SV Steps, Genetics Synapse, Imaging Synapse, and start of Readouts of Synapse

directed MT-based vesicle transport seems to be an essential mechanism for delivering SVPs to presynaptic sites,

Transported by Fast axonal transport

SV Steps

1. SV 생성

synaptic vesicle proteins (eg. Synaptophysin, synaptotagmin, VGLUT1, synaptobrevin) are produced and packaged into SVPs in the cell body

→ SVPs are trafficked along the axon to presynaptic sites → synaptic vesicle proteins (eg. Synaptophysin, synaptotagmin, VGLUT1, synaptobrevin) 들이 SV 를 만듬

2. SV 방출

이 SV 들이 neurotransmitter(neurotransmitter들은 presynaptic 에서 생성됨) 를 담고 있다가 exocytosis 에 의해 synaptic cleft 로 release 함.

3. SV recycling (수천번이상!, {Saheki, 2012 #1222}): {Nguyen, 2019 #922}

3-1) clathrin-mediated pathway (major pathway)

(1) Invagination/constriction: Following the recruitment of adaptor and clathrin-coat proteins to the plasma membrane, endophilin A1 regulates the curvature of the emerging vesicle. Endophilin A1 is also responsible for the recruitment of dynamin to the neck of the clathrin-coated vesicle (CCV).

→ (2) Fission: Dynamin then constricts the neck and mediates CCV fission from the plasma membrane. Endophilin A1 also recruits synaptojanin 1, whose phosphatase activity dephosphorylates synaptic vesicle membrane lipids to release adaptor proteins, allowing auxilin to bind to the CCV.

→ (3) Clathrin uncoating: Auxilin is a cofactor for hsc70, which simulates the removal of the clathrin coat through its ATPase activity.

→ (4) Packaging: Once the clathrin coat is fully removed, dopamine can be packaged into the nascent vesicle.

→ (5) Vesicular dopamine: The dopamine-loaded vesicle is available for the next cycle of neurotransmitter release. Dopamine sequestration inside the vesicle also mitigates elevation of cytosolic levels and prevents dopamine from becoming oxidized in the cytosol.

3-2) kiss and run pathway

Nguyen et al      Page 15

(1) Invagination/constriction   (2) Fission   (3) Clathrin uncoating   (4) Packaging   (5) Vesicular dopamine

Legend: Dynamin, Endophilin A1, Synaptojanin 1, Auxilin, Hsc70, Clathrin, Dopamine, Synapse, Synaptic cleft

3-3) several variations of bulk endocytosis such as ultrafast and activity-dependent bulk endocytosis

Genetics Synapse

Dysfunction in SVE in dopaminergic neurons can lead to increased levels of unpackaged, cytosolic DA that is subject to oxidation and pathogenic downstream effects

Mechanism category	Genes	category		Mechanism
Synaptic endocytic gene	DNAJC6 (auxilin, =PARK19),	PD-linked gene	Case YOPD
	SYNJ1 (synaptojanin 1),	PD-linked gene	?
	SH3GL2 (endophilin A1),	PD risk gene	?
Non-Synaptic endocytic gene	LRRK2		Regulates SVE	{Nguyen, 2019 #922}Normal LRRK2 serine/threonine kinase activity is critical for proper SVE; chemical inhibition of LRRK2 was shown to delay endocytosis [46]. In addition, LRRK2 mutant mice displayed an accumulation of CCVs and decreased synaptic vesicle density in dopaminergic terminals. Many synaptic interacting partners and substrates have been described for LRRK2, but those specifically involved in SVE regulation have only recently been identified. Dynamin, which mediates the fission from the plasma membrane, was identified as a LRRK2 interactor, highlighting a potential role for LRRK2 in the regulation of dynamin GTPase activity [7,48]. Moreover, LRRK2 was shown to phosphorylate endophilin A1 at positions T73 and S75 located in its BAR domain [17,18]. Subsequent investigations confirmed that LRRK2-mediated phosphorylation of endophilin A1 at S75 acted as a critical switch in mediating endophilin A1 function at the synapse [18]……
	Park2		Regulates SVE	{Nguyen, 2019 #922}parkin ubiquitinate endophilin A1 as well as its major binding partners dynamin, synaptojanin 1 [38]. Ubiquitination by parkin may be responsible for either modulating the endophilin A1 expression level, as previously reported, or regulating its ability to bind, recruit, and engage its interaction partners at the plasma membrane or CCV interface [38]. Ubiquitination-interaction motifs were first mapped in the endocytic protein epsin, which was recently identified as an accessory factor in SVE, supporting the idea that ubiquitination is necessary to facilitate endocytic functions [56,57]. Furthermore, ubiquitination of epsin rendered the protein partially resistant to proteasomal degradation thereby allowing it to interact with other endocytic proteins [56]. Interestingly, parkin was recently shown to ubiquitinate VPS35, which did not result in proteasomal degradation of the protein [58]. Therefore, parkin may also alter SVE through retromer-dependent endosomal sorting. These data suggest that the parkin E3 ubiquitin ligase function is potentially an important regulator of synaptic vesicle recycling and that PRKN mutations that lead to loss of parkin function may negatively affect the stepwise progression of SVE.

Imaging Synapse

[11C]UCB-J PET	[11C]UCB-J has previously been found to be specific for SV2A and not for SV2B or SV2C.19, Synaptic vesicle protein 2A (SV2A) is a transmembrane protein widely expressed in presynaptic terminals throughout the brain	Js: 장점: this is neuron nonspecific to neuronal type), MC1처럼 이 역시 SV2A 의 Density만 보여 줌 (Van Vliet, 2009 #1217) 'a few scattered SV2A positive astrocytes'인 것 인지 글짤 cell 에도 SV2A 일부 이상 있나?
	Risk: synaptic loss 가 아니라 SV dysfunction and/or cycling만을 반영할 수도 있다.	{Van Vliet, 2009 #1217} 'a few scattered SV2A positive astrocytes'인 것을 보면 cell 에도 SV2A 일부 이상 있나?
For SV2C	MJF award (Studies have shown that SV2C is altered in PD.), n humans, SV2C is expressed in evolutionarily old brain regions, including striatum, substantia nigra nuclei in the pons and medulla oblongata. Low levels are found in olfactory bulb, cerebrum, cerebellum, and hippocampus (Bartholome et al., 2017; Rossi et al., 2022). SV2C is expressed in dopaminergic neurons, certain GABAergic neurons, such as Purkinje cells of the cerebellum, and in some cholinergic neurons (Bartholome et al., 2017; Rossi et al., 2022). SV2C regulates dopamine release (Dunn et al., 2017),	The three SV2 genes in mammals encode three isoforms SV2A, SV2B, and SV2C.

Readouts of synapse

아래 표는 overall 2018 Verstraelen https://doi.org/10.3389/fnins.2018.00389

Structural

	Pre-synapse			animal	human	Post-synapse			animal	human
synapse density (direct readout)	Synaptophysin (gold standard)	a major integral membrane glycoprotein of neuronal SV present in virtually all synapses		↓ in frontal cortex of ADLP-APP/PS1 mouse (WB, 504)		PSD95	Glutamatergic, scaffold proteins (		↓ from cortex of ADLP-APP/PS1 mouse (WB, 504)
neurite density & complexity (length and branching points), general health and connectivity of the neuronal network.	VGlut1 or VGlut2	glutamatergic					neurotransmitter (NT) receptors (e.g., AMPA-R) or
dendritic spine density & plasticity	{Matuskey, 2020 #923} SV2A: As SV2A has a relatively consistent copy number per vesicle,	localized in cytoplasmic vesicle, secretory vesicle, and the synaptic vesicle, a multi-pass membrane protein that is an integral membrane glycoprotein in all SVs			[11C]UCB-J: (Wilson 2020) ↓
	Vesicular glutamate transporter 1 (VGLUT1)	preferentially associated with the membranes of synaptic vesicles and functions in glutamate transport
	Vesicle associated membrane proteins (VAMP2)= synaptobrevins	constituents of the synaptic vesicles
	SNAP-25	Synaptosomal-Associated Protein, 25kDa (SNAP-25) is a presynaptic protein		also, maybe a safety biomarker for excessive synaptic pruning  [ADx logo + small icon thumbnail]

(neurogranin row, leftmost cell): neurogranin is presumed to measure synaptic generation and loss (Jack et al., 2018, PMID)

Uncertain Spans

location	transcription	uncertainty
LRRK2 row, mechanism column	trailing [18]……	mechanism cell continues past the right edge of the visible crop; trailing detail at S75 mechanism is partly cut.
Park2 row, mechanism column	parkin may also alter SVE through retromer-dependent endosomal sorting	reads as written; the cell wraps long and the trailing two sentences are reconstructed from body_full where the right column is partly cut at the page edge.
Imaging Synapse SV2A	'a few scattered SV2A positive astrocytes'인 것 인지 글짤 cell 에도	the OCR shows 글짤 which is likely a Korean handwriting/typo for 글리아 (glia); reads as 글짤 in the captured image so transcribed verbatim.
Readouts of synapse, ADx logo cell	[ADx logo + small icon thumbnail]	the cell contains a small product/biomarker brand image and a thin box-and-whisker style icon; described as labels because the source text in the cell is also, maybe a safety biomarker for excessive synaptic pruning rather than a separate caption.