Role of Skeletal Muscle Lymphatics in Duchenne Muscular Dystrophy Regulation - Duchenne muscular dystrophy (DMD) is an incurable, X chromosome-linked muscle disease that exhibits skeletal muscle wasting/weakness and the associated inflammation and dysfunction. Though available data on anti-inflammatory drugs in DMD patients and animal models are promising in diminishing inflammation and promoting muscle healing in patients, further understanding the inflammatory mechanisms and DMD pathogenesis is critical to develop the next generation of DMD drugs. The lymphatics have emerged as a central player in the process of inflammation and play active roles in both the resolution and progression of inflammation. This proposal brings a novel perspective for treatment of DMD. Since the lymphatic system plays active roles in both the resolution and progression of inflammation, the idea is that further increasing lymphangiogenesis in muscle tissues will augment lymph transport, and consequently, lessen inflammation and improve muscle health in DMD muscle. Preliminary data demonstrate: i) lymph transport in the distal pelvic limb is decreased while lymphatic vessel density is increased in tibialis anterior muscle from the severely affected, D2mdx mice; ii) skeletal muscle-specific overexpression of vascular endothelial growth factor (VEGF)-D increases lymphangiogenesis in normal muscle, with an increase in muscle weight and a positive trend in improving forelimb grip strength and iii) augments lymph transport in denervated muscle. Hence, central hypotheses are: 1) Inflammatory lymphangiogenesis combined with a decrease in lymphatic contractile activity cause a decrease in lymph transport, thereby causing chronic inflammatory status in muscles of DMD animals and 2) further augmenting lymphangiogenesis with VEGF-D overexpression beyond the level of inflammatory lymphangiogenesis observed in dystrophic muscle will improve lymph transport in skeletal muscle, and consequently, resolve the inflammation and attenuate muscle weakness and dysfunction in DMD animals. Specific Aims are: 1) To determine the changes in lymphatic structure and function in skeletal muscle of DMD mouse and canine models and 2) To determine whether experimentally increasing lymphangiogenesis in skeletal muscle improves muscle health in D2.mdx mice and golden retriever muscular dystrophy (GRMD) dogs. Different age groups of D2.mdx mice and wildtype control DBA/2J mice will be used. GRMD dogs and muscle biopsy collections from muscle dystrophy patients of various dog breeds will also be used. Overexpression of VEGF-D in D2.mdx mice and in GRMD will be achieved by genetic or adeno-associated virus approaches. Lymphangiogenesis, inflammation, lymphatic contractility and lymph transport, muscle health and function will be evaluated in controls and experimental animals. This proposal will provide novel information regarding the therapeutic role of lymphangiogenesis in improving muscle health in DMD animal models.
