Connexins (Cxs) are a family of transmembrane proteins comprising 21 members in humans that forms gap junction channels (GJCs). Connexins are divided in four groups: α, β, γ and δ. Cx37 is also named α4 since it is the fourth connexin of the alpha group that was identified^1,2. 

Connexins do not function as single proteins; six connexins assemble into connexons (hemi-channels), and two connexons from neighboring cells dock in the extracellular space to form a full gap junction channel. Connexins are responsible for mediating direct communication between adjacent cells by the exchange of ions and small signaling molecules and cytosolic factors^1,3. Their structure consists of four transmembrane helices, two extracellular loops, a cytoplasmic loop, a cytoplasmic NH₂- and COOH-termini^1,2.

Connexin-37 is encoded by the GJA4 gene and is expressed in vascular endothelial cells. The protein is responsible for regulating and controlling the growth, proliferation and regeneration of the vascular endothelium by mediating the signal transduction between smooth muscle and endothelial cells. Cx37 knockout mice have a tendency for developing endarterium atheromatous plaques⁴. Also, a polymorphism in the gene that encodes for Cx37, is associated with increased risk for atherosclerosis and myocardial infarction¹.