Protein-losing enteropathy (PLE) is a life-threatening gastrointestinal disorder in dogs in which intestinal lymphatic dysfunction can drive leakage of protein- and lymphocyte-rich lymph into the gut lumen. Despite its central role in disease, the cellular and molecular mechanisms governing intestinal lymphatic dysfunction in canine PLE remain poorly understood. Our preliminary studies identify the villus smooth muscle -lacteal complex (SMLC) as a potentially critical regulator of lymphatic function. We discovered that lacteal development depends on adjacent smooth muscle cells, which subsequently contract to promote lymph and nutrient transport. Importantly, we identified major disruptions of the myofibroblast -smooth muscle network in canine intestinal lymphangiectasia (IL), a common cause of PLE, and intestinal lymphatic hypoplasia (ILH), a rare and often fatal form of PLE. These findings suggest that altered SMLC development or maintenance may contribute directly to lymphatic dysfunction. A second critical regulator of lacteal function is endothelial junctional architecture. Lacteal endothelial junctions dynamically transition between closed, zipper-like and open, button-like configurations that regulate lymph drainage and lipid transport. Steroids can promote junctional opening in mice, raising the possibility that junctional remodeling contributes to variable responses to steroid therapy in dogs with PLE.

In this proposal, we will define gut-specific lymphatic mechanisms underlying canine PLE through two aims: Aim 1 will characterize molecular, cellular, and functional alterations in villus smooth muscle in dogs with IL and ILH and determine their relationships with clinical disease. Aim 2 will characterize and quantify lacteal endothelial junctional states in dogs with IL and determine their associations with lacteal dilation, lymphatic dysfunction, and clinical outcomes. This work will establish fundamental mechanisms linking intestinal lymphatic structure and function to canine PLE, identify potential biomarkers of disease severity and treatment response, and provide a foundation for improved diagnostic and therapeutic strategies. By addressing a major gap in lymphatic biology, this collaborative research has important translational implications for both veterinary and human gastrointestinal disease.