Disruption of Exocytosis in Sympathoadrenal Chromaffin Cells from Mouse Models of Neurodegenerative Diseases

Endoplasmic reticulum stress impedes regulated secretion by governing key exocytotic and granulogenic molecular switches

Dense core vesicles (DCVs) and synaptic vesicles are specialised secretory vesicles in neurons and neuroendocrine cells, and abnormal release of their cargo is associated with various pathophysiologies. Endoplasmic reticulum (ER) stress and inter-organellar communication are also associated with disease biology. To investigate the functional status of regulated exocytosis arising from the crosstalk of a stressed ER and DCVs, ER stress was modelled in PC12 neuroendocrine cells using thapsigargin. DCV exocytosis was severely compromised in ER-stressed PC12 cells and was reversed to varying magnitudes by ER stress attenuators. Experiments with tunicamycin, an independent ER stressor, yielded similar results. Concurrently, ER stress also caused impaired DCV exocytosis in insulin-secreting INS-1 cells. Molecular analysis revealed blunted SNAP25 expression, potentially attributed to augmented levels of ATF4, an inhibitor of CREB that binds to the CREB-binding site. The effects of loss of function of ATF4 in ER-stressed cells substantiated this attribution. Our studies revealed severe defects in DCV exocytosis in ER-stressed cells for the first time, mediated by reduced levels of key exocytotic and granulogenic switches regulated via the eIF2α (EIF2A)-ATF4 axis.

Analytical Determination of Serotonin Exocytosis in Human Platelets with BDD-on-Quartz MEA Devices

Amperometry is arguably the most widely used technique for studying the exocytosis of biological amines. However, the scarcity of human tissues, particularly in the context of neurological diseases, poses a challenge for exocytosis research. Human platelets, which accumulate 90% of blood serotonin, release it through exocytosis. Nevertheless, single-cell amperometry with encapsulated carbon fibers is impractical due to the small size of platelets and the limited number of secretory granules on each platelet. The recent technological improvements in amperometric multi-electrode array (MEA) devices allow simultaneous recordings from several high-performance electrodes. In this paper, we present a comparison of three MEA boron-doped diamond (BDD) devices for studying serotonin exocytosis in human platelets: (i) the BDD-on-glass MEA, (ii) the BDD-on-silicon MEA, and (iii) the BDD on amorphous quartz MEA (BDD-on-quartz MEA). Transparent electrodes offer several advantages for observing living cells, and in the case of platelets, they control activation/aggregation. BDD-on-quartz offers the advantage over previous materials of combining excellent electrochemical properties with transparency for microscopic observation. These devices are opening exciting perspectives for clinical applications.

MASH1 induces neuron transdifferentiation of adrenal medulla chromaffin cells

OBJECTIVES

Nerve growth factor (NGF) induces neuron transdifferentiation of adrenal medulla chromaffin cells (AMCCs) and consequently downregulates the secretion of epinephrine (EPI), which may be involved in the pathogenesis of bronchial asthma. Mammalian achaete scute-homologous 1 (MASH1), a key regulator of neurogenesis in the nervous system, has been proved to be elevated in AMCCs with neuron transdifferentiation in vivo. This study aims to explore the role of MASH1 in the process of neuron transdifferentiation of AMCCs and the mechanisms.

METHODS

Rat AMCCs were isolated and cultured. AMCCs were transfected with siMASH1 or MASH1 overexpression plasmid, then were stimulated with NGF and/or dexamethasone, PD98059 (a MAPK kinase-1 inhibitor) for 48 hours. Morphological changes were observed using light and electron microscope. Phenylethanolamine-N-methyltransferase (PNMT, the key enzyme for epinephrine synthesis) and tyrosine hydroxylase were detected by immunofluorescence. Western blotting was used to test the protein levels of PNMT, MASH1, peripherin (neuronal markers), extracellular regulated protein kinases (ERK), phosphorylated extracellular regulated protein kinases (pERK), and JMJD3. Real-time RT-PCR was applied to analyze the mRNA levels of MASH1 and JMJD3. EPI levels in the cellular supernatant were measured using ELISA.

RESULTS

Cells with both tyrosine hydroxylase and PNMT positive by immunofluorescence were proved to be AMCCs. Exposure to NGF, AMCCs exhibited neurite-like processes concomitant with increases in pERK/ERK, peripherin, and MASH1 levels (all P<0.05). Additionally, impairment of endocrine phenotype was proved by a signifcant decrease in the PNMT level and the secretion of EPI from AMCCs (all P<0.01). MASH1 interference reversed the effect of NGF, causing increases in the levels of PNMT and EPI, conversely reduced the peripherin level and cell processes (all P<0.01). MASH1 overexpression significantly increased the number of cell processes and peripherin level, while decreased the levels of PNMT and EPI (all P<0.01). Compared with the NGF group, the levels of MASH1, JMJD3 protein and mRNA in AMCCs in the NGF+PD98059 group were decreased (all P<0.05). After treatment with PD98059 and dexamethasone, the effect of NGF on promoting the transdifferentiation of AMCCs was inhibited, and the number of cell processes and EPI levels were decreased (both P<0.05). In addition, the activity of the pERK/MASH1 pathway activated by NGF was also inhibited.

CONCLUSIONS

MASH1 is the key factor in neuron transdifferentiation of AMCCs. NGF-induced neuron transdifferentiation is probably mediated via pERK/MASH1 signaling.

Mitochondrial dysfunction in chromaffin cells from the R6/1 mouse model of Huntington's disease: Impact on exocytosis and calcium current regulation

From a pathogenic perspective, Huntington's disease (HD) is being considered as a synaptopathy. As such, alterations in brain neurotransmitter release occur. As the activity of the sympathoadrenal axis is centrally controlled, deficits in the exocytotic release of catecholamine release may also occur. In fact, in chromaffin cells (CCs) of the adrenal medulla of the R6/1 model of HD, decrease of secretion and altered kinetics of the exocytotic fusion pore have been reported. Those alterations could be linked to mitochondrial deficits occurring in peripheral CCs, similar to those described in brain mitochondria. Here we have inquired about alterations in mitochondrial structure and function and their impact on exocytosis and calcium channel currents (I_Ca). We have monitored various parameters linked to those events, in wild type (WT) and the R6/1 mouse model of HD at a pre-disease stage (2 months age, 2 m), and when motor deficits are present (7 months age, 7 m). In isolated CCs from 7 m and in the adrenal medulla of R6/1 mice, we found the following alterations (with respect 7 m WT mice): (i) augmented fragmented mitochondria and oxidative stress with increased oxidized glutathione; (ii) decreased basal and maximal respiration; (iii) diminution of ATP cell levels; (iv) mitochondrial depolarization; (v) drastic decrease of catecholamine release with poorer potentiation by protonophore FCCP; (vi) decreased I_Ca inhibition by FCCP; and (vii) lesser potentiation by BayK8644 of I_Ca and smaller prolongation of current deactivation. Of note was the fact several of these alterations were already manifested in CCs from 2 m R6/1 mice at pre-disease stages. Based on those results, a plausible hypothesis can be raised in the sense that altered mitochondrial function seems to be an early primary event in HD pathogenesis. This is in line with an increasing number of mitochondrial, metabolic, and inflammatory alterations being recently reported in various HD peripheral tissues.

Alterations of the Sympathoadrenal Axis Related to the Development of Alzheimer’s Disease in the 3xTg Mouse Model

Simple Summary

Alzheimer’s disease (AD), the most common form of dementia, is becoming a global health problem and public health priority. In the advanced stages of AD, besides the initial cognitive symptoms, behavioral problems, particularly agitation and aggressiveness, become prevalent in AD patients. These non-cognitive symptoms could be related to alterations in the regulatory mechanism of the sympathetic nervous system. In this study, we used chromaffin cells (CCs) isolated from the adrenal gland of 3xTg (an AD mouse model) mice to characterize potential alterations in the regulation of the responses to stress mediated by the secretion of catecholamines. We compared these regulatory mechanisms in mice at two different ages: in 2-month-old mice, where no AD symptoms were observed, and in mice over 12 months of age, when AD-related cognitive impairment related was fully established. We found that the modulation of neurotransmitter release was stronger in CCs isolated from the adrenal medulla of 3xTg mice older than 12 months of age, an effect likely related to disease progression as it was not observed in CCs from age-matched wild-type (WT) mice. This enhanced modulation leads to an increased catecholamine release in response to stressful situations, which may explain the non-cognitive behavioral problems found in AD patients.

Abstract

Alzheimer’s disease (AD), the most common form of dementia, is becoming a global health problem and public health priority. In the advanced stages of AD, besides the initial cognitive symptoms, behavioral problems, particularly agitation and aggressiveness, become prevalent in AD patients. These non-cognitive symptoms could be related to a noradrenergic overactivation. In this study, we used chromaffin cells (CCs) isolated from the adrenal gland of 3xTg AD model mice to characterize potential alterations in the autocrine-paracrine modulation of voltage-dependent calcium channels (VDCCs), which in turn serve to regulate the release of catecholamines. We used mice at the presymptomatic stage (2 months) and mice over 12 months of age, when AD-related cognitive impairment was fully established. We found that the modulation of inward currents through VDCCs induced by extracellular ATP was stronger in CCs isolated from the adrenal medulla of 3xTg mice older than 12 months of age, an effect likely related to disease progression as it was not observed in CCs from age-matched WT mice. This enhanced modulation leads to increased catecholamine release in response to stressful situations, which may explain the non-cognitive behavioral problems found in AD patients.

Exocytotic vesicle fusion classification for early disease diagnosis using a mobile GPU microsystem

This work addresses monitoring vesicle fusions occurring during the exocytosis process, which is the main way of intercellular communication. Certain vesicle behaviors may also indicate certain precancerous conditions in cells. For this purpose we designed a system able to detect two main types of exocytosis: a full fusion and a kiss-and-run fusion, based on data from multiple amperometric sensors at once. It uses many instances of small perceptron neural networks in a massively parallel manner and runs on Jetson TX2 platform, which uses a GPU for parallel processing. Based on performed benchmarking, approximately 140,000 sensors can be processed in real time within the sensor sampling period equal to 10 ms and an accuracy of 99$$\%$$ % . The work includes an analysis of the system performance with varying neural network sizes, input data sizes, and sampling periods of fusion signals.