BMPRIa mimetic peptide treatments for bone and cartilage formation and repair
Date
2016
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Osteoporosis and osteoarthritis, are two most common skeletal disorders that are idiopathic in nature. Osteoporosis is characterized by excessive bone resorption and inadequate formation of bone resulting in skeletal fragility. Osteoarthritis (OA) is characterized by degradation of articular cartilage (AC) that surrounds the diarthrodial joints followed by the formation of osteophytes that calcification of cartilaginous tissue. While there are pharmacotherapeutics today that can slow the progress of bone loss due to osteoporosis induced bone loss, the long term effects are not effective and atypical fractures are commonly observed (Schilcher et al., 2014). In OA there is no drug today that can slow the progression of the disease nor help regenerate the lost cartilage. Therefore, there is a dire need for research to find effective targets for pharmacological development that can slow the process of disease progression and also regenerate the lost tissue. It is beneficial to exploit the basic molecular mechanisms that control the overall tissue generation to identify therapeutic targets. Growth factors greatly influence the process of bone and cartilage formation. Among the growth factors Bone Morphogenetic Proteins (BMPs) are essential for formation and maintenance of long bones and AC. -- Among BMPs, BMP2 is important for embryogenesis, development, and maintenance of adult tissue homeostasis (Wang et al., 2014). BMP2 is a potent growth factor that is essential for limb patterning and proper bone and cartilage formation. BMP2 is present in all stages of chondrocyte development and also regulates osteoblastogenesis and indirectly osteoclastogenesis. BMP2 is pleiotropic in nature and influence many bodily functions. In musculoskeletal disorders such as osteoporosis or OA, BMP2 plays varied roles contributing to the progression of the diseases. In osteoporosis, the BMP2 effect of osteoblastogenesis is reduced but increases osteoclastogenesis and adipogenesis (Donoso et al., 2015; Itoh et al., 2001). In OA increased physiological levels of BMP2 induce chondrocyte hypertrophy and cartilage degradation followed by subchondral bone alterations and osteophyte formation (van der Kraan et al., 2010). BMP2 and BMP7 are approved by the FDA for bone fracture healing and are also in consideration for osteoporotic and osteoarthritic therapy. However, as mentioned earlier BMP2 can elicit both anabolic and catabolic activities. Therefore, by targeting these specific signaling mechanisms can help us in therapeutic development. -- Nohe has demonstrated previously a novel Bone Morphogenetic Protein Receptor Type Ia (BMPRIa) interaction with Casein Kinase 2 (CK2) (Bragdon et al., 2010). It is demonstrated that upon BMP2 binding to the serine/threonine kinase receptor complex CK2 dissociates from BMPRIa allowing the phosphorylation of downstream signals (Bragdon et al., 2010). Using prosite search Nohe lab has identified three potential BMPRIa CK2 interaction sites. Nohe lab has developed three mimetic peptides (CK2.3, CK2.2, and CK2.1) that encompass the site specific sequences that could block the interaction of CK2 with BMPRIa. In this study I investigated the potential of the peptides CK2.3, and CK2.1 in activating BMPRIa downstream signaling for inducing bone and cartilage formation respectively. Nohe lab previously demonstrated the effect of CK2.3 in osteogenesis and bone formation in mice calvaria (Bragdon et al., 2011b). In this study I examined the effect of CK2.3 in trabecular bone formation (Akkiraju et al., 2015). Where CK2.3 induced trabecular bone growth by inducing osteoblastogenesis and inhibiting osteoclastogenesis and osteoclast activity as compared to BMP2 that activated both osteoblast and osteoclast activity. -- Moreover, I demonstrated here CK2.1 induced chondrogenesis but not osteogenesis in vitro by activating the BMPRIa downstream signaling and cartilage formation and cartilage repair in vivo. Peptide CK2.1 induced chondrogenesis in mesenchymal stem cells (MSC) and demonstrated positive chondrogenic differentiation and extracellular matrix (ECM) secretion without the induction of chondrocyte hypertrophy both in vitro and in vivo. CK2.1 induced chondrogenic regulation resulted in positive secretion of collagen type II and collagen type IX formation without collagen type X (hypertrophic marker). In mice, CK2.1 systemic injections lead to increased cartilage formation in a similar capacity as BMP2. Furthermore, in an OA mice model that underwent Destabilization of Medial Meniscus (DMM) that AC damage through secondary injury was injected intra-articularly with slow release system of CK2.1 conjugated with hyaluronic acid based gels (HGPs). This HGP-CK2.1 intra-articular injections completely restored the lost cartilage comparable to SHAM treated mice. Moreover, both systemic treatments and DMM mice femurs injected with CK2.1 demonstrated proteoglycan secretion and collagen type II and collagen type IX but not collagen type X. This is in sharp contrast with the systemic BMP2 injected group that demonstrated up regulation of collagen type II and also collagen type X thereby enhancing chondrocyte hypertrophy. Peptide CK2.3 specifically induced osteogenesis in MSCs and bone formation in similar capacity to BMP2 treatments in mice without activating osteoclastogenesis as did BMP2 treatment. Similarly, CK2.1 induced specifically chondrogenesis and cartilage formation and repair without inducing chondrocyte hypertrophy or cartilage degradation. Both peptides CK2.3 and CK2.1 may specifically regulate BMPRIa downstream signaling for bone and cartilage formation respectively. Understanding these signaling cascades can help identify the molecular targets necessary for inducing bone and cartilage growth. In this study I have successfully demonstrated the potential of peptide CK2.3 in bone formation and peptide CK2.1 in cartilage formation and cartilage repair. Taken together, these peptides present a unique opportunity for identifying the therapeutic targets that can used for treating bone and cartilage disorders like osteoporosis or OA.