Diabetes mellitus induces endothelial JAM-A upregulation, accelerating monocytic transmigration but not adhesion

Introduction Due to its high prevalence with more than 540 million people worldwide afflicted with Diabetes mellitus (DM) and its high rates of cardiovascular diseases and death, DM is one of the costliest diseases. DM induces endothelial dysfunction and reinforces monocytic recruitment and accumulation, which triggers a local inflammation and thereby promotes atherogenesis. Purpose As the underlying mechanisms of atherosclerosis are not fully uncovered, we investigated the potential impact of Junctional Adhesion molecule A (JAM-A) on monocytic recruitment in contexts of diabetes mellitus and atherosclerosis. Methods Human coronary artery endothelial cells (HCAEC) were stimulated with serum of non-diabetic (nonDM) patients, the serum of patients with type II diabetes mellitus (T2DM) or exposed to hyperglycemic (HG) conditions. The expression of endothelial JAM-A and soluble JAM-A were assessed by FACS, RT-qPCR and ELISA. JAM-A expression was investigated by immunohistochemistry in diabetic mice and human arteries or plaques obtained from DM patients. Functional analysis was carried out using flow assays, either by a knockdown of JAM-A using a silencing RNA approach or overexpression of JAM-A by plasmid DNA transfection in HCAEC. Cells were seeded as confluent monolayer and exposed to T2DM patient serum. Afterwards, the endothelial monolayer was perfused with primary human monocytes obtained from healthy donors under physiological flow conditions found in microvessels. Monocytic-endothelial interaction was tracked during the assay by phase contrast microscopy and analysed by single-cell tracking. Results Stimulation of HCAEC with T2DM patient serum lead to a twofold increase in surface JAM-A expression and an elevation of soluble JAM-A by 70%. HG-preconditioning of HCAEC resulted in a comparable increase in JAM-A expression. In human and murine DM arterial sections, JAM-A expression was elevated. We were able to prove a central role for JAM-A in monocytic diapedesis. JAM-A knockdown resulted in a 70% reduced transmigration (TEM) capacity of monocytes (p<0.0001) while adhesion was unimpaired. Furthermore, the initiation of TEM was delayed (1.5 times, p=0.016) and TEM phase was twofold prolonged (p<0.0001). Preincubation of monocytes with recombinant human JAM-A prior flow assay corroborated the previous findings. In the presence of higher JAM-A surface levels, an earlier initiation of TEM and shorter TEM phase could be observed. These effects were diminished by JAM-A blockade. Conclusion Our study reveals for the first time an association between DM-induced JAM-A upregulation and the quality of TEM of CD14++ monocytes. The results demonstrate that an increase in JAM-A is associated with enhanced TEM capacity in monocytes Moreover, JAM-A induces rapid monocyte TEM. Given the established role of monocyte migration in atherosclerosis, it is plausible to associate elevated JAM-A levels in DM to the progression of atherosclerosis.