Lymphatic function is regulated by a coordinated expression of lymphangiogenic and anti-lymphangiogenic cytokines

Abstract

Lymphangiogenic cytokines such as vascular endothelial growth factor-C (VEGF-C) are critically required for lymphatic regeneration; however, in some circumstances, lymphatic function is impaired despite normal or elevated levels of these cytokines. The recent identification of anti-lymphangiogenic molecules such as interferon-γ (IFN-γ), transforming growth factor-β1, and endostatin has led us to hypothesize that impaired lymphatic function may represent a dysregulated balance in the expression of pro/anti-lymphangiogenic stimuli. We observed that nude mice have significantly improved lymphatic function compared with wild-type mice in a tail model of lymphedema. We show that gradients of lymphatic fluid stasis regulate the expression of lymphangiogenic cytokines (VEGF-A, VEGF-C, and hepatocyte growth factor) and that paradoxically the expression of these molecules is increased in wild-type mice. More importantly, we show that as a consequence of T-cell-mediated inflammation, these same gradients also regulate expression patterns of anti-lymphangiogenic molecules corresponding temporally and spatially with impaired lymphatic function in wild-type mice. We show that neutralization of IFN-γ significantly increases inflammatory lymph node lymphangiogenesis independently of changes in VEGF-A or VEGF-C expression, suggesting that alterations in the balance of pro- and anti-lymphangiogenic cytokine expression can regulate lymphatic vessel formation. In conclusion, we show that gradients of lymphatic fluid stasis regulate not only the expression of pro-lymphangiogenic cytokines but also potent suppressors of lymphangiogenesis as a consequence of T-cell inflammation and that modulation of the balance between these stimuli can regulate lymphatic function.

Adaptive Immune Responses Regulate the Pathophysiology of Lymphedema

“…This hypothesis is supported by recent findings demonstrating that T cells can regulate lymphangiogenesis [11,21,22] and are known to play a role in fibrotic disorders and may therefore contribute to the pathologic fibrosis that is associated with chronic lymphedema.…”

“…[14] Similarly, our hypothesis is supported by our previous studies demonstrating that mice deficient in all T cells (nude mice) have significantly decreased tail lymphedema, fibrosis, and lymphatic dysfunction as compared with wild-type littermates. [21] The hypothesis that inflammation contributes to the pathology of lymphedema is also supported by previous studies by Rockson and colleagues demonstrating that inhibition of generalized inflammatory responses using ketoprofen, a non-steroidal anti-inflammatory medication, markedly improves lymphatic function and decreases lymphedema in the mouse tail model. [29] Finally, the hypothesis that CD4+ cells either directly or indirectly contribute to the initiation and progression of lymphedema is supported by the fact that these responses have been implicated in the pathology of obesity including metabolic dysfunction and adipose deposition.…”

“…To test the hypothesis that inhibition of fibrosis is specific to Th2 differentiation rather than a generalized anti-inflammatory effect, we performed tail skin/lymphatic excision on wild type mice followed by treatment with either with an inhibitor of JAK1/2 (AZD1480) [20,21] or vehicle control for 6 weeks. We chose to block this pathway since IL4/IL13 signal through JAK3/STAT6 rather than JAK1/2/STAT3 and because JAK1/2 signaling by a variety of inflammatory cytokines, including IL6, is an important regulator of acute/chronic inflammation.…”

“…[20,21] C57BL/6Jmice were administered 60 mg/kg AZD1480 (in 0.5% HPMC/0.1% Tween80) or vehicle control daily by oral gavage for 6 weeks beginning immediately after tail skin/lymphatic excision.…”

Inflammation-associated lymphangiogenesis: a double-edged sword?

“…It is particularly important for post-inflammatory regression of the already expanded neo-lymphatic network within the regional LN (34). TGF-β1 (35-37), endostatin (38), and thrombospondin (39) also have an antilymphatic role (40). However, our knowledge of the negative regulatory mechanisms of IAL remains relatively limited, and further studies are necessary to identify other antilymphatic signaling pathways.…”