Distinct signaling properties of mitogen-activated protein kinase kinases 4 (MKK4) and 7 (MKK7) in embryonic stem cell (ESC) differentiation

Combining single-cell tracking and omics improves blood stem cell fate regulator identification

Molecular programs initiating cell fate divergence (CFD) are difficult to identify. Current approaches usually compare cells long after CFD initiation, therefore missing molecular changes at its start. Ideally, single cells that differ in their CFD molecular program but are otherwise identical are compared early in CFD. This is possible in diverging sister cells, which were identical until their mother's division and thus differ mainly in CFD properties. In asymmetrically dividing cells, divergent daughter fates are prospectively committed during division, and diverging sisters can thus be identified at the start of CFD. Using asymmetrically dividing blood stem cells, we developed a pipeline (ie, trackSeq) for imaging, tracking, isolating, and transcriptome sequencing of single cells. Their identities, kinship, and histories are maintained throughout, massively improving molecular noise filtering and candidate identification. In addition to many identified blood stem CFD regulators, we offer here this pipeline for use in CFDs other than asymmetric division.

MKK7-mediated phosphorylation of JNKs regulates the proliferation and apoptosis of human spermatogonial stem cells

BACKGROUND

Human spermatogonial stem cells (SSCs) are the basis of spermatogenesis. However, little is known about the developmental regulatory mechanisms of SSC due to sample origin and species differences.

AIM

To investigates the mechanisms involved in the proliferation of human SSC.

METHODS

The expression of mitogen-activated protein kinase kinase 7 (MKK7) in human testis was identified using immunohistochemistry and western blotting (WB). MKK7 was knocked down using small interfering RNA, and cell proliferation and apoptosis were detected by WB, EdU, cell counting kit-8 and fluorescence-activated cell sorting. After bioinformatic analysis, the interaction of MKK7 with c-Jun N-terminal kinases ( JNKs ) was verified by protein co-immunoprecipitation and WB. The phosphorylation of JNKs was inhibited by SP600125, and the phenotypic changes were detected by WB, cell counting kit-8 and fluorescence-activated cell sorting.

RESULTS

MKK7 is mainly expressed in human SSCs, and MKK7 knockdown inhibits SSC proliferation and promotes their apoptosis. MKK7 mediated the phosphorylation of JNKs, and after inhibiting the phosphorylation of JNKs, the phenotypic changes of the cells were similar to those after MKK7 downregulation. The expression of MKK7 was significantly downregulated in patients with abnormal spermatogenesis, suggesting that abnormal MKK7 may be associated with spermatogenesis impairment.

CONCLUSION

MKK7 regulates the proliferation and apoptosis of human SSC by mediating the phosphorylation of JNKs.

MK2 promotes Tfcp2l1 degradation via β-TrCP ubiquitin ligase to regulate mouse embryonic stem cell self-renewal

Tfcp2l1 can maintain mouse embryonic stem cell (mESC) self-renewal. However, it remains unknown how Tfcp2l1 protein stability is regulated. Here, we demonstrate that β-transducin repeat-containing protein (β-TrCP) targets Tfcp2l1 for ubiquitination and degradation in a mitogen-activated protein kinase (MAPK)-activated protein kinase 2 (MK2)-dependent manner. Specifically, β-TrCP1 and β-TrCP2 recognize and ubiquitylate Tfcp2l1 through the canonical β-TrCP-binding motif DSGDNS, in which the serine residues have been phosphorylated by MK2. Point mutation of serine-to-alanine residues reduces β-TrCP-mediated ubiquitylation and enhances the ability of Tfcp2l1 to promote mESC self-renewal while repressing the speciation of the endoderm, mesoderm, and trophectoderm. Similarly, inhibition of MK2 reduces the association of Tfcp2l1 with β-TrCP1 and increases the self-renewal-promoting effects of Tfcp2l1, whereas overexpression of MK2 or β-TrCP genes decreases Tfcp2l1 protein levels and induces mESC differentiation. Collectively, our study reveals a posttranslational modification of Tfcp2l1 that will expand our understanding of the regulatory network of stem cell pluripotency.

Isolation and long-term expansion of murine epidermal stem-like cells

Epidermis is the most outer layer of the skin and a physical barrier protecting the internal tissues from mechanical and environmental insults. The basal keratinocytes, which, through proliferation and differentiation, supply diverse cell types for epidermal homeostasis and injury repair. Sustainable culture of murine keratinocyte, however, is a major obstacle. Here we developed murine keratinocyte lines using low-Ca²⁺ (0.06 mM) keratinocyte serum-free medium (KSFM-Ca²⁺) without feeder cells. Cells derived in this condition could be subcultured for >70 passages. They displayed basal epithelial cell morphology and expressed keratin (Krt) 14, but lacked the epithelial-characteristic intercellular junctions. Moreover, these cells could be adapted to grow in the Defined-KSFM (DKSFM) media containing 0.15 mM Ca²⁺, and the adapted cells established tight- and adherens-junctions and exhibited increased Krt1/10 expression while retained subculture capacity. Global gene expression studies showed cells derived in KSFM-Ca²⁺ media had enriched stem/proliferation markers and cells adapted in DKSFM media had epithelial progenitor signatures. Correspondingly, KSFM-Ca²⁺-derived cells exhibited a remarkable capacity of clonal expansion, whereas DKSFM-adapted cells could differentiate to suprabasal epithelial cell types in 3-dimentional (3D) organoids. The generation of stem-like murine keratinocyte lines and the conversion of these cells to epithelial progenitors capable of terminal differentiation provide the critically needed resources for skin research.

Recent advances on signaling pathways and their inhibitors in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by systemic synovitis leading to joint destruction in which imbalances in pro-inflammatory and anti-inflammatory cytokines promote the induction of autoimmunity. Some pro-inflammatory cytokines can trigger the signaling pathways which responsible for immune-mediated inflammation in RA, and the activated signaling pathways produce pro-inflammatory cytokines, resulting in aggravation of RA. Hence, understanding of the signaling pathways and their inhibitors might be advantageous in the development of therapeutic targets and new drugs for RA. In the current review, we summarize the signaling pathways involved in the pathogenesis of RA as well as the potential role of specific inhibitors in its management. We hope this paper may serve a reference for future studies on signaling pathways implicated in the pathogenesis of RA and benefit the treatment of RA.

Silencing of Sphingosine kinase 1 Affects Maturation Pathways in Mouse Neonatal Cardiomyocytes

Sphingosine kinase-1 (Sphk1) and its product, sphingosine-1-phosphate (S1P) are important regulators of cardiac growth and function. Numerous studies have reported that Sphk1/S1P signaling is essential for embryonic cardiac development and promotes pathological cardiac hypertrophy in adulthood. However, no studies have addressed the role of Sphk1 in postnatal cardiomyocyte (CM) development so far. The present study aimed to assess the molecular mechanism(s) by which Sphk1 silencing might influence CMs development and hypertrophy in vitro. Neonatal mouse CMs were transfected with siRNA against Sphk1 or negative control, and subsequently treated with 1 µM angiotensin II (AngII) or a control buffer for 24 h. The results of RNASeq analysis revealed that diminished expression of Sphk1 significantly accelerated neonatal CM maturation by inhibiting cell proliferation and inducing developmental pathways in the stress (AngII-induced) conditions. Importantly, similar effects were observed in the control conditions. Enhanced maturation of Sphk1-lacking CMs was further confirmed by the upregulation of the physiological hypertrophy-related signaling pathway involving Akt and downstream glycogen synthase kinase 3 beta (Gsk3β) downregulation. In summary, we demonstrated that the Sphk1 silencing in neonatal mouse CMs facilitated their postnatal maturation in both physiological and stress conditions.

Proteomic profile alterations in porcine conceptuses during early stages of development

The dynamic embryo development during the early stages of gestation requires precise molecular changes, including proteomic ones. We aimed to find unique proteins for porcine conceptuses specifically during the peri-implantation period, i.e. on days 15-16 of pregnancy. The proteomic profile of these conceptuses was compared with conceptuses at an earlier stage of the development, i.e. collected during maternal recognition of pregnancy on days 12-13 of pregnancy. The 2DE, gel image analysis, and MALDI TOF mass spectrometry were used 500 protein spots were annotated as common to conceptuses harvested during both studied periods. Proteomic profile of the conceptuses collected during the peri-implantation period contains 24 unique proteins. Identified unique for the peri-implantation period proteins are involved in adhesion processes, cadherin, and actin-binding, and actin filament organization, extracellular matrix organization, and cytoskeleton organization. Systemic analysis of identified proteins confirmed their involvement in cell adhesion and cytoskeletal organization as being two major affected functions. The unique proteins might be recognized as factors conditioning the proper peri-implantation embryo development and gaining competences for implantation. In further studies, BRCA1 might be considered as a candidate for a potential marker of embryonic competences for implantation in pigs.

Dioxin Disrupts Dynamic DNA Methylation Patterns in Genes That Govern Cardiomyocyte Maturation

Congenital heart disease (CHD), the leading birth defect worldwide, has a largely unknown etiology, likely to result from complex interactions between genetic and environmental factors during heart development, at a time when the heart adapts to diverse physiological and pathophysiological conditions. Crucial among these is the regulation of cardiomyocyte development and postnatal maturation, governed by dynamic changes in DNA methylation. Previous work from our laboratory has shown that exposure to the environmental toxicant tetrachlorodibenzo-p-dioxin (TCDD) disrupts several molecular networks responsible for heart development and function. To test the hypothesis that the disruption caused by TCDD in the heart results from changes in DNA methylation and gene expression patterns of cardiomyocytes, we established a stable mouse embryonic stem cell line expressing a puromycin resistance selectable marker under control of the cardiomyocyte-specific Nkx2-5 promoter. Differentiation of these cells in the presence of puromycin induces the expression of a large suite of cardiomyocyte-specific markers. To assess the consequences of TCDD treatment on gene expression and DNA methylation in these cardiomyocytes, we subjected them to transcriptome and methylome analyses in the presence of TCDD. Unlike control cardiomyocytes maintained in vehicle, the TCDD-treated cardiomyocytes showed extensive gene expression changes, with a significant correlation between differential RNA expression and DNA methylation in 111 genes, many of which are key elements of pathways that regulate cardiovascular development and function. Our findings provide an important clue toward the elucidation of the complex interactions between genetic and epigenetic mechanisms after developmental TCDD exposure that may contribute to CHD.

Inhibition of the JNK/MAPK signaling pathway by myogenesis-associated miRNAs is required for skeletal muscle development

Skeletal muscle differentiation is controlled by multiple cell signaling pathways, however, the JNK/MAPK signaling pathway dominating this process has not been fully elucidated. Here, we report that the JNK/MAPK pathway was significantly downregulated in the late stages of myogenesis, and in contrast to P38/MAPK pathway, it negatively regulated skeletal muscle differentiation. Based on the PAR-CLIP-seq analysis, we identified six elevated miRNAs (miR-1a-3p, miR-133a-3p, miR-133b-3p, miR-206-3p, miR-128-3p, miR-351-5p), namely myogenesis-associated miRNAs (mamiRs), negatively controlled the JNK/MAPK pathway by repressing multiple factors for the phosphorylation of the JNK/MAPK pathway, including MEKK1, MEKK2, MKK7, and c-Jun but not JNK protein itself, and as a result, expression of transcriptional factor MyoD and mamiRs were further promoted. Our study revealed a novel double-negative feedback regulatory pattern of cell-specific miRNAs by targeting phosphorylation kinase signaling cascade responsible for skeletal muscle development.

MKK7 confers different activities to viral infection of Singapore grouper iridovirus (SGIV) and nervous necrosis virus (NNV) in grouper

Mitogen-activated protein kinase 7 (MKK7) is one of the major stress-activated protein kinase (SAPK)-activating kinases in response to environmental or physiological stimuli. Here a MKK7 named as Ec-MKK7 was identified from orange-spotted grouper, Epinephelus coioides. The full-length cDNA of Ec-MKK7 was 1853 bp, with an open reading frame (ORF) of 1272 bp encoding a putative protein of 423 amino acids. A characteristic S-K-A-K-T motif was contained in the domain of dual-specificity protein kinase, mitogen-activated protein kinase kinase 7 (PKc_MKK7). Intracellular localization showed that Ec-MKK7 was localized in both the cytoplasm and the nucleus of grouper spleen (GS) and/or grouper brain (EAGB) cells. Moreover, Ec-MKK7 was universally expressed in all examined tissues and showed expression modulation to challenges of lipopolysacchride (LPS), Singapore grouper iridovirus (SGIV) and polyriboinosinic polyribocytidylic acid (poly I:C) in vivo. A gene targeting strategy over-expressing Ec-MKK7 was performed to examine the activities of MKK7 to viral infection in vitro. Our data showed that Ec-MKK7 was involved in the evasion and replication of SGIV but played an antiviral role to the infection of nervous necrosis virus (NNV). All results demonstrated that Ec-MKK7 could play important roles in grouper innate immunity and show distinct functions on virus infection.

JNK/SAPK Signaling Is Essential for Efficient Reprogramming of Human Fibroblasts to Induced Pluripotent Stem Cells

Reprogramming of somatic cells to the phenotypic state termed “induced pluripotency” is thought to occur through three consecutive stages: initiation, maturation, and stabilisation. The initiation phase is stochastic but nevertheless very important as it sets the gene expression pattern that permits completion of reprogramming; hence a better understanding of this phase and how this is regulated may provide the molecular cues for improving the reprogramming process. c‐Jun N‐terminal kinase (JNK)/stress‐activated protein kinase (SAPKs) are stress activated MAPK kinases that play an essential role in several processes known to be important for successful completion of the initiation phase such as cellular proliferation, mesenchymal to epithelial transition (MET) and cell cycle regulation. In view of this, we postulated that manipulation of this pathway would have significant impacts on reprogramming of human fibroblasts to induced pluripotent stem cells. Accordingly, we found that key components of the JNK/SAPK signaling pathway increase expression as early as day 3 of the reprogramming process and continue to rise in reprogrammed cells throughout the initiation and maturation stages. Using both chemical inhibitors and RNA interference of MKK4, MKK7 and JNK1, we tested the role of JNK/SAPK signaling during the initiation stage of neonatal and adult fibroblast reprogramming. These resulted in complete abrogation of fully reprogrammed colonies and the emergence of partially reprogrammed colonies which disaggregated and were lost from culture during the maturation stage. Inhibition of JNK/SAPK signaling resulted in reduced cell proliferation, disruption of MET and loss of the pluripotent phenotype, which either singly or in combination prevented establishment of pluripotent colonies. Together these data provide new evidence for an indispensable role for JNK/SAPK signaling to overcome the well‐established molecular barriers in human somatic cell induced reprogramming. Stem Cells2016;34:1198–1212

Jun-Mediated Changes in Cell Adhesion Contribute to Mouse Embryonic Stem Cell Exit from Ground State Pluripotency

Embryonic stem cells (ESC) are able to give rise to any somatic cell type. A lot is known about how ESC pluripotency is maintained, but comparatively less is known about how differentiation is promoted. Cell fate decisions are regulated by interactions between signaling and transcriptional networks. Recent studies have shown that the overexpression or downregulation of the transcription factor Jun can affect the ESC fate. Here we have focussed on the role of the Jun in the exit of mouse ESCs from ground state pluripotency and the onset of early differentiation. Transcriptomic analysis of differentiating ESCs reveals that Jun is required to upregulate a programme of genes associated with cell adhesion as ESCs exit the pluripotent ground state. Several of these Jun-regulated genes are shown to be required for efficient adhesion. Importantly this adhesion is required for the timely regulated exit of ESCs from ground state pluripotency and the onset of early differentiation events. Stem Cells 2016;34:1213-1224.

Pluripotent Conversion of Muscle Stem Cells Without Reprogramming Factors or Small Molecules

Muscle derived stem cells (MDSCs) are multipotent stem cells that can differentiate into several lineages including skeletal muscle precursor cells. Here, we show that MDSCs from myostatin null mice (Mstn (-/-) ) can be readily induced into pluripotent stem cells without using reprogramming factors. Microarray studies revealed a strong upregulation of markers like Leukemia Inhibitory factor (LIF) and Leukemia Inhibitory factor receptor (LIFR) in Mstn (-/-) MDSCs as compared to wild type MDSCs (WT-MDSCs). Furthermore when cultured in mouse embryonic stem cell media with LIF for 95 days, Mstn (-/-) MDSCs formed embryonic stem cell (ES) like colonies. We termed such ES like cells as the culture-induced pluripotent stem cells (CiPSC). CiPSCs from Mstn (-/-) MDSCs were phenotypically similar to ESCs, expressed high levels of Oct4, Nanog, Sox2 and SSEA-1, maintained a normal karyotype. Furthermore, CiPSCs formed embryoid bodies and teratomas when injected into immunocompromised mice. In addition, CiPSCs differentiated into somatic cells of all three lineages. We further show that culturing in ES cell media, resulted in hypermethylation and downregulation of BMP2 in Mstn(-/-) MDSCs. Western blot further confirmed a down regulation of BMP2 signaling in Mstn (-/-) MDSCs in supportive of pluripotent reprogramming. Given that down regulation of BMP2 has been shown to induce pluripotency in cells, we propose that lack of myostatin epigenetically reprograms the MDSCs to become pluripotent stem cells. Thus, here we report the successful establishment of ES-like cells from adult stem cells of the non-germline origin under culture-induced conditions without introducing reprogramming genes.

Cardiomyocyte differentiation of pluripotent stem cells with SB203580 analogues correlates with Wnt pathway CK1 inhibition independent of p38 MAPK signaling

Differentiation of human pluripotent stem cells as embryoid bodies (EBs) has been achieved previously with p38alfa MAPK inhibitors such as SB203580 with moderate efficiency of 10-15%. We synthesized and screened 42 compounds that are 2,4,5-trisubstituted azole analogues of SB203580 for efficient cardiomyocyte differentiation. Our screen identified novel compounds that have similar cardiac differentiation activity as SB203580. However, the cardiac differentiation did not correlate with p38alfa MAPK inhibition, indicating an alternative mechanism in cardiac differentiation. Upon profiling several 2,4,5-trisubstituted azole compounds against a panel of 97 kinases we identified several off targets, among them casein kinases 1 (CK1). The cardiomyogenic activities of SB203580 and its analogues showed a correlation with post mesoderm Wnt/beta-catenin pathway inhibition of CK1 epsilon and delta. These findings united the mechanism of 2,4,5-trisubstituted azole with the current theory of Wnt/beta-catenin regulated pathway of cardiac differentiation. Consequently an efficient cardiomyocyte protocol was developed with Wnt activator CHIR99021 and 2,4,5-trisubstituted azoles to give high yields of 50-70% cardiomyocytes and a 2-fold increase in growth.

The formation of proximal and distal definitive endoderm populations in culture requires p38 MAPK activity

Endoderm formation in the mammal is a complex process with two lineages forming during the first weeks of development, the primitive (or extraembryonic) endoderm, which is specified in the blastocyst, and the definitive endoderm that forms later, at gastrulation, as one of the germ layers of the embryo proper. Fate mapping evidence suggests that the definitive endoderm arises as two waves, which potentially reflect two distinct cell populations. Early primitive ectoderm-like (EPL) cell differentiation has been used successfully to identify and characterise mechanisms regulating molecular gastrulation and lineage choice during differentiation. The roles of the p38 MAPK family in the formation of definitive endoderm were investigated using EPL cells and chemical inhibitors of p38 MAPK activity. These approaches define a role for p38 MAPK activity in the formation of the primitive streak and a second role in the formation of the definitive endoderm. Characterisation of the definitive endoderm populations formed from EPL cells demonstrates the formation of two distinct populations, defined by gene expression and ontogeny, that were analogous to the proximal and distal definitive endoderm populations of the embryo. Formation of the proximal definitive endoderm was found to require p38 MAPK activity and is correlated with molecular gastrulation, defined by the expression of brachyury (T). Distal definitive endoderm formation also requires p38 MAPK activity but can form when T expression is inhibited. Understanding lineage complexity will be a prerequisite for the generation of endoderm derivatives for commercial and clinical use.

Assessing developmental roles of MKK4 and MKK7 in vitro

In vivo gene knockout studies in mice have revealed essential roles of the mitogen-activated protein kinases (MAPKs) in embryogenesis, but due to early lethality of the knockout embryos, the underlying mechanisms and specific developmental programs regulated by the MAPK pathways have remained largely unknown. In vitro differentiation of mouse embryonic stem cells (ESCs) have opened new possibilities for understanding lineage segregation and gene function in the developmental stages that are not normally accessible in vivo. Building on this technology, in combination with gene knockout cells, we investigated the roles of MKK4 and MKK7, two upstream kinases of the MAPKs, in early lineage specification. Our results show that MKK4 and MKK7 differentially regulate the JNK and p38 MAPKs and make distinct contributions to differentiation programs. In vitro ESC differentiation is a valuable system to investigate the molecular and signaling mechanisms of early embryogenesis.