JANUS under stress--role of JAK/STAT signaling pathway in vascular diseases.

They were more than just another kinases (JAK), when they were first described in the late 80s and named JAK kinases. The mandatory role of this novel family of dual active janus kinases (JAK) and their substrates the signal transducers and activators of transcription (STAT) was demonstrated in mice who died during embryogenesis when lacking a functional allele, e.g. that of JAK2. Initially, the JAK/STAT signaling pathway was discovered as the primary mediator of intracellular signaling induced by interferon in hematopoietic and immune cells. Nowadays, it is well accepted that JAK kinases and STAT proteins are constitutively expressed in the vessel wall in a cell type specific manner and transfer intracellular signaling events of various receptor families, e.g. that of cytokines, growth factors and vasoactive peptides such as angiotensin II (Ang II) or endothelin. The potential impact of the JAK/STAT signaling pathway on cardiovascular pathophysiology and disease development arise from reports describing that JAKs may bind directly to the angiotensin II type I (AT(1)) receptor, thereby enhancing their phosphorylation in various cell types of the vessel wall. More interestingly, these signaling events are modulated by NAD(P)H oxidase-derived superoxide anions which directly phosphorylate JAK2 and thereby control JAK2 activity. A potential impact was also described for atherosclerotic plaque development in which the activation of JAKs and STATs seems to be critical. Based on these observations, we here review the role of the JAK/STAT signaling pathways as critical regulator for cardiovascular disease development, i.e. atherosclerotic plaque progression or the manifestation of arterial hypertension.