Myeloid Krüppel-Like Factor 2 Critically Regulates K/BxN Serum-Induced Arthritis

Regulation of differentiation and generation of osteoclasts in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA), which affects nearly 1% of the world's population, is a debilitating autoimmune disease. Bone erosion caused by periarticular osteopenia and synovial pannus formation is the most destructive pathological changes of RA, also leads to joint deformity and loss of function,and ultimately affects the quality of life of patients. Osteoclasts (OCs) are the only known bone resorption cells and their abnormal differentiation and production play an important role in the occurrence and development of RA bone destruction; this remains the main culprit behind RA.

METHOD

Based on the latest published literature and research progress at home and abroad, this paper reviews the abnormal regulation mechanism of OC generation and differentiation in RA and the possible targeted therapy.

RESULT

OC-mediated bone destruction is achieved through the regulation of a variety of cytokines and cell-to-cell interactions, including gene transcription, epigenetics and environmental factors. At present, most methods for the treatment of RA are based on the regulation of inflammation, the inhibition of bone injury and joint deformities remains unexplored.

DISCUSSION

This article will review the mechanism of abnormal differentiation of OC in RA, and summarise the current treatment oftargeting cytokines in the process of OC generation and differentiation to reduce bone destruction in patients with RA, which isexpected to become a valuable treatment choice to inhibit bone destruction in RA.

Heterozygous premature termination in zinc-finger domain of Krüppel-like factor 2 gene associates with dysregulated immunity

Krüppel-like factor 2 (KLF2) is a transcription factor with significant roles in development, maturation, differentiation, and proliferation of several cell types. In immune cells, KLF2 regulates maturation and trafficking of lymphocytes and monocytes. KLF2 participates in regulation of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Although pulmonary arterial hypertension (PAH) related to KLF2 genetic variant has been suggested, genetic role of KLF2 associated with immune dysregulation has not been described. We identified a family whose members suffered from lymphopenia, autoimmunity, and malignancy. Whole exome sequencing revealed a KLF2 p.(Glu318Argfs*87) mutation disrupting the highly conserved zinc finger domain. We show a reduced amount of KLF2 protein, defective nuclear localization and altered protein-protein interactome. The phenotypically variable positive cases presented with B and T cell lymphopenia and abnormalities in B and T cell maturation including low naive T cell counts and low CD27+IgD-IgM- switched memory B cells. KLF2 target gene (CD62L) expression was affected. Although the percentage of (CD25+FOXP3+, CD25+CD127-) regulatory T cells (Treg) was high, the naive Treg cells (CD45RA+) were absent. Serum IgG1 levels were low and findings in one case were consistent with common variable immunodeficiency (CVID). Transcription of NF-κβ pathway genes and p65/RelA phosphorylation were not significantly affected. Inflammasome activity, transcription of genes related with JAK/STAT pathway and interferon signature were also comparable to controls. Evidence of PAH was not found. In conclusion, KLF2 variant may be associated with familial immune dysregulation. Although the KLF2 deficient family members in our study suffered from lymphopenia, autoimmunity or malignancy, additional study cohorts are required to confirm our observations.

Epigallocatechin-3-gallate inhibits osteoclastic differentiation by modulating mitophagy and mitochondrial functions

A natural plant product, epigallocatechin-3-gallate (EGCG), was evaluated for its effectiveness in the regulation of osteoclastogenesis. We found that EGCG inhibited the osteoclast (OC) differentiation in vitro, and in primary bone marrow cells in a dose-dependent manner. Quantitative RT-PCR studies showed that the EGCG reduced the expression of OC differentiation markers. DCFDA, MitoSOX, and JC-1 staining revealed that the EGCG attenuated the reactive oxygen species (ROS), and mitochondrial membrane potential; and flux analysis corroborated the effect of EGCG. We further found that the EGCG inhibited mRNA and protein expressions of mitophagy-related molecules. We confirmed that the OC differentiation was inhibited by EGCG by modulating mitophagy through AKT and p38MAPK pathways. Furthermore, in silico analysis revealed that the binding of RANK and RANKL was blocked by EGCG. Overall, we defined the mechanisms of osteoclastogenesis during arthritis for developing a new therapy using a natural compound besides the existing therapeutics.

Polyphenolic Compounds Inhibit Osteoclast Differentiation While Reducing Autophagy through Limiting ROS and the Mitochondrial Membrane Potential

Polyphenolic compounds are a diverse group of natural compounds that interact with various cellular proteins responsible for cell survival, differentiation, and apoptosis. However, it is yet to be established how these compounds interact in myeloid cells during their differentiation and the molecular and intracellular mechanisms involved. Osteoclasts are multinucleated cells that originate from myeloid cells. They resorb cartilage and bone, maintain bone homeostasis, and can cause pathogenesis. Autophagy is a cellular mechanism that is responsible for the degradation of damaged proteins and organelles within cells and helps maintain intracellular homeostasis. Imbalances in autophagy cause various pathological disorders. The current study investigated the role of several polyphenolic compounds, including tannic acid (TA), gallic acid (GA), and ellagic acid (EA) in the regulation of osteoclast differentiation of myeloid cells. We demonstrated that polyphenolic compounds inhibit osteoclast differentiation in a dose-dependent manner. Quantitative real-time PCR, immunocytochemistry, and western blotting revealed that osteoclast markers, such as NFATc1, Cathepsin K, and TRAP were inhibited after the addition of polyphenolic compounds during osteoclast differentiation. In our investigation into the molecular mechanisms, we found that the addition of polyphenolic compounds reduced the number of autophagic vesicles and the levels of LC3B, BECN1, ATG5, and ATG7 molecules through the inactivation of Akt, thus inhibiting the autophagy process. In addition, we found that by decreasing intracellular calcium and decreasing ROS levels, along with decreasing mitochondrial membrane potential, polyphenolic compounds inhibit osteoclast differentiation. Together, this study provides evidence that polyphenolic compounds inhibit osteoclast differentiation by reducing ROS production, autophagy, intracellular Ca²⁺ level, and mitochondrial membrane potentials.

Ferutinin induces osteoblast differentiation of DPSCs via induction of KLF2 and autophagy/mitophagy

Osteoblast differentiation is critically reduced in various bone-related pathogenesis, including arthritis and osteoporosis. For future development of effective regenerative therapeutics, herein, we reveal the involved molecular mechanisms of a phytoestrogen, ferutinin-induced initiation of osteoblast differentiation from dental pulp-derived stem cell (DPSC). We demonstrate the significantly increased expression level of a transcription factor, Kruppel-like factor 2 (KLF2) along with autophagy-related molecules in DPSCs after induction with ferutinin. The loss-of-function and the gain-of-function approaches of KLF2 confirmed that the ferutinin-induced KLF2 modulated autophagic and OB differentiation-related molecules. Further, knockdown of the autophagic molecule (ATG7 or BECN1) from DPSC resulted not only in a decreased level of KLF2 but also in the reduced levels of OB differentiation-related molecules. Moreover, mitochondrial membrane potential-related molecules were increased and induction of mitophagy was observed in DPSCs after the addition of ferutinin. The reduction of mitochondrial as well as total ROS generations; and induction of intracellular Ca²⁺ production were also observed in ferutinin-treated DPSCs. To test the mitochondrial respiration in DPSCs, we found that the cells treated with ferutinin showed a reduced extracellular acidification rate (ECAR) than that of their vehicle-treated counterparts. Furthermore, mechanistically, chromatin immunoprecipitation (ChIP) analysis revealed that the addition of ferutinin in DPSCs not only induced the level of KLF2, but also induced the transcriptionally active epigenetic marks (H3K27Ac and H3K4me3) on the promoter region of the autophagic molecule ATG7. These results provide strong evidence that ferutinin stimulates OB differentiation via induction of KLF2-mediated autophagy/mitophagy.

SETD2-mediated epigenetic regulation of noncanonical Wnt5A during osteoclastogenesis

To define the role of SETD2 in the WNT5a signaling in the context of osteoclastogenesis, we exploited two different models: in vitro osteoclast differentiation, and K/BxN serum-induced arthritis model. We found that SETD2 and WNT5a were upregulated during osteoclast differentiation and after induction of arthritis. Using gain- and loss-of-function approaches in the myeloid cell, we confirmed that SETD2 regulated the osteoclast markers, and WNT5a via modulating active histone marks by enriching H3K36me3, and by reducing repressive H3K27me3 mark. Additionally, during osteoclastic differentiation, the transcription of Wnt5a was also associated with the active histone H3K9 and H4K8 acetylations. Mechanistically, SETD2 directed induction of NF-κβ expression facilitated the recruitment of H3K9Ac and H4K8Ac around the TSS region of the Wnt5a gene, thereby, assisting osteoclast differentiation. Together these findings for the first time revealed that SETD2 mediated epigenetic regulation of Wnt5a plays a critical role in osteoclastogenesis and induced arthritis. Model for the Role of SETD2 dependent regulation of osteoclastic differentiation. A In monocyte cells SETD2-dependent H3K36 trimethylation help to create open chromatin region along with active enhancer mark, H3K27Ac. This chromatin state facilitated the loss of a suppressive H3K27me3 mark. B Additionally, SETD2 mediated induction of NF-κβ expression leads to the recruitment of histone acetyl transferases, P300/PCAF, to the Wnt5a gene and establish H3K9Ac and H4K8Ac marks. Along with other activation marks, these acetylation marks help in Wnt5a transcription which leads to osteoclastogenesis.

Dental pulp-derived stem cells inhibit osteoclast differentiation by secreting osteoprotegerin and deactivating AKT signalling in myeloid cells

Osteoclasts (OCs) differentiate from the monocyte/macrophage lineage, critically regulate bone resorption and remodelling in both homeostasis and pathology. Various immune and non‐immune cells help initiating activation of myeloid cells for differentiation, whereas hyper‐activation leads to pathogenesis, and mechanisms are yet to be completely understood. Herein, we show the efficacy of dental pulp–derived stem cells (DPSCs) in limiting RAW 264.7 cell differentiation and underlying molecular mechanism, which has the potential for future therapeutic application in bone‐related disorders. We found that DPSCs inhibit induced OC differentiation of RAW 264.7 cells when co‐cultured in a contact‐free system. DPSCs reduced expression of key OC markers, such as NFATc1, cathepsin K, TRAP, RANK and MMP‐9 assessed by quantitative RT‐PCR, Western blotting and immunofluorescence detection methods. Furthermore, quantitative RT‐PCR analysis revealed that DPSCs mediated M2 polarization of RAW 264.7 cells. To define molecular mechanisms, we found that osteoprotegerin (OPG), an OC inhibitory factor, was up‐regulated in RAW 264.7 cells in the presence of DPSCs. Moreover, DPSCs also constitutively secrete OPG that contributed in limiting OC differentiation. Finally, the addition of recombinant OPG inhibited OC differentiation in a dose‐dependent manner by reducing the expression of OC differentiation markers, NFATc1, cathepsin K, TRAP, RANK and MMP9 in RAW 264.7 cells. RNAKL and M‐CSF phosphorylate AKT and activate PI3K‐AKT signalling pathway during osteoclast differentiation. We further confirmed that OPG‐mediated inhibition of the downstream activation of PI3K‐AKT signalling pathway was similar to the DPSC co‐culture–mediated inhibition of OC differentiation. This study provides novel evidence of DPSC‐mediated inhibition of osteoclastogenesis mechanisms.

Role of KLF2: New insight in inflammatory acne pathogenesis

BACKGROUND

Acne is an inflammatory skin condition of pilosebaceous unit. Its pathogenesis is multifactorial with a central role of inflammatory and pro-inflammatory cytokines mediators. Downregulated Kruppel-like factor 2 (KLF2) leads to rapid secretion of many cytokines that are involved in acne pathogenesis.

AIMS

This study aimed at evaluating the level of KLF2 mRNA, clarifying its role in acne pathogenesis and its relation to acne lesion type, degree of severity, and outcome.

PATIENTS AND METHODS

The level of KLF2 mRNA was measured in 100 patients with acne and 50 age- and sex-matched healthy controls by using quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

The value of KLF2 mRNA was lower in acne patients than control group (P < .001), being lowest in inflammatory acne group (grades III, IV, and V) than noninflammatory acne group (grades I and II) and highest in the control group (P < .001). KLF2 mRNA was decreased significantly with increased acne severity grade (P < .001). KLF2 mRNA was lower in cases healed by scars than those healed by postinflammatory hyperpigmentation.

CONCLUSIONS

Decreased serum level of KLF2 is not only a claimed for AV pathogenesis but also a predictor for degree of acne severity and outcome.

KLF2 regulates dental pulp-derived stem cell differentiation through the induction of mitophagy and altering mitochondrial metabolism

To define the regulatory role of Kruppel-like factor 2 (KLF2) during osteoblast (OB) differentiation of dental pulp-derived stem cell (DPSC)s, herein, we show that the levels of KLF2 and autophagy-related molecules were significantly increased in differentiated cells. Gain-of-function and loss-of-function approaches of KLF2 confirmed that KLF2 modulated autophagic and OB differentiation-related molecules. In addition, knockdown of the autophagic molecule (ATG7 or BECN1) in DPSCs resulted in reduced levels of KLF2 and OB differentiation-related molecules. Conversely, the induction of autophagy increased levels of KLF2 and OB differentiation-related molecules. Moreover, OB differentiation induced mitophagy and mitochondrial membrane potential-related molecules. In addition, OB differentiation reduced the generation of total and mitochondrial ROS productions and induced intracellular Ca²⁺ production. Measurements of glycolysis and oxidative phosphorylation simultaneously in live cells revealed that OB differentiation decreased the oxygen consumption rate, which is an indicator of mitochondrial respiration and reduced the level of ATP production. Furthermore, flux analysis also revealed that OB differentiation increased the extracellular acidification rate (ECAR) in the non-glycolytic acidification, and the glycolytic capacity conditions, increasing the lactate production and reducing the metabolic activity of the cells. Thus, a metabolic shift from mitochondrial respiration to the glycolytic pathway was observed during OB differentiation. Finally, chromatin immunoprecipitation (ChIP) analysis confirmed that the KLF2 and active epigenetic marks (H3K27Ac and H3K4me3) were upregulated in the promoter region of ATG7 during OB differentiation. These results provide evidence that the mitophagy process is important during OB differentiation, and KLF2 critically regulates it.

Transcriptional Regulation of Osteoclastogenesis: The Emerging Role of KLF2

Dysregulation of osteoclastic differentiation and its activity is a hallmark of various musculoskeletal disease states. In this review, the complex molecular factors underlying osteoclastic differentiation and function are evaluated. The emerging role of KLF2 in regulation of osteoclastic differentiation is examined, specifically in the context of rheumatoid arthritis in which it has been most extensively studied among the musculoskeletal diseases. The therapies that exist to manage diseases associated with osteoclastogenesis are numerous and diverse. They are varied in their mechanisms of action and in the outcomes they produce. For this review, therapies targeting osteoclasts will be emphasized, though it should be noted that many therapies exist which bolster the action of osteoblasts. A new targeted molecular approach is under investigation for the future potential therapeutic development of rheumatoid arthritis.