Tuning the Size of Large Dense‐Core Vesicles and Quantal Neurotransmitter Release via Secretogranin II Liquid–Liquid Phase Separation

Abstract

Large dense‐core vesicles (LDCVs) are larger in volume than synaptic vesicles, and are filled with multiple neuropeptides, hormones, and neurotransmitters that participate in various physiological processes. However, little is known about the mechanism determining the size of LDCVs. Here, it is reported that secretogranin II (SgII), a vesicle matrix protein, contributes to LDCV size regulation through its liquid–liquid phase separation in neuroendocrine cells. First, SgII undergoes pH‐dependent polymerization and the polymerized SgII forms phase droplets with Ca2+ in vitro and in vivo. Further, the Ca2+‐induced SgII droplets recruit reconstituted bio‐lipids, mimicking the LDCVs biogenesis. In addition, SgII knockdown leads to significant decrease of the quantal neurotransmitter release by affecting LDCV size, which is differently rescued by SgII truncations with different degrees of phase separation. In conclusion, it is shown that SgII is a unique intravesicular matrix protein undergoing liquid–liquid phase separation, and present novel insights into how SgII determines LDCV size and the quantal neurotransmitter release.

ER Stress Impedes Regulated Secretion by Governing Key Exocytotic and Granulogenic Molecular Switches

“…We observed an increase in the mRNA and protein level of ATF4 in the ER-stressed cells, which reverted towards control levels upon DHA co-treatment (Fig. 8D, 8E Furthermore, experiments on the specificity of altered abundances for other molecular players, such as key SNARES, tethers and rabs, were also tested without significant differences (Supp ER, stress lowers the abundance of key granulogenic signatures: Given the welldocumented evidence about the granulogenic potential of chromogranins, specifically Secretogranin II (SCGII) and Chromogranin A (CGA) (Kim et al, 2001;Lin et al, 2022), we wanted to test if there are any significant changes in the relative abundances of chromogranins in ER-stressed cells. Interestingly, CGA levels were significantly decreased at the mRNA and protein levels, which surprisingly remained unchanged in DHA co-treated cells (Fig.…”

Liquid-liquid phase separation within dense-core vesicles in sympathetic adrenal chromaffin cells

“…Recently, two independent groups reported that chromogranin proteins regulate the biogenesis of DCVs through LLPS in adrenal chromaffin cells [1, 2] . By integrating cutting-edge methods from diverse disciplines such as physiology/electrochemistry and biochemistry/structural biology, we have provided compelling evidence demonstrating that the intra-vesicular matrix protein SgII serves as a pivotal scaffold protein in determining the DCV size via LLPS, and substantially regulating quantal release of both catecholamine and neuropeptides in native neuroendocrine ACCs [2] . Moreover, von Blume’s team found that another intravesicular matrix protein CgB underwent LLPS in the lumen of the trans-Golgi network (TGN), and recruited proinsulin to the condensates in a cell-culture model of pancreatic β-cells (INS1 832/13) [1] .…”

“…The LLPS process concentrates specific components to create a liquid and dynamic membrane-less compartment, facilitating targeted biochemical reactions and playing a crucial role in essential physiological processes [5, 12] . While, LLPS has also been revealed to facilitate the biogenesis of membranous organelles-DCVs [1, 2] . Here we highlight the role of LLPS in recruiting biolipids and the DCVs biogenesis, and tuning neurotransmitters and neuropeptides release.…”

“…The LLPS of synapsin I has been demonstrated to form tight clusters of SVs at synapse, resembling dense structures [16] . Recent studies have also shown that DCV matrix proteins CgA, CgB and SgII undergo LLPS, which contributes to vesicular cargo package and vesicle volume determination [1, 2] . These collective findings strongly support the significance of LLPS in biological processes and its association with dense-like features observed under TEM.…”

“…Recent studies have revealed that liquid-liquid phase separation (LLPS) of matrix protein-chromogranins plays pivotal roles in the formation of DCVs and the sorting process of neurotransmitters/neuromodulators in endocrine cells. Here we highlight recent advancements in mechanisms of LLPS’s regulation of DCVs [1, 2] , which selectively affect release of some co-transmitters (catecholamines) but not others (i.e. ATP) [3] .…”