DNA methylation and FoxO3a regulate PHLPP1 expression in chondrocytes

RNA binding protein PUM2 promotes IL-1β-induced apoptosis of chondrocytes via regulating FOXO3 expression

Objective

RNA-binding proteins (RBPs) have been recently proven to be involved in the pathogenesis of several diseases. However, few studies elaborated RBPs in regulating osteoarthritis. This study aims to define the function and mechanism of RBPs-PUM2 in chondrocyte apoptosis during osteoarthritis.

Methods

Cartilage tissue samples and human juvenile chondrocyte cell line C28/I2 were collected for further study. PUM2 expression in the human tissues and cells was determined using qRT-PCR. Chondrocyte viability and apoptosis were determined by MTT and flow cytometry. ROS generation was determined by flow cytometry. The regulation of PUM2 on FOXO3 translation was evaluated by RNA immunoprecipitation, RNA pull-down, and Luciferase gene reporter analysis.

Results

PUM2 is upregulated in both cartilage tissue of osteoarthritis patients and IL-1β-stimulated chondrocytes. PUM2 overexpression reduces cell viability and promotes cell apoptosis and ROS generation of chondrocytes. PUM2 silencing increases cell viability and ameliorates cell apoptosis as well as ROS generation in chondrocytes induced by IL-1β. PUM2 inhibits FOXO3 expression via binding its mRNA 3'-UTR. PUM2 forms a signaling axis with FOXO3 in IL-1β induced chondrocyte damage.

Conclusion

PUM2 is upregulated in cartilage tissue of osteoarthritis and positively regulates chondrocytes apoptosis through controlling FOXO3 protein expression.

On the PHLPPside: Emerging roles of PHLPP phosphatases in the heart

PH domain leucine-rich repeat protein phosphatase (PHLPP) is a family of enzymes made up of two isoforms (PHLPP1 and PHLPP2), whose actions modulate intracellular activity via the dephosphorylation of specific serine/threonine (Ser/Thr) residues on proteins such as Akt. Recent data generated in our lab, supported by findings from others, implicates the divergent roles of PHLPP1 and PHLPP2 in maintaining cellular homeostasis since dysregulation of these enzymes has been linked to various pathological states including cardiovascular disease, diabetes, ischemia/reperfusion injury, musculoskeletal disease, and cancer. Therefore, development of therapies to modulate specific isoforms of PHLPP could prove to be therapeutically beneficial in several diseases especially those targeting the cardiovascular system. This review is intended to provide a comprehensive summary of current literature detailing the role of the PHLPP isoforms in the development and progression of heart disease.

The umbilical cord mesenchymal stem cell-derived exosomal lncRNA H19 improves osteochondral activity through miR-29b-3p/FoxO3 axis

BACKGROUND

Our previous study revealed that the exosomal lncRNA H19 derived from umbilical cord mesenchymal stem cells (UMSCs) plays a pivotal role in osteochondral regeneration. In this study, we investigated whether the exosomal lncRNA H19 could act as a competing endogenous RNA (ceRNA) to potentiate osteochondral activity in chondrocytes.

METHODS

Dual-luciferase reporter assay, RNA pull-down, RNA immunoprecipitation (RIP), and fluorescence in situ hybridization (FISH) were carried to verify the interaction between miR-29b-3p and both lncRNA H19 and the target mRNA FoxO3. Chondrocytes were treated with UMSC-derived exosomes, which highly expressing lncRNA H19 expression, followed by apoptosis, migration, senescence, and matrix secretion assessments. An in vivo SD rat cartilage defect model was carried out to explore the role and mechanism of lncRNA H19/miR-29b-3p.

RESULTS

UMSCs were successfully identified, and exosomes were successfully extracted. Exosomes exhibited the ability to transfer lncRNA H19 to chondrocytes. Mechanistically, exosomal lncRNA H19 potentiated osteochondral activity by acting as a competing endogenous sponge of miR-29b-3p, and miR-29b-3p directly targeted FoxO3. Intra-articular injection of exosomes overexpressing lncRNA H19 could promote sustained cartilage repair; however, this effect could be undermined by miR-29b-3p agomir.

CONCLUSIONS

Our study revealed a significant role in the development of strategies against cartilage defects for UMSC-derived exosomes that overexpress lncRNA H19. Exosomal H19 was found to promote chondrocyte migration, matrix secretion, apoptosis suppression, as well as senescence suppression, both in vitro and in vivo. The specific mechanism lies in the fact that exosomal H19 acts as a ceRNA against miR-29b-3p to upregulate FoxO3 in chondrocytes.

Hdac3 deletion in myeloid progenitor cells enhances bone healing in females and limits osteoclast fusion via Pmepa1

Previous studies examining the role of the histone deacetylase Hdac3 within myeloid cells demonstrated that Hdac3 promotes M2 activation and tissue healing in inflammatory conditions. Since myeloid lineage cells are required for proper bone formation and regeneration, in this study we examined the functions of Hdac3 during bone healing. Conditional deletion of Hdac3 within myeloid progenitors accelerates healing of cortical bone defects. Moreover, reduced osteoclast numbers within the defect site are correlated with Hdac3 suppression. Ex vivo osteoclastogenesis assays further demonstrate that Hdac3 deficiency limits osteoclastogenesis, the number of nuclei per cell and bone resorption, suggesting a defect in cell fusion. High throughput RNA sequencing identified the transmembrane protein Pmepa1 as a differentially expressed gene within osteoclast progenitor cells. Knockdown of Pmepa1 partially restores defects in osteoclastogenesis induced by Hdac3 deficiency. These results show that Hdac3 is required for optimal bone healing and osteoclast fusion, potentially via its regulation of Pmepa1 expression.

Genome-Wide Occupancy Profiling Reveals Critical Roles of FoxO1 in Regulating Extracellular Matrix and Circadian Rhythm Genes in Human Chondrocytes

OBJECTIVE

Osteoarthritis (OA) is the most common age-related joint disease. With aging and in OA, the expression of FoxO transcription factors is reduced, diminishing their chondroprotective actions. In order to elucidate the molecular mechanisms by which FoxO1 protects chondrocytes, we sought to identify the genome-wide occupancy profile of FoxO1.

METHODS

We performed FoxO1 chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-Seq) on human primary chondrocytes. ChIP-Seq data were integrated with RNA sequencing (RNA-Seq) data sets. Bioinformatics results were confirmed in primary chondrocytes that were treated with a FoxO1 inhibitor.

RESULTS

Analysis of FoxO1 ChIP-Seq on human primary chondrocytes showed that pathways implicated in OA pathogenesis are mainly regulated by FoxO1 binding to tissue-specific enhancers with suboptimal binding sites (20% of the peaks), while more ubiquitous FoxO1 pathways are regulated at the promoter level through interaction with its canonical binding motif (7% of the peaks). Integrating FoxO1 occupancy data with RNA-Seq data comparing OA and healthy human cartilage revealed 428 putative FoxO1 target genes that are dysregulated in OA. Pathway analysis showed enrichment for genes belonging to the senescence pathway (logP = -6.73), extracellular matrix (ECM) pathway (logP = -12.97), and circadian clock pathway (logP = -6.30), which suggests that FoxO1 dysregulation plays an important role in their abnormal expression in OA. Using an inhibitor of FoxO1, we confirmed that FoxO1 regulates these pathways in cultured human chondrocytes.

CONCLUSION

FoxO1 regulates ubiquitous and cartilage-specific genes in chondrocytes by using different mechanisms. The FoxO1 transcriptional network is a key player in regulating homeostasis, ECM, and circadian clock genes and plays an important role in the abnormal expression of these pathways observed in OA pathogenesis.