Role of Protein Phosphatase 2A in Osteoblast Differentiation and Function

Transcriptomic and proteomic strategies to reveal the mechanism of Gymnocypris przewalskii scale development

BACKGROUND

Fish scales are typical products of biomineralization and play an important role in the adaptation of fish to their environment. The Gymnocypris przewalskii scales are highly specialized, with scales embedded in only specific parts of the dermis, such as the areas around the anal fin and branchiostegite, making G. przewalskii an ideal material for biomineralization research. In this study, we aimed to unveil genes and pathways controlling scale formation through an integrated analysis of both transcriptome and proteome, of which G. przewalskii tissues of the dorsal skin (no scales) and the rump side skin (with scales) were sequenced. The sequencing results were further combined with cellular experiments to clarify the relationship between genes and signaling pathways.

RESULTS

The results indicated the following: (1) a total of 4,904 differentially expressed genes were screened out, including 3,294 upregulated genes and 1,610 downregulated genes (with a filtering threshold of |log2Fold-Change|> 1 and p-adjust < 0.05). The identified differentially expressed genes contained family members such as FGF, EDAR, Wnt10, and bmp. (2) A total of 535 differentially expressed proteins (DEPs) were filtered out from the proteome, with 204 DEPs downregulated and 331 DEPs upregulated (with a filtering threshold of |Fold-Change|> 1.5 and p < 0.05). (3) Integrated analyses of transcriptome and proteome revealed that emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were important genes contributing to scale development and that PI3K-AKT was the most important signaling pathway involved. (4) With the use of the constructed G. przewalskii fibroblast cell line, emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were confirmed to be positively regulated by the PI3K-AKT signaling pathway.

CONCLUSION

This study provides experimental evidence for PI3K-AKT controlled scale development in G. przewalskii and would benefit further study on stress adaptation, scale biomineralization, and the development of skin appendages.

Microcystin-leucine-arginine impairs bone microstructure and biomechanics by activating osteoimmune response and inhibiting osteoblasts maturation in developing rats

Microcystin-LR (MC-LR) affects bone health in adult mice via osteo-immunomodulation. However, its effect on osteoblasts and bone development is unclear. This study investigated the effect of MC-LR on bone osteoimmune and osteoblasts in the developing period. 18 Four-week-old male Sprague Dawley rats were divided into two groups (n = 9 per group) and exposed to 0 (control) and 1 μg/kg b.w. MC-LR (exposure) by intraperitoneal injection for four weeks. The heart blood was collected for serological examination, and the femur for morphological, histopathological, and biomechanical analysis. MC-LR exposure significantly weakened bone microstructures (bone volume, bone volume/total volume, bone trabecular number, connectivity density) and biomechanics (maximum loads and maximum deflection) (P < 0.05). Besides, MC-LR decreased serum procollagen type І car-boxy-terminal propeptide, osteocalcin, bone morphogenetic protein-2, osteoprotegerin, and receptor activator of nuclear factor κB ligand, while elevating osteoclasts number, matrix metalloproteinase-9, β-catenin, Runt-related transcription factor 2, and osterix in bone, and bone alkaline phosphate, C-terminal cross-linked telopeptide of type-I collagen, tartrate-resistant acid phosphatase-5b in serum (P < 0.05). Moreover, MC-LR increased CD4+ T-cells, CD4+/CD8+, M1 and M2 macrophages, and cells apoptosis in the bone marrow, interleukin-6, interleukin-17, and tumor necrosis factor-α in serum, decreased serum interleukin-10 (P < 0.05). Overall, MC-LR can promote bone resorption by activating osteoclasts via osteoimmunology, which may involve macrophages besides lymphocytes. MC-LR may inhibit bone formation by stopping the osteoblasts at an immature stage. Thus, MC-LR weakened bone microstructure and biomechanics in developing period. Its risk on bone development needs further study.

Enhanced osteogenesis of human urine-derived stem cells by direct delivery of 30Kc19α-Lin28A protein

Urine-derived stem cells (USCs) are a promising source for regenerative medicine because of their advantages such as easy and non-invasive collection from the human body, stable expansion, and the potential to differentiate into multiple lineages, including osteoblasts. In this study, we propose a strategy to enhance the osteogenic potential of human USCs using Lin28A, a transcription factor that inhibits let-7 miRNA processing. To address concerns regarding the safety of foreign gene integration and potential risk of tumorigenicity, we intracellularly delivered Lin28A as a recombinant protein fused with a cell-penetrating and protein-stabilizing protein, 30Kc19α. 30Kc19α-Lin28A fusion protein exhibited improved thermal stability and was delivered into USCs without significant cytotoxicity. 30Kc19α-Lin28A treatment elevated calcium deposition and upregulated several osteoblast-specific gene expressions in USCs derived from multiple donors. Our results indicate that intracellularly delivered 30Kc19α-Lin28A enhances the osteoblastic differentiation of human USCs by affecting the transcriptional regulatory network involved in metabolic reprogramming and stem cell potency. Therefore, 30Kc19α-Lin28A may provide a technical advancement toward developing clinically feasible strategies for bone regeneration.

Transcriptome Analysis Reveals Modulation of Human Stem Cells from the Apical Papilla by Species Associated with Dental Root Canal Infection

Interaction of oral bacteria with stem cells from the apical papilla (SCAP) can negatively affect the success of regenerative endodontic treatment (RET). Through RNA-seq transcriptomic analysis, we studied the effect of the oral bacteria Fusobacterium nucleatum and Enterococcus faecalis, as well as their supernatants enriched by bacterial metabolites, on the osteo- and dentinogenic potential of SCAPs in vitro. We performed bulk RNA-seq, on the basis of which differential expression analysis (DEG) and gene ontology enrichment analysis (GO) were performed. DEG analysis showed that E. faecalis supernatant had the greatest effect on SCAPs, whereas F. nucleatum supernatant had the least effect (Tanimoto coefficient = 0.05). GO term enrichment analysis indicated that F. nucleatum upregulates the immune and inflammatory response of SCAPs, and E. faecalis suppresses cell proliferation and cell division processes. SCAP transcriptome profiles showed that under the influence of E. faecalis the upregulation of VEGFA, Runx2, and TBX3 genes occurred, which may negatively affect the SCAP's osteo- and odontogenic differentiation. F. nucleatum downregulates the expression of WDR5 and TBX2 and upregulates the expression of TBX3 and NFIL3 in SCAPs, the upregulation of which may be detrimental for SCAPs' differentiation potential. In conclusion, the present study shows that in vitro, F. nucleatum, E. faecalis, and their metabolites are capable of up- or downregulating the expression of genes that are necessary for dentinogenic and osteogenic processes to varying degrees, which eventually may result in unsuccessful RET outcomes. Transposition to the clinical context merits some reservations, which should be approached with caution.

Cip2A modulates osteogenic differentiation via the ERK-Runx2 pathway in MG63 cells

Cancerous inhibitor of protein phosphatase 2A (Cip2A) is an oncoprotein that promotes the development of several types of cancer. However, its molecular function in osteoblast differentiation remains unclear. In this study, we found that Cip2A was upregulated under osteogenic conditions in MG63 cells. Besides, overexpression of Cip2A significantly increased the expression of Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). Inversely, the knockdown of Cip2A in MG63 cells suppressed osteoblast differentiation. Cip2A expression during osteogenic differentiation was mediated by extracellular signal-regulated kinase (ERK) activation. Taken together, our results suggest that Cip2A plays important role in regulating osteoblast differentiation by inducing ERK phosphorylation in MG63 cells.

The PP2A/4/6 subfamily of phosphoprotein phosphatases regulates DAF-16 and confers resistance to environmental stress in postreproductive adult C. elegans

Insulin and insulin-like growth factors are longevity determinants that negatively regulate Forkhead box class O (FoxO) transcription factors. In C. elegans mutations that constitutively activate DAF-16, the ortholog of mammalian FoxO3a, extend lifespan by two-fold. While environmental insults induce DAF-16 activity in younger animals, it also becomes activated in an age-dependent manner in the absence of stress, modulating gene expression well into late adulthood. The mechanism by which DAF-16 activity is regulated during aging has not been defined. Since phosphorylation of DAF-16 generally leads to its inhibition, we asked whether phosphatases might be necessary for its increased transcriptional activity in adult C. elegans. We focused on the PP2A/4/6 subfamily of phosphoprotein phosphatases, members of which had been implicated to regulate DAF-16 under low insulin signaling conditions but had not been investigated during aging in wildtype animals. Using reverse genetics, we functionally characterized all C. elegans orthologs of human catalytic, regulatory, and scaffolding subunits of PP2A/4/6 holoenzymes in postreproductive adults. We found that PP2A complex constituents PAA-1 and PPTR-1 regulate DAF-16 transcriptional activity during aging and that they cooperate with the catalytic subunit LET-92 to protect adult animals from ultraviolet radiation. PP4 complex members PPH-4.1/4.2, and SMK-1 also appear to regulate DAF-16 in an age-dependent manner, and together with PPFR-2 they contribute to innate immunity. Interestingly, SUR-6 but no other subunit of the PP2A complex was necessary for the survival of pathogen-infected animals. Finally, we found that PP6 complex constituents PPH-6 and SAPS-1 contribute to host defense during aging, apparently without affecting DAF-16 transcriptional activity. Our studies indicate that a set of PP2A/4/6 complexes protect adult C. elegans from environmental stress, thus preserving healthspan. Therefore, along with their functions in cell division and development, the PP2A/4/6 phosphatases also appear to play critical roles later in life.

Mechanisms of miR‑128‑3p in inhibiting osteoblast differentiation from bone marrow‑derived mesenchymal stromal cells

The authors' previous study demonstrated that miR-128 may exert an inhibitory effect on the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BM-MSCs), but its downstream mechanisms remain to be elucidated. The aim of the present study was to investigate the microRNA (miRNA/miR) and mRNA profiles of differentiated and undifferentiated BM-MSCs and explore new downstream targets for miR-128. The sequencing datasets of GSE107279 (miRNA) and GSE112318 (mRNA) were downloaded from the Gene Expression Omnibus database. The differentially expressed miRNAs (DEMs) and genes (DEGs) were identified using the DESeq2 method. The target genes of DEMs were predicted by the miRwalk 2.0 database. The hub target genes of miR-128 were screened by constructing the protein-protein interaction (PPI) network and module analysis. The expression levels of miR-128 and crucial target genes were validated by reverse transcription-quantitative (RT-q) PCR before or after transfection of miR-128 mimics to BM-MSCs. The miRNA expression profile analysis identified miR-128 as one of the significantly downregulated DEMs (total 338) in differentiated BM-MSCs compared with the undifferentiated control. A total of 103 predicted target genes of miR-128-3p were overlapped with upregulated DEGs. By calculating the topological properties of each protein in the PPI network, 6 upregulated genes (KIT, NTRK2, YWHAB, GAB1, AXIN1 and RUNX1; fold change was the highest for NTRK2) were considered to be hub genes. Of these, 4 were enriched in module 4 (RUNX1, KIT, GAB1 and AXIN1; RUNX1 was particularly crucial as it can interact with the others), while one was enriched in module 7 (YWHAB). The expression levels of miR-128 and these 6 target genes during the osteogenic differentiation were experimentally confirmed by RT-qPCR. In addition, the expression levels of these 6 genes were significantly reversed after transfection of miR-128-3p mimics into rat BM-MSCs compared with the miR-control group. These findings indicated that miR-128-3p may inhibit the osteoblast differentiation of BM-MSCs by downregulation of these 6 genes, particularly RUNX1, YWHAB and NTRK2.

LncRNA-mRNA expression profiles and functional networks in osteoclast differentiation

Human osteoclasts are differentiated from CD14⁺ monocytes and are responsible for bone resorption. Long non‐coding RNAs (lncRNAs) have been proved to be significantly involved in multiple biologic processes, especially in cell differentiation. However, the effect of lncRNAs in osteoclast differentiation is less appreciated. In our study, RNA sequencing (RNA‐seq) was used to identify the expression profiles of lncRNAs and mRNAs in osteoclast differentiation. The results demonstrated that expressions of 1117 lncRNAs and 296 mRNAs were significantly altered after osteoclast differentiation. qRT‐PCR assays were performed to confirm the expression profiles, and the results were almost consistent with the RNA‐seq data. GO and KEGG analyses were used to predict the functions of these differentially expressed mRNA and lncRNAs. The Path‐net analysis demonstrated that MAPK pathway, PI3K‐AKT pathway and NF‐kappa B pathway played important roles in osteoclast differentiation. Co‐expression networks and competing endogenous RNA networks indicated that ENSG00000257764.2‐miR‐106a‐5p‐TIMP2 may play a central role in osteoclast differentiation. Our study provides a foundation to further understand the role and underlying mechanism of lncRNAs in osteoclast differentiation, in which many of them could be potential targets for bone metabolic disease.

Influence of Chronic Alcohol Use on Osteoblastic Differentiation of Bone Marrow Cells, Bone Properties, and Hepatic and Renal Morphology of Rats

Chronic alcohol exposure can affect the osteoblastic activity and the proliferation and differentiation of cells due to its toxic effect, which can affect negatively bone repair and bone microarchitecture. The aim of this study was to evaluate the effects of chronic use of 20% alcohol on rats regarding osteoblastic differentiation, extrinsic and intrinsic properties of the tibia, and hepatic and renal morphology. Wistar rats were divided into three groups (n = 9) in accordance with a 24-week diet. After euthanasia, kidneys, liver, and tibias were removed for analysis and femurs mesenchymal cells were collected. The results showed that chronic use of 20% alcohol influenced neither the alkaline phosphatase production nor total protein (p > 0.05) in rats, with similar formation of nodules in all groups (p > 0.05). However, significant changes in the liver and kidneys and adverse effects on the mechanical properties of the tibia were observed. According to the results, it can be concluded that the chronic use of alcohol for 24 weeks had no negative influence on the activity and differentiation of osteoblasts, but the mechanical properties of the tibia were impaired and the organs responsible for metabolism and excretion were also affected due to the consumption of alcohol.

The phosphatase PPM1A controls monocyte-to-macrophage differentiation

Differentiation of circulating monocytes into tissue-bound or tissue-resident macrophages is a critical regulatory process affecting host defense and inflammation. However, the regulatory signaling pathways that control the differentiation of monocytes into specific and distinct functional macrophage subsets are poorly understood. Herein, we demonstrate that monocyte-to-macrophage differentiation is controlled by the Protein Phosphatase, Mg2+/Mn2+-dependent 1A (PPM1A). Genetic manipulation experiments demonstrated that overexpression of PPM1A attenuated the macrophage differentiation program, while knockdown of PPM1A expression accelerated the ability of monocytes to differentiate into macrophages. We identify imiquimod and Pam3CSK4 as two Toll-like receptor agonists that induce PPM1A expression, and show that increased expression of PPM1A at the onset of differentiation impairs cellular adherence, reduces expression of inflammatory (M1) macrophage-specific markers, and inhibits the production of inflammatory cytokines. Our findings reveal PPM1A as a negative threshold regulator of M1-type monocyte-to-macrophage differentiation, establishing it as a key phosphatase that orchestrates this program.