealed an increased number of mitochondria together with elevated mitochondrial and cristae volume density {cristae volume density (%) = [sum of cristae area (µm 2 ) / mitochondrial area (µm 2 )] × 100}, as well as crista area, in CCN6-depleted cells ( Fig.…”

“…Samples were anonymized, and morphometric measurements were made randomly from different cells as described previously (Pasqua et al, 2015). The line segment tool in NIH ImageJ 1.49 software was used to measure the distance between ER and mitochondria.…”

“…The sum of the area of the mitochondria was divided by the area of the cytoplasm and multiplied by 100 to determine the mitochondrial volume density (%). For determination of the cristae volume density (%), the sum of the area of the cristae was divided by the outer area of the mitochondria and multiplied by 100, as described previously (Pasqua et al, 2015). A 19×23-cm rectangular grid was overlaid on each image to count the number of mitochondria in each image, and the mitochondria number is presented per 10 µm 2 area of the cytoplasm.…”

Chromogranin A in the early steps of the neurosecretory pathway

“…Despite compensatory effects of other granins in granule biogenesis, CgA knockout mice systematically exhibited an elevation of catecholamine levels, suggesting nevertheless a specific role of CgA in the regulation of catecholamine storage and secretion. More recently, a morphological study of chromaffin cell SG from CgA‐KO mice revealed a decrease in both the diameter and the volume density, and an increase in the ratio between their size and that of their dense core, implying SG swelling that could be due to increased free catecholamines . Altogether, these observations suggest therefore the existence of a link between CgA expression and the formation of functional SG in neuroendocrine cells.…”

Inhibition of chronic lymphocytic leukemia progression by full-length chromogranin A and its N-terminal fragment in mouse models

“…CgA has an intracellular function in secretory granule biogenesis [12, 13], as well as important extracellular functions as a precursor of various bioactive peptides involved in the regulation of metabolism, innate immunity, cardiovascular system, vascular contractility, and endothelial barrier function [1, 2]. A growing body of evidence suggests that CgA and its N-terminal fragment 1-76, called vasostatin-1 (VS-1), can also have a role in tumor biology.…”