Ca2+/Calmodulin-dependent kinase II signaling causes skeletal overgrowth and premature chondrocyte maturation

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

Wnt signalling in the articular cartilage: A matter of balance

Degradation of the articular cartilage is a hallmark of osteoarthritis, a progressive and chronic musculoskeletal condition, affecting millions of people worldwide. The activation of several signalling cascades is altered during disease development: among them, the Wnt signalling plays a pivotal role in the maintenance of tissue homeostasis. Increasing evidence is showing that its activation needs to be maintained within a certain range to avoid the triggering of degenerative mechanisms. In this review, we summarise our current knowledge about how a balanced activation of the Wnt signalling is maintained in the articular cartilage, with a particular focus on receptor-mediated mechanisms.

Initiation and progression of dental-stimulated temporomandibular joints osteoarthritis

Temporomandibular joint (TMJ), a site that is often impacted by osteoarthritis (OA), is biomechanically linked with dental occlusion. Tissue responses in TMJ condyle to biomechanical stimulation could be investigated by intervention of the dental occlusion in animals. Unilateral anterior crossbite, an experimental malocclusion, has been demonstrated to induce TMJ-OA lesions, showing primarily as enhanced cartilage calcification and subchondral cortical bone formation at the osteochondral interface, causing the osteochondral interface thickening and stiffening. The changed interface would worsen the local biomechanical environment. At the cartilage side, the matrix degenerates. In the case of insufficient restoration of the matrix, the cells in the deep zone flow into the ones undergoing autophagy, apoptosis, and terminal differentiation while the cells in the superficial zone are promoted to differentiate to supply the loss of the deep zone cells. At the meantime, the bone marrow stromal cells are stimulated to bone formation in the subchondral cortical region which is uncoupled with the sites of the osteoclast-mediated resorption process that is predominantly observed at the subchondral trabecular bone region. Overall, the thickening and stiffening osteochondral interface, due greatly to the enhanced endochondral ossification in deep zone cartilage, should be a central pathological process that links with cartilage decay and subchondral bone remodelling in OA joints. The residual chondrocytes locating in the cartilage superficial zone have the progenitor-like qualities that can proliferate, and also differentiate into the deep zone chondrocytes, thus should be critical in progression and rehabilitation of TMJ-OA.

Calcium calmodulin kinase II activity is required for cartilage homeostasis in osteoarthritis

WNT ligands can activate several signalling cascades of pivotal importance during development and regenerative processes. Their de-regulation has been associated with the onset of different diseases. Here we investigated the role of the WNT/Calcium Calmodulin Kinase II (CaMKII) pathway in osteoarthritis. We identified Heme Oxygenase I (HMOX1) and Sox-9 as specific markers of the WNT/CaMKII signalling in articular chondrocytes through a microarray analysis. We showed that the expression of the activated form of CaMKII, phospho-CaMKII, was increased in human and murine osteoarthritis and the expression of HMOX1 was accordingly reduced, demonstrating the activation of the pathway during disease progression. To elucidate its function, we administered the CaMKII inhibitor KN93 to mice in which osteoarthritis was induced by resection of the anterior horn of the medial meniscus and of the medial collateral ligament in the knee joint. Pharmacological blockade of CaMKII exacerbated cartilage damage and bone remodelling. Finally, we showed that CaMKII inhibition in articular chondrocytes upregulated the expression of matrix remodelling enzymes alone and in combination with Interleukin 1. These results suggest an important homeostatic role of the WNT/CaMKII signalling in osteoarthritis which could be exploited in the future for therapeutic purposes.

Endochondral ossification and the evolution of limb proportions

Mammals have remarkably diverse limb proportions hypothesized to have evolved adaptively in the context of locomotion and other behaviors. Mechanistically, evolutionary diversity in limb proportions is the result of differential limb bone growth. Longitudinal limb bone growth is driven by the process of endochondral ossification, under the control of the growth plates. In growth plates, chondrocytes undergo a tightly orchestrated life cycle of proliferation, matrix production, hypertrophy, and cell death/transdifferentiation. This life cycle is highly conserved, both among the long bones of an individual, and among homologous bones of distantly related taxa, leading to a finite number of complementary cell mechanisms that can generate heritable phenotype variation in limb bone size and shape. The most important of these mechanisms are chondrocyte population size in chondrogenesis and in individual growth plates, proliferation rates, and hypertrophic chondrocyte size. Comparative evidence in mammals and birds suggests the existence of developmental biases that favor evolutionary changes in some of these cellular mechanisms over others in driving limb allometry. Specifically, chondrocyte population size may evolve more readily in response to selection than hypertrophic chondrocyte size, and extreme hypertrophy may be a rarer evolutionary phenomenon associated with highly specialized modes of locomotion in mammals (e.g., powered flight, ricochetal bipedal hopping). Physical and physiological constraints at multiple levels of biological organization may also have influenced the cell developmental mechanisms that have evolved to produce the highly diverse limb proportions in extant mammals. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Regulation of Organ Diversity Comparative Development and Evolution > Organ System Comparisons Between Species.

Basic Calcium Phosphate Crystals Induce Osteoarthritis-Associated Changes in Phenotype Markers in Primary Human Chondrocytes by a Calcium/Calmodulin Kinase 2-Dependent Mechanism

Chondrocytes in osteoarthritis undergo a phenotype shift leading to increased production of cartilage-degrading enzymes. There are similarities between the phenotype of osteoarthritic chondrocytes and those of growth plate chondrocytes. Hydroxyapatite can promote chondrocyte differentiation in the growth plate. Basic calcium phosphate (BCP) crystals (which consist of hydroxyapatite, octacalcium apatite and tricalcium phosphate) are frequently found in osteoarthritic joints. The objective of this study was to determine whether BCP crystals induce disease-associated changes in phenotypic marker expression in chondrocytes. Primary human chondrocytes isolated from macroscopically normal cartilage were treated with BCP for up to 48 h. Expression of indian hedgehog (IHH), matrix metalloproteinase 13 (MMP13), interleukin-6 (IL-6) and type X collagen (COLX) were higher, and expression of sry-box 9 (SOX9) lower, in BCP-treated chondrocytes (50 µg/mL) compared to untreated controls. COLX protein was also present in BCP-treated chondrocytes. Intracellular calcium and levels of phosphorylated and total calcium/calmodulin kinase 2 (CaMK2) were elevated following BCP treatment due to BCP-induced release of calcium from intracellular stores. CaMK2 inhibition or knockdown ameliorated the BCP-induced changes in SOX9, IHH, COLX, IL-6 and MMP13 expression. BCP crystals induce osteoarthritis-associated changes in phenotypic marker expression in chondrocytes by calcium-mediated activation of CaMK2. The presence of BCP crystals in osteoarthritic joints may contribute to disease progression.

CaMKII inhibition in human primary and pluripotent stem cell-derived chondrocytes modulates effects of TGFβ and BMP through SMAD signaling

OBJECTIVE

Upregulation of calcium/calmodulin-dependent kinase II (CaMKII) is implicated in the pathogenesis of osteoarthritis (OA) and reactivation of articular cartilage hypertrophy. However, direct inhibition of CaMKII unexpectedly augmented symptoms of OA in animal models. The role of CaMKII in OA remains unclear and requires further investigation.

METHODS

Analysis of CaMKII expression was performed in normal human and OA articular chondrocytes, and signaling mechanisms were assessed in articular, fetal and Pluripotent Stem Cell (PSC)-derived human chondrocytes using pharmacological (KN93), peptide (AC3-I) and small interfering RNA (siRNA) inhibitors of CaMKII.

RESULTS

Expression levels of phospho-CaMKII (pCaMKII) were significantly and consistently increased in human OA specimens. BMP2/4 activated expression of pCaMKII as well as COLII and COLX in human adult articular chondrocytes, and also increased the levels and nuclear localization of SMADs1/5/8, while TGFβ1 showed minimal or no activation of the chondrogenic program in adult chondrocytes. Targeted blockade of CaMKII with specific siRNAs decreased levels of pSMADs, COLII, COLX and proteoglycans in normal and OA adult articular chondrocytes in the presence of both BMP4 and TGFβ1. Both human fetal and PSC-derived chondrocytes also demonstrated a decrease of chondrogenic differentiation in the presence of small molecule and peptide inhibitors of CaMKII. Furthermore, immunoprecipitation for SMADs1/5/8 or 2/3 followed by western blotting for pCaMKII showed direct interaction between SMADs and pCaMKII in primary chondrocytes.

CONCLUSION

Current study demonstrates a direct role for CaMKII in TGF-β and BMP-mediated responses in primary and PSC-derived chondrocytes. These findings have direct implications for tissue engineering of cartilage tissue from stem cells and therapeutic management of OA.

Inhibition of CaMKK2 Enhances Fracture Healing by Stimulating Indian Hedgehog Signaling and Accelerating Endochondral Ossification

Approximately 10% of all bone fractures do not heal, resulting in patient morbidity and healthcare costs. However, no pharmacological treatments are currently available to promote efficient bone healing. Inhibition of Ca2+ /calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) reverses age-associated loss of trabecular and cortical bone volume and strength in mice. In the current study, we investigated the role of CaMKK2 in bone fracture healing and show that its pharmacological inhibition using STO-609 accelerates early cellular and molecular events associated with endochondral ossification, resulting in a more rapid and efficient healing of the fracture. Within 7 days postfracture, treatment with STO-609 resulted in enhanced Indian hedgehog signaling, paired-related homeobox (PRX1)-positive mesenchymal stem cell (MSC) recruitment, and chondrocyte differentiation and hypertrophy, along with elevated expression of osterix, vascular endothelial growth factor, and type 1 collagen at the fracture callus. Early deposition of primary bone by osteoblasts resulted in STO-609-treated mice possessing significantly higher callus bone volume by 14 days following fracture. Subsequent rapid maturation of the bone matrix bestowed fractured bones in STO-609-treated animals with significantly higher torsional strength and stiffness by 28 days postinjury, indicating accelerated healing of the fracture. Previous studies indicate that fixed and closed femoral fractures in the mice take 35 days to fully heal without treatment. Therefore, our data suggest that STO-609 potentiates a 20% acceleration of the bone healing process. Moreover, inhibiting CaMKK2 also imparted higher mechanical strength and stiffness at the contralateral cortical bone within 4 weeks of treatment. Taken together, the data presented here underscore the therapeutic potential of targeting CaMKK2 to promote efficacious and rapid healing of bone fractures and as a mechanism to strengthen normal bones. © 2018 American Society for Bone and Mineral Research.

Calcium-/calmodulin-dependent protein kinase II in occlusion-induced degenerative cartilage of rat mandibular condyle

Activated calcium-/calmodulin-dependent protein kinaseII (CaMKII) is important to promote chondrocytes from proliferative to pre-hypertrophic state, which probably plays a role in osteoarthritis (OA), a widespread degeneration disease with enhanced aberrant chondrocyte differentiation. Our aim was to detect the role of CaMKII, and its relationship with the feedback loop of Indian hedgehog (Ihh) and Parathyroid-related peptide (PTHrP) in the temporomandibular joints (TMJs) OA. KN93, the competitive inhibitor of CaMKII, was added to the culture medium in vitro and was locally injected to rats TMJs (n = 54, female) every other day for 4 weeks from the beginning of the 5th and 9th week after installing of unilateral anterior crossbite (UAC), termed as 4 wk+4 wk and 8 wk+4 wk, accordingly. The RNA expression of CaMKII α (1.49 ± 0.09), CaMKII β (3.36 ± 0.20), Ihh (1.88 ± 0.06) and PTHrP (1.87 ± 0.12) was all enhanced, especially at 24 dyn/cm² in vitro (all P < .05), accompanied with downregulated expression of cartilage matrix, but upregulated markers of chondrocytes differentiation (all P < 0.05). Similarity was observed in the 4 wk+4 wk group in vivo. In the 8 wk+4 wk group, UAC upregulated the RNA expression of CaMKII α (1.81 ± 0.24), CaMKII β (1.36 ± 0.07) and Ihh (1.70 ± 0.21), however, down-regulated PTHrP (0.53 ± 0.04) (all P < .05), in consonance with the protein expression. All these changes were attenuated by KN93 (all P < .05). In conclusion, CaMKII took a role, via Ihh and PTHrP pathways, in promoting biomechanically induced TMJ chondrocytes differentiation, the initiation issue of UAC stimulated osteoarthritic changes in rodent TMJs. Inhibiting CaMKII is helpful to rescue the biomechanically stimulated cartilage degradation and prospective to be a target treatment of OA.

Non-canonical Wnt induces chondrocyte de-differentiation through Frizzled 6 and DVL-2/B-raf/CaMKIIα/syndecan 4 axis

Dysregulation of Wnt signaling has been implicated in developmental defects and in the pathogenesis of many diseases such as osteoarthritis; however, the underlying mechanisms are poorly understood. Here, we report that non-canonical Wnt signaling induced loss of chondrocyte phenotype through activation of Fz-6/DVL-2/SYND4/CaMKIIα/B-raf/ERK1/2 cascade. We show that in response to Wnt-3a, Frizzled 6 (Fz-6) triggers the docking of CaMKIIα to syndecan 4 (SYND4) and that of B-raf to DVL-2, leading to the phosphorylation of B-raf by CaMKIIα and activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling, which leads to chondrocyte de-differentiation. We demonstrate that CaMKIIα associates and phosphorylates B-raf in vitro and in vivo. Our study reveals the mechanism by which non-canonical Wnt activates ERK1/2 signaling that induces loss of chondrocyte phenotype, and demonstrates a direct functional relationship between CaMKIIα and B-raf during chondrocyte de-differentiation. The identification of Fz-6, SYND4, and B-raf as novel physiological regulators of chondrocyte phenotype may provide new potential anti-osteoarthritic targets.

CaMKII Signaling Stimulates Mef2c Activity In Vitro but Only Minimally Affects Murine Long Bone Development in vivo

The long bones of vertebrate limbs form by endochondral ossification, whereby mesenchymal cells differentiate into chondrogenic progenitors, which then differentiate into chondrocytes. Chondrocytes undergo further differentiation from proliferating to prehypertrophic, and finally to hypertrophic chondrocytes. Several signaling pathways and transcription factors regulate this process. Previously, we and others have shown in chicken that overexpression of an activated form of Calcium/calmodulin-dependent kinase II (CaMKII) results in ectopic chondrocyte maturation. Here, we show that this is not the case in the mouse. Although, in vitro Mef2c activity was upregulated by about 55-fold in response to expression of an activated form of CaMKII (DACaMKII), transgenic mice that expressed a dominant-active form of CaMKII under the control of the Col2a1 regulatory elements display only a very transient and mild phenotype. Here, only the onset of chondrocyte hypertrophy at E12.5 is accelerated. It is also this early step in chondrocyte differentiation that is temporarily delayed around E13.5 in transgenic mice expressing the peptide inhibitor CaM-KIIN from rat (rKIIN) under the control of the Col2a1 regulatory elements. Yet, ultimately DACaMKII, as well as rKIIN transgenic mice are born with completely normal skeletal elements with regard to their length and growth plate organization. Hence, our in vivo analysis suggests that CaMKII signaling plays a minor role in chondrocyte maturation in mice.

β-catenin activity in late hypertrophic chondrocytes locally orchestrates osteoblastogenesis and osteoclastogenesis

Trabecular bone formation is the last step in endochondral ossification. This remodeling process of cartilage into bone involves blood vessel invasion and removal of hypertrophic chondrocytes (HTCs) by chondroclasts and osteoclasts. Periosteal- and chondrocyte-derived osteoprogenitors utilize the leftover mineralized HTC matrix as a scaffold for primary spongiosa formation. Here, we show genetically that β-catenin (encoded by Ctnnb1), a key component of the canonical Wnt pathway, orchestrates this remodeling process at multiple levels. Conditional inactivation or stabilization of β-catenin in HTCs by a Col10a1-Cre line locally modulated osteoclastogenesis by altering the Rankl:Opg ratio in HTCs. Lack of β-catenin resulted in a severe decrease of trabecular bone in the embryonic long bones. Gain of β-catenin activity interfered with removal of late HTCs and bone marrow formation, leading to a continuous mineralized hypertrophic core in the embryo and resulting in an osteopetrotic-like phenotype in adult mice. Furthermore, β-catenin activity in late HTCs is required for chondrocyte-derived osteoblastogenesis at the chondro-osseous junction. The latter contributes to the severe trabecular bone phenotype in mutants lacking β-catenin activity in HTCs.

Summary: The conditional modulation of β-catenin activity in late hypertrophic chondrocytes locally regulates osteoclast differentiation and the transdifferentiation of chondrocytes into osteoblasts.

The Involvement of TRP Channels in Bone Homeostasis

Calcium and bone homeostasis are intimately related. On the one hand, bone relies on a sufficient supply of calcium to maintain its structural and mechanical properties and thus largely depends on calcium absorption in the intestine and calcium reabsorption in the kidney. On the other hand, bone serves as a calcium reserve from which calcium is mobilized to maintain normal calcium levels in blood. A negative external calcium balance will therefore at all times impair skeletal integrity. In addition to the external calcium balance, skeletal homeostasis also depends on the proper differentiation and functioning of bone cells, which relies for a large part on intracellular Ca(2+) signaling. Members of the transient receptor potential (TRP) family of ion channels affect skeletal homeostasis by mediating processes involved in the extracellular as well as intracellular Ca(2+) balance, including intestinal calcium absorption (TRPV6), renal calcium reabsorption (TRPV5), and differentiation of osteoclasts (TRPV1, TRPV2, TRPV4, TRPV5), chondrocytes (TRPV4), and possibly osteoblasts (TRPV1). In this review, we will give a brief overview of the systemic calcium homeostasis and the intracellular Ca(2+) signaling in bone cells with special focus on the TRP channels involved in these processes.

WNT-3A modulates articular chondrocyte phenotype by activating both canonical and noncanonical pathways

A single Wnt can simultaneously activate different pathways with distinct and independent outcomes and reciprocal regulation in human articular chondrocytes.

Activation and disruption of Wnt/β-catenin signaling both result in cartilage breakdown via unknown mechanisms. Here we show that both WNT-3A and the Wnt inhibitor DKK1 induced de-differentiation of human articular chondrocytes through simultaneous activation of β-catenin–dependent and independent responses. WNT-3A activates both the β-catenin–dependent canonical pathway and the Ca²⁺/CaMKII noncanonical pathways, with distinct transcriptional targets. WNT-3A promotes cell proliferation and loss of expression of the chondrocyte markers COL2A1, Aggrecan, and SOX9; however, proliferation and AXIN2 up-regulation are downstream of the canonical pathway and are rescued by DKK1, whereas the loss of differentiation markers is CaMKII dependent. Finally, we showed that in chondrocytes, the Ca²⁺/CaMKII-dependent and β-catenin–dependent pathways are reciprocally inhibitory, thereby explaining why DKK1 can induce loss of differentiation through de-repression of the CaMKII pathway. We propose a novel model in which a single WNT can simultaneously activate different pathways with distinct and independent outcomes and with reciprocal regulation. This offers an opportunity for selective pharmacological targeting.

Calcium/calmodulin-dependent protein kinase II activity regulates the proliferative potential of growth plate chondrocytes

For tissues that develop throughout embryogenesis and into postnatal life, the generation of differentiated cells to promote tissue growth is at odds with the requirement to maintain the stem cell/progenitor cell population to preserve future growth potential. In the growth plate cartilage, this balance is achieved in part by establishing a proliferative phase that amplifies the number of progenitor cells prior to terminal differentiation into hypertrophic chondrocytes. Here, we show that endogenous calcium/calmodulin-dependent protein kinase II (CamkII, also known as Camk2) activity is upregulated prior to hypertrophy and that loss of CamkII function substantially blocks the transition from proliferation to hypertrophy. Wnt signaling and Pthrp-induced phosphatase activity negatively regulate CamkII activity. Release of this repression results in activation of multiple effector pathways, including Runx2- and β-catenin-dependent pathways. We present an integrated model for the regulation of proliferation potential by CamkII activity that has important implications for studies of growth control and adult progenitor/stem cell populations.

WNT5A regulates chondrocyte differentiation through differential use of the CaN/NFAT and IKK/NF-kappaB pathways

Although genetic evidence demonstrated a requirement for Wnt5a during cartilage development, little is known about the mechanisms underlying Wnt5a-regulated chondrocyte growth and differentiation. We therefore investigated the signaling pathways by which Wnt5a influences chondrogenesis and differentiation to hypertrophy. Wnt5a treatment of chondroprogenitor cells increased chondrocyte hypertrophy and was associated with an increase in nuclear factor of activated T cells (NFAT) and a decrease in nuclear factor-kappaB (NF-kappaB) activation. In contrast, Wnt5a inhibited chondrocyte hypertrophy. This inhibition of hypertrophy occurred with the reciprocal signaling activation, in that a decrease in NFAT and an increase in NF-kappaB activation was observed. Furthermore, the increase in chondroprogenitor cell differentiation with Wnt5a treatment was blocked by calmodulin kinase or NFAT loss of function. In addition, the repression of chondrocyte hypertrophy observed was abrogated by NF-kappaB loss of function. Activation of the NFAT pathway downstream of Wnt5a also negatively regulated NF-kappaB activity, providing evidence of antagonism between these two pathways. Mechanistically, Wnt5a acts to increase chondrocyte differentiation at an early stage through calmodulin kinase /NFAT-dependent induction of Sox9. Conversely, Wnt5a represses chondrocyte hypertrophy via NF-kappaB-dependent inhibition of Runx2 expression. These data indicate that Wnt5a regulates chondrogenesis and chondrocyte hypertrophy in a stage-dependent manner through differential utilization of NFAT- and NF-kappaB-dependent signal transduction.