Adventitial lymphatic capillary expansion impacts on plaque T cell accumulation in atherosclerosis

Abstract

During plaque progression, inflammatory cells progressively accumulate in the adventitia, paralleled by an increased presence of leaky vasa vasorum. We here show that next to vasa vasorum, also the adventitial lymphatic capillary bed is expanding during plaque development in humans and mouse models of atherosclerosis. Furthermore, we investigated the role of lymphatics in atherosclerosis progression. Dissection of plaque draining lymph node and lymphatic vessel in atherosclerotic ApoE−/− mice aggravated plaque formation, which was accompanied by increased intimal and adventitial CD3+ T cell numbers. Likewise, inhibition of VEGF-C/D dependent lymphangiogenesis by AAV aided gene transfer of hVEGFR3-Ig fusion protein resulted in CD3+ T cell enrichment in plaque intima and adventitia. hVEGFR3-Ig gene transfer did not compromise adventitial lymphatic density, pointing to VEGF-C/D independent lymphangiogenesis. We were able to identify the CXCL12/CXCR4 axis, which has previously been shown to indirectly activate VEGFR3, as a likely pathway, in that its focal silencing attenuated lymphangiogenesis and augmented T cell presence. Taken together, our study not only shows profound, partly CXCL12/CXCR4 mediated, expansion of lymph capillaries in the adventitia of atherosclerotic plaque in humans and mice, but also is the first to attribute an important role of lymphatics in plaque T cell accumulation and development.

Cardiac lymphatics in health and disease

“…In atherosclerotic lesions, macrophage foam cells have been suggested as a significant source of lymphangiogenic VEGF-C 110 . Similar findings have been reported for other atherosclerotic arteries in humans, including iliac arteries 111,112 , and the abdominal aorta, where adventitial lymphatic densities were increased and correlated with intimal thickness, notably in advanced or ruptured atherosclerotic lesions 113 , where also VEGF-D expression may be increased 114 .…”

“…Interestingly, therapeutic inhibition of plaque lymphangiogenesis, by overexpression of a VEGF-C/VEGF-D trap, led to accelerated atherosclerosis in the descending aorta in both ApoE-deficient and in atherogenic LDLR −/− /ApoB 100/100 mice 108,116 . Similarly, it was recently reported that surgical dissection of aortic plaque-draining lymph nodes led to aggravated plaque formation in ApoE-deficient mice, including increased intraplaque and adventitial T cell densities 113 . Further, a potential role for additional lymphangiogenic factors in plaque lymphangiogenesis was shown by local silencing of the CXCL12 (SDF-1α) chemokine in the carotid artery of ApoE-deficient mice, which resulted in reduced adventitial lymphangiogenesis and increased T cell density 113 .…”

“…Similarly, it was recently reported that surgical dissection of aortic plaque-draining lymph nodes led to aggravated plaque formation in ApoE-deficient mice, including increased intraplaque and adventitial T cell densities 113 . Further, a potential role for additional lymphangiogenic factors in plaque lymphangiogenesis was shown by local silencing of the CXCL12 (SDF-1α) chemokine in the carotid artery of ApoE-deficient mice, which resulted in reduced adventitial lymphangiogenesis and increased T cell density 113 . Taken together, these studies suggest a beneficial role of peri-advential lymphatics in limiting both cholesterol accumulation and chronic plaque inflammation during atherosclerosis.…”

“…Experimental studies in atherosclerosis mouse models have yielded comparable findings, including increased lymphatic density in carotid atheroma plaques in mice 113 . However, one recent study instead found decreased adventitial lymphatic vessel density in atheromatous plaques in the abdominal aorta of aged ApoE-deficient mice, despite locally elevated VEGF-C expression 115 .…”

Arterial Lymphatics in Atherosclerosis: Old Questions, New Insights, and Remaining Challenges

“…Atherosclerosis and its cardiovascular consequences claim more lives than all types of cancer combined and it represents an enormous health care burden in western societies [10,11]. In recent years, the lymphatic network has attracted the attention of vascular biologists due to its role in immune cell trafficking, removal of cholesterol-loaded HDL from the periphery via reverse cholesterol transport (RCT), and the regulation of the inflammatory response in general [12,13,14,15,16]. Previous studies demonstrated the presence of LVs in atherosclerotic arteries, yet, our knowledge about the mechanisms regulating lymphangiogenesis and lymphatic function in the vessel wall and the role of LVs in the pathogenesis of atherosclerosis is limited.…”