Project Grant R01AR083462

DISCOVERY OF A STEM CELL GOVERNING VERTEBRAL PHYSIOLOGY - PROJECT SUMMARY VERTEBRAE AND LONG BONES DISPLAY MARKED DIFFERENCES ACROSS A RANGE OF CLINICAL AND BASIC PROPERTIES, SUCH AS THEIR BASIC ARCHITECTURE, RESPONSIVENESS TO PTH, THEIR RATE OF SEEDING WITH SOLID TUMOR METASTASES, OR THE TYPES OF DEVELOPMENTAL AND DEGENERATIVE DISEASES PRESENT. THE ETIOLOGY OF THESE DIFFERENCES HAS REMAINED ELUSIVE, IN PART DUE TO THE CURRENT STATE OF SKELETAL STEM CELL (SSC) BIOLOGY THAT LARGELY CONSIDERS SKELETAL STEM CELLS IN A MONOLITHIC MANNER, WITHOUT DRAWING CLEAR DISTINCTIONS IN CELL TYPE BASED ON BONE OF ORIGIN. HERE, WE HAVE IDENTIFIED A VERTEBRAL SKELETAL STEM CELL (VSSC), HAVING ESTABLISHED THAT IT DISPLAYS A COMPREHENSIVE SET OF STEMNESS FEATURES, INCLUDING THE ABILITY TO SELF-RENEW ACROSS MULTIPLE ROUNDS OF TRANSPLANTATION, THE ABILITY TO SERIALLY FORM BONE ORGANOIDS ACROSS MULTIPLE ROUNDS OF TRANSPLANTATION AND REISOLATION, LONG-TERM LABEL RETENTION AFTER A PULSE WITH A CHROMATIN BOUND H2B-GFP MARKER, IN VIVO MULTIPOTENCY THROUGH AN ABILITY TO GIVE RISE TO CHONDROCYTES, OSTEOBLASTS AND ADIPOCYTE IN VIVO, AND BEING LONG-LIVED IN VIVO. THIS VSSC TYPE IS SPECIFIC FOR VERTEBRAE, BEING COMPLETELY ABSENT FROM LONG BONES. THESE VSSCS HAVE A CLEAR PHYSIOLOGIC CONTRIBUTION TO VERTEBRAL MINERALIZATION, AS DELETING GENES REQUIRED FOR OSTEOBLAST DIFFERENTIATION WITH A ZIC1- CRE CREATED FOR THIS PROJECT TARGETING THE LINEAGE OF THIS VSSC PRODUCED MARKED DEFECTS IN THE MINERALIZATION OF BOTH THE DORSAL NEURAL ARCH AND THE VERTEBRAL BODY AND NO DETECTABLE PHENOTYPE IN LONG BONES. THUS, WE HAVE HERE IDENTIFIED A VSSC, INCLUDING GENERATING 2 CRE LINES TARGETING THIS CELL, THAT MEETS ALL PUBLISHED CRITERIA TO BE DEFINED AS A NOVEL SSC TYPE. HERE, WE PROPOSE TO ADDRESS A SERIES OF KEY ISSUES ENABLED BY THIS DISCOVERY TO FURTHER DEVELOP THE CLINICAL AND PHYSIOLOGIC ROLE OF THIS NEW STEM CELL TYPE. FIRST, (AIM 1) WE WILL DETERMINE THE UNIQUE CELLULAR FEATURES OF THE VERTEBRAL BONE VERSUS LONG BONES, DEMONSTRATE WHICH OF THESE FEATURES ARE DUE TO ZIC1+VSSCS, THE RELATIONSHIP OF ZIC1+VSSCS TO OTHER SKELETAL PROGENITOR CELL TYPES IDENTIFIED IN THE LITERATURE AND THE FUNCTION OF VSSC-SPECIFIC TRANSCRIPTION FACTORS AND SECRETED LIGANDS. NEXT (AIM 2), WE WILL ESTABLISH THAT THIS VSSC IS A KEY CELL MEDIATING SPINE FUSION, A COMMON ORTHOPEDIC MANAGEMENT STRATEGY TO TREAT A VARIETY OF SPINE DEGENERATIVE DISORDERS. LASTLY (AIM 3), WE WILL BUILD UPON PRELIMINARY EFFORTS IDENTIFYING A HUMAN COUNTERPART OF THE MURINE VSSC TO FULLY ESTABLISH THE IDENTITY AND DIFFERENTIATION HIERARCHY OF THE HUMAN VSSC AND TO DETERMINE THE FUNCTIONAL CONSERVATION OF VSSC-LINEAGE DEFINING TRANSCRIPTION FACTORS. ALTOGETHER, THIS PROJECT WILL ESTABLISH THE EXISTENCE AND UNIQUE PROPERTIES OF A NEW AND DISTINCT VSSC CELL TYPE IN HUMANS AND MICE AND FACILITATE SUBSEQUENT STUDIES INTO HOW THIS VSSC MEDIATES VERTEBRAL SKELETAL DISORDERS OR HOW THESE DISORDERS CAN BE THERAPEUTICALLY ADDRESSED BY TARGETING THIS NEW STEM CELL.