Introduction: Adiponectin (Ad) is a hormone secreted primarily by adipocytes and is known to have anti-inflammatory and protective effects on vascular endothelial cells specifically via the 5’ AMP-activated protein kinase (AMPK) signaling pathway. It is also known to protect against the development of albuminuria including in diabetes. Albuminuria is indicative of dysfunction of the glomerular filtration barrier of the kidney and therefore of the cells which make up the barrier: glomerular endothelial cells (GEnC) and podocytes. In particular, damage to the endothelial glycocalyx leads to an increase in albuminuria in disease states such as diabetes.
Aim: The aim of this work is to determine whether Ad acts directly on GEnC and whether as a result it can protect the glycocalyx against inflammatory mediators implicated in diabetes.
Methods: in vitro studies were performed in well-characterized conditionally immortalised human GEnC line (CiGEnC) and in sieved glomeruli from diabetic mouse models to investigate the effect of adiponectin on cell signaling and TNF-α-induced disruption of the glycocalyx.
Results: The AMPK pathway was activated when CiGEnC were stimulated with globular adiponectin (gAd) through Adiponectin Receptor 1. High glucose and tumor necrosis factor α (TNF-α) inactivated this pathway but it was restored by co-treatment with gAd. By quantitative PCR (qPCR) and Western blot, I showed that there was an upregulation of syndecan-4 (SDC4), a glycocalyx proteoglycan, at both the mRNA (2.8 fold) and protein level (1.7 fold) in response to 2-hour treatment with 10ng/ml TNF-α. Adiponectin prevented this increase. There was also a significant increase (* p<0.05) in the mRNA expression of the
metalloproteinase MMP2, which is known to induce the shedding of glycocalyx
components, in response to TNF-α. Again, gAd prevented this increase. However, gAd treatment of CiGEnC in which MMP2 had been knocked down did not completely prevent the increase of SDC4 in response to TNF-α, suggesting that other MMPs might be involved.
Conclusion: These findings show that adiponectin-induced signalling in CiGEnC protects the glycoclayx in vitro and ex vivo and therefore fully understanding these pathways has the potential to provide new therapeutic targets to decrease albuminuria in diabetes in vivo.