WISP1 Protects Against Chondrocyte Senescence and Apoptosis by Regulating αvβ3 and PI3K/Akt Pathway in Osteoarthritis

Novel insight on IRE1 in the regulation of chondrocyte dedifferentiation through ER stress independent pathway

Inositol-requiring enzyme-1 (IRE1) is the master regulator of the unfolded protein response pathway, associated with the endoplasmic reticulum (ER) in sensing and regulating cell stress. The activity of IRE1 is highly explored and well-characterized in cancer and other cells. However, the IRE1 molecular mechanism in chondrocytes is poorly understood. The present study explored the effect of IRE1 on chondrocytes regarding its chondrogenic gene expression and its correlation with different cellular pathways and cell behavior. Chondrocytes transfected with the cDNA of IRE1 reduced the expression of type II collagen, disrupting chondrocyte differentiation as confirmed by western blotting and immunofluorescence. Upon siRNA treatment, the influence of IRE1 on chondrocyte differentiation is restored by reviving the normal expression of type II collagen. Different molecular pathways were explored to investigate the role of IRE1 in causing chondrocyte dedifferentiation. However, we found no significant correlation, as IRE1 induces dedifferentiation through independent pathways. In response to various endoplasmic reticulum (ER) agonists (2-deoxy-D-glucose), and ER stress antagonists (tauroursodeoxycholic acid and salubrinal), IRE1 overexpression did not affect GRP78/94, as implicated in the pathogenesis of ER stress. Moreover, when IRE1 overexpression was correlated with the inflammation pathway, nuclear factor-kappa B (NFκB), IRE1 substantially increased the expression of p50 while decreasing the expression of nuclear factor kappa light polypeptide alpha (IκBα). These results suggest that IRE1 induces dedifferentiation in chondrocytes by modulating inflammatory pathways that cause dedifferentiation by disrupting type II collagen expression.

P53: A Key Target in the Development of Osteoarthritis

Osteoarthritis (OA), a chronic degenerative disease characterized mainly by damage to the articular cartilage, is increasingly relevant to the pathological processes of senescence, apoptosis, autophagy, proliferation, and differentiation of chondrocytes. Clinical strategies for osteoarthritis can only improve symptoms and even along with side effects due to age, sex, disease, and other factors. Therefore, there is an urgent need to identify new ideas and targets for current clinical treatment. The tumor suppressor gene p53, which has been identified as a potential target for tumor therapeutic intervention, is responsible for the direct induction of the pathological processes involved in OA modulation. Consequently, deciphering the characteristics of p53 in chondrocytes is essential for investigating OA pathogenesis due to p53 regulation in an array of signaling pathways. This review highlights the effects of p53 on senescence, apoptosis, and autophagy of chondrocytes and its role in the development of OA. It also elucidates the underlying mechanism of p53 regulation in OA, which may help provide a novel strategies for the clinical treatment of OA.

Rutaecarpine ameliorates osteoarthritis by inhibiting PI3K/AKT/NF‑κB and MAPK signalling transduction through integrin αVβ3

Osteoarthritis (OA) is a chronic progressive articular illness which commonly affects older‑aged adults, presenting with cartilage inflammation and degradation. Rutaecarpine (RUT) has been shown to exert promising anti‑inflammatory effects; however, the efficacy of RUT in the treatment of OA is debatable. The present study investigated the potential of RUT in alleviating OA in a mouse model. Treatment with RUT inhibited the inflammatory response and extracellular matrix degradation by suppressing process regulators in interleukin (IL)‑1β‑stimulated chondrocytes. Moreover, treatment with RUT in vitro upregulated the gene expression of anabolic agents, such as collagen type II, aggrecan and SRY‑box transcription factor 9, indicating that RUT contributed to cartilage repair. Additionally, flow cytometric assays, and the measurement of β‑galactosidase levels, autophagic flux and related protein expression revealed that RUT effectively attenuated IL‑1β‑induced chondrocyte apoptosis, senescence and autophagy impairment. In addition, bioinformatics analysis and in vitro experiments demonstrated that RUT protected cartilage by mediating the phosphoinositide‑3‑kinase (PI3K)/Akt/nuclear factor‑κB (NF‑κB) and mitogen‑activated protein kinase (MAPK) pathways. The ameliorative effects of RUT on IL‑1β‑stimulated chondrocytes were abrogated when siRNA was used to knock down integrin αVβ3. Furthermore, the results of immunohistochemical analysis and microcomputed tomography confirmed the in vivo therapeutic effects of RUT in mice with OA. On the whole, the present study demonstrates that RUT attenuates the inflammatory response and cartilage degradation in mice with OA by suppressing the activation of the PI3K/AKT/NF‑κB and MAPK pathways. Integrin αVβ3 may play a pivotal role in these effects.

Recent progress on the role of cellular communication network factors (CCN) 3, 4 and 6 in regulating adiposity, liver fibrosis and pancreatic islets

CCN/WISP (cellular communication network factors, or Wnt-inducted secreted proteins) family of proteins consists of six extracellular matrix (ECM)-associated proteins that regulate development, cell adhesion and proliferation, ECM remodeling, inflammation, and tumorigenesis. In the last two decades, metabolic regulation by these matricellular proteins has been studied extensively, several excellent reviews have covered the roles of CCN1, -2 and - 5. In this brief review, we will focus on those lesser-known members and more recent discoveries, together with other recent articles presenting a more complete picture of the current state of knowledge. We have found that CCN2, -4, and - 5 promote pancreatic islet function, while CCN3 plays a unique and negative role. CCN3 and - 4 are pro-adiposity leading to insulin resistance, but CCN5 and - 6 are anti-adiposity. While CCN2 and - 4 promote tissue fibrosis and inflammation, all other four members are clearly anti-fibrotic. As for cellular signaling, they are known to interact with integrins, other cell membrane proteins and ECM thereby regulate Akt/protein kinase B, myocardin-related transcription factor (MRTF), and focal adhesion kinase. Yet, a cohesive mechanism of action to comprehensively explain those major functions is still lacking.

WNT1-inducible signalling pathway protein 1 stabilizes atherosclerotic plaques in apolipoprotein-E-deficient mice via the focal adhesion kinase/mitogen-activated extracellular signal-regulated kinase/extracellular signal-regulated kinase pathway

BACKGROUND

The migration, proliferation and apoptosis of vascular smooth muscle cells (VSMCs) are critical for plaque stability. WNT-inducible signalling pathway protein-1 (WISP1), a member of the CCN family of extracellular matrix proteins, can expedite the migration and proliferation of VSMCs. However, its underlying mechanism and relationship with atherosclerosis remain elusive. The relationship between WISP1 and apoptosis of VSMCs has not been determined previously.

METHOD

In the study, we aimed to investigate the relationship between WISP1 and plaque stability and its related mechanism.ApoE-/- mice were divided following groups: the null lentivirus (NC), lentivirus WISP1 (IvWISP1) and WISP1-shRNA (shWISP1) groups. Immunofluorescence, Oil Red O and Masson's staining of the carotid arteries were performed. Transwell wound healing assay, CCK8 assay, and TdT-mediated dUTP nick-end labeling (TUNEL) staining were performed using VSMCs. The levels of WISP1, P38, C-Jun N-terminal kinase, extracellular signal-regulated kinase (ERK), mitogen-activated extracellular signal-regulated kinase (MEK), focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), Akt (also known as PKB, protein kinase B), mammalian target of rapamycin (mTOR), cleaved caspase3, Bcl2 and Bax were detected by western blotting.

RESULTS

The relative area of lipids and monocytes/macrophages in the shWISP1 group increased compared with that of the NC group. However, the relative area of smooth muscle cell and collagen in the IvWISP1 group increased compared with that in the NC group. Therefore, WISP1 could stabilize atherosclerotic plaques. Besides, WISP1 accelerate the migration and proliferation of VSMCs via integrin α5β1 and FAK/MEK/ERK signalling pathways. In addition, WISP1 can inhibit the apoptosis of VSMCs via the PI3K/Akt/mTOR pathway.

CONCLUSION

WISP1 not only inhibits the apoptosis of VSMCs via the PI3K/Akt/mTOR pathway but also enhances the migration and proliferation of VSMCs via the integrin α5β1 and FAK/MEK/ERK pathways. Therefore, WISP1 could enhance the stability of atherosclerotic plaques.

OPN inhibits autophagy through CD44, integrin and the MAPK pathway in osteoarthritic chondrocytes

Background

To investigate whether osteopontin (OPN) affects autophagy in human osteoarthritic chondrocytes and determine the roles of CD44, αvβ3 integrin and the Mitogen-activated protein kinase (MAPK) pathway in this progress.

Methods

First, we compared the autophagy levels in the human osteoarthritis (OA) and normal cartilage, then, we cultured human OA chondrocytes in vitro and treated cells with recombinant human OPN (rhOPN) to determine autophagy changes. Next, the anti-CD44 and anti-CD51/61 monoclonal antibodies (Abs) or isotype IgG were used to determine the possible role of CD44 and αvβ3 integrin; subsequently, an inhibitor of the ERK MAPK pathway was used to investigate the role of ERK MAPK. Western blotting was used to measure the Beclin1, LC3 II and MAPK proteins expressions, mRFP-GFP-LC3 confocal imaging and transmission electron microscopy were also used to detect the autophagy levels. Cell Counting Kit-8 (CCK-8) was used to assay the proliferation and activity of chondrocytes.

Results

The LC3 protein was greatly decreased in OA cartilage compared to normal cartilage, and OPN suppressed the autophagy activity in chondrocytes in vitro. Blocking experiments with anti-CD44 and anti-CD51/61 Abs indicated that OPN could suppress the expression of LC3II and Beclin1 through αvβ3 integrin and CD44. Our results also indicated that the ratio of p-ERK/ERK but not p-P38/P38 and p-JNK/JNK was increased after the rhOPN treatment. The ERK inhibitor inhibited the activity of OPN in the suppression of autophagy, and the CCK-8 results showed that rhOPN could promote chondrocyte proliferation.

Conclusion

OPN inhibited chondrocyte autophagy through CD44 and αvβ3 integrin receptors and via the ERK MAPK signaling pathway.

Physalin A Inhibits MAPK and NF-κB Signal Transduction Through Integrin αVβ3 and Exerts Chondroprotective Effect

Osteoarthritis (OA) is a common articular ailment presented with cartilage loss and destruction that is common observed in the elderly population. Physalin A (PA), a natural bioactive withanolide, exerts anti-inflammatory residences in more than a few diseases; however, little is known about its efficacy for OA treatment. Here, we explored the therapeutic effects and potential mechanism of PA in mouse OA. After the in vitro administration of PA, the expression of inflammation indicators including inducible nitric oxide synthase and cyclooxygenase-2 was low, indicating that PA could alleviate the IL-1β-induced chondrocyte inflammation response. Moreover, PA reduced IL-1β-induced destruction of the extracellular matrix by upregulating the gene expression of anabolism factors, including collagen II, aggrecan, and sry-box transcription factor 9, and downregulating the gene expression of catabolic factors, including thrombospondin motif 5 and matrix metalloproteinases. In addition, the chondroprotective effect of PA was credited to the inhibition of mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signaling pathways. Furthermore, in vivo experiments showed that intra-articular injection of PA could alleviate cartilage destruction in a mouse OA model. However, the anti-inflammatory, anabolism enhancing, catabolism inhibiting, and MAPK and NF-κB signaling pathway inhibiting properties of PA on IL-1β-induced chondrocytes could be reversed when integrin αVβ3 is knocked down by siRNA. In conclusion, our work demonstrates that PA exhibits a chondroprotective effect that may be mediated by integrin αVβ3. Thus, PA or integrin αVβ3 might be a promising agent or molecular target for the treatment of OA.

Integrins, cadherins and channels in cartilage mechanotransduction: perspectives for future regeneration strategies

Articular cartilage consists of hyaline cartilage, is a major constituent of the human musculoskeletal system and has critical functions in frictionless joint movement and articular homoeostasis. Osteoarthritis (OA) is an inflammatory disease of articular cartilage, which promotes joint degeneration. Although it affects millions of people, there are no satisfying therapies that address this disease at the molecular level. Therefore, tissue regeneration approaches aim at modifying chondrocyte biology to mitigate the consequences of OA. This requires appropriate biochemical and biophysical stimulation of cells. Regarding the latter, mechanotransduction of chondrocytes and their precursor cells has become increasingly important over the last few decades. Mechanotransduction is the transformation of external biophysical stimuli into intracellular biochemical signals, involving sensor molecules at the cell surface and intracellular signalling molecules, so-called mechano-sensors and -transducers. These signalling events determine cell behaviour. Mechanotransducing ion channels and gap junctions additionally govern chondrocyte physiology. It is of great scientific and medical interest to induce a specific cell behaviour by controlling these mechanotransduction pathways and to translate this knowledge into regenerative clinical therapies. This review therefore focuses on the mechanotransduction properties of integrins, cadherins and ion channels in cartilaginous tissues to provide perspectives for cartilage regeneration.