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Indiana University-Purdue University Indianapolis (IUPUI) / Pyk2: Potential Regulator of Post-Menopausal Bone Loss H.W. LARGURA1,2*, P. ELENISTE2, S. HUANG2, S. LIU1, M. ALLEN3, A. BRUZZANITI2. 1Indiana University School of Dentistry Department Orthodontics and Oral Facial Development, 2Indiana University School of Dentistry Department of Oral Biology, 3Indiana University School of Medicine Department of Anatomy and Cell Biology, Indianapolis, Indiana, USA Osteoporosis is a pathologic condition of bone, commonly found in post-menopausal women, which occurs from an imbalance between bone formation and resorption. Following menopause, the bone resorbing activity of osteoclasts exceeds bone formation by osteoblasts, resulting in decreased trabecular and cortical bone and a subsequent decrease in bone mass. Reduced bone mass increases the risk of pathologic fracture of bones. Due to adverse effects associated with current treatment protocols for bone loss, alternative treatment modalities with reduced adverse effects are needed. Estrogen plays a role in maintaining balance in the bone remodeling cycle by controlling remodeling activation, osteoblast and osteoclast numbers, and their respective effectiveness in formation and resorption. With declining estrogen levels, this elegantly balanced interaction is altered and bone resorption exceeds bone formation, resulting in bone loss and increased bone fragility. Pyk2 is a protein tyrosine kinase that plays an important role in regulating bone resorption by osteoclasts, as well as osteoblast proliferation and differentiation. Deletion of the Pyk2 gene in mice leads to an increase in bone mass, in part due to dysfunctional osteoclast and osteoblast activity. In this study, we examined the role of Pyk2 in the effects of estrogen on bone mass. We used wild type (WT) and Pyk2 knock-out (KO) mice that had been ovariectomized (OVX) and treated with or without estrogen (E2)-releasing pellets. Control mice included sham OVX surgery receiving placebo pellet. We found that deletion of Pyk2 conferred increased bone mass in sham, OVX and OVX+E2 mice. In addition, Pyk2 KO mice supplemented with 17estradiol exhibited a marked increase in bone volume/trabecular volume, trabecular number, and trabecular thickness, but not cortical bone parameters compared to WT mice. Results of this study provide evidence for the role of Pyk2 in the effects of estrogen on bone mass. Understanding the role of Pyk2 in bone could lead to the development of new pharmaceutical targets for the treatment of bone loss associated with osteoporosis.

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Ddi1-like protein family has been recently raised into the spotlight by the scientific community due to its important roles in cellular homeostasis maintenance. It represents a specific group among shuttling proteins of the ubiquitin-proteasome system. When compared to other shuttles, Ddi1-like protein family members harbor a unique retroviral-protease like domain besides the conventional ubiquitin-like (UBL) domain and domains interacting with ubiquitin. In addition, a helical domain of Ddi (HDD) has been recently found in most of the orthologs. In this thesis, I focus on characterization of several members of Ddi1-like protein family, both on molecular level using NMR and in model mouse strains via a variety of biological methods. Solution structure of the UBL domain of Ddi1p of S. cerevisiae was solved and its characteristics were compared to those of the UBL domain of its human ortholog. Furthermore, we show that human DDI2 specifically binds to ubiquitin with its terminal domains, both the UBL and the UIM; however, with very low affinity in contrast to binding properties of its yeast counterpart. Our study also show that hDDI2 does not form a head-to-tail homodimer. Based on our structural studies, we hypothesize that human DDI2 might have evolved a different function compared to its yeast...

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