Kappa opioid receptor signaling protects cartilage tissue against posttraumatic degeneration

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Abstract

Osteoarthritis is the most common form of arthritis, and pain relief with opioid-like drugs is a commonly used therapeutic for osteoarthritic patients. Recent studies published by our group showed that the kappa opioid receptor (KOR) is highly expressed during human development in joint-forming cells. However, the precise role of this receptor in the skeletal system remains elusive. The main aim of the current study was to investigate the role of KOR signaling in synovial and cartilaginous tissues in pathological conditions. Our data demonstrate that KOR null mice exhibit accelerated cartilage degeneration after injury when compared with WT mice. Activation of KOR signaling increased the expression of anabolic enzymes and inhibited cartilage catabolism and degeneration in response to proinflammatory cytokines such as TNF-α. In addition, selective KOR agonists increased joint lubrication via the activation of cAMP/CREB signaling in chondrocytes and synovial cells. Taken together, these results demonstrate direct effects of KOR agonists on cartilage and synovial cells and reveals a protective effect of KOR signaling against cartilage degeneration after injury. In addition to pain control, local administration of dynorphin or other KOR agonist represents an attractive therapeutic approach in patients with early stages of osteoarthritis.

Authors

Ling Wu, Shu Zhang, Ruzanna Shkhyan, Siyoung Lee, Francesca Gullo, Claire D. Eliasberg, Frank A. Petrigliano, Kai Ba, Jing Wang, Yunfeng Lin, Denis Evseenko

PLEKHM1/DEF8/RAB7 complex regulates lysosome positioning and bone homeostasis

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Abstract

Mutations of the Plekhm1 gene in humans and rats cause osteopetrosis, an inherited bone disease characterized by diminished bone resorption by osteoclasts. PLEKHM1 binds to RAB7 and is critical for lysosome trafficking. However, the molecular mechanisms by which PLEKHM1 regulates lysosomal pathways remain unknown. Here, we generated germline and conditional Plekhm1-deficient mice. These mice displayed no overt abnormalities in major organs, except for an increase in trabecular bone mass. Furthermore, loss of PLEKHM1 abrogated the peripheral distribution of lysosomes and bone resorption in osteoclasts. Mechanistically, we indicated that DEF8 interacts with PLEKHM1 and promotes its binding to RAB7, whereas the binding of FAM98A and NDEL1 with PLEKHM1 connects lysosomes to microtubules. Importantly, suppression of these proteins results in lysosome positioning and bone resorption defects similar to those of Plekhm1-null osteoclasts. Thus, PLHKEM1, DEF8, FAM98A, and NDEL1 constitute a molecular complex that regulates lysosome positioning and secretion through RAB7.

Authors

Toshifumi Fujiwara, Shiqiao Ye, Thiago Castro-Gomes, Caylin G. Winchell, Norma W. Andrews, Daniel E. Voth, Kottayil I. Varughese, Samuel G. Mackintosh, Yunfeng Feng, Nathan Pavlos, Takashi Nakamura, Stavros C. Manolagas, Haibo Zhao

Pulsed low-dose RANKL as a potential therapeutic for postmenopausal osteoporosis

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Abstract

A number of studies in model animal systems and in the clinic have established that RANKL promotes bone resorption. Paradoxically, we found that pulsing ovariectomized mice with low-dose RANKL suppressed bone resorption, decreased the levels of proinflammatory effector T cells and led to increased bone mass. This effect of RANKL is mediated through the induction of FoxP3⁺CD25⁺ regulatory CD8⁺ T cells (Tc_REG) by osteoclasts. Here, we show that pulses of low-dose RANKL are needed to induce Tc_REG, as continuous infusion of identical doses of RANKL by pump did not induce Tc_REG. We also show that low-dose RANKL can induce Tc_REG at 2, 3, 6, and 10 weeks after ovariectomy. Our results show that low-dose RANKL treatment in ovariectomized mice is optimal at once-per-month doses to maintain the bone mass. Finally, we found that treatment of ovariectomized mice with the Cathepsin K inhibitor odanacatib also blocked Tc_REG induction by low-dose RANKL. We interpret this result to indicate that antigens presented to CD8⁺ T cells by osteoclasts are derived from the bone protein matrix because Cathepsin K degrades collagen in the bone. Taken together, our studies provide a basis for using low-dose RANKL as a potential therapeutic for postmenopausal osteoporosis.

Authors

Anna Cline-Smith, Jesse Gibbs, Elena Shashkova, Zachary S. Buchwald, Rajeev Aurora

Asfotase alfa therapy for children with hypophosphatasia

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Abstract

Background. Hypophosphatasia (HPP) is caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Consequently, cell-surface deficiency of TNSALP phosphohydrolase activity leads to extracellular accumulation of inorganic pyrophosphate, a natural substrate of TNSALP and inhibitor of mineralization. Children with HPP can manifest rickets, skeletal pain, deformity, fracture, muscle weakness, and premature deciduous tooth loss. Asfotase alfa is a recombinant, bone-targeted, human TNSALP injected s.c. to treat HPP. In 2012, we detailed the 1-year efficacy of asfotase alfa therapy for the life-threatening perinatal and infantile forms of HPP.

Methods. Here, we evaluated the efficacy and safety of asfotase alfa treatment administered to children 6–12 years of age at baseline who were substantially impaired by HPP. Two radiographic scales quantitated HPP skeletal disease, including comparisons to serial radiographs from similarly affected historical control patients.

Results. Twelve children receiving treatment were studied for 5 years. The 6-month primary endpoint was met, showing significant radiographic improvement. Additional significant improvements included patient growth, strength, motor function, agility, and quality of life, which for most patients meant achieving normal values for age- and sex-matched peers that were sustained at 5 years of treatment. For most, pain and disability resolved. Mild to moderate injection-site reactions were common and were sometimes associated with lipohypertrophy. Low anti–asfotase alfa antibody titers were noted in all patients. No evidence emerged for clinically important ectopic calcification or treatment resistance.

Conclusions. Asfotase alfa enzyme replacement therapy has substantial and sustained efficacy with a good safety profile for children suffering from HPP.

Trial Registration. ClinicalTrials.gov NCT00952484 (https://clinicaltrials.gov/ct2/show/NCT00952484) and NCT01203826 (https://clinicaltrials.gov/ct2/show/NCT01203826).

Funding. Alexion Pharmaceuticals Inc. and Shriners Hospitals for Children.

Authors

Michael P. Whyte, Katherine L. Madson, Dawn Phillips, Amy L. Reeves, William H. McAlister, Amy Yakimoski, Karen E. Mack, Kim Hamilton, Kori Kagan, Kenji P. Fujita, David D. Thompson, Scott Moseley, Tatjana Odrljin, Cheryl Rockman-Greenberg

NFAT restricts osteochondroma formation from entheseal progenitors

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Abstract

Osteochondromas are common benign osteocartilaginous tumors in children and adolescents characterized by cartilage-capped bony projections on the surface of bones. These tumors often cause pain, deformity, fracture, and musculoskeletal dysfunction, and they occasionally undergo malignant transformation. The pathogenesis of osteochondromas remains poorly understood. Here, we demonstrate that nuclear factor of activated T cells c1 and c2 (NFATc1 and NFATc2) suppress osteochondromagenesis through individual and combinatorial mechanisms. In mice, conditional deletion of NFATc1 in mesenchymal limb progenitors, Scleraxis-expressing (Scx-expressing) tendoligamentous cells, or postnatally in Aggrecan-expressing cells resulted in osteochondroma formation at entheses, the insertion sites of ligaments and tendons onto bone. Combinatorial deletion of NFATc1 and NFATc2 gave rise to larger and more numerous osteochondromas in inverse proportion to gene dosage. A population of entheseal NFATc1- and Aggrecan-expressing cells was identified as the osteochondroma precursor, previously believed to be growth plate derived or perichondrium derived. Mechanistically, we show that NFATc1 restricts the proliferation and chondrogenesis of osteochondroma precursors. In contrast, NFATc2 preferentially inhibits chondrocyte hypertrophy and osteogenesis. Together, our findings identify and characterize a mechanism of osteochondroma formation and suggest that regulating NFAT activity is a new therapeutic approach for skeletal diseases characterized by defective or exaggerated osteochondral growth.

Authors

Xianpeng Ge, Kelly Tsang, Lizhi He, Roberto A. Garcia, Joerg Ermann, Fumitaka Mizoguchi, Minjie Zhang, Bin Zhou, Bin Zhou, Antonios O. Aliprantis