Project Grant R01AR083155

ENGINEERING HETEROCELLULAR HUMAN SKELETAL MUSCLE TISSUES TO RECREATE AND STUDY NATIVE STEM CELL NICHE FUNCTION - HEALTHY SKELETAL MUSCLE IS CAPABLE OF MULTIPLE CYCLES OF REGENERATION IN RESPONSE TO SMALL TEARS THAT OCCUR DURING DAILY ACTIVITY AND EXERCISE. CENTRAL TO THIS REGENERATIVE CAPACITY ARE THE MUSCLE STEM CELLS TERMED SATELLITE CELLS (SCS), WHICH RESIDE IN SPECIALIZED TISSUE "NICHES" AND IN RESPONSE TO INJURY ACTIVATE, PROLIFERATE, AND FUSE TO FORM NEW OR REPAIR DAMAGED MUSCLE FIBERS. DYSREGULATION OF SC NICHE LEADS TO LOSS OF MUSCLE REPAIR ABILITY FOUND IN AGING, CONGENITAL NEUROMUSCULAR AND METABOLIC DISORDERS, AND ACQUIRED DISEASES SUCH AS CANCER OR VOLUMETRIC MUSCLE LOSS. FUNCTION OF HEALTHY SC NICHE IS REGULATED BY A COMPLEX INTERPLAY OF BIOCHEMICAL AND BIOPHYSICAL INPUTS FROM SURROUNDING EXTRACELLULAR MATRIX, MUSCLE FIBERS, BLOOD VESSELS, NEURONS, IMMUNE AND CONNECTIVE TISSUE CELLS. WHILE SPECIFIC ROLES OF THESE REGULATORY MECHANISMS ARE DIFFICULT TO DISSECT IN VIVO, ENGINEERED 3- DIMENSIONAL (3D) SKELETAL MUSCLE TISSUES OFFER THE OPPORTUNITY TO RECAPITULATE AND SYSTEMATICALLY STUDY SC NICHE FUNCTION IN VITRO. HOWEVER, CURRENT ENGINEERED MUSCLE TISSUES LACK THE COMPLEX HETEROCELLULAR MILIEU OF NATIVE MUSCLE, ALONG WITH THE FACTORS KNOWN TO CONTROL SC NICHE HOMEOSTASIS AND RESPONSE TO INJURY. OUR GROUP HAS BEEN THE FIRST TO ENGINEER 3D FUNCTIONAL HUMAN SKELETAL MUSCLE TISSUES ("MYOBUNDLES") FROM PRIMARY MYOBLASTS AND INDUCED PLURIPOTENT STEM CELLS AND UTILIZE THEM FOR STUDIES OF MUSCLE EXERCISE, METABOLISM, INFLAMMATION, DRUG RESPONSE, AND MODELING OF CONGENITAL MUSCLE DISEASES. WHILE IN HUMAN MYOBUNDLES MADE OF MYOGENIC CELLS, SCS ATTAIN A PERI-MYOFIBER POSITION, QUIESCENT PHENOTYPE, AND HETEROGENEITY AKIN TO THOSE OF NATIVE SCS IN VIVO, THEIR REGENERATIVE RESPONSE IS LESS ROBUST THAN OBSERVED IN NATIVE SKELETAL MUSCLE. WE THUS PROPOSE TO INCREASE THE CELLULAR COMPLEXITY OF SC NICHES IN MYOBUNDLES TO APPROXIMATE THAT OF NATIVE SKELETAL MUSCLE BY INCORPORATING CAPILLARY NETWORKS AND FUNCTIONAL MOTONEURONS KNOWN TO SUPPORT NICHE FUNCTION IN VIVO. THE IMPROVED BIOMIMETIC NATURE OF VASCULARIZED AND INNERVATED MYOBUNDLES DEVELOPED IN THIS PROJECT WILL ALLOW US TO FURTHER INVESTIGATE CELL-SPECIFIC ROLES AND CROSS-CELLULAR INTERACTIONS REGULATING THE HUMAN SC NICHE MAINTENANCE, HETEROGENEITY, AND RESPONSE TO MUSCLE EXERCISE AND INJURY. ULTIMATELY, WE ANTICIPATE THAT THIS NOVEL HETEROCELLULAR MODEL OF ENGINEERED SKELETAL MUSCLE TISSUE WILL ENABLE IMPROVED IN VITRO MODELING, MECHANISTIC, AND THERAPEUTIC STUDIES OF HUMAN MUSCLE DISORDERS INVOLVING DYSREGULATION OF SC NICHE.