Obesity‐Induced Lymphatic Valve Dysfunction

A two‐way connection between obesity and lymphatic dysfunction has now been established. Clinical studies have demonstrated that obesity significantly increases the risk for developing secondary lymphedema. Using animal‐models, obesity has been linked to different aspects of lymphatic dysfunction including impaired contractility, flow‐mediated responses, and fluid transport, as well as increased permeability, and impaired dendritic cell migration among others. Dysfunction of lymphatic valves is a main form of lymphatic dysfunction, known to result in severe edematous phenotypes; however, the extent of lymphatic valve deficiency in secondary lymphedema, including obesity‐induced lymphedema, remains unknown. Therefore, the aim of the present study was to determine whether obesity resulted in lymphatic valve dysfunction. We quantitatively assessed and compared valve function in isolated popliteal and mesenteric collecting lymphatic vessels from control and diet‐induced obese mice. Feeding a western diet (N=7) for 14 weeks induced obesity, resulting in significant gain of body weight, i.e., 18.8±1.4 g, versus 9.7±0.7 g for mice fed a control diet (N=6). Obese mice displayed significantly higher non‐fasted blood glucose concentration when compared to controls. The function of lymphatic valves in popliteal lymphatics was not affected by diet‐induced obesity; however, obesity resulted in significant back‐leak of pressure in mesenteric lymphatic valves (0.1±0.1 versus 0.7±0.1 cmH 2 O for control (n=11) and obese (n=16) groups respectively). Dysfunctional, leaky valves from obese animals required significantly higher adverse pressure to trigger valve closure (i.e., 5.5±1.6 cmH 2 O, versus 0.9±0.3 cmH 2 O for controls, when upstream pressure was maintained at 0.5 cmH 2 O). In obese animals, valve dysfunction in mesenteric lymphatics was associated with structural and mechanical modifications including shortening of valve leaflets, enlargement of the lymphatic vasculature, and increased cross‐sectional distensibility. This is the first study that reports on quantitative assessment of lymphatic valve function in an animal model of obesity, and the first to link obesity with lymphatic valve dysfunction. Finally, utilizing a newly developed method for the isolation and culturing of primary lymphatic endothelial cells (LECs) from collecting vessels, our current and future experiments seek to assess and understand functional modifications to LECs induced by obesity in‐vitro. Specifically, using high‐speed confocal microscopy, mouse lines carrying genetically encoded Ca 2+ indicators (i.e., Cdh5‐GCaMP8 and acta2‐RCaMP), and lymphatic cellular co‐cultures, we aim to determine whether obesity results in intracellular calcium dysregulation in LECs, and/or abnormal crosstalk between LECs and lymphatic muscle cells.