Continuous Endothelium

Continuous endothelium is characterized by tightly connected endothelial cells (ECs) with low, regulated transcytosis, supported by a continuous basement membrane. This type of endothelium forms barrier functions in most arteries and veins, as well as in skeletal muscle, heart, lung, adipose tissue, skin, and the central nervous system (CNS).

The blood-brain barrier (BBB) represents the most restrictive continuous endothelium, tightly controlling the brain’s microenvironment. While pericytes and astrocytes contribute, barrier properties are primarily determined by the endothelial layer. CNS ECs express the Mfsd2a gene, which suppresses transcytosis; loss of Mfsd2a leads to a leaky BBB despite intact tight junctions. Transcriptome analyses show that brain ECs possess a unique gene signature, including selective transmembrane transporters (e.g., Abcb1a, Slco1c1) and proteins involved in vascular remodeling (Itih5, Apcdd1), enabling precise regulation of molecule transport and potential targeted therapies.

This specialization of CNS ECs highlights the critical role of continuous endothelium in maintaining tissue homeostasis and presents opportunities for selective drug delivery to the brain.