Does the bone hormone osteocalcin suppress inflammation within human aortic endothelial cells

S. A. Millar, S. I. Anderson, S. E. O'Sullivan. Division of Medical Sciences and Graduate Entry Medicine, University of Nottingham, Derby, UNITED KINGDOM.

Introduction: The bone hormone osteocalcin (OCN) has been recently connected to a number of extra-osseous functions, particular its undercarboxylated (ucOCN) form. Research into the effects of both ucOCN and the carboxylated (cOCN) form in the vasculature has resulted in a number of revelations including increased Akt phosphorylation and nitric oxide production in Human Aortic Endothelial Cells (HAoECs) and improved endothelial function in ApoE-/- mice when treated with OCN (1, 2). We hypothesised that OCN may therefore have a protective role in the vasculature and in atherosclerosis and may suppress inflammation.

Methods: HAoECs were grown until confluent in 24-well cell culture plates at passages ≤6. Cells were treated with or without 10ng/ml of ucOCN or cOCN. A 24 hour inflammatory protocol was followed in which cells were treated with IFN-γ and TNF-α (10ng/ml) or vehicle (n=8 for all conditions). Following the protocol cell media and lysates were collected appropriately. The inflammatory protocol was characterized by assessing phosphorylation status of VCAM-1, JNK, p38, IL-6 and IL-8.

Results: Treatment of HAoECs with ucOCN and cOCN did not affect any measured markers of inflammation, including the anti-inflammatory marker IL-10 (Figure 1).

Conclusions: Osteocalcin does not affect inflammation in HAoECs thus any potential protective role of OCN in atherosclerosis remains elusive. OCN may produce a different response in other vascular cells such as human aortic smooth muscle cells.

References:

1. Jung CH, et al. (2013). Metabolism 62(9): 1250-7.

2. Dou J, et al. (2014). Cardiovasc Diabetol 13: 74.

Figure 1. Mean % change of measured markers of inflammation relative to the control and standard error of the mean (SEM) following different treatment conditions. *p<0.05 **p<0.01 ***p<0.001 ****p<0.0001. Abbreviations: ucOCN, undercarboxylated osteocalcin; cOCN carboxylated osteocalcin; inflm, inflammation.