Anatomy, Cell Biology & Physiology Department Theses and Dissertations

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IUPUI Department of Anatomy, Cell Biology & Physiology

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Browsing Anatomy, Cell Biology & Physiology Department Theses and Dissertations by Author "Allen, Matthew"

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    CaMKK2 Signaling in Metabolism and Skeletal Disease: A New Axis with Therapeutic Potential
    (2022-07) Williams, Justin N.; Sankar, Uma; Evans-Molina, Carmella; Bonewald, Lynda; Burr, David; Allen, Matthew
    Type 2 diabetes mellitus (T2DM) is a growing problem globally and is associated with increased fracture risk and delayed bone healing. Novel approaches are needed in the treatment of T2DM and the resulting diabetic osteopathy. Recent studies highlight the role of bone as an endocrine organ producing factors that communicate with distant tissues to modulate systemic glucose metabolism. Ca2+/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) is a potent regulator of whole-body energy metabolism, inflammation, bone remodeling and fracture healing. Genetic ablation of CaMKK2 protects from diet-induced obesity, insulin resistance and inflammation, while enhancing pancreatic β cell survival and insulin secretion. Deletion or inhibition of CaMKK2 promotes bone accrual by stimulating osteoblast-mediated bone formation and suppressing osteoclast-mediated bone resorption; however, its specific role in osteocytes, the master regulator of bone remodeling remains unknown. Here we demonstrate that conditional deletion of CaMKK2 from osteocytes enhances bone mass in 3-month-old female, but not male mice, due to suppression of osteoclasts. Conditioned media experiments and proteomics analysis revealed that female osteocytes lacking CaMKK2 suppressed osteoclast formation and function through enhanced secretion of calpastatin, a potent inhibitor of calpains, which are calciumdependent cysteine proteases that support osteoclasts. Further, to determine if CaMKK2- deficient osteocytes regulate whole-body glucose homeostasis, we placed these mice on a high-fat diet (HFD) for a period of 16 weeks. Although the diet did not significantly impact bone mass or strength, we found that conditional deletion of CaMKK2 in osteocytes enhanced bone microarchitecture in 6-month-old male and female mice. We also observed that conditional deletion of CaMKK2 from osteocytes protected male and female mice from HFD-induced obesity and insulin insensitivity. Taken together, these findings highlight CaMKK2 as a potent regulator of osteocyte-mediated modulation of bone remodeling and whole-body energy metabolism.
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    Neurodegeneration Risk Factor TREM2 R47H Mutation Causes Distinct Sex- and Age- Dependent Musculoskeletal Phenotype
    (2022-05) Essex, Alyson Lola; Plotkin, Lillian I.; Bonetto, Andrea; Allen, Matthew; Landreth, Gary E.
    Triggering Receptor Expressed on Myeloid Cells 2 (TREM2), a receptor expressed in myeloid cells including microglia in brain and osteoclasts in bone has been proposed as a link between brain and bone disease. Previous studies identified an AD-associated mutation (R47H) which is known to confer an increased risk for developing AD. In these studies, we used a heterozygous model of the TREM2 R47H variant (TREM2R47H/+), which does not exhibit cognitive defects, as a translational model of genetic risk factors that contribute to AD, and investigated whether alterations to TREM2 signaling could also contribute to bone and skeletal muscle loss, independently of central nervous system defects. Our study found that female TREM2R47H/+ animals experience bone loss in the femoral mid-diaphysis between 4 and 13 months of age as measured by microCT, which stalls out by 20 months of age. Female TREM2R47H/+ animals also experience significant decreases in the mechanical and material properties of the femur measured by three-point bending at 13 months of age, but not at 4 or 20 months. Interestingly, male TREM2R47H/+ animals do not demonstrate any discernable differences in bone geometry or strength until 20 months of age, where we observed slight changes in the bone volume and material properties of male TREM2R47H/+ bones. Ex vivo osteoclast differentiation assays demonstrate that only male TREM2R47H/+ osteoclasts differentiate more after 7 days with osteoclast differentiation factors compared to WT, but qPCR follow-up showed sexdependent differences in intracellular signaling. However, bone is not the only musculoskeletal tissue affected by the TREM2 R47H variant. Skeletal muscle strength measured by both in vivo plantar flexion and ex vivo contractility of the soleus is increased and body composition is altered in female TREM2R47H/+ mice compared to WT, and this is not likely due to bone-muscle crosstalk. These studies suggests that TREM2 R47H expression in the bone and skeletal muscle are likely impacting each tissue independently. These data demonstrate that AD-associated variants in TREM2 can alter bone and skeletal muscle strength in a sex-dimorphic manner independent of the presence of central neuropathology.