Secondary lymphedema in the mouse tail: Lymphatic hyperplasia, VEGF-C upregulation, and the protective role of MMP-9

Abstract

Disturbances in the microcirculation can lead to secondary lymphedema, a common pathological condition that, despite its frequency, still lacks a cure. Lymphedema is clinically well described, but while the genetic underpinnings that cause lymphatic malformations and primary lymphedema are being discovered, the pathophysiology and pathobiology of secondary lymphedema remain poorly understood, partly due to the lack of well-described experimental models. Here, we provide a detailed characterization of secondary lymphedema in the mouse tail and correlate the evolution of tissue swelling to changes in tissue architecture, infiltration of immune cells, deposition of lipids, and proliferation and morphology of the lymphatic vessels. We show that sustained swelling leads to lymphatic hyperplasia and upregulation of vascular endothelial growth factor (VEGF)-C, which may exacerbate the edema because the hyperplastic vessels are poorly functional. The onset of lymphatic hyperplasia occurred prior to the onset of lipid accumulation and peak VEGF-C expression. Langerhans dendritic cells were seen in the dermis migrating from the epidermis to the lymphatic capillaries in edematous tissue. Furthermore, these results were consistent between two different normal mouse strains, but swelling was significantly greater in a matrix metalloproteinase (MMP)-9 null strain. Thus, by characterizing this highly reproducible model of secondary lymphedema, we conclude that VEGF-C upregulation and lymphatic hyperplasia resulting from dermal lymphatic ligation and lymphedema leads to decreased drainage function and that MMP-9 may be important in counteracting tissue swelling.

IL-6 regulates adipose deposition and homeostasis in lymphedema

“…Therefore, the ALND model enables us to study the effects of lymph stasis without significant adipose deposition. In contrast, the mouse tail model used in this study enables us to analyze the effects of more profound lymphatic injury and adipose deposition, since we and others have previously shown that this treatment results in substantial subcutaneous adipose deposition and that this process is chronic lasting as long as 12 wk postop (4,11,32,33). Using a direct comparison of these models, we found that IL-6 expression, activation of its downstream mediator, and serum changes in IL-6 concentration occur to a more significant degree in the tail model as compared with the ALND model.…”

A driving force for change: interstitial flow as a morphoregulator

“…Lymphedema is a condition in which interstitial fluid flow is severely reduced due to either malformations in the lymphatic system (primary lymphedema) or blockage downstream, such as that which occurs after lymph node resection (secondary lymphedema). The accumulation, rather than clearance, of fluid from the interstitial space results in inflammation and extensive tissue remodeling, lymphatic hyperplasia, and adipocyte growth and lipid accumulation [38,39]. Fluid stagnation in lymphedema also prevents normal immune cell trafficking in the affected tissue, which can exacerbate the pathology.…”

Role of Lymphatic Vessels in Tumor Immunity: Passive Conduits or Active Participants?

“…Without flow, as in the case of lymphedema, lymphatic endothelium becomes hyperplastic (i.e. the diameter of lymphatic capillaries increases while their density remains unchanged) [50]. In general, lymphatic hyperplasia and lymphangiogenesis have not been carefully distinguished in the literature, even though these are likely to have different effects on tissue fluid clearance and drainage to the lymph node [1,28,51].…”