Abstract 305: HDL Antagonizes the Defects in the Lymphatic System that Contribute to the Pathogenesis of Rheumatoid Arthritis

Abstract

Rheumatoid arthritis (RA) is a common inflammatory erosive arthropathy that increases cardiovascular (CV) risk two-fold. Lymphatic dysfunction, a hallmark of chronic inflammation, is considered an attractive target to resolve synovial inflammation. Given the strong vascular anti-inflammatory properties of high-density lipoprotein (HDL) and its key apolipoprotein (apo)A-I, we hypothesized that they may promote inflammation resolution in RA by improving lymphatic endothelial function via up-regulation of the homeobox-containing transcription factor, Prox-1,a key regulator of inflammation-induced lymphangiogenesis (IIL) . Primary human dermal lymphatic endothelial cells (LEC) were treated for 3 days with TNFα (10 ng/mL) or pre-incubated with apoA-I (1.2 mg/mL) for 24 h, followed by TNFα exposure for 3 days. Prox1 mRNA levels were quantified by qPCR. For the tube formation assay, LECs were seeded into a pre-coated Matrigel 24-well plate, and treated with TNFα for 6 h or pre-incubated with apoA-I for 24 h, followed by TNFα exposure for 6 h. Mouse thoracic ducts (TD) were isolated from 2-4 month old C57Bl/6 mice for studying lymphatic vessel (LV) sprouting. TD rings (1 mm) were implanted into a 3-D culture system containing Matrigel under hypoxic conditions and either treated with TNFα, or pre-incubated for 24 h with apoA-I then exposed to TNFα. Incubation with TNFα decreased LEC Prox1 mRNA levels by about 56% (P<0.05). Prior exposure of LECs to apoA-I blocked TNFα-mediated Prox-1 suppression (P<0.05). TNFα also reduced LEC tube formation by about 55% (p<0.05) and completely inhibited LV sprouting from TD rings (p<0.05). ApoA-I protected against TNFα-mediated inhibition of LEC tube formation (44.7±8.1 versus 81.9±15.0% of control; P<0.05) and the inhibitory effect of TNFα on LV sprouting (P<0.05). These results suggest that apoA-I directly regulates IIL by upregulating Prox1 and protecting against TNFα-mediated restriction of lymphatic sprouting and growth in vitro. Hence, raising HDL may provide dual therapeutic benefits in RA by targeting inflammation and reducing cardiovascular risk. New classes of HDL-raising drugs will allow us to study the long term effects of increasing HDL levels on RA progression and CV risk.