BBB	Blood–Brain Barrier
BRB	Blood–Retinal Barrier
iBRB	Inner Blood–Retinal Barrier
oBRB	Outer Blood–Retinal Barrier
Cldn5	Claudin-5
TJs	Tight Junctions
ECs	Endothelial Cells
EVs	Extracellular Vesicles
CNS	Central Nervous System
ZO-1	Zonula Occludens-1
GDNF	Glial Cell Line-Derived Neurotrophic Factor
MAPK	Mitogen-Activated Protein Kinase
ERK	Extracellular Signal-Regulated Kinase
PI3K	Phosphoinositide 3-Kinase
Akt	Protein Kinase B
FOXO1	Forkhead Box O1
MS	Multiple Sclerosis
EAE	Experimental Autoimmune Encephalomyelitis
CD	Cluster of Differentiation (e.g., CD4+ T cells)
HG	High Glucose
AGE	Advanced Glycation End Products
TEER	Transendothelial/Transepithelial Electrical Resistance
HIV	Human Immunodeficiency Virus
OCD	Obsessive–Compulsive Disorder
IL-6	Interleukin-6
IR	Insulin Receptor
VEC	Vascular Endothelial Cadherin
VDR	Vitamin D Receptor
IBD	Inflammatory Bowel Disease
PBS	Phosphate-Buffered Saline
DKD	Diabetic Kidney Disease
DN	Diabetic Nephropathy
CKD	Chronic Kidney Disease
cSCC	Cutaneous Squamous Cell Carcinoma
EpV	Epidermodysplasia Verruciformis
LPS	Lipopolysaccharide
MMP3	Matrix Metalloproteinase 3
JAM-A	Junctional Adhesion Molecule-A
VE-cadherin	Vascular Endothelial Cadherin
SH-SY5Y	Human Neuroblastoma Cell Line
U251	Human Glioblastoma Astrocytoma Cell Line
hCMEC/D3	Human Cerebral Microvascular Endothelial Cells (immortalized line)