Early Phase Of Differentiation Research Articles

Differentiation of primary pre‐adipocytes into adipose tissue in a microfluidic chip

The growing problem of obesity has reached epidemic proportion worldwide and with over 1.5 billion adults aged 20 years and older characterized as being overweight [1]. Being overweight or obese remarkably increases the risks of developing other metabolic diseases such as diabetes. Adipose tissue is a key player in metabolic disorders including obesity and diabetes. Recent studies highlight the critical role adipose plays in maintaining metabolic homeostasis [2, 3]. Development of in vitro models of adipose tissue is highly desirable to improve our understanding of disease biology of obesity and metabolic diseases. Microfluidic on‐chip in vitro models offer advantages compared to traditional static culture system in terms of mimicking the complex physiological environment for culturing, differentiating, and stimulating adipocytes in a small‐volume perfused cell culture system [4, 5]. Here, we aim to establish a model for differentiation of pre‐adipocytes into mature adipose depots on a microfluidic chip. Mouse primary pre‐adipocytes isolated from subcutaneous white adipose tissue (WAT) were differentiated into mature white adipocytes in a microfluidic chip under perfused flow of 5μL/h. Our unique microfluidic chip enables for long‐term culture of cells and allows stimulation of cells through perfusion – we can culture, differentiate, and maintain the differentiated adipose tissue for over 21 days in the device. Upon differentiation, the cells increasingly accumulated triglycerides, which was quantified using fluorescence microscopy. Further confirmation of the differentiation was assessed by measuring the gene expression of markers including leptin and adiponectin. In addition, we collected and analyzed the perfusate for adipose secretions including adiponectin. Our results indicate an improved understanding of adipose differentiation under dynamic conditions and can serve as disease models for obesity and other metabolic disorders.Support or Funding InformationThis work was supported by NIH grant DK095984. [1] Ahima RS. Digging deeper into obesity. Journal of Clinical Investigation 2011;121:2076–9.[2] Clark AM, Sousa KM, Chisolm CN, MacDougald OA, Kennedy RT. Reversibly sealed multilayer microfluidic device for integrated cell perfusion and on‐line chemical analysis of cultured adipocyte secretions. Analytical and Bioanalytical Chemistry 2010;397:2939–47.[3] Lee PL, Tang Y, Li H, Guertin DA. Raptor/mTORC1 loss in adipocytes causes progressive lipodystrophy and fatty liver disease. Molecular Metabolism 2016;5:422–32.[4] Engler AJ, Hemmingsen M, Vedel S, Skafte‐Pedersen P, Sabourin D, Collas P, et al. The Role of Paracrine and Autocrine Signaling in the Early Phase of Adipogenic Differentiation of Adipose‐derived Stem Cells. PLoS ONE 2013;8:e63638.[5] Godwin LA, Brooks JC, Hoepfner LD, Wanders D, Judd RL, Easley CJ. A microfluidic interface for the culture and sampling of adiponectin from primary adipocytes. The Analyst 2015;140:1019–25.

WNK4 is an Adipogenic Factor and Its Deletion Reduces Diet-Induced Obesity in Mice

The with-no-lysine kinase (WNK) 4 gene is a causative gene in pseudohypoaldosteronism type II. Although WNKs are widely expressed in the body, neither their metabolic functions nor their extrarenal role is clear. In this study, we found that WNK4 was expressed in mouse adipose tissue and 3T3-L1 adipocytes. In mouse primary preadipocytes and in 3T3-L1 adipocytes, WNK4 was markedly induced in the early phase of adipocyte differentiation. WNK4 expression preceded the expression of key transcriptional factors PPARγ and C/EBPα. WNK4-siRNA-transfected 3T3-L1 cells and human mesenchymal stem cells showed reduced expression of PPARγ and C/EBPα and lipid accumulation. WNK4 protein affected the DNA-binding ability of C/EBPβ and thereby reduced PPARγ expression. In the WNK4−/− mice, PPARγ and C/EBPα expression were decreased in adipose tissues, and the mice exhibited partial resistance to high-fat diet-induced adiposity. These data suggest that WNK4 may be a proadipogenic factor, and offer insights into the relationship between WNKs and energy metabolism.

APOBEC2 negatively regulates myoblast differentiation in muscle regeneration

Recently we found that the deficiency of APOBEC2, a member of apoB mRNA editing enzyme, catalytic polypeptide-like family, leads to a diminished muscle mass and increased myofiber with centrally-located nuclei known as dystrophic phenotypes. APOBEC2 expression is predominant in skeletal and cardiac muscles and elevated exclusively at the early-differentiation phase of wild-type (WT) myoblast cultures; however the physiological significance is still un-known. Here we show that APOBEC2 is a key negative regulator of myoblast differentiation in muscle regeneration. APOBEC2-knockout (A2KO) mice myoblast cultures displayed a normal morphology of primary myotubes along with earlier increase in fusion index and higher expression levels of myosin heavy chain (MyHC), myogenin and its cooperating factor MEF2C than WT myoblasts. Similar response was observable in APOBEC2-knockdown cultures of WT myoblasts that were transfected with the specific siRNA at the differentiation phase (not proliferation phase). Importantly, cardiotoxin-injured A2KO gastrocnemius muscle provided in vivo evidence by showing larger up-regulation of neonatal MyHC and myogenin and hence earlier regeneration of myofiber structures with diminished cross-sectional areas and minimal Feret diameters. Therefore, the findings highlight a promising role for APOBEC2 in normal progression of regenerative myogenesis at the early-differentiation phase upon muscle injury.

Inhibition of Protein Kinase CK2 Prevents Adipogenic Differentiation of Mesenchymal Stem Cells Like C3H/10T1/2 Cells.

Protein kinase CK2 as a holoenzyme is composed of two catalytic α- or α’-subunits and two non-catalytic β-subunits. Knock-out experiments revealed that CK2α and CK2β are required for embryonic development. Little is known about the role of CK2 during differentiation of stem cells. Mesenchymal stem cells (MSCs) are multipotent cells which can be differentiated into adipocytes in vitro. Thus, MSCs and in particular C3H/10T1/2 cells are excellent tools to study a possible role of CK2 in adipogenesis. We found downregulation of the CK2 catalytic subunits as well as a decrease in CK2 kinase activity with progression of differentiation. Inhibition of CK2 using the potent inhibitor CX-4945 impeded differentiation of C3H/10T1/2 cells into adipocytes. The inhibited cells lacked the observed decrease in CK2 expression, but showed a constant expression of all three CK2 subunits. Furthermore, inhibition of CK2 resulted in decreased cell proliferation in the early differentiation phase. Analysis of the main signaling cascade revealed an elevated expression of C/EBPβ and C/EBPδ and reduced expression of the adipogenic master regulators C/EBPα and PPARγ2. Thus, CK2 seems to be implicated in the regulation of different steps early in the adipogenic differentiation of MSC.

Glucocorticoid Receptor Accelerates, but Is Dispensable for, Adipogenesis.

Dexamethasone (DEX), a synthetic ligand for glucocorticoid receptor (GR), is routinely used to stimulate adipogenesis in culture. GR-depleted preadipocytes show adipogenesis defects 1 week after induction of differentiation. However, it has remained unclear whether GR is required for adipogenesis in vivo By deleting GR in precursors of brown adipocytes, we found unexpectedly that GR is dispensable for brown adipose tissue development in mice. In culture, GR-deficient primary or immortalized white and brown preadipocytes showed severely delayed adipogenesis 1 week after induction of differentiation. However, when differentiation was extended to 3 weeks, GR-deficient preadipocytes showed levels of adipogenesis marker expression and lipid accumulation similar to those of the wild-type cells, indicating that DEX-bound GR accelerates, but is dispensable for, adipogenesis. Consistently, DEX accelerates, but is dispensable for, adipogenesis in culture. We show that DEX-bound GR accelerates adipogenesis by directly promoting the expression of adipogenic transcription factors CCAAT/enhancer-binding protein alpha (C/EBPα), C/EBPβ, C/EBPδ, KLF5, KLF9, and peroxisome proliferator-activated receptor γ (PPARγ) in the early phase of differentiation. Mechanistically, DEX-bound GR recruits histone H3K27 acetyltransferase CBP to promote activation of C/EBPβ-primed enhancers of adipogenic genes. These results clarify the role of GR in adipogenesis in vivo and demonstrate that DEX-mediated activation of GR accelerates, but is dispensable for, adipogenesis.

Accessible Chromatin Landscape Reveals a Proliferative Osteoprogenitor Transcriptional Program in Bone Marrow Mesenchymal Stromal Cells from Patients with Primary Myelofibrosis

Primary myelofibrosis (PMF) is chronic myeloproliferative neoplasm characterized by clonal hematopoietic alterations contributing to myeloproliferation, egress of CD34+ cells from bone marrow to spleen associated with extra-medullary hematopoiesis, myelofibrosis with neo-ossification, leading to an osteomyelosclerosis as a result of increased CD146+ osteoprogenitor compartment. Recent studies from our laboratory have reported that bone marrow (BM) mesenchymal stromal cells (MSCs) from PMF patients (PMF-MSCs) showed a transcriptome and functional profile in agreement with an imprinted alteration of their osteogenic potential1&2.We performed advanced in silico analysis of accessible chromatin landscape of proliferative hFOB cells (human Fetal OsteoBlastic cell line) and identified 1183 target promoters during early phase of osteoblastic differentiation. Integration of these osteoblastic promoters in the transcriptome of PMF versus healthy donors (HD) BM-MSCs2 revealed an overexpression of 222 genes in the mesenchymal transcriptional program of patients (False discovery rate: FDR<5%), corresponding to a genomic enrichment of 5.95 (Fisher Exact test: p-value<2.2E-16) of the osteoblastic program in PMF-MSC transcriptome. Unsupervised principal component analysis significantly discriminated PMF patients from HD samples (p-value=7.92E-6). Actually, the osteoblastic transcriptional program activated in BM-MSCs from PMF patients shows an enrichment of genes coding for cell functions such as mRNA processing (-log p-value=11.39), MAPK pathway (-log p-value=6.39) and transcription start sites (TSS) bound by the ETS-domain transcription factor ELK1 (-log10 p-value=8.99). Geneset enrichment analysis (GSEA) also reveals an increase of MYC targets in the PMF-MSC transcriptome which shared 11 targets with ELK1 (NES=2.69, p-value<0.001). Interestingly, ELK1-ETS transcription factor downstream of Erk-MAPK is increased in PMF-MSC transcriptome (p-value = 0.0017) and is a target of MYC. These results suggest that the osteoblastic program is over expressed in PMF BM-MSCs and that it is likely controlled by MAPK and MYC.We also showed that a majority of transcription factors link to osteoblastic differentiation such as JUN, NFATC1, SP7, DLX5, FOS, RUNX2 were down regulated in PMF-MSC transcriptome (GSEA NES=-2.79, p-value<0.001), suggesting an imbalance in the proliferative vs. differentiation transcription program in these cells. Erk1/Erk2 was found to be hyperphosphorylated in PMF-MSCs by flow cytometry. Inhibition of the MAPK pathway by PD98059 during the early phase of in vitro MSC osteoblastic differentiation reveals an increase expression of collagen, a marker of differentiation, as shown by confocal microscopy. This is less the case with myc-inhibitor I (Calbiochem), suggesting the participation of the MAPK pathway in the proliferative vs. differentiation balance of MSCs/osteoprogenitors.In conclusion, integration of the open chromatin genomic landscape of the hFOB osteoblast fetal cells in the PMF BM-MSC transcriptome reveals a proliferative program of MSCs/osteoprogenitors associated in vitro with a repression of the differentiation in accordance with an increase proliferative osteoprogenitor priming of PMF-MSCs1 and with the presence of large size osteoblastic cells in vicinity of the neo-ossification area observed in the BM of PMF patients with osteomyelosclerosis.Martinaud C et al., Cancer Res. 2015 Nov 15;75(22):4753-65Martinaud C et al., Genom Data. 2015 Sep; 5: 1-2 DisclosuresVannucchi:Novartis: Honoraria, Speakers Bureau.

MTOR has distinct functions in generating versus sustaining humoral immunity.

Little is known about the role of mTOR signaling in plasma cell differentiation and function. Furthermore, for reasons not understood, mTOR inhibition reverses antibody-associated disease in a murine model of systemic lupus erythematosus. Here, we have demonstrated that induced B lineage-specific deletion of the gene encoding RAPTOR, an essential signaling adaptor for rapamycin-sensitive mTOR complex 1 (mTORC1), abrogated the generation of antibody-secreting plasma cells in mice. Acute treatment with rapamycin recapitulated the effects of RAPTOR deficiency, and both strategies led to the ablation of newly formed plasma cells in the spleen and bone marrow while also obliterating preexisting germinal centers. Surprisingly, although perturbing mTOR activity caused a profound decline in serum antibodies that were specific for exogenous antigen or DNA, frequencies of long-lived bone marrow plasma cells were unaffected. Instead, mTORC1 inhibition led to decreased expression of immunoglobulin-binding protein (BiP) and other factors needed for robust protein synthesis. Consequently, blockade of antibody synthesis was rapidly reversed after termination of rapamycin treatment. We conclude that mTOR signaling plays critical but diverse roles in early and late phases of antibody responses and plasma cell differentiation.

Schisandrae fructus enhances myogenic differentiation and inhibits atrophy through protein synthesis in human myotubes.

Schisandrae fructus (SF) has recently been reported to increase skeletal muscle mass and inhibit atrophy in mice. We investigated the effect of SF extract on human myotube differentiation and its acting pathway. Various concentrations (0.1–10 μg/mL) of SF extract were applied on human skeletal muscle cells in vitro. Myotube area and fusion index were measured to quantify myotube differentiation. The maximum effect was observed at 0.5 μg/mL of SF extract, enhancing differentiation up to 1.4-fold in fusion index and 1.6-fold in myotube area at 8 days after induction of differentiation compared to control. Phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 and 70 kDa ribosomal protein S6 kinase, which initiate translation as downstream of mammalian target of rapamycin pathway, was upregulated in early phases of differentiation after SF treatment. SF also attenuated dexamethasone-induced atrophy. In conclusion, we show that SF augments myogenic differentiation and attenuates atrophy by increasing protein synthesis through mammalian target of rapamycin/70 kDa ribosomal protein S6 kinase and eukaryotic translation initiation factor 4E-binding protein 1 signaling pathway in human myotubes. SF can be a useful natural dietary supplement in increasing skeletal muscle mass, especially in the aged with sarcopenia and the patients with disuse atrophy.

C-Myc regulation by Notch Signaling Modulates T Cell Differentiation

Abstract Notch signaling is essential for T lineage commitment and further required during early phases of thymocyte differentiation. Active Notch signaling during early stages of T cell development inhibits other lineage potentials, such as B cell and myeloid cell (e.g., dendritic cell) potentials. However, the intracellular signaling pathways by which Notch signaling regulates T cell differentiation remain unknown. Here we show that the transcriptional factor c-Myc is controlled by Notch signaling which regulates T cell differentiation. In a well-established in vitro differentiation of T lymphocytes from stem cells, Notch signaling directly controls c-Myc expression. Overexpression of active c-Myc promotes while dominant-negative (dn) c-Myc inhibits early cell differentiation. Moreover, c-Myc expression mediated by Notch signaling modulates survivin, an inhibitor of apoptosis (IAP) protein, which is crucial for T cell development. Overexpression of active c-Myc increases while dn c-Myc reduces survivin expression, which corresponds to T cell differentiation within the in vitro differentiation system. These results identify c-Myc, together with survivin, as regulators of the differentiation of T cells from Notch signaling.

TonEBP/NFAT5 inhibits adipocyte differentiation via modulation of mitotic clonal expansion during early phase of differentiation in 3T3‐L1 cells

Obesity resulting from excessive accumulation of white adipose tissue is closely related to the chronic diseases such as diabetes, hyperlipidemia, and hypertension. White adipose mass is determined by the number and size of adipocytes. Preadipocyte like 3T3‐L1 cells undergo terminal differentiation manifested by formation of lipid droplets as well as adipocyte specific protein. TonEBP/NFAT5 belongs to the Rel family of transcription factors and plays important roles in the development and maintenance of kidney, immunity, arthritis, and cancer metastasis. Although the functions of TonEBP/NFAT5 during osteogenesis, chondrogenesis and myogenesis are reported recently, its role in the adipogenesis is not well known. In this study, we analyzed the role of TonEBP/NFAT5 in adipogenesis using 3T3‐L1 cells. TonEBP/NFAT5 expression was dramatically reduced during adipocyte differentiation of 3T3‐L1 cells. RNAi‐mediated knock down of TonEBP/NFAT5 facilitated adipogenesis. Whereas sustained expression of TonEBP/NFAT5 using adenovirus suppressed the formation of lipid droplet and the expression of FABP4, marker for terminally differentiated adipocytes. Also, TonEBP/NFAT5 inhibited the expression of PPARγ, master regulator of terminal adipocytes. TonEBP/NFAT5 suppressed adipogenesis in the early phase of the differentiation via modulation of Akt activity and mitotic clonal expansion. These results suggest that TonEBP/NFAT5 may be an important regulatory factor in the differentiation of adipocytes.Support or Funding InformationThis research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (NRF‐2013R1A1A2060736, NRF‐2014R1A6A1029617)

Characterization of Notch Signaling During Osteogenic Differentiation in Human Osteosarcoma Cell Line MG63

Osteogenic differentiation is a multi-step process controlled by a complex molecular framework. Notch is an evolutionarily conserved intercellular signaling pathway playing a prominent role in cell fate and differentiation, although the mechanisms by which this pathway regulates osteogenesis remain controversial. This study aimed to investigate, in vitro, the involvement of Notch pathway during all the developmental stages of osteogenic differentiation in human osteosarcoma cell line MG63. Cells were cultured in basal condition (control) and in osteoinductive medium (OM). Notch inhibitors were also added in OM to block Notch pathway. During osteogenic differentiation, early (alkaline phosphatase activity and collagen type I) and late osteogenic markers (osteocalcin levels and matrix mineralization), as well as the gene expression of the main osteogenic transcription factors (Runx2, Osterix, and Dlx5) increased. Time dependent changes in the expression of specific Notch receptors were identified in OM versus control with a significant reduction in the expression of Notch1 and Notch3 receptors in the early phase of differentiation, and an increase of Notch2 and Notch4 receptors in the late phase. Among Notch nuclear target genes, Hey1 expression was significantly higher in OM than control, while Hes5 expression decreased. Osteogenic markers were reduced and Hey1 was significantly inhibited by Notch inhibitors, suggesting a role for Notch through the canonical pathway. In conclusion, Notch pathway might be involved with a dual role in osteogenesis of MG63, through the activation of Notch2, Notch4, and Hey1, inducing osteoblast differentiation and the depression of Notch1, Notch3, and Hes5, maintaining an undifferentiated status. J. Cell. Physiol. 231: 2652-2663, 2016. © 2016 Wiley Periodicals, Inc.

HMGA2 promotes adipogenesis by activating C/EBPβ-mediated expression of PPARγ

Adipogenesis is orchestrated by a highly ordered network of transcription factors including peroxisome-proliferator activated receptor-gamma (PPARγ) and CCAAT-enhancer binding protein (C/EBP) family proteins. High mobility group protein AT-hook 2 (HMGA2), an architectural transcription factor, has been reported to play an essential role in preadipocyte proliferation, and its overexpression has been implicated in obesity in mice and humans. However, the direct role of HMGA2 in regulating the gene expression program during adipogenesis is not known. Here, we demonstrate that HMGA2 is required for C/EBPβ-mediated expression of PPARγ, and thus promotes adipogenic differentiation. We observed a transient but marked increase of Hmga2 transcript at an early phase of differentiation of mouse 3T3-L1 preadipocytes. Importantly, Hmga2 knockdown greatly impaired adipocyte formation, while its overexpression promoted the formation of mature adipocytes. We found that HMGA2 colocalized with C/EBPβ in the nucleus and was required for the recruitment of C/EBPβ to its binding element at the Pparγ2 promoter. Accordingly, HMGA2 and C/EBPβ cooperatively enhanced the Pparγ2 promoter activity. Our results indicate that HMGA2 is an essential constituent of the adipogenic transcription factor network, and thus its function may be affected during the course of obesity.

The Tocotrienol-Rich Fraction Is Superior to Tocopherol in Promoting Myogenic Differentiation in the Prevention of Replicative Senescence of Myoblasts.

Aging results in a loss of muscle mass and strength. Myoblasts play an important role in maintaining muscle mass through regenerative processes, which are impaired during aging. Vitamin E potentially ameliorates age-related phenotypes. Hence, this study aimed to determine the effects of the tocotrienol-rich fraction (TRF) and α-tocopherol (ATF) in protecting myoblasts from replicative senescence and promoting myogenic differentiation. Primary human myoblasts were cultured into young and senescent stages and were then treated with TRF or ATF for 24 h, followed by an analysis of cell proliferation, senescence biomarkers, cellular morphology and differentiation. Our data showed that replicative senescence impaired the normal regenerative processes of myoblasts, resulting in changes in cellular morphology, cell proliferation, senescence-associated β-galactosidase (SA-β-gal) expression, myogenic differentiation and myogenic regulatory factors (MRFs) expression. Treatment with both TRF and ATF was beneficial to senescent myoblasts in reclaiming the morphology of young cells, improved cell viability and decreased SA-β-gal expression. However, only TRF treatment increased BrdU incorporation in senescent myoblasts, as well as promoted myogenic differentiation through the modulation of MRFs at the mRNA and protein levels. MYOD1 and MYOG gene expression and myogenin protein expression were modulated in the early phases of myogenic differentiation. In conclusion, the tocotrienol-rich fraction is superior to α-tocopherol in ameliorating replicative senescence-related aberration and promoting differentiation via modulation of MRFs expression, indicating vitamin E potential in modulating replicative senescence of myoblasts.

TonEBP suppresses adipocyte differentiation via modulation of early signaling in 3T3-L1 cells.

TonEBP belongs to the Rel family of transcription factors and plays important roles in inflammation as well as kidney homeostasis. Recent studies suggest that TonEBP expression is also involved in differentiation of several cell types such as myocytes, chondrocytes, and osteocytes. In this study, we investigated the roles of TonEBP during adipocyte differentiation in 3T3-L1 cells. TonEBP mRNA and protein expression was dramatically reduced during adipocyte differentiation. Sustained expression of TonEBP using an adenovirus suppressed the formation of lipid droplets as well as the expression of FABP4, a marker of differentiated adipocytes. TonEBP also inhibited the expression of PPARγ, a known master regulator of adipocytes. RNAi-mediated knock down of TonEBP promoted adipocyte differentiation. However, overexpression of TonEBP did not affect adipogenesis after the initiation of differentiation. Furthermore, TonEBP expression suppressed mitotic clonal expansion and insulin signaling, which are required early for adipocyte differentiation of 3T3-L1 cells. These results suggest that TonEBP may be an important regulatory factor in the early phase of adipocyte differentiation.

Application of mutant JAK2V617F for in vitro generation of red blood cells

In vitro generation of red blood cells (RBCs) from hematopoietic stem cells (HSCs) has been reported, but the collection of 1 × 10(5) to 1 × 10(6) CD34+ cells present in cord and peripheral blood is too small for expansion to 1 × 10(12) cells in 1 unit of RBCs. We transduced JAK2V617F gene, the most common mutation with polycythemia vera (PV), into cord blood-derived CD34+ cells. This PV model was expected to increase cell proliferation without the addition of erythropoietin (EPO) in early phase of differentiation. Empty vector (control), wild-type JAK2 (wJAK2), and mutant JAK2V617F (mJAK2) were transduced into CD34+ cells using a lentivirus system. The CD34+ cells were then differentiated to the RBCs in a culture system. The cells were analyzed for cell number, differential count, and morphologic changes. Cultured RBCs were tested for oxygen equilibrium. wJAK2- and mJAK2-transduced cells showed higher proliferation capacity until Day 21 than control cells; interestingly, only mJAK2-transduced cells were highly increased on Day 7 during EPO-free culture. However, both wJAK2- and mJAK2-tranduced cells had more delayed differentiation than control, but they had a higher portion of completely matured RBCs and orthochromatic erythroblasts. Furthermore, mJAK2-tranduced cells showed more differentiation into RBCs than wJAK2-transduced cells and they had a normal hemoglobin dissociation curve. This is the first trial to use a PV erythropoiesis model for RBC differentiation from stem cells. The transduction of HSCs with mJAK2 increased their proliferation capacity in EPO-free culture conditions. This model may also be useful for investigating the pathogenesis of PV.

Polyamine and Its Metabolite H2O2 Play a Key Role in the Conversion of Embryogenic Callus into Somatic Embryos in Upland Cotton (Gossypium hirsutum L.).

The objective of this study was to increase understanding about the mechanism by which polyamines (PAs) promote the conversion of embryogenic calli (EC) into somatic embryos in cotton (Gossypium hirsutum L.). We measured the levels of endogenous PAs and H2O2, quantified the expression levels of genes involved in the PAs pathway at various stages of cotton somatic embryogenesis (SE), and investigated the effects of exogenous PAs and H2O2 on differentiation and development of EC. Putrescine (Put), spermidine (Spd), and spermine (Spm) significantly increased from the EC stage to the early phase of embryo differentiation. The levels of Put then decreased until the somatic embryo stage whereas Spd and Spm remained nearly the same. The expression profiles of GhADC genes were consistent with changes in Put during cotton SE. The H2O2 concentrations began to increase significantly at the EC stage, during which time both GhPAO1 and GhPAO4 expressions were highest and PAO activity was significantly increased. Exogenous Put, Spd, Spm, and H2O2 not only enhanced embryogenic callus growth and embryo formation, but also alleviated the effects of D-arginine and 1, 8-diamino-octane, which are inhibitors of PA synthesis and PAO activity. Overall, the results suggest that both PAs and their metabolic product H2O2 are essential for the conversion of EC into somatic embryos in cotton.

Changes in Laminin Expression Pattern during Early Differentiation of Human Embryonic Stem Cells.

Laminin isoforms laminin-511 and -521 are expressed by human embryonic stem cells (hESC) and can be used as a growth matrix to culture these cells under pluripotent conditions. However, the expression of these laminins during the induction of hESC differentiation has not been studied in detail. Furthermore, the data regarding the expression pattern of laminin chains in differentiating hESC is scarce. In the current study we aimed to fill this gap and investigated the potential changes in laminin expression during early hESC differentiation induced by retinoic acid (RA). We found that laminin-511 but not -521 accumulates in the committed cells during early steps of hESC differentiation. We also performed a comprehensive analysis of the laminin chain repertoire and found that pluripotent hESC express a more diverse range of laminin chains than shown previously. In particular, we provide the evidence that in addition to α1, α5, β1, β2 and γ1 chains, hESC express α2, α3, β3, γ2 and γ3 chain proteins and mRNA. Additionally, we found that a variant of laminin α3 chain—145 kDa—accumulated in RA-treated hESC showing that these cells produce prevalently specifically modified version of α3 chain in early phase of differentiation.

Transmembrane proteoglycans syndecan-2, 4, receptor candidates for the impact of HGF and FGF2 on semaphorin 3A expression in early-differentiated myoblasts.

Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed an unexplored role of resident myogenic stem cell (satellite cell)-derived myoblasts as a key presenter of a secreted neural chemorepellent semaphorin 3A (Sema3A); hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) triggered its expression exclusively at the early differentiation phase. In order to advance this concept, the present study described that transmembrane heparan/chondroitin sulfate proteoglycans syndecan-2, 4 may be the plausible receptor candidates for HGF and FGF2 to signal Sema3A expression. Results showed that mRNA expression of syndecan-2, 4 was abundant (two magnitudes higher than syndecan-1, 3) in early-differentiated myoblasts and their in vitro knockdown diminished the HGF/FGF2-induced expression of Sema3A down to a baseline level. Pretreatment with heparitinase and chondroitinase ABC decreased the HGF and FGF2 responses, respectively, in non–knockdown cultures, supporting a possible model that HGF and FGF2 may bind to heparan and chondroitin sulfate chains of syndecan-2, 4 to signal Sema3A expression. The findings, therefore, extend our understanding that HGF/FGF2-syndecan-2, 4 association may stimulate a burst of Sema3A secretion by myoblasts recruited to the site of muscle injury; this would ensure a coordinated delay in the attachment of motoneuron terminals onto fibers early in muscle regeneration, and thus synchronize the recovery of muscle fiber integrity and the early resolution of inflammation after injury with reinnervation toward functional recovery.

Separating myoblast differentiation from muscle cell fusion using IGF-I and the p38 MAP kinase inhibitor SB202190.

The p38 MAP kinases play critical roles in skeletal muscle biology, but the specific processes regulated by these kinases remain poorly defined. Here we find that activity of p38α/β is important not only in early phases of myoblast differentiation, but also in later stages of myocyte fusion and myofibrillogenesis. By treatment of C2 myoblasts with the promyogenic growth factor insulin-like growth factor (IGF)-I, the early block in differentiation imposed by the p38 chemical inhibitor SB202190 could be overcome. Yet, under these conditions, IGF-I could not prevent the later impairment of muscle cell fusion, as marked by the nearly complete absence of multinucleated myofibers. Removal of SB202190 from the medium of differentiating myoblasts reversed the fusion block, as multinucleated myofibers were detected several hours later and reached ∼90% of the culture within 30 h. Analysis by quantitative mass spectroscopy of proteins that changed in abundance following removal of the inhibitor revealed a cohort of upregulated muscle-enriched molecules that may be important for both myofibrillogenesis and fusion. We have thus developed a model system that allows separation of myoblast differentiation from muscle cell fusion and should be useful in identifying specific steps regulated by p38 MAP kinase-mediated signaling in myogenesis.

BAMBI Promotes C2C12 Myogenic Differentiation by Enhancing Wnt/β-Catenin Signaling.

Bone morphogenic protein and activin membrane-bound inhibitor (BAMBI) is regarded as an essential regulator of cell proliferation and differentiation that represses transforming growth factor-β and enhances Wnt/β-catenin signaling in various cell types. However, its role in skeletal muscle remains largely unknown. In the current study, we found that the expression level of BAMBI peaked in the early differentiation phase of the C2C12 rodent myoblast cell line. Knockdown of BAMBI via siRNA inhibited C2C12 differentiation, indicated by repressed MyoD, MyoG, and MyHC expression as well as reductions in the differentiation and fusion indices. BAMBI knockdown reduced the activity of Wnt/β-catenin signaling, as characterized by the decreased nuclear translocation of β-catenin and the lowered transcription of Axin2, which is a well-documented target gene of the Wnt/β-catenin signaling pathway. Furthermore, treatment with LiCl, an activator of Wnt/β-catenin signaling, rescued the reduction in C2C12 differentiation caused by BAMBI siRNA. Taken together, our data suggest that BAMBI is required for normal C2C12 differentiation, and that its role in myogenesis is mediated by the Wnt/β-catenin pathway.