title: Role of AMP-activated protein kinase (AMPK) in regulation of perivascular adipose tissue (PVAT) function
Creators: name: Al Ferjani, Ali Abdulmajed Ali
Publisher: name: University of Glasgow
Year: 2024

description: Most blood vessels are surrounded by a layer of adipose tissue known as perivascular adipose tissue (PVAT). PVAT has an endocrine role, releasing a wide array of biologically active molecules, including adipokines, cytokines/chemokines, growth factors, reactive oxygen species, nitric oxide, and hydrogen sulphide (H2S), and other factors yet undetermined. These molecules exert a profound influence on vascular function under both physiological and pathophysiological conditions. While some of these factors possess vasorelaxant properties, referred to as PVAT-derived relaxing factors (PVRFs), others influence vascular tone by inducing vasoconstriction.

The exact mechanism(s) underlying the anti-contractile effect of PVAT remain incompletely understood, although much evidence suggests that PVRFs may activate K+ channels on vascular smooth muscle cells (VSMCs) or endothelial nitric oxide synthase (eNOS) in endothelial cells possibly via AMP-activated protein kinase (AMPK). AMPK is a serine/threonine kinase with many potential physiological functions, including regulation of energy haemostasis. AMPK is expressed in all layers of the blood vessel, including the PVAT, and it is known that activation of AMPK leads to vascular dilatation via both endothelium- and non-endothelium-dependent mechanisms.

A previous study in our laboratory has demonstrated that AMPK mediates the anticontractile effect of PVAT on VSMCs. Therefore, this project aimed to investigate the contribution of AMPK to the endothelium-dependent anticontractile effect of PVAT in two distinct anatomical locations: the thoracic and abdominal aorta.

Experiments were conducted using wild type (WT) and global AMPKα1 knockout (KO) mice aortae. The anti-contractile effect of PVAT was studied by measuring the relaxation response to AMPK-independent vasodilator cromakalim in vessels contracted with phenylephrine using wire myography. Whereas the secretory function of the PVAT was tested using an immunoblotting array and ELISA. Immunoblotting methods were used to test eNOS and AMPK activity in the cultured Human Umbilical Vein Endothelial Cells (HUVECs).

Endothelium-intact thoracic and abdominal aortic rings from WT and KO mice were mounted on a wire myograph in the presence and absence of PVAT. The responses to the AMPK-independent vasodilator cromakalim were subsequently assessed. Relaxation responses to cromakalim in the WT abdominal vessels were significantly higher compared to abdominal vessels from KO mice. However, no significant difference in response to cromakalim were reported in thoracic aortae of both genotypes.

Adipokine array and ELISA demonstrated that fibroblast growth factor-21 (FGF-21) release is significantly reduced in conditioned media (CM) from the abdominal-aortic PVAT of KO mice in comparison with WT CM. FGF-21, known for its impact on endothelial cells, did not induce alterations in eNOS activity or nitric oxide release in HUVECs or 3T3-L1 adipocytes. Moreover, addition of FGF-21 had no effect on the PE-induced contraction and did not alter acetylcholine-induced relaxation in WT vessels lacking PVAT. However, there are some considerations (as discussed later) that need to be addressed.

In conclusion, this study suggests that AMPKα1 plays a significant role in maintaining the anti-contractile effect of abdominal PVAT; potentially through regulating adipokine secretion. Although FGF-21 did not show a significant effect on eNOS phosphorylation and nitric oxide release, its expression and release by abdominal PVAT, and likely other white adipose tissue depots is regulated by AMPK. This finding could be of clinical importance as both AMPK and FGF-21 share a different metabolic profile and could be promising candidates for drug development targeting metabolic diseases such as type 2 diabetes and metabolic syndrome.