Ddit3 suppresses the differentiation of mouse chondroprogenitor cells

DDIT3/CHOP promotes LPS/ATP-induced pyroptosis in osteoblasts via mitophagy inhibition

Inflammatory environments can trigger endoplasmic reticulum (ER) stress and lead to pyroptosis in various tissues and cells, including liver, brain, and immune cells. As a key factor of ER stress, DNA damage-inducible transcript 3 (DDIT3)/CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) is upregulated in osteoblasts during inflammatory stimulation. DDIT3/CHOP may therefore regulate osteoblast pyroptosis in inflammatory conditions. During this investigation, we found that lipopolysaccharides (LPS)/adenosine 5'-triphosphate (ATP) stimulation in vitro induced osteoblasts to undergo pyroptosis, and the expression of DDIT3/CHOP was increased during this process. The overexpression of DDIT3/CHOP further promoted osteoblast pyroptosis as evidenced by the increased expression of the inflammasome NLR family pyrin domain containing 3 (NLRP3) and ratios of caspase-1 p20/caspase-1 and cleaved gasdermin D (GSDMD)/GSDMD. To explore the specific mechanism of this effect, we found through fluorescence imaging and Western blot analysis that LPS/ATP stimulation promoted PTEN-induced kinase 1 (PINK1)/E3 ubiquitin-protein ligase parkin (Parkin)-mediated mitophagy in osteoblasts, and this alteration was suppressed by the DDIT3/CHOP overexpression, resulting in increased ratio of pyroptosis compared with the control groups. The impact of DDIT3/CHOP on pyroptosis in osteoblasts was reversed by the application of carbonyl cyanide 3-chlorophenylhydrazone (CCCP), a specific mitophagy agonist. Therefore, our data demonstrated that DDIT3/CHOP promotes osteoblast pyroptosis by inhibiting PINK1/Parkin-mediated mitophagy in an inflammatory environment.

CDKN1A regulation on chondrogenic differentiation of human chondrocytes in osteoarthritis through single-cell and bulk sequencing analysis

Objective

Chondrocyte death is the hallmark of cartilage degeneration during osteoarthritis (OA). However, the specific pathogenesis of cell death in OA chondrocytes has not been elucidated. This study aims to validate the role of CDKN1A, a key programmed cell death (PCD)-related gene, in chondrogenic differentiation using a combination of single-cell and bulk sequencing approaches.

Design

OA-related RNA-seq data (GSE114007, GSE55235, GSE152805) were downloaded from Gene Expression Omnibus database. PCD-related genes were obtained from GeneCards database. RNA-seq was performed to annotate the cell types in OA and control samples. Differentially expressed genes (DEGs) among those cell types (scRNA-DEGs) were screened. A nomogram of OA was constructed based on the featured genes, and potential drugs targeting the featured genes were predicted. The presence of key genes was confirmed using Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR), Western blot (WB), and immunohistochemistry (IHC). Micromass culture and Alcian blue staining were used to determine the effect of CDKN1A on chondrogenesis.

Results

Six cell types, namely HomC, HTC, RepC, preFC, FC, and RegC, were annotated in scRNA-seq data. Five featured genes (JUN, CDKN1A, HMGB2, DDIT3, and DDIT4) were screened by multiple biological information analysis methods. TAXOTERE had the highest ability to dock with DDIT3. Functional analysis indicated that CDKN1A was enriched in processes related to collagen catabolism and acts as a positive regulator of autophagy. Additionally, CDKN1A was found to be associated with several KEGG pathways, including those involved in acute myeloid leukemia and autoimmune thyroid disease. CDKN1A was confirmed down-regulated in the joint tissues of OA mouse model and OA model cell. Inhibiting the expression of CDKN1A can significantly suppress the differentiation of OA chondrocytes.

Conclusion

Our findings highlight the critical role of CDKN1A in promoting cartilage formation in both in vivo and in vitro and suggest its potential as a therapeutic target for OA treatment.

Identification of aging-related genes in diagnosing osteoarthritis via integrating bioinformatics analysis and machine learning

BACKGROUND

Osteoarthritis (OA) is one of the main causes of pain and disability in the world, it may be caused by many factors. Aging plays a significant role in the onset and progression of OA. However, the mechanisms underlying it remain unknown. Our research aimed to uncover the role of aging-related genes in the progression of OA.

METHODS

In Human OA datasets and aging-related genes were obtained from the GEO database and the HAGR website, respectively. Bioinformatics methods including Gene Ontology (GO), Kyoto Encyclopedia of Genes Genomes (KEGG) pathway enrichment, and Protein-protein interaction (PPI) network analysis were used to analyze differentially expressed aging-related genes (DEARGs) in the normal control group and the OA group. And then weighted gene coexpression network analysis (WGCNA), the least absolute shrinkage and selection operator (LASSO) regression, and the Random Forest (RF) machine learning algorithms were used to find the hub genes.

RESULTS

Four overlapping hub genes: HMGB2, CDKN1A, JUN, and DDIT3 were identified. According to the nomogram model and receiver operating characteristic (ROC) curve analysis, four hub DEARGs had good diagnostic value in distinguishing normal from OA. Furthermore, the qRT-PCR test demonstrated that HMGB2, CDKN1A, JUN, and DDIT3 mRNA expression levels were lower in OA group than in normal group.

CONCLUSION

Finally, these four-hub aging-related genes may help us understand the underlying mechanism of aging in osteoarthritis and could be used as possible diagnostic and therapeutic targets.

DDIT3 regulates key enzymes in the methionine cycle and flux during embryonic development

One-carbon metabolism is a key metabolic network that integrates nutritional signals with embryonic development. However, the response of one-carbon metabolism to methionine status and the regulatory mechanisms are poorly understood. Herein, we found that methionine supplementation during pregnancy significantly increased fetal number and average fetal weight. In addition, methionine modulated one-carbon metabolism primarily through 2 metabolic enzymes, cystathionine β-synthase (CBS) and methionine adenosyltransferase 2A (MAT2A), which were significantly increased in fetal liver tissues and porcine trophoblast (pTr) cells in response to proper methionine supplementation. CBS and MAT2A overexpression enhanced the DNA synthesis in pTr cells. More importantly, we identified a transcription factor, DNA damage-inducible transcript 3 (DDIT3), that was the primary regulator of CBS and MAT2A, which bound directly to promoters and negatively regulated the expression of CBS and MAT2A. Taken together, our findings identified that DDIT3 targeting CBS and MAT2A was a novel regulatory pathway that mediated cellular one-carbon metabolism in response to methionine signal and provided promising targets to improve pregnancy health.

DDIT3/CHOP mediates the inhibitory effect of ER stress on chondrocyte differentiation by AMPKα-SIRT1 pathway

Endoplasmic reticulum (ER) stress is an evolutionarily conserved cellular stress response related to multiple diseases, including temporomandibular joint (TMJ) cartilage-related diseases. Recent studies have indicated that DDIT3/CHOP (a downstream transcription factor of ER stress) is an important effector in mediating ER stress to inhibit chondrogenesis. However, the underlying mechanism by which DDIT3 regulates chondrogenesis remains unclear. In this study, tunicamycin (an ER stress agonist)-induced ER stress inhibited chondrocyte differentiation and matrix synthesis in vitro and led to an osteoarthritis-like phenotype in mouse TMJ cartilage. Meanwhile, DDIT3 expression in chondrocytes was robustly upregulated. Loss-of-function experiments validated the inhibiting effect of DDIT3 on chondrocyte differentiation and matrix synthesis. Mechanistically, the inhibiting effect was attributed to the direct and indirect regulatory effect of DDIT3 on SIRT1 (sirtuin1, silent mating type information regulation protein type 1, a member of NAD+ dependent class III histone deacetylases). On one hand, DDIT3 directly promoted the transcription of SIRT1. On the other hand, DDIT3 indirectly increased the expression of SIRT1 by promoting AMPKα phosphorylation and activation. Furthermore, activation of AMPKα or SIRT1 with the corresponding agonist AICAR or resveratrol in the DDIT3-knockdown cells partially restored the inhibiting effect of DDIT3 on chondrocyte differentiation and matrix synthesis. Collectively, these novel findings indicate that DDIT3 regulates the inhibitory effect of ER stress on chondrocyte differentiation and matrix synthesis partially via the AMPKα-SIRT1 pathway. A thorough understanding of ER stress in regulating chondrocyte homeostasis and its role in the onset of osteoarthritis may be promising to develop therapeutic targets and prevent condyle cartilage destruction.

USP7 Attenuates Endoplasmic Reticulum Stress and NF-κB Signaling to Modulate Chondrocyte Proliferation, Apoptosis, and Inflammatory Response under Inflammation

The purpose of this research was to observe the functions and mechanisms of ubiquitin-specific peptidase 7 (USP7) on chondrocytes under tumor necrosis factor alpha- (TNF-α-) induced inflammation. Knee osteoarthritis (OA) models of mice were constructed by anterior cruciate ligament transection. The knee joint of mice was observed by histological staining, and the expression of USP7 was measured by immunohistochemistry staining. After knocking down or inhibiting USP7, chondrocyte proliferation was measured by histological staining and the CCK-8 assay; apoptosis was measured by western blot, flow cytometry, Caspase-3 activity, and TUNEL staining; and inflammatory response was measured by qRT-PCR and ELISA. The 4-phenylbutyric acid (4-PBA), siRNA of CHOP (si-CHOP), and QNZ were used to verify the signaling pathways. It was found that USP7 was reduced in the knee joint cartilage of OA mice. The knockdown of USP7 or its inhibitor decreased chondrocyte proliferation and accelerated apoptosis and inflammatory response under inflammation. The USP7 inhibitor exacerbated cartilage destruction in mice with OA. The knockdown of USP7 or its inhibitor activated the BiP-eIF2α-ATF4-CHOP signaling of endoplasmic reticulum stress (ERS) and NF-κB/p65 signaling. 4-PBA, si-CHOP, and QNZ partly reversed chondrocyte proliferation, apoptosis, and inflammatory response caused by USP7 knockdown. In conclusion, through inhibiting the BiP-eIF2α-ATF4-CHOP signaling of ERS and NF-κB/p65 signaling, USP7 promotes chondrocyte proliferation and suppresses the apoptosis and inflammatory response under TNF-α-induced inflammation.

DDIT3/CHOP promotes autophagy in chondrocytes via SIRT1-AKT pathway

Endoplasmic reticulum (ER) stress can initiate autophagy via unfolded protein response (UPR). As a key downstream gene of UPR, DDIT3/CHOP is expressed in chondrocytes. However, the regulation mechanism of DDIT3/CHOP on autophagy in chondrocytes remains unclear. In this study, the expression levels of autophagic markers Beclin1 and LC3B were found to decrease while p62 increase in the tibial growth plate and costal primary chondrocytes from DDIT3/CHOP KO mice. In vitro, overexpressing DDIT3/CHOP induced autophagy in ATDC5 chondrocytes, displaying an elevated immunofluorescence signal of LC3B and elevated numbers of autophagosomes and autolysosomes. Analysis of the gain- and loss-of-function indicated that the protein level of Beclin1 and the ratio of LC3BII/I increased in DDIT3/CHOP overexpression cells, whereas decreased in DDIT3/CHOP knockdown cells. The decreased level of p62 and additional accumulation of LC3BII caused by chloroquine (CQ) further indicated that DDIT3/CHOP enhanced autophagic flux. Mechanistically, we found that DDIT3/CHOP binds directly to the promoter of SIRT1 to promote its expression by CHIP, qRT-PCR, and Western blot analysis. In addition, SIRT1 enhanced autophagic activity in ATDC5 cells, and inhibition or activation of SIRT1 partially reversed the effect of overexpressing or downregulating DDIT3/CHOP on autophagy. Furthermore, AKT signaling was found to be responsible for DDIT3/CHOP-regulated autophagy in ATDC5 cells. SIRT1 knockdown reversed the effect of DDIT3/CHOP overexpression on AKT signaling. In conclusion, our data clarifies that DDIT3/CHOP promotes autophagy in ATDC5 chondrocytes through the SIRT1-AKT pathway. These results were also confirmed in the primary chondrocytes.

Gene expression of type II collagen is regulated by direct interaction with Kruppel-like factor 4 and AT-rich interactive domain 5B

We have previously found and characterized two pairs of enhancer elements, E1 and E2, in the type II collagen alpha 1 chain (COL2A1) gene. Subsequent studies have suggested that these enhancers function differently in the regulation of gene expression. For example, histone deacetylase 10 modifies only the E2 enhancer region to affect gene expression. Therefore, in this study, we aimed to clarify the transcriptional complex formed at each enhancer region by identifying transcription factors that specifically bind to each enhancer element. To this end, we used chondrocytic cell lines established using our unique silent reporter system and overexpressed candidate transcription factors in these cells. We found two transcription factors, other than the SOX trio, that directly bound to COL2A1 and regulated its expression. The first was Kruppel-like factor-4 (KLF4), which bound to the promoter proximal region, and the second was AT-rich interactive domain 5B (ARID5B) which bound to the E1 enhancer element. Further studies are needed to identify factors that specifically bind to the E2 enhancer element. In any case, our findings provide an important insight into the molecular mechanisms underlying the regulation of COL2A1. In this paper, we reevaluated the previous analysis of transcription factors involved in the regulation of COL2A1 expression.

DDIT3 regulates cementoblast mineralization by isocitrate dehydrogenase 1 through nuclear factor-κB pathway

DDIT3 is of great importance in endoplasmic reticulum stress and is involved in many inflammatory diseases and mineralization processes. The cementum protects teeth from periodontitis and provides attachment for Sharpey's fibers of the periodontal ligament. However, the effect of DDIT3 on cementoblast differentiation remains largely unknown. In this study, we found that DDIT3 was suppressed during cementoblast differentiation. Knockdown of DDIT3 increased the messenger RNA (mRNA) and protein levels of several key osteogenic markers in vitro, including alkaline phosphatase, runt-related transcription factor 2, and osteocalcin (OCN). In addition, isocitrate dehydrogenase 1 (IDH1) was increased during cementoblast differentiation, and knockdown of DDIT3 increased the protein and mRNA levels of IDH1. Furthermore, inhibition of IDH1 could partially reduce the effect of DDIT3 on cementoblast differentiation. The DDIT3 knockdown activated nuclear factor-κB (NF-κB) transcriptional activity and upregulated the expression of p-p65 and p-IκBα. The increased osteogenic differentiation ability and IDH1 expression, as induced by the DDIT3 knockdown, could be partially turned over by the addition of NF-κB inhibitor BAY 11-7082. Overall, our data clarified that DDIT3 suppresses cementoblast differentiation through IDH1, via the NF-κB pathway.

The transcriptional coactivator YAP1 is overexpressed in osteoarthritis and promotes its progression by interacting with Beclin-1

Osteoarthritis (OA) constitutes the most common disease of degenerative joints, with chondrocytes playing an important role in disease progression. However, the underlying pathobiological mechanisms have not been fully characterized. In this study, we investigated the role of Yes-associated protein 1 (YAP1)-regulated autophagy in chondrocyte proliferation, apoptosis, and differentiation. The data showed that YAP1, a transcriptional coactivator, was overexpressed in OA tissues from a murine model of OA, as analyzed by real time PCR and western blot. Overexpression of YAP1 significantly suppressed ATDC5 chondrogenic cell proliferation and decreased the expression of differentiation-related genes including Runx2, osteocalcin, and collagen I, and elevated cell apoptosis, whereas these cellular processes were reversed by knockdown of YAP1. Immunofluorescence analysis demonstrated that YAP1 co-localized with the autophagy regulator beclin1. Co-immunoprecipitation experiments indicated that this interaction was enhanced in OA tissues. In contrast, YAP1 lacking the internal WW domains failed to interact with beclin1 and was unable to inhibit beclin1 ubiquitination. This resulted in upregulated autophagy, which significantly improved OA by increasing chondrocyte proliferation and differentiation. Notably, YAP1 expression was significantly downregulated by various anti-OA drugs. Finally, the Yap1 promoter was activated by transcriptional factors AP2α and SP1, whereas its 3'UTR was targeted by miR-5624-5p, miR-33-3p, and miR-6918-5p. In conclusion, inhibition of YAP1 could facilitate beclin1-regulated autophagy in OA, suggesting a potential therapeutic approach to combat OA.

Effects of connective tissue growth factor (CTGF/CCN2) on condylar chondrocyte proliferation, migration, maturation, differentiation and signalling pathway

CCN2, also known as connective tissue growth factor (CTGF), is a 38 kDa cysteine-rich extracellular matrix protein that regulates a sequence of cellular functions and participates in multiple complex biological processes, such as chondrogenesis and osteogenesis. In the present study, we provided the first evidence describing the physiological role of CCN2 in condylar chondrocyte proliferation, migration, maturation and differentiation. CCN2 was widely expressed throughout the whole layers of condylar cartilage and predominantly distributed in the proliferative zone. Recombinant CCN2 promoted the proliferation, migration, proteoglycan synthesis and differentiation capacity of isolated condylar chondrocytes. The stimulatory effect of CCN2 on chondrocyte proliferation was associated with the activation of phosphatidylinositol 3-kinase/Akt signalling pathway. The blocking of this pathway by its inhibitor LY294002 impaired the proliferative effect of CCN2 on chondrocytes. These results suggested a novel physiological role of CCN2 in the development of condylar cartilage.

miR-1271 inhibits ERα expression and confers letrozole resistance in breast cancer

Attenuation of estrogen receptor α (ERα) expression via unknown mechanism(s) is a hallmark of endocrine-resistant breast cancer (BCa) progression. Here, we report that miR-1271 was significantly down-regulated in letrozole-resistant BCa tissues and in letrozole-resistant BCa cells. miR-1271 directly targeted the chromatin of DNA damage-inducible transcript 3 (DDIT3) gene. miR-1271 expression level was inversely correlated to DDIT3 mRNA level in BCa biopsies. Form a mechanistic standpoint, reintroduction of exogenous miR-1271 could effectively restore ERα level via inhibiting DDIT3 expression, thereby potentiating letrozole sensitivity in BCa cells. Moreover, DDIT3 deregulation promoted letrozole-resistance by acting as a potent corepressor of ESR1 transcription. Taken together, we have identified that disruption of the miR-1271/DDIT3/ERα cascade plays a causative role in the pathogenesis of letrozole resistance in BCa.