COX-2 expression mediated by calcium-TonEBP signaling axis under hyperosmotic conditions serves osmoprotective function in nucleus pulposus cells

Osmolar Modulation Drives Reversible Cell Cycle Exit and Human Pluripotent Cell Differentiation via NF-κВ and WNT Signaling

Terminally differentiated cells are commonly regarded as the most stable cell state in adult organisms, characterized by growth arrest while fulfilling their specialized functions. A better understanding of the mechanisms involved in promoting cell cycle exit will improve the ability to differentiate pluripotent cells into mature tissues for both pharmacological and therapeutic use. Here, it demonstrates that a hyperosmolar environment enforces a protective p53-independent quiescent state in immature hepatoma cells and in pluripotent stem cell-derived models of human hepatocytes and endothelial cells. Prolonged culture in hyperosmolar conditions stimulates changes in gene expression promoting functional cell maturation. Interestingly, hyperosmolar conditions do not only trigger growth arrest and cellular maturation but are also necessary to maintain this maturated state, as switching back to plasma osmolarity reverses the changes in expression of maturation and proliferative markers. Transcriptome analysis revealed sequential stages of osmolarity-regulated growth arrest followed by cell maturation, mediated by activation of NF-κВ, and repression of WNT signaling, respectively. This study reveals that a modulated increase in osmolarity serves as a biochemical signal to promote long-term growth arrest and cellular maturation into different lineages, providing a practical method to generate differentiated hiPSCs that resemble their mature counterpart more closely.

TonEBP expression is essential in the IL-1β-induced migration and invasion of human A549 lung cancer cells

Lung cancer has the highest mortality rate among all cancers, in part because it readily metastasizes. The tumor microenvironment, comprising blood vessels, fibroblasts, immune cells, and macrophages [including tumor-associated macrophages (TAMs)], is closely related to cancer cell growth, migration, and invasion. TAMs secrete several cytokines, including interleukin (IL)-1β, which participate in cancer migration and invasion. p21-activated kinase 1 (PAK1), an important signaling molecule, induces cell migration and invasion in several carcinomas. Tonicity-responsive enhancer-binding protein (TonEBP) is also known to participate in cancer cell growth, migration, and invasion. However, the mechanisms by which it increases lung cancer migration remain unclear. Therefore, in this study, we aimed to elucidate the mechanisms by which IL-1β and TonEBP affect lung cancer cell migration and invasion. We found that A549 cocultured-MΦ-secreted IL-1β induced A549 cell migration and invasion via the PAK1 pathway. TonEBP deficiency reduced A549 cell migration and invasion and increased responsiveness to IL-1β-induced migration and invasion. PAK1 phosphorylation, which was promoted by IL-1β, was reduced when TonEBP was depleted. These results suggest that TonEBP plays an important role in IL-1β induction and invasiveness of A549 cells via the PAK1 pathway. These findings could be valuable in identifying potential targets for lung cancer treatment.

Effect of felodipine on indomethacin-induced gastric ulcers in rats

Felodipine is a calcium channel blocker with antioxidant and anti-inflammatory properties. Researchers have stated that oxidative stress and inflammation also play a role in the pathophysiology of gastric ulcers caused by nonsteroidal anti-inflammatory drugs. The aim of this study was to investigate the antiulcer effect of felodipine on indomethacin-induced gastric ulcers in Wistar rats and compare it with that of famotidine. The antiulcer activities of felodipine (5 mg/kg) and famotidine were investigated biochemically and macroscopically in animals treated with felodipine (5 mg/kg) and famotidine in combination with indomethacin. The results were compared with those of the healthy control group and the group administered indomethacin alone. It was observed that felodipine suppressed the indomethacin-induced malondialdehyde increase (P<0.001); reduced the decrease in total glutathione amount (P<0.001), reduced the decrease superoxide dismutase (P<0.001), and catalase activities (P<0.001); and significantly inhibited ulcers (P<0.001) at the tested dose compared with indomethacin alone. Felodipine at a dose of 5 mg/kg reduced the indomethacin-induced decrease in cyclooxygenase-1 activity (P<0.001) but did not cause a significant reduction in the decrease in cyclooxygenase-2 activity. The antiulcer efficacy of felodipine was demonstrated in this experimental model. These data suggest that felodipine may be useful in the treatment of nonsteroidal anti-inflammatory drug-induced gastric injury.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Cannabinoids Reduce Melanoma Cell Viability and Do Not Interfere with Commonly Used Targeted Therapy in Metastatic Melanoma In Vivo and In Vitro

Background: Cannabinoids are mainly used for recreational purposes, but also made their way into oncology, since these substances can be taken to increase appetite in tumour cachexia. Since there are some hints in the literature that cannabinoids might have some anti-cancerous effects, the aim of this study was to study if and how cannabinoids mediate pro-apoptotic effects in metastatic melanoma in vivo and in vitro and its value besides conventional targeted therapy in vivo. Methods: Several melanoma cell lines were treated with different concentrations of cannabinoids, and anti-cancerous efficacy was assessed by proliferation and apoptosis assays. Subsequent pathway analysis was performed using apoptosis, proliferation, flow cytometry and confocal microscopy data. The efficacy of cannabinoids in combination with trametinib was studied in NSG mice in vivo. Results: Cannabinoids reduced cell viability in multiple melanoma cell lines in a dose-dependent way. The effect was mediated by CB1, TRPV1 and PPARα receptors, whereby pharmacological blockade of all three receptors protected from cannabinoid-induced apoptosis. Cannabinoids initiated apoptosis by mitochondrial cytochrome c release with consecutive activation of different caspases. Essentially, cannabinoids significantly decreased tumour growth in vivo and were as potent as the MEK inhibitor trametinib. Conclusions: We could demonstrate that cannabinoids reduce cell viability in several melanoma cell lines, initiate apoptosis via the intrinsic apoptotic pathway by cytochrome c release and caspase activation and do not interfere with commonly used targeted therapy.

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

Zinc(II) niflumato complex effects on MMP activity and gene expression in human endometrial cell lines

Endometriosis is a chronic inflammatory disease which increasingly affects young women under 35 years of age and leads to subfertility even infertility. Analysis of the cytotoxic effect of zinc(II) niflumato complex with neocuproine ([Zn(neo)(nif)2] or Zn-Nif) on immortalized human endometriotic cell line (12Z) and on control immortalized human endometrial stromal cell line (hTERT) was performed using xCELLigence technology for approximately 72 h following the treatment with Zn-Nif as well as cell viability Trypan Blue Assay. 12Z cell line proliferated more slowly compared to unaffected cells, whereas hTERT cells did not show similar behavior after treatment. The complex probably reduces the effect of pro-inflammatory pathways due to the effect of NSAID, while presence of zinc might reduce the level of ROS and regulate ER2 levels and MMP activity. The observed effects and high selectivity for rapidly proliferating cells with increased inflammatory activity suggest a good prognosis of successful decrease of endometriosis stage with this complex.

Investigating the physiological relevance of ex vivo disc organ culture nutrient microenvironments using in silico modeling and experimental validation

BACKGROUND

Ex vivo disc organ culture systems have become a valuable tool for the development and pre-clinical testing of potential intervertebral disc (IVD) regeneration strategies. Bovine caudal discs have been widely selected due to their large availability and comparability to human IVDs in terms of size and biochemical composition. However, despite their extensive use, it remains to be elucidated whether their nutrient microenvironment is comparable to human degeneration.

AIMS

This work aims to create the first experimentally validated in silico model which can be used to predict and characterize the metabolite concentrations within ex vivo culture systems.

MATERIALS & METHODS

Finite element models of cultured discs governed by previously established coupled reaction-diffusion equations were created using COMSOL Multiphysics. Experimental validation was performed by measuring oxygen, glucose and pH levels within discs cultured for 7 days, in a static compression bioreactor.

RESULTS

The in silico model was successfully validated through good agreement between the predicted and experimentally measured concentrations. For an ex vivo organ cultured in high glucose medium (4.5 g/L or 25 mM) and normoxia, a larger bovine caudal disc (Cd1-2 to Cd3-4) had a central concentration of ~2.6 %O2, ~8 mM of glucose and a pH value of 6.7, while the smallest caudal discs investigated (Cd6-7 and Cd7-8), had a central concentration of ~6.5 %O2, ~12 mM of glucose and a pH value of 6.9.

DISCUSSION

This work advances the knowledge of ex vivo disc culture microenvironments and highlights a critical need for optimization and standardization of culturing conditions.

CONCLUSION

Ultimately, for assessment of cell-based therapies and successful clinical translation based on nutritional demands, it is imperative that the critical metabolite values within organ cultures (minimum glucose, oxygen and pH values) are physiologically relevant and comparable to the stages of human degeneration.

NSP2 Is Important for Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus to Trigger High Fever-Related COX-2-PGE2 Pathway in Pigs

In 2006, atypical porcine reproductive and respiratory syndrome (PRRS) caused by a highly pathogenic PRRSV (HP-PRRSV) strain broke out in China. Atypical PRRS is characterized by extremely high fever and high mortality in pigs of all ages. Prostaglandin E2 (PGE2) derived from arachidonic acid through the activation of the rate-limiting enzyme cyclooxygenase type 1/2 (COX-1/2) plays an important role in fever. Here, we showed that HP-PRRSV infection increased PGE2 production in microglia via COX-2 up-regulation depending on the activation of MEK1-ERK1/2-C/EBPβ signaling pathways. Then, we screened HP-PRRSV proteins and demonstrated that HP-PRRSV nonstructural protein 2 (NSP2) activated MEK1-ERK1/2-C/EBPβ signaling pathways by interacting with 14-3-3ζ to promote COX-2 expression, leading to PGE2 production. Furthermore, we identified that the amino acid residues 500-596 and 658-777 in HP-PRRSV NSP2 were essential to up-regulate COX-2 expression and PGE2 production. Finally, we made mutant HP-PRRS viruses with the deletion of residues 500-596 and/or 658-777, and found out that these viruses had impaired ability to up-regulate COX-2 and PGE2 production in vitro and in vivo. Importantly, pigs infected with the mutant viruses had relieved fever, clinical symptoms, and mortality. These data might help us understand the molecular mechanisms underlying the high fever and provide clues for the development of HP-PRRSV attenuated vaccines.

The TLR-2/TonEBP signaling pathway regulates 29-kDa fibronectin fragment-dependent expression of matrix metalloproteinases

Tonicity-responsive enhancer-binding protein (TonEBP; nuclear factor of activated T cells 5) is a transcription factor that responds to changes in osmolality. However, recent studies have shown that it also modulates immune responses under inflammatory conditions independently of hyperosmolality. Fibronectin fragments (FN-fs), which are abundant in the synovial fluid of patients with osteoarthritis (OA), induce expression of matrix metalloproteinases (MMPs) via the toll-like receptor-2 (TLR-2) signaling pathway. In this study we examined whether TonEBP is involved in 29-kDa FN-f-induced expression of MMPs. The expression of TonEBP was significantly higher in human osteoarthritis compared with normal cartilage samples. 29-kDa FN-f affected the expression of MMPs 1, 3, and 13 via TonEBP, and expression and nuclear accumulation of TonEBP were induced by activation of the phospholipase C/NF-κB/MAPK signaling pathway and, in particular, modulated by TLR-2. In addition, 29-kDa FN-f induced the expression of osmoregulatory genes, including Tau-T, SMIT, and AR, as well as voltage-dependent calcium channels via the TonEBP/TLR-2 signaling pathway. These results show that 29-kDa FN-f upregulates MMPs in chondrocytes via the TLR-2/TonEBP signaling pathway.

Hyperosmolarity benefits cartilage regeneration by enhancing expression of chondrogenic markers and reducing inflammatory markers

Application of hyperosmolarity can be a promising strategy to promote chondrogenic differentiation in adipose-derived mesenchymal stem cells (ADSCs). Growth factors may promote different signaling pathways in parallel that is why in this study we monitor undesired pathologic or unwanted side effects as well as chondroinductive impacts of hyperosmolarity in differentiating ADSCs. Quantified gene expression, immunocytochemistry, glycosaminoglycan deposition and angiogenic secretion assays performed along with immunoassay. We observed that hyperosmolarity pressure of 480 mOsm over-expressed cartilage specific markers at gene expression level in the extra cellular matrix. Meanwhile, hyperosmolarity of 480 mOsm diminished the expression of cartilage associated pathologic markers, i.e., inflammatory and angiogenic attributes. Certain dose of hyperosmolarity could benefit chondrogenesis in a dual way, first by increasing chondrogenic markers and second by lowering tissue mineralization and angiogenic potential. The chondroprotective potential of hyperosmolarity could have a promising benefit in cartilage cell therapy and tissue engineering.

TonEBP regulates the hyperosmotic expression of aquaporin 1 and 5 in the intervertebral disc

The central region of the intervertebral disc (IVD) is rich in proteoglycans, leading to a hyperosmotic environment, which fluctuates with daily loading. The cells of the nucleus pulposus (NP cells) have adapted to this environment via the function of tonicity enhancer binding protein (TonEBP), and NP cells have been shown to express several water channels known as aquaporins (AQP). We have previously shown that AQP1 and 5 decrease during IVD degeneration. Here, the regulation of AQP1 and 5 by hyperosmotic conditions and the role of TonEBP in this regulation was investigated. AQP1 and 5 gene expression was upregulated by hyperosmotic conditions mimicking the osmolality of the healthy IVD, which was abrogated by TonEBP knockdown. Furthermore, AQP1 and 5 immunopositivity was significantly reduced in TonEBP^Δ/Δ E17.5 mice when compared with wildtype controls, indicating in vivo expression of AQP1 and 5 is controlled at least in part by TonEBP. This hyperosmotic regulation of AQP1 and 5 could help to explain the decreased AQP1 and 5 expression during degeneration, when the osmolality of the NP decreases. Together this data suggests that TonEBP-regulated osmo-adaptation may be disrupted during IVD degeneration when the expression of both AQPs is reduced.

Hypertonicity counteracts MCL-1 and renders BCL-XL a synthetic lethal target in head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is an aggressive and difficult-to-treat cancer entity. Current therapies ultimately aim to activate the mitochondria-controlled (intrinsic) apoptosis pathway, but complex alterations in intracellular signaling cascades and the extracellular microenvironment hamper treatment response. On the one hand, proteins of the BCL-2 family set the threshold for cell death induction and prevent accidental cellular suicide. On the other hand, controlling a cell's readiness to die also determines whether malignant cells are sensitive or resistant to anticancer treatments. Here, we show that HNSCC cells upregulate the proapoptotic BH3-only protein NOXA in response to hyperosmotic stress. Induction of NOXA is sufficient to counteract the antiapoptotic properties of MCL-1 and switches HNSCC cells from dual BCL-XL/MCL-1 protection to exclusive BCL-XL addiction. Hypertonicity-induced functional loss of MCL-1 renders BCL-XL a synthetically lethal target in HNSCC, and inhibition of BCL-XL efficiently kills HNSCC cells that poorly respond to conventional therapies. We identify hypertonicity-induced upregulation of NOXA as link between osmotic pressure in the tumor environment and mitochondrial priming, which could perspectively be exploited to boost efficacy of anticancer drugs.

Integrated Pathways of COX-2 and mTOR: Roles in Cell Sensing and Alzheimer's Disease

Cyclooxygenases (COX) are enzymes catalyzing arachidonic acid into prostanoids. COX exists in three isoforms: COX-1, 2, and 3. COX-1 and COX-2 have been widely studied in order to explore and understand their involvement in Alzheimer’s disease (AD), a progressive neuroinflammatory dementia. COX-2 was traditionally viewed to be expressed only under pathological conditions and to have detrimental effects in AD pathophysiology and neurodegeneration. However, an increasing number of reports point to much more complex roles of COX-2 in AD. Mammalian/mechanistic target of rapamycin (mTOR) has been considered as a hub which integrates multiple signaling cascades, some of which are also involved in AD progression. COX-2 and mTOR are both involved in environmental sensing, growth, and metabolic processes of the cell. They are also known to act in cooperation in many different cancers and thus, their role together in normal cellular functions as well as AD has been explored in this review. Some of the therapeutic approaches targeting COX-2 and mTOR in AD and cancer are also discussed.

Alterations in ECM signature underscore multiple sub-phenotypes of intervertebral disc degeneration

The intervertebral disc is a specialized connective tissue critical for absorption of mechanical loads and providing flexibility to the spinal column. The disc ECM is complex and plays a vital role in imparting tissue its biomechanical function. The central NP is primarily composed of large aggregating proteoglycans (PGs) while surrounding AF is composed of fibrillar collagens, I and II. Aggrecan and versican in particular, due to their high concentration of sulfated GAG chains form large aggregates with hyaluronic acid (HA) and provide water binding capacity to the disc. Degradation of aggrecan core protein due to aggrecanase and MMP activity, SNPs that affect number of chondroitin sulfate (CS) substitutions and alteration in enzymes critical in synthesis of CS chains can impair the aggrecan functionality. Similarly, levels of many matrix and matrix-related molecules e.g. Col2, Col9, HAS2, ccn2 are dysregulated during disc degeneration and genetic animal models have helped establish causative link between their expression and disc health. In the degenerating and herniated discs, increased levels of inflammatory cytokines such as TNF-α, IL-1β and IL-6 are shown to promote matrix degradation through regulating expression and activity of critical proteases and stimulate immune cell activation. Recent studies of different mouse strains have better elucidated the broader impact of spontaneous degeneration on disc matrix homeostasis. SM/J mice showed an increased cell apoptosis, loss of cell phenotype, and cleavage of aggrecan during early stages followed by tissue fibrosis evident by enrichment of several collagens, SLRPs and fibronectin. In summary, while disc degeneration encompasses wide spectrum of degenerative phenotypes extensive matrix degradation and remodeling underscores all of them.

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The intervertebral disc absorbs loads and provides flexibility to the spine.

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The ECM is complex and vital for imparting tissue its biomechanical function.

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Numerous types of proteoglycans and collagens designate the quality of the disc.

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Many matrix and matrix-related molecules are dysregulated during disc degeneration.

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Matrix degradation and remodeling underscores wide spectrum of phenotype.

Differential Effect of Long-Term Systemic Exposure of TNFα on Health of the Annulus Fibrosus and Nucleus Pulposus of the Intervertebral Disc

The inflammatory cytokine tumor necrosis factor alpha (TNFα) is considered to play a key role in the pathogenesis of intervertebral disc disease. To evaluate the importance of this cytokine we examined the inflammatory environment and spinal phenotype of 9-month-old human TNFα overexpressing transgenic (hTNFα-TG) mice. The mice evidenced increased circulating levels of interleukin-1β (IL-1β), IL-2, keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO), and monocyte chemoattractant protein-1 (MCP-1) along with thinning of the cortical and trabecular vertebral bone. Surprisingly, although the nucleus pulposus (NP) of these mice was intact and healthy, the caudal annulus fibrosus (AF) evidenced robust cell death and immune cell infiltration. Despite these differences, there were no obvious alterations in the collagen or aggrecan content in the NP and AF. However, there was a reduction in cartilage oligomeric matrix protein (COMP), suggesting destabilization of the AF matrix. Microarray analysis of the NP from hTNFα-TG mice cells revealed minimal changes in global gene expression. These findings lend support to the notion that NP tissue is isolated from systemic inflammation. In contrast, the severe AF phenotype suggests that systemic inflammation interferes with AF health, predisposing discs to herniation as opposed to directly causing NP degeneration. © 2020 American Society for Bone and Mineral Research.

Duhuo jisheng decoction suppresses matrix degradation and apoptosis in human nucleus pulposus cells and ameliorates disc degeneration in a rat model

ETHNOPHARMACOLOGICAL RELEVANCE

The lower back pain (LBP) caused by intervertebral disc (IVD) degeneration brings a heavy burden to society. A classic treatment method of Chinese medicine, fangji-duhuo jisheng decoction (DHJSD), has been effective in the clinical treatment of LBP, although the underlying mechanism remains unknown.

AIM OF THE STUDY

In this work, the main objective was to study the effects of DHJSD on in vitro IVD degeneration of human nucleus pulposus (NP) cells after pressure treatment and on an in vivo interrupted IVD degeneration rat model.

MATERIALS AND METHODS

The effects of DHJSD on the viability of NP cells were detected using Cell Counting Kit-8. RT-qPCR, western blotting, TUNEL assay, transmission electron microscopy, and immunofluorescence staining were performed to explore the molecular mechanism underlying protection against compression-induced matrix degradation and apoptosis in NP cells by DHJSD. Furthermore, the effects of DHJSD on IVD degeneration in a rat IDD model were also determined.

RESULTS

We found that DHJSD increased the viability of NP cells in a concentration- and time-dependent manner. Furthermore, DHJSD significantly reduced compression-induced NP matrix degeneration and apoptosis, activated autophagy, and inhibited the p38/MAPK signaling pathway in NP cells subjected to compression. Autophagy inhibitor 3-MA and p38/MAPK signaling pathway activator anisomycin reversed the beneficial effects of DHJSD in NP cells, indicating that DHJSD protects against IVD degeneration by autophagy activation and P38/MAPK signaling pathway inhibition. Furthermore, DHJSD treatment effectively delayed IVD degeneration in a puncture-induced IDD rat model.

CONCLUSIONS

DHJSD prevents compression-induced matrix degradation and cell apoptosis through regulating autophagy and the P38/MAPK signaling pathway. The mechanism underlying the effects of DHSJD elucidated in this study provides a new direction for LBP treatment.

Arp2/3 inactivation causes intervertebral disc and cartilage degeneration with dysregulated TonEBP-mediated osmoadaptation

Extracellular matrix and osmolarity influence the development and homeostasis of skeletal tissues through Rho GTPase-mediated alteration of the actin cytoskeleton. This study investigated whether the actin-branching Arp2/3 complex, a downstream effector of the Rho GTPases Cdc42 and Rac1, plays a critical role in maintaining the health of matrix-rich and osmotically loaded intervertebral discs and cartilage. Mice with constitutive intervertebral disc- and cartilage-specific deletion of the critical Arp2/3 subunit Arpc2 (Col2-Cre; Arpc2fl/fl) developed chondrodysplasia and spinal defects. Since these mice did not survive to adulthood, we generated mice with inducible Arpc2 deletion in disc and cartilage (Acan-CreERT2; Arpc2fl/fl). Inactivation of Arp2/3 at skeletal maturity resulted in growth plate closure, loss of proteoglycan content in articular cartilage, and degenerative changes in the intervertebral disc at 1 year of age. Chondrocytes with Arpc2 deletion showed compromised cell spreading on both collagen and fibronectin. Pharmacological inhibition of Cdc42 and Arp2/3 prevented the osmoadaptive transcription factor TonEBP/NFAT5 from recruiting cofactors in response to a hyperosmolarity challenge. Together, these findings suggest that Arp2/3 plays a critical role in cartilaginous tissues through the regulation of cell-extracellular matrix interactions and modulation of TonEBP-mediated osmoadaptation.

TonEBP-deficiency accelerates intervertebral disc degeneration underscored by matrix remodeling, cytoskeletal rearrangements, and changes in proinflammatory gene expression

The tonicity-responsive enhancer binding protein (TonEBP) plays an important role in intervertebral disc and axial skeleton embryogenesis. However, the contribution of this osmoregulatory transcription factor in postnatal intervertebral disc homeostasis is not known in vivo. Here, we show for the first time that TonEBP-deficient mice have pronounced age-related degeneration of the intervertebral disc with annular and endplate herniations. Using FTIR-imaging spectroscopy, quantitative immunohistochemistry, and tissue-specific transcriptomic analysis, we provide morphological and molecular evidence that the overall phenotype is driven by a replacement of water-binding proteoglycans with fibrocartilaginous matrix. Whereas TonEBP deficiency in the AF compartment caused tissue fibrosis associated with alterations in actin cytoskeleton and adhesion molecules, predominant changes in pro-inflammatory pathways were seen in the NP compartment of mutants, underscoring disc compartment-specific effects. Additionally, TonEBP-deficient mice presented with compromised trabecular bone properties of vertebrae. These results provide the first in vivo support to the long-held hypothesis that TonEBP is crucial for postnatal homeostasis of the spine and controls a multitude of functions in addition to cellular osmoadaptation.

Nucleus pulposus primary cilia alter their length in response to changes in extracellular osmolarity but do not control TonEBP-mediated osmoregulation

The nucleus pulposus (NP) cells adapt to their physiologically hyperosmotic microenvironment through Tonicity-responsive enhancer binding protein (TonEBP/nuclear factor of activated T-cell5 [NFAT5])-mediated osmoregulation. Primary cilia in different organs serve diverse roles including osmosensing, but its contribution to NP cell osmoadaptive response is unknown. A high percentage of cultured primary NP cells possessed primary cilia that changed length in response to osmotic stimuli. Stable silencing of Intraflagellar Transport 88 (Ift88) or Kinesin Family Member 3 A (Kif3a) to inhibit the formation of primary cilia did not affect hyperosmotic upregulation of TonEBP. While ShKif3a blocked hyperosmotic increase of TonEBP-Transactivation Domain (TAD) activity, overall the knockdown of either gene did not alter the hyperosmotic status of proximal promoter activities and transcription of key TonEBP targets. On the other hand, a small decrease in TonEBP level under hypoosmotic condition was attenuated by Ift88 or Kif3a knockdown. Noteworthy, none of the TonEBP target genes were responsive to hypoosmotic stimulus in control and Ift88 or Kif3a knockdown cells, suggesting the primary role of TonEBP in the hyperosmotic adaptation of NP cells. Similarly, in Kif3a null mouse embryonic fibroblasts (MEFs), the overall TonEBP-dependent hyperosmotic responses were preserved. Unlike NP cells, TonEBP targets were responsive to hypoosmolarity in wild-type MEFs, and these responses remained intact in Kif3a null MEFs. Together, these results suggest that primary cilia are dispensable for TonEBP-dependent osmoadaptive response.

Regulatory T cells protected against abdominal aortic aneurysm by suppression of the COX-2 expression

CD4⁺CD25⁺ regulatory T cells (Tregs) have been shown to protect against the development of abdominal aortic aneurysm (AAA). Cyclooxygenase‐2 (COX‐2), a pro‐inflammatory protein, can convert arachidonic acid into prostaglandins (PGs). The present study was aimed to investigate the effect of Tregs on COX‐2 expression in angiotension II (Ang II)‐induced AAA in ApoE^−/− mice. Tregs were injected via tail vein in every 2 weeks. Ang II was continuously infused by a micropump for 28 days to induce AAA. In vivo, compared with the control group, adoptive transfer of Tregs significantly reduced the incidence of AAA, maximal diameter, and the mRNA and protein expression of COX‐2 in mice. Immunofluorescence showed that Tregs treatment reduced COX‐2 expression both in smooth muscle cells (SMCs) and macrophages in AAA. In vitro, the Western blot analysis showed that Tregs reduced Ang II‐induced COX‐2 expression in macrophages and SMCs. Meanwhile, ELISA showed that Tregs reduced Ang II‐induced prostaglandin E₂ (PGE₂) secretion. Moreover, Tregs increased SMC viability and induced transition of macrophages phenotype from M1 to M2. In conclusion, Tregs treatment dramatically decreased the expression of COX‐2 in vivo and in vitro, suggesting that Tregs could protect against AAA through inhibition of COX‐2. The study may shed light on the immune treatment of AAA.

Osmolarity and calcium regulate connective tissue growth factor (CTGF/CCN2) expression in nucleus pulposus cells

OBJECTIVE

The objective of our study was to verify the hypothesis that the expression of connective tissue growth factor (CTGF/CCN2), a key molecule essential for the maintenance of nucleus pulposus (NP) matrix homeostasis, is regulated by osmolarity and intracellular calcium in NP cells.

METHODS

Gene and protein expression levels of CCN2 were assessed using quantitative real-time PCR and western blot. Transfections and dual luciferase assays were performed to measure the effect of hyperosmolarity, tonicity enhancer binding protein (TonEBP) and Ca²⁺-calcineurin (Cn)-NFAT signaling on CCN2 promoter activity.

RESULTS

Cultured in hyperosmotic media, there was a significant decrease in the levels of CCN2 promoter activity, gene and protein expression in NP cells. The JASPAR database was used to analyze the construction of human CCN2 promoter, we found conserved TonE and NFAT binding sites. We then investigated whether TonEBP controlled CCN2 expression. Forced expression of TonEBP in NP cells showed that TonEBP negatively regulated CCN2 promoter activity, while suppression of TonEBP induced CCN2 promoter activity and expression. We then examined if Ca²⁺-Cn-NFAT signaling participated in the regulation of CCN2 expression. Co-expression of CCN2 reporter with individual NFAT1-4 expression plasmids and/or calcineurin A/B constructs suggested this signaling pathway played a role in the regulation of CCN2expression in NP cells.

CONCLUSIONS

Results of these studies illustrated that the expression of CCN2 in NP cells was regulated by the NFAT family through a signaling pathway network involving both activator (Ca²⁺-Cn-NFAT signaling) and suppressor (Hyperosmolarity-TonEBP) molecules.

The Role of p38 MAPK in Triacylglycerol Accumulation during Apoptosis

Lipids are emerging as key regulators of apoptosis. Specific lipid species are associated with apoptosis with important functional roles, but the understanding of the regulation of these lipid species is still limited. It has been previously shown by our laboratory that polyunsaturated triacylglycerols accumulate and get stored within lipid droplets during apoptosis via activated glycerolipid biosynthesis. In this work, the biochemical mechanisms that result in the activation of glycerolipid biosynthesis and, consequently, triacylglycerol and lipid droplet accumulation during apoptosis are investigated. The transcriptomes of control and apoptotic HCT-116 cells are compared and gene enrichment analysis revealed the upregulation of p38 mitogen-activated protein kinase (MAPK). It is shown that p38 MAPK regulates triacylglycerol biosynthesis through diacylglycerol acyltransferase1 during apoptosis. Perilipin 2 and cytosolic phospholipase A2delta are also shown to be involved in lipid droplet and polyunsaturated triacylglycerol accumulation in this process. Overall, the results provide new insights into the upregulation of glycerolipid synthesis during apoptosis.