WNT1-induced Secreted Protein-1 (WISP1), a Novel Regulator of Bone Turnover and Wnt Signaling

Gene expression analysis of human adipose tissue-derived stem cells during the initial steps of in vitro osteogenesis

Mesenchymal stem cells (MSCs) have been widely studied with regard to their potential use in cell therapy protocols and regenerative medicine. However, a better comprehension about the factors and molecular mechanisms driving cell differentiation is now mandatory to improve our chance to manipulate MSC behavior and to benefit future applications. In this work, we aimed to study gene regulatory networks at an early step of osteogenic differentiation. Therefore, we analyzed both the total mRNA and the mRNA fraction associated with polysomes on human adipose tissue-derived stem cells (hASCs) at 24 h of osteogenesis induction. The RNA-seq results evidenced that hASC fate is not compromised with osteogenesis at this time and that 21 days of continuous cell culture stimuli are necessary for full osteogenic differentiation of hASCs. Furthermore, early stages of osteogenesis induction involved gene regulation that was linked to the management of cell behavior in culture, such as the control of cell adhesion and proliferation. In conclusion, although discrete initial gene regulation related to osteogenesis occur, the first 24 h of induction is not sufficient to trigger and drive in vitro osteogenic differentiation of hASCs.

Differential time-dependent transcriptional changes in the osteoblast lineage in cortical bone associated with sclerostin antibody treatment in ovariectomized rats

Inhibition of sclerostin with sclerostin antibody (Scl-Ab) results in stimulation of bone formation on cancellous (Cn), endocortical (Ec), and periosteal (Ps) surfaces in rodents and non-human primates. With long-term dosing of Scl-Ab, the increase in bone formation is not sustained, attenuating first on Cn surfaces and later on Ec and Ps surfaces. In Cn bone, the attenuation in bone formation (self-regulation) is associated with transcriptional changes in the osteocyte (OCy) that would limit mitogenesis and are sustained with continued dosing. The expression changes in Cn OCy occur coincident with a decrease in osteoprogenitor (OP) numbers that may directly or indirectly be a consequence of the transcriptional changes in the OCy to limit OP proliferation. To characterize the Scl-Ab–mediated changes in cortical (Ct) bone and compare these changes to Cn bone, densitometric, histomorphometric, and transcriptional analyses were performed on femur diaphyses from aged ovariectomized rats. Animals were administered 50 mg/kg/wk of Scl-Ab or vehicle for up to 6 months (183 days), followed by a treatment-free period (up to 126 days). Scl-Ab increased Ct mass and area through day 183, which declined slightly when treatment was discontinued. Ps and Ec bone formation was sustained through the dosing on both Ct surfaces, with evidence of a decline in bone formation only at day 183 on the Ec surface. This is in contrast to Cn bone, where reduced bone formation was observed after day 29. TaqMan analysis of 60 genes with functional roles in the bone using mRNA isolated from laser capture micro-dissection samples enriched for Ec osteoblasts and Ct OCy suggest a pattern of gene expression in Ct bone that differed from Cn, especially in the OCy, and that corresponded to observed differences in the timing of phenotypic changes. Notable with Scl-Ab treatment was a “transcriptional switch” in Ct OCy at day 183, coincident with the initial decline in bone formation on the endocortex. A consistent sustained increase of expression for most genes in response to Scl-Ab was observed from day 8 through day 85 at the times of maximal bone formation on both Ct surfaces; however, at day 183, this increase was reversed, with expression of these genes generally returning to control values or decreasing compared to vehicle. Genes exhibiting this pattern included Wnt inhibitors Sost and Dkk1, though both had been up-regulated until the end of dosing in Cn OCy. Changes in cell cycle genes such as Cdkn1a and Ndrg1 in Ct OCy suggested up-regulation of p53 signaling, as observed in Cn OCy; however, unlike in Cn bone, p53 signaling was not associated with decreased bone formation and was absent at day 183, when bone formation began to decline on the Ec surface. These data demonstrate involvement of similar molecular pathways in Ct and Cn bone in response to Scl-Ab but with a different temporal relationship to bone formation and suggest that the specific mechanism underlying self-regulation of Scl-Ab–induced bone formation may be different between Cn and Ct bone.

•

Sclerostin antibody stimulates bone formation that attenuates over time.

•

Attenuation (self-regulation) is delayed in cortical versus cancellous bone.

•

Self-regulation coincides with transcriptional changes in cortical osteocytes.

•

Response of Wnt inhibitors differs between cortical and cancellous bone.

•

Results suggest a distinct mechanism for self-regulation in cortical bone.

Angiokine Wisp-1 is increased in myocardial infarction and regulates cardiac endothelial signaling

Myocardial infarctions (MIs) cause the loss of myocytes due to lack of sufficient oxygenation and latent revascularization. Although the administration of histone deacetylase (HDAC) inhibitors reduces the size of infarctions and improves cardiac physiology in small-animal models of MI injury, the cellular targets of the HDACs, which the drugs inhibit, are largely unspecified. Here, we show that WNT-inducible secreted protein-1 (Wisp-1), a matricellular protein that promotes angiogenesis in cancers as well as cell survival in isolated cardiac myocytes and neurons, is a target of HDACs. Further, Wisp-1 transcription is regulated by HDACs and can be modified by the HDAC inhibitor, suberanilohydroxamic acid (SAHA/vorinostat), after MI injury. We observe that, at 7 days after MI, Wisp-1 is elevated 3-fold greater in the border zone of infarction in mice that experience an MI injury and are injected daily with SAHA, relative to MI alone. Additionally, human coronary artery endothelial cells (HCAECs) produce WISP-1 and are responsive to autocrine WISP-1-mediated signaling, which functionally promotes their proangiogenic behavior. Altering endogenous expression of WISP-1 in HCAECs directly impacts their network density in vitro. Therapeutic interventions after a heart attack define the extent of infarct injury, cell survival, and overall prognosis. Our studies shown here identify a potentially novel cardiac angiokine, Wisp-1, that may contribute to beneficial post-MI treatment modalities.

Characterization of bone morphology in CCN5/WISP5 knockout mice

CCN5/WISP2 is part of the CCN family of matricellular proteins, but is distinct in that it lacks the C-terminal (CT) domain. Although CCN5 has been shown to impact cell proliferation and differentiation in vitro, its role in vivo is unclear. We therefore generated mice using ES cells developed by the Knockout Mouse Project (KOMP) in which exons 2-5, which encode the all of the conserved protein coding regions, are replaced by a lacZ cassette. Ccn5 ^LacZ/LacZ mice were viable and apparently normal. Based on previous studies showing that CCN5 impacts osteoblast proliferation and differentiation, we performed an analysis of adult bone phenotype. LacZ expression was examined in adult bone, and was found to be strong within the periosteum, but not in trabecular bone or bone marrow. Micro-CT analysis revealed no apparent changes in bone mineral density (BMD) or bone tissue volume (BV/TV) in Ccn5 ^LacZ/LacZ mice. These studies indicate that CCN5 is not required for normal bone formation, but they do not rule out a role in mechanotransduction or repair processes. The availability of Ccn5 ^LacZ mice enables studies of CCN5 expression and function in multiple tissues.

Dampening of the bone formation response following repeat dosing with sclerostin antibody in mice is associated with up-regulation of Wnt antagonists

Administration of antibodies to sclerostin (Scl-Ab) has been shown to increase bone mass, bone mineral density (BMD) and bone strength by increasing bone formation and decreasing bone resorption in both animal studies and human clinical trials. In these studies, the magnitude and rate of increase in bone formation markers is attenuated upon repeat dosing with Scl-Ab despite a continuous and progressive increase in BMD. Here, we investigated whether the attenuation in the bone formation response following repeated administration of Scl-Ab was associated with increased expression of secreted antagonists of Wnt signalling and determined how the circulating marker of bone formation, P1NP, responded to single, or multiple doses, of Scl-Ab four days post-dosing. Female Balb/c mice were treated with Scl-Ab and we demonstrated that the large increase in serum P1NP observed following the first dose was reduced following administration of multiple doses of Scl-Ab. This dampening of the P1NP response was not due to a change in the kinetics of the bone formation marker response, or differences in exposure to the drug. The abundance of transcripts encoding several secreted Wnt antagonists was determined in femurs collected from mice following one or six doses of Scl-Ab, or vehicle treatment. Compared with vehicle controls, expression of SOST, SOST-DC1, DKK1, DKK2, SFRP1, SFRP2, FRZB, SFRP4 and WIF1 transcripts was significantly increased (approximately 1.5-4.2 fold) following a single dose of Scl-Ab. With the exception of SFRP1, these changes were maintained or further increased following six doses of Scl-Ab and the abundance of SFRP5 was also increased. Up-regulation of these Wnt antagonists may exert a negative feedback to increased Wnt signalling induced by repeated administration of Scl-Ab and could contribute to self-regulation of the bone formation response over time. After an antibody-free period of four weeks or more, the P1NP response was comparable to the naïve response, and a second phase of treatment with Scl-Ab following an antibody-free period elicited additional gains in BMD. Together, these data demonstrate that the rapid dampening of the bone formation response in the immediate post-dose period which occurs after repeat dosing of Scl-Ab is associated with increased expression of Wnt antagonists, and a treatment-free period can restore the full bone formation response to Scl-Ab.

CCN4/WISP1 controls cutaneous wound healing by modulating proliferation, migration and ECM expression in dermal fibroblasts via α5β1 and TNFα

Understanding the mechanisms that control cutaneous wound healing is crucial to successfully manage repair of damaged skin. The goal of the current study was to uncover novel extracellular matrix (ECM) components that control the wound healing process. Full thickness skin defects were created in mice and used to show CCN4 up-regulation during wound-healing as early as 1 day after surgery, suggesting a role in inflammation and subsequent dermal migration and proliferation. To determine how CCN4 could regulate wound healing we used Ccn4-KO mice and showed they had delayed wound closure accompanied by reduced expression of Col1a1 and Fn mRNA. Boyden chamber assays using Ccn4-deficient dermal fibroblasts showed they have reduced migration and proliferation compared to WT counterparts. To confirm CCN4 has a role in proliferation and migration of dermal cells, siRNA knockdown and transduction of CCN4 adenoviral transduction were used and resulted in reduced or enhanced migration of human adult dermal fibroblast (hADF) cells respectively. The induced migration of the dermal fibroblasts by CCN4 appears to work via α5β1 integrin receptors that further stimulates down-stream ERK/JNK signaling. The regulation of CCN4 by TNF-α prompted us look further at their potential relationship. Treatment of hADFs with CCN4 and TNF-α alone or together showed CCN4 counteracted the inhibition of TNF-α on COL1A1 and FN mRNA expression and the stimulation of TNF-α on MMP-1 and MMP3 mRNA expression. CCN4 appeared to counterbalance the effects of TNF-α by inhibiting downstream NF-κB/p-65 signaling. Taken together we show CCN4 stimulates dermal fibroblast cell migration, proliferation and inhibits TNF-α stimulation, all of which could regulate wound healing.

WISP1/CCN4 aggravates cartilage degeneration in experimental osteoarthritis

OBJECTIVE

Increased Wisp1 expression was previously reported in experimental and human osteoarthritis (OA). Moreover, adenoviral overexpression of Wisp1 in naïve mouse knee joints resulted in early OA-like cartilage lesions. Here, we determined how the matricellular protein WISP1 is involved in the pathology that occurs in the complex osteoarthritic environment with aging and experimental OA in wild type (WT) and Wisp1^-/- mice.

METHODS

WT and Wisp1^-/- mice were aged or experimental OA was induced with intraarticular collagenase injection, destabilization of the medial meniscus (DMM) or anterior cruciate ligament transection (ACLT). Joint pathology was assessed using histology and microCT. Protease expression was evaluated with qRT-PCR and activity was determined by immunohistochemical staining of the aggrecan neoepitope NITEGE. Protease expression in human end-stage OA synovial tissue was determined with qRT-PCR after stimulation with WISP1.

RESULTS

With aging, spontaneous cartilage degeneration in Wisp1^-/- was not decreased compared to their WT controls. However, we observed significantly decreased cartilage degeneration in Wisp1^-/- mice after induction of three independent experimental OA models. While the degree of osteophyte formation was comparable between WT and Wisp1^-/- mice, increased cortical thickness and reduced trabecular spacing was observed in Wisp1^-/- mice. In addition, we observed decreased MMP3/9 and ADAMTS4/5 expression in Wisp1^-/- mice, which was accompanied by decreased levels of NITEGE. In line with this, stimulation of human OA synovium with WISP1 increased the expression of various proteases.

CONCLUSIONS

WISP1 plays an aggravating role in the development of post-traumatic experimental OA.

Small leucine rich proteoglycans, a novel link to osteoclastogenesis

Biglycan (Bgn) and Fibromodulin (Fmod) are subtypes of the small leucine-rich family of proteoglycans (SLRP). In this study we examined the skeletal phenotype of BgnFmod double knockout (BgnFmod KO) mice and found they were smaller in size and have markedly reduced bone mass compared to WT. The low bone mass (LBM) phenotype is the result of both the osteoblasts and osteoclasts from BgnFmod KO mice having higher differentiation potential and being more active compared to WT mice. Using multiple approaches, we showed that both Bgn and Fmod directly bind TNFα as well as RANKL in a dose dependent manner and that despite expressing higher levels of both TNFα and RANKL, BgnFmod KO derived osteoblasts cannot retain these cytokines in the vicinity of the cells, which leads to elevated TNFα and RANKL signaling and enhanced osteoclastogenesis. Furthermore, adding either Bgn or Fmod to osteoclast precursor cultures significantly attenuated the cells ability to form TRAP positive, multinucleated giant cells. In summary, our data indicates that Bgn and Fmod expressed by the bone forming cells, are novel coupling ECM components that control bone mass through sequestration of TNFα and/or RANKL, thereby adjusting their bioavailability in order to regulate osteoclastogenesis.

Inhibition of bone formation in rats by aluminum exposure via Wnt/β-catenin pathway

The previous research found that aluminum trichloride (AlCl₃) inhibited rat osteoblastic differentiation through inactivation of Wnt/β-catenin signaling pathway in vitro. On that basis, the experiment in vivo was conducted in this study. Rats were orally exposed to 0 (control group) and 0.4 g/L AlCl₃ (AlCl₃-treated group) for 30, 60, 90 or 120 days, respectively. We found that mRNA expressions of type I collagen and insulin-like growth factor-1, mRNA and protein expressions of Runx2 and survivin, ratio of p-GSK3β/GSK3β and protein expression of β-catenin were all decreased, whereas the mRNA and protein expressions Dkk1 and sFRP1 and the mRNA expressions and activity of Caspase-3 were increased in the AlCl₃-treated group compared with the control group with time prolonged. These results suggest that AlCl₃ inhibits bone formation and induces bone impairment by inhibiting the Wnt/β-catenin signaling pathway in young growing rats.

Design and Analysis of CCN Gene Activity Using CCN Knockout Mice Containing LacZ Reporters

Two developments have greatly facilitated the construction of CCN mutant mouse strains. The first is the availability of modified embryonic stem (ES) cells and mice developed through several large-scale government-sponsored research programs. The second is the advent of CRISPR/Cas9 technology. In this chapter, we describe the available mouse strains generated by gene targeting techniques and the CCN targeting vectors and genetically modified ES cells that are available for the generation of CCN mutant mice. Many of these mutant mouse lines and ES cells carry a β-galactosidase reporter that can be used to track CCN expression, facilitating phenotypic analysis and revealing new sites of CCN action. Therefore, we also describe a method for β-galactosidase staining.

Members of the Cyr61/CTGF/NOV Protein Family: Emerging Players in Hepatic Progenitor Cell Activation and Intrahepatic Cholangiocarcinoma

Hepatic stem/progenitor cells (HPC) reside quiescently in normal biliary trees and are activated in the form of ductular reactions during severe liver damage when the replicative ability of hepatocytes is inhibited. HPC niches are full of profibrotic stimuli favoring scarring and hepatocarcinogenesis. The Cyr61/CTGF/NOV (CCN) protein family consists of six members, CCN1/CYR61, CCN2/CTGF, CCN3/NOV, CCN4/WISP1, CCN5/WISP2, and CCN6/WISP3, which function as extracellular signaling modulators to mediate cell-matrix interaction during angiogenesis, wound healing, fibrosis, and tumorigenesis. This study investigated expression patterns of CCN proteins in HPC and cholangiocarcinoma (CCA). Mouse HPC were induced by the biliary toxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Differential expression patterns of CCN proteins were found in HPC from DDC damaged mice and in human CCA tumors. In addition, we utilized reporter mice that carried Ccn2/Ctgf promoter driven GFP and detected strong Ccn2/Ctgf expression in epithelial cell adhesion molecule (EpCAM)+ HPC under normal conditions and in DDC-induced liver damage. Abundant CCN2/CTGF protein was also found in cytokeratin 19 (CK19)+ human HPC that were surrounded by α-smooth muscle actin (α-SMA)+ myofibroblast cells in intrahepatic CCA tumors. These results suggest that CCN proteins, particularly CCN2/CTGF, function in HPC activation and CCA development.

WISP1-αvβ3 integrin signaling positively regulates TLR-triggered inflammation response in sepsis induced lung injury

We recently noted that the matricellular protein WISP1 contributes to sepsis induced acute lung injury (ALI) via integrin β6. In the current study, we pursued further aspects of WISP1 modulation of TLR signaling in lungs of mice after sepsis and TLR4 mediated release of TNF-α in macrophages. After confirming that TLR4 and CD14 are critical in transducing sepsis mediated ALI, we now demonstrate that intrapulmonary αvβ3 is increased by polymicrobrial sepsis in a TLR4, CD14 dependent fashion. Comparison of cultured macrophages revealed that WISP1 increased release of TNF-α from RAW264.7 cells with baseline expression of αvβ3, but primary cultures of peritoneal macrophages (PMø) required activation of TLR4 to induce de novo synthesis of αvβ3 enabling WISP1 to stimulate release of TNF-α. The specific requirement for β3 integrin was apparent when the effect of WISP1 was lost in PMø isolated from β3(-/-) mice. WISP1 enhanced TLR4 mediated ERK signaling and U0126 (an ERK inhibitor) blocked LPS induced β3 integrin expression and WISP1 enhanced TNF-α release. Collectively these data suggest that WISP1-αvβ3 integrin signaling is involved in TLR4 pathways in macrophages and may be an important contributor to TLR4/CD14 mediated inflammation in sepsis induced lung injury.

Involvement of multiple CCN family members in platelets that support regeneration of joint tissues

OBJECTIVES

Platelet-rich plasma (PRP) has been widely used to enhance the regeneration of damaged joint tissues, such as osteoarthritic and rheumatoid arthritic cartilage. The aim of this study is to clarify the involvement of all of the CCN family proteins that are crucially associated with joint tissue regeneration.

METHODS

Cyr61-CTGF-NOV (CCN) family proteins in human platelets and megakaryocytic cells were comprehensively analyzed by Western blotting analysis. Production of CCN family proteins in megakaryocytes in vivo was confirmed by immunofluorescence analysis of mouse bone marrow cells. Effects of CCN family proteins found in platelets on chondrocytes were evaluated by using human chondrocytic HCS-2/8 cells.

RESULTS

Inclusion of CCN2, a mesenchymal tissue regenerator, was confirmed. Of note, CCN3, which counteracts CCN2, was newly found to be encapsulated in platelets. Interestingly, these two family members were not detectable in megakaryocytic cells, but their external origins were suggested. Furthermore, we found for the first time CCN5 and CCN1 that inhibits ADAMTS4 in both platelets and megakaryocytes. Finally, application of a CCN family cocktail mimicking platelets onto HCS-2/8 cells enhanced their chondrocytic phenotype.

CONCLUSIONS

Multiple inclusion of CCN1, 2 and 3 in platelets was clarified, which supports the harmonized regenerative potential of PRP in joint therapeutics.

Time-dependent cellular and transcriptional changes in the osteoblast lineage associated with sclerostin antibody treatment in ovariectomized rats

Inhibition of sclerostin with sclerostin antibody (Scl-Ab) has been shown to stimulate bone formation, decrease bone resorption, and increase bone mass in both animals and humans. To obtain insight into the temporal cellular and transcriptional changes in the osteoblast (OB) lineage associated with long-term Scl-Ab treatment, stereological and transcriptional analyses of the OB lineage were performed on lumbar vertebrae from aged ovariectomized rats. Animals were administered Scl-Ab 3 or 50mg/kg/wk or vehicle (VEH) for up to 26weeks (d183), followed by a treatment-free period (TFP). At 50mg/kg/wk, bone volume (BV/total volume [TV]) increased through d183 and declined during the TFP. Bone formation rate (BFR/bone surface [BS]) and total OB number increased through d29, then progressively declined, coincident with a decrease in total osteoprogenitor (OP) numbers from d29 through d183. Analysis of differentially expressed genes (DEGs) from microarray analysis of mRNA isolated from laser capture microdissection samples enriched for OB, lining cells, and osteocytes (OCy) revealed modules of genes that correlated with BFR/BS, BV/TV, and osteoblastic surface (Ob.S)/BS. Expression change of canonical Wnt target genes was similar in all three cell types at d8, including upregulation of Twist1 and Wisp1. At d29, the pattern of Wnt target gene expression changed in the OCy, with Twist1 returning to VEH level, sustained upregulation of Wisp1, and upregulation of several other Wnt targets that continued into the TFP. Predicted activation of pathways recognized to integrate with and regulate canonical Wnt signaling were also activated at d29 in the OCy. The most significantly affected pathways represented transcription factor signaling known to inhibit cell cycle progression (notably p53) and mitogenesis (notably c-Myc). These changes occurred at the time of peak BFR/BS and continued as BFR/BS declined during treatment, then trended toward VEH level in the TFP. Concurrent with this transcriptional switch was a reduction in OP numbers, an effect that would ultimately limit bone formation. This study confirms that the initial transcriptional response in response to Scl-Ab is activation of canonical Wnt signaling and the data demonstrate that there is induction of additional regulatory pathways in OCy with long-term treatment. The interactions between Wnt and p53/c-Myc signaling may be key in limiting OP populations, thus contributing to self-regulation of bone formation with continued Scl-Ab administration.

CCN4/WISP-1 positively regulates chondrogenesis by controlling TGF-β3 function

The CCN family of proteins plays important roles in development and homeostasis of bone and cartilage. To understand the role of CCN4 in chondrogenesis, human bone marrow stromal cells (hBMSCs) were transduced with CCN4 adenovirus (adCCN4) or siRNA to CCN4 (siCCN4) in the presence or absence of transforming growth factor-β3 (TGF-β3). Overexpression of CCN4 enhanced TGF-β3-induced SMAD2/3 phosphorylation and chondrogenesis of hBMSCs in an in vitro assay using a micromass culture model. On the other hand, knockdown of CCN4 inhibited the TGF-β3-induced SMAD2/3 phosphorylation and synthesis of cartilage matrix in micromass cultures of hBMSCs. Immunoprecipitation-western blot analysis revealed that CCN4 bound to TGF-β3 and regulated the ability of TGF-β3 to bind to hBMSCs. In vivo analysis confirmed there was a significant decrease in the gene expression levels of chondrocyte markers in cartilage samples from Ccn4-knock out (KO) mice, compared to those from wild type (WT) control. In order to investigate the regenerative properties of the articular cartilage in Ccn4-KO mice, articular cartilage defects were surgically performed in the knee joints of young mice, and the results showed that the cartilage was partially repaired in WT mice, but not in Ccn4-KO mice. In conclusion, these results show, for the first time, that CCN4 has a positive influence on chondrogenic differentiation by modulating the effects of TGF-β3.

CCN: core regulatory proteins in the microenvironment that affect the metastasis of hepatocellular carcinoma?

Hepatocellular carcinoma (HCC) results from an underlying chronic liver inflammatory disease, such as chronic hepatitis B or C virus infections, and the general prognosis of patients with HCC still remains extremely dismal because of the high frequency of HCC metastases. Throughout the process of tumor metastasis, tumor cells constantly communicate with the surrounding microenvironment and improve their malignant phenotype. Therefore, there is a strong rationale for targeting the tumor microenvironment as primary treatment of HCC therapies. Recently, CCN family proteins have emerged as localized multitasking signal integrators in the inflammatory microenvironment. In this review, we summarize the current knowledge of CCN family proteins in inflammation and the tumor. We also propose that the CCN family proteins may play a central role in signaling the tumor microenvironment and regulating the metastasis of HCC.

Picking a bone with WISP1 (CCN4): new strategies against degenerative joint disease

As the world's population continues to age, it is estimated that degenerative joint disease disorders such as osteoarthritis will impact at least 130 million individuals throughout the globe by the year 2050. Advanced age, obesity, genetics, gender, bone density, trauma, and a poor level of physical activity can lead to the onset and progression of osteoarthritis. However, factors that lead to degenerative joint disease and involve gender, genetics, epigenetic mechanisms, and advanced age are not within the control of an individual. Furthermore, current therapies including pain management, improved nutrition, and regular programs for exercise do not lead to the resolution of osteoarthritis. As a result, new avenues for targeting the treatment of osteoarthritis are desperately needed. Wnt1 inducible signaling pathway protein 1 (WISP1), a matricellular protein and a downstream target of the wingless pathway Wnt1, is one such target to consider that governs cellular protection, stem cell proliferation, and tissue regeneration in a number of disorders including bone degeneration. However, increased WISP1 expression also has been associated with the progression of osteoarthritis. WISP1 has an intricate relationship with a number of proliferative and protective pathways that include phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), interleukin -6 (IL-6), transforming growth factor-β, matrix metalloproteinase, small non-coding ribonucleic acids (RNAs), sirtuin silent mating type information regulation 2 homolog 1 (Saccharomyces cerevisiae) (SIRT1), and the mechanistic target of rapamycin (mTOR). Taken together, this complex association WISP1 holds with these signaling pathways necessitates a fine biological regulation of WISP1 activity that can offset the progression of degenerative joint disease, but not limit the cellular protective capabilities of the WISP1 pathway.

Regeneration in the nervous system with erythropoietin

Globally, greater than 30 million individuals are afflicted with disorders of the nervous system accompanied by tens of thousands of new cases annually with limited, if any, treatment options. Erythropoietin (EPO) offers an exciting and novel therapeutic strategy to address both acute and chronic neurodegenerative disorders. EPO governs a number of critical protective and regenerative mechanisms that can impact apoptotic and autophagic programmed cell death pathways through protein kinase B (Akt), sirtuins, mammalian forkhead transcription factors, and wingless signaling. Translation of the cytoprotective pathways of EPO into clinically effective treatments for some neurodegenerative disorders has been promising, but additional work is necessary. In particular, development of new treatments with erythropoiesis-stimulating agents such as EPO brings several important challenges that involve detrimental vascular outcomes and tumorigenesis. Future work that can effectively and safely harness the complexity of the signaling pathways of EPO will be vital for the fruitful treatment of disorders of the nervous system.

FoxO proteins in the nervous system

Acute as well as chronic disorders of the nervous system lead to significant morbidity and mortality for millions of individuals globally. Given the ability to govern stem cell proliferation and differentiated cell survival, mammalian forkhead transcription factors of the forkhead box class O (FoxO) are increasingly being identified as potential targets for disorders of the nervous system, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and auditory neuronal disease. FoxO proteins are present throughout the body, but they are selectively expressed in the nervous system and have diverse biological functions. The forkhead O class transcription factors interface with an array of signal transduction pathways that include protein kinase B (Akt), serum- and glucocorticoid-inducible protein kinase (SgK), IκB kinase (IKK), silent mating type information regulation 2 homolog 1 (S. cerevisiae) (SIRT1), growth factors, and Wnt signaling that can determine the activity and integrity of FoxO proteins. Ultimately, there exists a complex interplay between FoxO proteins and their signal transduction pathways that can significantly impact programmed cell death pathways of apoptosis and autophagy as well as the development of clinical strategies for the treatment of neurodegenerative disorders.