Molecular biology of the chromaffin cell

Forty years of the adrenal chromaffin cell through ISCCB meetings around the world

This historical review focuses on the evolution of the knowledge accumulated during the last two centuries on the biology of the adrenal medulla gland and its chromaffin cells (CCs). The review emerged in the context of a series of meetings that started on the Spanish island of Ibiza in 1982 with the name of the International Symposium on Chromaffin Cell Biology (ISCCB). Hence, the review is divided into two periods namely, before 1982 and from this year to 2022, when the 21st ISCCB meeting was just held in Hamburg, Germany. The first historical period extends back to 1852 when Albert Kölliker first described the fine structure and function of the adrenal medulla. Subsequently, the adrenal staining with chromate salts identified the CCs; this was followed by the establishment of the embryological origin of the adrenal medulla, and the identification of adrenaline-storing vesicles. By the end of the nineteenth century, the basic morphology, histochemistry, and embryology of the adrenal gland were known. The twentieth century began with breakthrough findings namely, the experiment of Elliott suggesting that adrenaline was the sympathetic neurotransmitter, the isolation of pure adrenaline, and the deciphering of its molecular structure and chemical synthesis in the laboratory. In the 1950s, Blaschko isolated the catecholamine-storing vesicles from adrenal medullary extracts. This switched the interest in CCs as models of sympathetic neurons with an explosion of studies concerning their functions, i.e., uptake of catecholamines by chromaffin vesicles through a specific coupled transport system; the identification of several vesicle components in addition to catecholamines including chromogranins, ATP, opioids, and other neuropeptides; the calcium-dependence of the release of catecholamines; the underlying mechanism of exocytosis of this release, as indicated by the co-release of proteins; the cross-talk between the adrenal cortex and the medulla; and the emission of neurite-like processes by CCs in culture, among other numerous findings. The 1980s began with the introduction of new high-resolution techniques such as patch-clamp, calcium probes, marine toxins-targeting ion channels and receptors, confocal microscopy, or amperometry. In this frame of technological advances at the Ibiza ISCCB meeting in 1982, 11 senior researchers in the field predicted a notable increase in our knowledge in the field of CCs and the adrenal medulla; this cumulative knowledge that occurred in the last 40 years of history of the CC is succinctly described in the second part of this historical review. It deals with cell excitability, ion channel currents, the exocytotic fusion pore, the handling of calcium ions by CCs, the kinetics of exocytosis and endocytosis, the exocytotic machinery, and the life cycle of secretory vesicles. These concepts together with studies on the dynamics of membrane fusion with super-resolution imaging techniques at the single-protein level were extensively reviewed by top scientists in the field at the 21st ISCCB meeting in Hamburg in the summer of 2022; this frontier topic is also briefly reviewed here. Many of the concepts arising from those studies contributed to our present understanding of synaptic transmission. This has been studied in physiological or pathophysiological conditions, in CCs from animal disease models. In conclusion, the lessons we have learned from CC biology as a peripheral model for brain and brain disease pertain more than ever to cutting-edge research in neurobiology. In the 22nd ISCCB meeting in Israel in 2024 that Uri Asheri is organizing, we will have the opportunity of seeing the progress of the questions posed in Ibiza, and on other questions that undoubtedly will arise.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Generation of Adrenal Chromaffin-like Cells from Human Pluripotent Stem Cells

Adrenomedullary chromaffin cells are catecholamine (CA)-producing cells originating from trunk neural crest (NC) via sympathoadrenal progenitors (SAPs). We generated NC and SAPs from human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) in vitro via BMP2/FGF2 exposure, ascertained by qPCR and immunoexpression of SOX10, ASCL1, TFAP2α, and PHOX2B, and by fluorescence-activated cell sorting selection for p75NTR and GD2, and confirmed their trunk-like HOX gene expression. We showed that continuing BMP4 and curtailing FGF2 in vitro, augmented with corticosteroid mimetic, induced these cells to upregulate the chromaffin cell-specific marker PNMT and other CA synthesis and storage markers, and we demonstrated noradrenaline and adrenaline by Faglu and high-performance liquid chromatography. We showed these human cells' SAP-like property of migration and differentiation into cells expressing chromaffin cell markers by implanting them into avian embryos in vivo and in chorio-allantoic membrane grafts. These cells have the potential for investigating differentiation of human chromaffin cells and for modeling diseases involving this cell type.

Myosin VI in PC12 cells plays important roles in cell migration and proliferation but not in catecholamine secretion

Myosin VI (MVI) is the only known myosin walking towards minus end of actin filaments and is believed to play distinct role(s) than other myosins. We addressed a role of this unique motor in secretory PC12 cells, derived from rat adrenal medulla pheochromocytoma using cell lines with reduced MVI synthesis (produced by means of siRNA). Decrease of MVI expression caused severe changes in cell size and morphology, and profound defects in actin cytoskeleton organization and Golgi structure. Also, significant inhibition of cell migration as well as cell proliferation was observed. Flow cytometric analysis revealed that MVI-deficient cells were arrested in G0/G1 phase of the cell cycle but did not undergo increased senescence as compared with control cells. Also, neither polyploidy nor aneuploidy were detected. Surprisingly, no significant effect on noradrenaline secretion was observed. These data indicate that in PC12 cells MVI is involved in cell migration and proliferation but is not crucial for stimulation-dependent catecholamine release.

L-arginine supplementation reduces cardiac noradrenergic neurotransmission in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) are known to have cardiac noradrenergic hyperactivity due to an impaired nitric oxide (NO)-cGMP pathway. We hypothesized that dietary l-arginine supplementation may correct this autonomic phenotype. Male SHR and Wistar Kyoto rats (WKY) aged 16-18 weeks were given l-arginine (10 g/L in drinking water) for 1 week. Separate control groups received no supplementation. The SHR control had a significantly lower plasma l-arginine than WKY control, but this was increased to a comparable level following l-arginine. Atrial cGMP was lower in the SHR control compared with the WKY control (2.4+/-0.4 pmol/mg vs 3.9+/-0.5 pmol/mg, p<0.05), but increased to 4.1+/-0.5 pmol/mg protein (n=8, p<0.05) with l-arginine. Evoked [(3)H]norepinephrine release in isolated spontaneously beating right atria from the SHR control (328+/-19%, n=19) was 28% higher than the WKY control (256+/-20%, n=14, p<0.05), but was reduced to 258+/-11% with l-arginine feeding (n=24, p<0.01). Soluble guanylyl cyclase (sGC) inhibition caused a greater increase of evoked norepinephrine release in the l-arginine fed SHR compared with the non-fed SHR. l-arginine feeding did not reduce evoked norepinephrine release in the WKY. In-vitro heart rate response to exogenous norepinephrine (0.1-5 mumol/L) was similar between l-arginine fed (n=13) and non-fed SHR (n=10), suggesting that l-arginine supplementation worked pre-synaptically. Myocardial tyrosine hydroxylase protein was decreased in SHR following l-arginine supplementation, providing a link to reduced synthesis of norepinephrine. In conclusion, l-arginine supplementation corrects local cardiac noradrenergic hyperactivity in the SHR, probably via increased pre-synaptic substrate availability of NOS-sGC-cGMP pathway and reduced tyrosine hydroxylase levels.

Cells of the sympathoadrenal lineage: Biological properties as donor tissue for cell-replacement therapies for Parkinson's disease

Sympathoadrenal (SA) cell lineage encompasses neural crest derivatives such as sympathetic neurons, small intensely fluorescent (SIF) cells of sympathetic ganglia and adrenal medulla, and chromaffin cells of adrenal medulla and extra-adrenal paraganglia. SA autografts have been used for transplantation in Parkinson's disease (PD) for three reasons: (i) as autologous donor tissue avoids graft rejection and the need for immunosuppressant therapy, (ii) SA cells express dopaminotrophic factors such as GNDF and TGFbetas, and (iii) although most of SA cells release noradrenaline, some of them are able to produce and release dopamine. Adrenal chromaffin cells were the first SA transplanted cells in both animal models of PD and PD patients. However, these autografts have met limited success because long-term cell survival is very poor, and this approach is no longer pursued clinically. Sympathetic neurons from the superior cervical ganglion have been also grafted in PD animal models and PD patients. Poor survival into brain parenchyma of grafted tissue is a serious disadvantage for its clinical application. However, cultured sympathetic cell grafts present a better survival rate, and they reduce the need for levodopa medication in PD patients by facilitating the conversion of exogenous levodopa. SA extra-adrenal chromaffin cells are located on paraganglia (i.e., the Zuckerkandl's organ), and have been used for grafting in a rodent model of PD. Preliminary results indicate that long-term survival of these cells is better than for other SA cells, exerting a more prolonged restorative neurotrophic action on denervated host striatum. The ability of SA extra-adrenal cells to respond to hypoxia, differently to SA sympathetic neurons or adrenal medulla cells, could explain their good survival rate after brain transplantation.

Plasma and tissue chromogranin in patients with adrenocortical adenomas

Adrenal adenomas frequently arise from cortical islets in the medulla, and these islets seem to present a greater risk for pathological growth than cortical cells within the adrenal cortex. Chromogranin A (CgA), a glycoprotein co-stored in secreting granules and co-released with resident hormones of chromaffin cells, behaves as a prohormone, generating several biologically active peptides capable of influencing growth, morphogenesis and progression of endocrine tumors. The aim of our study was to investigate whether chromaffin cells may be involved in the development and growth of adrenocortical adenomas. We enrolled 19 patients (12 females and 7 males, mean+/-SD age 54.9+/-11.2 yr, age range 34-75 yr) with incidental, non-functioning, benign adrenocortical adenomas, and measured circulating levels of CgA, catecholamines and creatinine before and 2 months after surgery. Plasma CgA was evaluated by immunoradiometric assay. Testing for CgA immunoreactivity in the removed tissues was performed by immunohistochemical analysis. Mean plasma CgA did not significantly change following surgery (before 73.7+/-15.2 ng/ml; after 68.9+/-14.8 ng/ml). Individual CgA values indicated that 4 patients had plasma CgA levels above our cut-off of normality. After mass removal, CgA further increased in 2 cases, decreased in 1 and normalized in 1. No variation in CgA levels was found in the other patients. No correlation was observed between CgA and the variables measured, except between CgA and plasma creatinine (r=0.472, p<0.05). Histopathological evaluation revealed adrenocortical adenomas in all cases and immunohistochemical analysis detected no CgA immunoreactivity in any specimen. Our results show that in human adrenocortical adenomas CgA is not expressed and that removal of the mass does not modify plasma CgA levels. For these reasons the endocrine involvement of local CgA in adrenocortical tumorigenesis is unlikely.