Intravital Quantification of Tissue Fluid Balance Changes In Lymphedema
Joseph M. Rutkowski and Melody A. Swartz. Institute of Bioengineering, École Polytechnique Fédérale de Lausanne (EPFL), Batiment AAB; Station 15, Lausanne, 1015, Switzerland
Hydraulic conductivity, as the physical tissue property that governs interstitial flow and transport in all tissues, is a potentially controlling factor in processes of tumor and immune cell trafficking, drug and vaccine delivery, and cell and tissue morphogenesis. Quantification of tissue hydraulic conductivity is therefore useful when exploring these processes, but, to date, determining this parameter in vivo has been challenging. Primary lymphedema is a congenital pathology of dysfunctional lymphatic drainage characterized by swelling of the limbs, thickening of the dermis, and fluid and lipid accumulation in the underlying tissue. We hypothesized that lymphedema presents an excellent model to demonstrate how matrix remodeling dictates the hydraulic conductivity of the tissue. We utilized two mouse models of lymphedema, the Chy mouse and the K14-VEGFR-3-Ig mouse, which exhibit dermal lymphedema symptomatically similar to the human condition resulting from deficient vascular endothelial growth factor receptor (VEGFR)-3 signaling and a subsequent lack of dermal lymphatic capillaries. Using a simple, reproducible, intravital technique, we infused a fluorescently-labeled dextran intradermally in the mouse tail at low pressures and quantitatively determined the functional interstitial transport implications resulting from these mutations. We found that despite similarities in increased skin hydration and elevated interstitial fluid pressure, dermal tissue adaptations were significantly different in the two mouse models. Chy mouse skin possessed much higher levels of collagen and fat, effectively densifying the matrix, minimizing interstitial flow, and normalizing hydraulic conductivity. Conversely, while the fat and collagen content in K14-VEGFR-3-Ig skin was relatively normal, the tissue conductivity was greatly increased due to the increased hydration. Thus, we hypothesize that the Chy mouse has adapted to a lack of initial lymphatics by decreasing interstitial transport, while the K14-VEGFR3-Ig mouse has adapted to increase or facilitate interstitial flow over longer distances. These responses to reduced lymphatic drainage (via missing initial lymphatics) suggest that tissue remodeling in lymphedema is not simply a consequence, but an adaption to limit tissue swelling by attempting to normalize the interstitial fluid balance.