Regulation of Adipogenesis by Lymphatic Fluid Stasis

Abstract

Background Although fat deposition is a defining clinical characteristic of lymphedema, the cellular mechanisms that regulate this response remain unknown. The goal of this study was to determine how lymphatic fluid stasis regulates adipogenic gene activation and fat deposition. Methods Adult female mice underwent tail lymphatic ablation and sacrifice at 1, 3, or 6 weeks post-operatively (n=8/group). Samples were analyzed by immunohistochemistry and western blot. An alternative group of mice underwent axillary dissections or sham incisions and limb tissues were harvested 3 weeks post-operatively (n=8/group). Results Lymphatic fluid stasis resulted in significant subcutaneous fat deposition and fibrosis in lymphedematous tail regions (p<0.001). Western blot analysis demonstrated that proteins regulating adipose differentiation including CCAAT/enhancer binding protein-alpha (CEBP-α) and adiponectin were markedly upregulated in response to lymphatic fluid stasis in the tail and axillary models. Expression of these markers increased in edematous tissues according to the gradient of lymphatic stasis distal to the wound. Immunohistochemical analysis further demonstrated that adiponectin and peroxisome proliferator-activated receptor gamma (PPAR-γ), another critical adipogenic transcription factor, followed similar expression gradients. Finally, adiponectin and PPAR-γ expression localized to a variety of cell types in newly formed subcutaneous fat. Conclusions The mouse-tail model of lymphedema demonstrates pathological findings similar to clinical lymphedema including fat deposition and fibrosis. We show that lymphatic fluid stasis potently upregulates the expression of fat differentiation markers both spatially and temporally. These studies elucidate mechanisms regulating abnormal fat deposition in lymphedema pathogenesis and therefore provide a basis for developing targeted treatments.

Molecular Analysis and Differentiation Capacity of Adipose-Derived Stem Cells from Lymphedema Tissue

“…Recent studies using a novel murine model of lymphedema have implicated lymphatic fluid stasis and inflammation in the pathophysiology of adipogenesis. 38,39 Similarly, abnormalities in the Prox1 pathway, which is critical for lymphatic vasculature, have been associated with increased adipose tissue accumulation and adult-onset obesity. 40 …”

The Lymphatic Vasculature: Its Role in Adipose Metabolism and Obesity

“…This disease affects millions of persons worldwide and most commonly involves swelling of the extremities, tissue fibrosis, susceptibility to infections, and accumulation of subcutaneous fat (Aschen et al, 2012; Brorson, 2016; Rockson, 2001; Witte et al, 2001). Complications of lymphedema include psychosocial morbidity, infection, functional disability, skin changes, and malignant transformation (Greene and Maclellan, 2013).…”

“…At the same time, excess FFAs in the enlarged adipocytes would facilitate endothelial damage, which also contributes to lymphatic function defects. At least in mice, any minor injury to the lymphatic system activates adipose differentiation genes and leads to adipose tissue hypertrophy and proliferation (Aschen et al, 2012). Finally, and as the lymphatic system is a physiologic regulator of inflammation and immune responses, obesity-induced lymphatic dysfunction may act in a feed-forward manner to amplify the pathological consequences of obesity.…”

Restoration of lymphatic function rescues obesity in Prox1-haploinsufficient mice

“…Lymphedema can be the consequence of a genetic defect (primary lymphedema) or injury to the lymphatic vasculature (secondary lymphedema) as a result of surgery, infection, or radiation therapy (1–3). The main features of lymphedema include swelling of the extremities, tissue fibrosis, susceptibility to infections, and accumulation of subcutaneous fat (1, 2, 4). Recent data support the view that impaired lymph drainage also causes changes in the immune and inflammatory responses, dysregulation of body fluid homeostasis, disturbances of lipid metabolism and transport, and alterations in the extent of cancer metastasis and obesity (5–7).…”

“…Despite some well-established connections between lymphatic function and lipid absorption and transport, the role of the lymphatic vasculature in adipose metabolism has only recently been recognized (12, 13), and it is known that chronic lymphedema leads to adipose tissue accumulation in the affected area (14, 15). Surgeons have indicated that, in lymphedema, the excess fluid is accompanied by “wet fat” (16) and that “lymphedema is clinically characterized by progressive fat deposition and tissue fibrosis” (4). Edema has also been associated with marked lipid accumulation.…”