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

“…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.…”

“…Secretogranin III (SgIII), another member in chromogranin family, has been proved to dissolve SgII-mediated LLPS in vitro and reduce the volume of DCVs in native ACCs through overexpression ( Fig. 1D ) [2] . Moreover, using CFE recording, we observed that the reduction in DCV volume caused by SgIII overexpression leads to a reduction in ACC quantal size [2] .…”

“…1D ) [2] . Moreover, using CFE recording, we observed that the reduction in DCV volume caused by SgIII overexpression leads to a reduction in ACC quantal size [2] . These findings highlight the unique role of SgII as an intravesicular matrix protein involved in LLPS and provide novel insights into how SgII regulates DCV biogenesis and the quantal release of neurotransmitters and neuropeptides ( Fig.…”

“…I n vitro experiments have demonstrated that reconstructed bio-lipids (comprising 250 μM DSPC, 150 μM DOPE, 50 μM SoyPI, 5 μM DMB PEG and 5 μM NBD PC) can effectively coat SgII-mediated LLPS assemblies, mimicing the physiological composition of TGN membrane ( Fig. 2A ) [2] . While circular coated bio-lipids features have not been observed in groups of Ca 2+ with bio-lipids ( Fig.…”