The role of CDK8 in mesenchymal stem cells in controlling osteoclastogenesis and bone homeostasis

Knockout of cyclin-dependent kinases 8 and 19 leads to depletion of cyclin C and suppresses spermatogenesis and male fertility in mice

CDK8 and CDK19 paralogs are regulatory kinases associated with the transcriptional Mediator complex. We have generated mice with the systemic inducible Cdk8 knockout on the background of Cdk19 constitutive knockout. Cdk8/19 double knockout (iDKO) males, but not single Cdk8 or Cdk19 KO, had an atrophic reproductive system and were infertile. The iDKO males lacked postmeiotic spermatids and spermatocytes after meiosis I pachytene. Testosterone levels were decreased whereas the amounts of the luteinizing hormone were unchanged. Single-cell RNA sequencing showed marked differences in the expression of steroidogenic genes (such as Cyp17a1, Star, and Fads) in Leydig cells concomitant with alterations in Sertoli cells and spermatocytes, and were likely associated with an impaired synthesis of steroids. Star and Fads were also downregulated in cultured Leydig cells after iDKO. The treatment of primary Leydig cell culture with a CDK8/19 inhibitor did not induce the same changes in gene expression as iDKO, and a prolonged treatment of mice with a CDK8/19 inhibitor did not affect the size of testes. iDKO, in contrast to the single knockouts or treatment with a CDK8/19 kinase inhibitor, led to depletion of cyclin C (CCNC), the binding partner of CDK8/19 that has been implicated in CDK8/19-independent functions. This suggests that the observed phenotype was likely mediated through kinase-independent activities of CDK8/19, such as CCNC stabilization.

CDK8 inhibitor KY-065 rescues skeletal abnormalities in achondroplasia model mice

Cyclin-dependent kinase 8 (CDK8) is a transcription-related CDK family member implicated in the regulation of bone homeostasis, and we recently demonstrated that our internally developed CDK8 inhibitor KY-065 can prevent postmenopausal osteoporosis in a mouse model. Achondroplasia (ACH), the most common form of genetic dwarfism in humans, is caused by a gain-of-function mutation in fibroblast growth factor receptor 3 (FGFR3), a receptor tyrosine kinase that activates downstream mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription (STAT) signaling pathways. The first precision drug approved for the treatment of ACH in children, the C-type natriuretic peptide analog vosoritide, antagonizes the MAPK pathway, while there are currently no effective and safe medications targeting the STAT1 pathway. Here, we demonstrate that KY-065 rescues impaired chondrogenesis and stunted long bone growth in the Fgfr3Ach mouse model of ACH. KY-065 inhibited CDK8 with high affinity in vitro by competing with ATP. The CDK8 expression and STAT1Ser727 phosphorylation were upregulated in chondrocytes isolated from ACH model mice, and KY-065 repressed its phosphorylation and restored normal chondrogenic differentiation without affecting MAPK activation. Moreover, daily administration of 10 mg/kg KY-065 to Fgfr3Ach mice (yielding a peak concentration of 22.0 ± 1.47 μM in plasma) resulted in significant elongation of long bone and improved growth plate cytoarchitecture. Collectively, these findings identify the CDK8 in chondrocytes as a potential therapeutic target for ACH and KY-065 as a promising candidate drug treatment for this debilitating skeletal disease.

Mediator kinase module proteins, genetic alterations and expression of super-enhancer regulated genes in colorectal cancer

BACKGROUND

Genetic alterations are well characterized as contributors to the pathogenesis of cancers. Epigenetic abnormalities can lead to perturbations of the expression of genes in cancer cells without structural defects. Deregulation of proteins of the transcription machinery may result in perturbations of target genes. Mediator, a multiprotein component of the transcription machinery facilitates the function of RNA polymerase II, which transcribes most human genes. A part of the mediator with kinase activity, called the Mediator kinase module shows genetic alterations in a sub-set of colorectal cancers.

METHODS

Data from publicly available genomic series of colorectal cancer patients were examined to determine alterations of Mediator kinase module component genes, including MED12, MED12L, MED13, MED13L, CDK8, CDK19, and CCNC. The prevalence of alterations in genomically defined colorectal cancer sub-sets was also interrogated. The effect of Mediator kinase module member gene expression on colorectal cancer relapse-free survival was investigated.

RESULTS

Mutations in genes of the Mediator kinase module were present in a small percentage of colorectal cancers, ranging between 2 to 10% for MED12 and MED13 and alternative units MED12L and MED13L and below 2% for kinases CDK8 and CDK19 and cyclin C. Amplifications of the CDK8 gene were observed in 3% to 5% of colorectal cancers. The highest prevalence of mutations was observed in MSI cancers and the equivalent CMS1 group, with other genomic groups showing much lower frequency. An association of higher expression of MED12 with inferior relapse-free survival was observed. In contrast, higher expression of cyclin C was associated with improved survival. Colorectal cancer cell lines with CDK8 amplifications displayed sensitivity to several small molecule inhibitors of the KRAS/PI3K pathway but not to BET inhibitors.

CONCLUSION

The Mediator kinase module is deregulated in a sub-set of colorectal cancers with differences observed in genomically defined groups. These variations may result in differences in sensitivity to targeted therapies and may have to be taken into consideration as such therapies are developed.

Nonthermal biocompatible plasma in stimulating osteogenic differentiation by targeting p38/ FOXO1 and PI3K/AKT pathways in hBMSCs

Osteoporosis is manifested by decreased bone density and deterioration of bone architecture, increasing the risk of bone fractures Human bone marrow mesenchymal stem cells (hBMSCs)-based tissue engineering serves as a crucial technique for regenerating lost bone and preventing osteoporosis. Non-thermal biocompatible plasma (NBP) is a potential new therapeutic approach employed in several biomedical applications, including regenerative medicine. NBP affects bone remodeling; however, its role in the regulation of osteogenic differentiation in hBMSCs remains largely unexplored. This study aimed to explore the efficiency of NBP in promoting osteogenic differentiation, and the molecular pathways through which these responses occurred in hBMSCs. We found that NBP facilitated osteogenic differentiation through the upregulation of the bone morphogenic protein signal (BMPs) cascade, which in turn induced the expression of p38 and inhibited the forkhead box protein O1 (FOXO1). To further gain insight into the mechanism through which NBP extensively triggers the initiation of osteogenic differentiation in hBMSCs, PI3K/AKT pathway was also analyzed. Overall, these results highlight that NBP enhances osteogenic differentiation in hBMSCs by the stimulation of the p38/FOXO1 through PI3K/AKT signaling pathways. Therefore, the application of NBP in hBMSCs may offer tremendous therapeutic prospects in the treatment of bone regeneration and osteoporosis prevention.

Perspectives on Osteoarthritis Treatment with Mesenchymal Stem Cells and Radix Achyranthis Bidentatae

Knee osteoarthritis, a widespread degenerative condition, impacts a younger population and leads to high disability rates. Nature often provides solutions for aging and disease prevention. Mesenchymal stem cells (MSCs) and Radix Achyranthis Bidentatae (AB) are natural substances with potential. MSCs can transform into various tissues, alleviating symptoms by releasing factors and miRNA, potentially slowing osteoarthritis progression. AB's compositions target knee joint cells, enhancing internal conditions and joint function. Both MSCs and AB share mechanisms for immune regulation, reducing cartilage apoptosis, promoting chondrocyte formation, and addressing osteoporosis. They also influence estrogen and gut flora. This article reviews their roles in treating osteoarthritis, discussing apoptosis reduction, chondrocyte growth, bone enhancement, angiogenesis, and regulation of estrogen and intestinal flora. It explores their relationship and suggests AB's potential in stimulating mesenchymal stem cell repair for knee osteoarthritis treatment.

Osteosarcoma cells exhibit functional interactions with stromal cells, fostering a lung microenvironment conducive to the establishment of metastatic tumor cells

BACKGROUND

Osteosarcoma (OS) stands out as the most common bone tumor, with approximately 20% of the patients receiving a diagnosis of metastatic OS at their initial assessment. A significant challenge lies in the frequent existence of undetected metastases during the initial diagnosis. Mesenchymal stem cells (MSCs) possess unique abilities that facilitate tumor growth, and their interaction with OS cells is crucial for metastatic spread.

METHODS AND RESULTS

We demonstrated that, in vitro, MSCs exhibited a heightened migration response toward the secretome of non-metastatic OS cells. When challenged to a secretome derived from lungs preloaded with OS cells, MSCs exhibited greater migration toward lungs colonized with metastatic OS cells. Moreover, in vivo, MSCs displayed preferential migratory and homing behavior toward lungs colonized by metastatic OS cells. Metastatic OS cells, in turn, demonstrated an increased migratory response to the MSCs' secretome. This behavior was associated with heightened cathepsin D (CTSD) expression and the release of active metalloproteinase 2 (MMP2) by metastatic OS cells.

CONCLUSIONS

Our assessment focused on two complementary tumor capabilities crucial to metastatic spread, emphasizing the significance of inherent cell features. The findings underscore the pivotal role of signaling integration within the niche, with a complex interplay of migratory responses among established OS cells in the lungs, prometastatic OS cells in the primary tumor, and circulating MSCs. Pulmonary metastases continue to be a significant factor contributing to OS mortality. Understanding these mechanisms and identifying differentially expressed genes is essential for pinpointing markers and targets to manage metastatic spread and improve outcomes for patients with OS.

Phlpp1 Expression in Osteoblasts Plays a Modest Role in Bone Homeostasis

Prior work demonstrated that Phlpp1 deficiency alters limb length and bone mass, but the cell types involved and requirement of Phlpp1 for this effect were unclear. To understand the function of Phlpp1 within bone-forming osteoblasts, we crossed Phlpp1 floxed mice with mice harboring type 1 collagen (Col1a12.3kb)-Cre. Mineralization of bone marrow stromal cell cultures derived from Phlpp1 cKOCol1a1 was unchanged, but levels of inflammatory genes (eg, Ifng, Il6, Ccl8) and receptor activator of NF-κB ligand/osteoprotegerin (RANKL/OPG) ratios were enhanced by either Phlpp1 ablation or chemical inhibition. Micro-computed tomography of the distal femur and L5 vertebral body of 12-week-old mice revealed no alteration in bone volume per total volume, but compromised femoral bone microarchitecture within Phlpp1 cKOCol1a1 conditional knockout females. Bone histomorphometry of the proximal tibia documented no changes in osteoblast or osteoclast number per bone surface but slight reductions in osteoclast surface per bone surface. Overall, our data show that deletion of Phlpp1 in type 1 collagen-expressing cells does not significantly alter attainment of peak bone mass of either males or females, but may enhance inflammatory gene expression and the ratio of RANKL/OPG. Future studies examining the role of Phlpp1 within models of advanced age, inflammation, or osteocytes, as well as functional redundancy with the related Phlpp2 isoform are warranted. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Analyzing Sex-Specific Dimorphism in Human Skeletal Stem Cells

Sex-related differences are a current topic in contemporary science. In addition to hormonal regulation, cell-autonomous mechanisms are important in bone homeostasis and regeneration. In this study, human skeletal stem cells (SSCs) from female and male adults were cultured and analyzed with immunological assays and osteogenic differentiation assessments. Female SSCs exhibited a mean doubling time of 100.6 h, whereas male SSCs displayed a mean doubling time of 168.0 h. Immunophenotyping revealed the expression of the stem cell markers Nestin, CD133, and CD164, accompanied by the neural-crest marker SOX9. Furthermore, multiparameter flow cytometric analyses revealed a substantial population of multipotent SSCs, comprising up to 80% in both sexes. An analysis of the osteogenic differentiation potential demonstrated a strong mineralization in both male and female SSCs under physiological conditions. Recognizing the prevailing association of bone diseases with inflammatory processes, we also analyzed the osteogenic potential of SSCs from both sexes under pro-inflammatory conditions. Upon TNF-α and IL-1β treatment, we observed no sexual dimorphism on osteogenesis. In summary, we demonstrated the successful isolation and characterization of SSCs capable of rapid osteogenic differentiation. Taken together, in vitro cultured SSCs might be a suitable model to study sexual dimorphisms and develop drugs for degenerative bone diseases.

Targeting cyclin-dependent kinases in rheumatoid arthritis and psoriasis - a review of current evidence

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with synovial proliferation and bone erosion, which leads to the structural and functional impairment of the joints. Immune cells, together with synoviocytes, induce a pro-inflammatory environment and novel treatment agents target inflammatory cytokines. Psoriasis is a chronic immune-mediated skin disease, and several cytokines are considered as typical mediators in the progression of the disease, including IL-23, IL-22, and IL-17, among others.

AREA COVERED

In this review, we try to evaluate whether cyclin-dependent kinases (CDK), enzymes that regulate cell cycle and transcription of various genes, could become novel therapeutic targets in RA and psoriasis. We present the main results of in vitro and in vivo studies, as well as scarce clinical reports.

EXPERT OPINION

CDK inhibitors seem promising for treating RA and psoriasis because of their multidirectional effects. CDK inhibitors may affect not only the process of osteoclastogenesis, thereby reducing joint destruction in RA, but also the process of apoptosis of neutrophils and macrophages responsible for the development of inflammation in both RA and psoriasis. However, assessing the efficacy of these drugs in clinical practice requires multi-center, long-term clinical trials evaluating the effectiveness and safety of CDK-blocking therapy in RA and psoriasis.

The emerging studies on mesenchymal progenitors in the long bone

Mesenchymal progenitors (MPs) are considered to play vital roles in bone development, growth, bone turnover, and repair. In recent years, benefiting from advanced approaches such as single-cell sequence, lineage tracing, flow cytometry, and transplantation, multiple MPs are identified and characterized in several locations of bone, including perichondrium, growth plate, periosteum, endosteum, trabecular bone, and stromal compartment. However, although great discoveries about skeletal stem cells (SSCs) and progenitors are present, it is still largely obscure how the varied landscape of MPs from different residing sites diversely contribute to the further differentiation of osteoblasts, osteocytes, chondrocytes, and other stromal cells in their respective destiny sites during development and regeneration. Here we discuss recent findings on MPs' origin, differentiation, and maintenance during long bone development and homeostasis, providing clues and models of how the MPs contribute to bone development and repair.

Genetically Engineered Mice Unveil In Vivo Roles of the Mediator Complex

The Mediator complex is a multi-subunit protein complex which plays a significant role in the regulation of eukaryotic gene transcription. It provides a platform for the interaction of transcriptional factors and RNA polymerase II, thus coupling external and internal stimuli with transcriptional programs. Molecular mechanisms underlying Mediator functioning are intensively studied, although most often using simple models such as tumor cell lines and yeast. Transgenic mouse models are required to study the role of Mediator components in physiological processes, disease, and development. As constitutive knockouts of most of the Mediator protein coding genes are embryonically lethal, conditional knockouts and corresponding activator strains are needed for these studies. Recently, they have become more easily available with the development of modern genetic engineering techniques. Here, we review existing mouse models for studying the Mediator, and data obtained in corresponding experiments.

Senescent mesenchymal stem/stromal cells in pre-metastatic bone marrow of untreated advanced breast cancer patients

Breast cancer is the predominant form of carcinoma among women worldwide, with 70% of advanced patients developing bone metastases, with a high mortality rate. In this sense, the bone marrow (BM) mesenchymal stem/stromal cells (MSCs) are critical for BM/bone homeostasis, and failures in their functionality, transform the BM into a pre-metastatic niche (PMN). We previously found that BM-MSCs from advanced breast cancer patients (BCPs, infiltrative ductal carcinoma, stage III-B) have an abnormal profile. This work aims to study some of the metabolic and molecular mechanisms underlying MSCs shift from a normal to an abnormal profile in this group of patients. A comparative analysis was undertaken, which included self-renewal capacity, morphology, proliferation capacity, cell cycle, reactive oxygen species (ROS) levels, and senescence-associated β‑galactosidase (SA‑β‑gal) staining of BM-derived MSCs isolated from 14 BCPs and 9 healthy volunteers (HVs). Additionally, the expression and activity of the telomerase subunit TERT, as well as telomere length, were measured. Expression levels of pluripotency, osteogenic, and osteoclastogenic genes (OCT-4, SOX-2, M-CAM, RUNX-2, BMP-2, CCL-2, M-CSF, and IL-6) were also determined. The results showed that MSCs from BCPs had reduced ,self-renewal and proliferation capacity. These cells also exhibited inhibited cell cycle progression and phenotypic changes, such as an enlarged and flattened appearance. Additionally, there was an increase in ROS and senescence levels and a decrease in the functional capacity of TERT to preserve telomere length. We also found an increase in pro-inflammatory/pro-osteoclastogenic gene expression and a decrease in pluripotency gene expression. We conclude that these changes could be responsible for the abnormal functional profile that MSCs show in this group of patients.

Effects of SIRT1 on Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells in Type 2 Diabetic Patients

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) are at high risk for osteoporosis. SIRT1 plays an important regulatory role in the occurrence and development of diabetes mellitus; however, it is still not clear whether SIRT1 is directly related to the osteogenic ability of bone marrow mesenchymal stem cells (BMSCs) in T2DM patients.

METHODS

We obtained BMSCs from patients with T2DM and healthy volunteers to determine the effect of SIRT1 expression on the osteogenic capacity of BMSCs. As a result, SIRT1 expression in BMSCs in T2DM was significantly lower compared to healthy volunteers, but the proliferative capacity of BMSCs in the T2DM group was not significantly different from that of healthy volunteers.

RESULTS

During osteogenic differentiation, the expression of SIRT1 in MSCs from T2DM patients was significantly decreased, and the osteogenic differentiation ability of MSCs from T2DM patients was significantly lower than healthy volunteers. After intervention with resveratrol, the expression of SIRT1 increased significantly, and the apoptotic rate of MSCs in T2DM patients decreased significantly. Moreover, resveratrol promoted osteoblast differentiation of MSCs.

CONCLUSION

Our study confirmed that the expression of SIRT1 is directly related to the osteogenic potential of BMSCs in patients with T2DM. Resveratrol promoted the osteogenic differentiation of BMSCs by increasing the expression of SIRT1. The increased expression of SIRT1 significantly reduced BMSC apoptosis during osteogenic differentiation, which is one of the important mechanisms by which SIRT1 regulates the osteogenic ability of BMSCs. Our data also provide strong evidence that resveratrol may be used in the treatment of osteoporosis in patients with T2DM.

Cytokine-mediated immunomodulation of osteoclastogenesis

Cytokines are an important set of proteins regulating bone homeostasis. In inflammation induced bone resorption, cytokines, such as RANKL, TNF-α, M-CSF, are indispensable for the differentiation and activation of resorption-driving osteoclasts, the process we know as osteoclastogenesis. On the other hand, immune system produces a number of regulatory cytokines, including IL-4, IL-10 and IFNs, and limits excessive activation of osteoclastogenesis and bone loss during inflammation. These unique properties make cytokines powerful targets as rheostat to maintain bone homeostasis and for potential immunotherapies of inflammatory bone diseases. In this review, we summarize recent advances in cytokine-mediated regulation of osteoclastogenesis and provide insights of potential translational impact of bench-side research into clinical treatment of bone disease.