Adhesion of mature polyploid megakaryocytes to fibronectin is mediated by beta 1 integrins and leads to cell damage

Restriction of growth and biofilm formation of ESKAPE pathogens by caprine gut-derived probiotic bacteria

The accelerated rise in antimicrobial resistance (AMR) poses a significant global health risk, necessitating the exploration of alternative strategies to combat pathogenic infections. Biofilm-related infections that are unresponsive to standard antibiotics often require the use of higher-order antimicrobials with toxic side effects and the potential to disrupt the microbiome. Probiotic therapy, with its diverse benefits and inherent safety, is emerging as a promising approach to prevent and treat various infections, and as an alternative to antibiotic therapy. In this study, we isolated novel probiotic bacteria from the gut of domestic goats (Capra hircus) and evaluated their antimicrobial and anti-biofilm activities against the 'ESKAPE' group of pathogens. We performed comprehensive microbiological, biochemical, and molecular characterizations, including analysis of the 16S-rRNA gene V1-V3 region and the 16S-23S ISR region, on 20 caprine gut-derived lactic acid bacteria (LAB). Among these, six selected Lactobacillus isolates demonstrated substantial biofilm formation under anaerobic conditions and exhibited robust cell surface hydrophobicity and autoaggregation, and epithelial cell adhesion properties highlighting their superior enteric colonization capability. Notably, these Lactobacillus isolates exhibited broad-spectrum growth inhibitory and anti-biofilm properties against 'ESKAPE' pathogens. Additionally, the Lactobacillus isolates were susceptible to antibiotics listed by the European Food Safety Authority (EFSA) within the prescribed Minimum Inhibitory Concentration limits, suggesting their safety as feed additives. The remarkable probiotic characteristics exhibited by the caprine gut-derived Lactobacillus isolates in this study strongly endorse their potential as compelling alternatives to antibiotics and direct-fed microbial (DFM) feed supplements in the livestock industry, addressing the escalating need for antibiotic-free animal products.

Integrins and their role in megakaryocyte development and function

Mature megakaryocytes, the platelet precursors, originate from hematopoietic stem cell progenitors, which, once committed to this lineage, undergo endomitosis leading to polyploidization. The process entails repeated rounds of DNA replication without cell division, yielding polyploid cells. Supporting the cell's developmental process and various cellular functions are integrin receptors, a conduit of communication between the extracellular environment and the cell actin cytoskeleton. Integrins are heterodimers of α and β subunits, where different combinations of the known 18 α and 8 β subunits confer specificity to the receptor. Integrin ligands range from extracellular matrices through soluble ligands, infectious agents, and counterreceptors, to cells. In this review, we describe the different integrins expressed on bone marrow megakaryocytes and their attributed roles in lineage development and cellular functions, including adhesion, spreading, proplatelet formation, and functional interaction with other cells. Pathologies associated with dysregulated megakaryocyte integrin expression are also reviewed.

Matrix Mechanosensation in the Erythroid and Megakaryocytic Lineages

The biomechanical properties of the bone marrow microenvironment emerge from a combination of interactions between various extracellular matrix (ECM) structural proteins and soluble factors. Matrix stiffness directs stem cell fate, and both bone marrow stromal and hematopoietic cells respond to biophysical cues. Within the bone marrow, the megakaryoblasts and erythroblasts are thought to originate from a common progenitor, giving rise to fully mature magakaryocytes (the platelet precursors) and erythrocytes. Erythroid and megakaryocytic progenitors sense and respond to the ECM through cell surface adhesion receptors such as integrins and mechanosensitive ion channels. While hematopoietic stem progenitor cells remain quiescent on stiffer ECM substrates, the maturation of the erythroid and megakaryocytic lineages occurs on softer ECM substrates. This review surveys the major matrix structural proteins that contribute to the overall biomechanical tone of the bone marrow, as well as key integrins and mechanosensitive ion channels identified as ECM sensors in context of megakaryocytosis or erythropoiesis.

Heat Shock Cognate Protein 70 Enhanced Integrin β1 Mediated Invasion in Cancer Cells

Purpose

Glioblastoma is one of the most common malignant cancers worldwide. In our previous work, we have shown that heat shock cognate protein 70 (Hsc70) functions as a positive growth regulator in glioma. We investigated the role of Hsc70 in integrin β1 mediated invasion of glioma cells.

Methods

In order to investigate whether the down-regulation of Hsc70 would affect the expression of integrin β1 subunit, HeLa cells were transiently transfected with Hsc70-AS or pcDNA3.0 vectors and the down-regulation of Hsc70 was confirmed by Western blotting. Human brain glioma U87 cells were stably transfected with Hsc70-AS or pcDNA3.0 vectors to further elucidate the relationship between Hsc70 and integrin β1 in human glioma cells. Cellular localization of integrin β1 was detected using immunofluorescence confocal microscopy analysis.

Results

Here we reported that down-regulation of the expression of Hsc70 in U87 cells by transfection with antisense cDNA specifically increased the expression of cell surface integrin β1 without changing its mRNA. Meanwhile, the integrin β1 125-kD mature form increased while 105-kD precursor form decreased when Hsc70 was down-regulated. Mechanically, the U87 cells transfected with antisense cDNA of Hsc70 decreased the Golgi localization of integrin β1, strengthened its interaction with integrin α5 subunit, and enhanced the adhesion ability to fibronectin (FN) and the phosphorylation level of focal adhesion kinase (FAK).

Conclusion

Overall, these results suggested that the down-regulation of Hsc70 expression could promote the expression of cell surface integrin β1 and subsequently inhibit glioma invasion phenotype.

Switch to high-level virus replication and HLA class I upregulation in differentiating megakaryocytic cells after infection with pathogenic hantavirus

Hantaan virus (HTNV), the prototype member of the Hantavirus genus in the family Bunyaviridae, causes hemorrhagic fever with renal syndrome (HFRS) in humans. Hemorrhage is due to endothelial barrier damage and a sharp decrease in platelet counts. The mechanisms underlying HTNV-associated acute thrombocytopenia have not been elucidated so far. Platelets are produced by mature megakaryocytes that develop during megakaryopoiesis. In this study, we show that HTNV targets megakaryocytic cells whereas rather non-pathogenic hantaviruses did not infect this cell type. After induction of differentiation megakaryocytic cells switched from low-level to high-level HTNV production without reduction in cell survival or alteration in differentiation. However, increased HTNV replication resulted in strong upregulation of HLA class I molecules although HTNV escaped type I interferon (IFN)-associated innate responses. Taken together, HTNV efficiently replicates in differentiating megakaryocytic cells resulting in upregulation of HLA class I molecules, the target structures for cytotoxic T cells (CTLs).

Tescalcin is an essential factor in megakaryocytic differentiation associated with Ets family gene expression

We show here that the process of megakaryocytic differentiation requires the presence of the recently discovered protein tescalcin. Tescalcin is dramatically upregulated during the differentiation and maturation of primary megakaryocytes or upon PMA-induced differentiation of K562 cells. This upregulation requires sustained signaling through the ERK pathway. Overexpression of tescalcin in K562 cells initiates events of spontaneous megakaryocytic differentiation, such as expression of specific cell surface antigens, inhibition of cell proliferation, and polyploidization. Conversely, knockdown of this protein in primary CD34+ hematopoietic progenitors and cell lines by RNA interference suppresses megakaryocytic differentiation. In cells lacking tescalcin, the expression of Fli-1, Ets-1, and Ets-2 transcription factors, but not GATA-1 or MafB, is blocked. Thus, tescalcin is essential for the coupling of ERK cascade activation with the expression of Ets family genes in megakaryocytic differentiation.

Adhesion receptor expression by CD34+ cells from peripheral blood or bone marrow grafts: correlation with time to engraftment

OBJECTIVE

This study was undertaken to define the pattern of cell adhesion receptor expression by the CD34+ progenitor cells from mobilized peripheral blood and bone marrow from normal and autologous donors, and to correlate the adhesion receptor profile with time to blood cell recovery for patients undergoing autologous transplant.

METHODS

Blood cell recovery was determined by absolute neutrophil count (> 500/microL), time to last red cell transfusion, and platelet count (> 50,000/microL and > 100,000/microL). The analysis for expression of adhesion receptors alphaL (CD11a), alpha2 (CD49b), alpha3 (CD49c), alpha4 (CD49d), alpha5 (CD49e), alpha6 (CD49f), beta1 (CD29), L-selectin (CD62L), ICAM-1 (CD54), PECAM-1 (CD31), HCAM (CD44), and P-selectin (CD62P) was performed by two-color flow cytometry. The Kruskal-Wallis test and Spearman's rank correlation were used for statistical analysis.

RESULTS

Statistical analysis of adhesion expression by the CD34+ population for patients undergoing autologous transplant demonstrated that the higher percent expression of PECAM-1 correlated with longer time to platelet recovery (> 100,000/microL, p = 0.049). In contrast, the higher the percent expression of alpha6 (p = 0.013) and the increased density of expression of alpha2 (p = 0.035), alpha3 (p = 0.023), alpha4 (p = 0.044), beta1 (p = 0.027), and ICAM-1 (p = 0.010) correlated with shorter time to platelet recovery. Neutrophil recovery time decreased with increased density of expression of alphaL (p = 0.014) and P-selectin (p = 0.007) receptors. Increased density of expression of CD44 (HCAM) was associated with longer time to red blood cell recovery (p = 0.05).

CONCLUSION

These data suggest that upregulation of specific adhesion receptors or selection of certain cell populations could result in earlier blood cell recovery after transplant.

Enforced adhesion of hematopoietic cells to culture dish induces endomitosis and polyploidy

Cells of epithelial or endothelial lineage when forced to grow in suspension undergo the detachment-induced death termed "anoikis". In the present study we explored the reverse situation namely the effect of enforcement of hematopoietic lineage cells that are normally maintained in suspension to grow attached. Towards this end murine L1210 or human HL-60 and Jurkat leukemia cells were cultured in slide chambers coated with poly-L- or poly-D- lysine, or with compound 48/80, the polycations attracting them electrostatically. Within minutes after the transfer L1210 cells strongly adhered to bottom surface of the dish and shortly thereafter binuclear-, and later on, polynuclear-cells become apparent. The frequency of nuclei per cell was increasing with time and polykaryons with up to 16 nuclei and high DNA ploidy (DI = 16.0) were apparent after 48 h. After 4 days the size (volume) of some polykaryons exceeded by over 340-fold the volume of mononuclear cells. The presence of mitotic figures and abnormal mitotic spindles in adhering polykaryons provided evidence of the impeded cytokinesis that led to endomitosis. Most polykaryons excluded trypan blue, had balanced growth (unchanged protein/DNA ratio compared to monokaryons), and showed no evidence of apoptosis. Individual nuclei within each polykaryon replicated DNA in synchrony. The strong cell attachment and aborted cytokinesis were cell line specific since no significant endomitosis was observed in Jurkat- or HL-60- cells which did not strongly attach to polycation-coated surfaces. Defective cytokinesis and induction of polyploidy by this mechanism, if occurs in vivo (e.g., mediated by integrins), may lead to aneuploidy and therefore have tumorigenic consequences. The phenomenon offers novel experimental model for induction of polyploidy and provides alternative to cytocholasin B to prevent cytokinesis in the mutagenicity cytokinesis-blocked micronucleus (CBMN) assay.

Modulation of human leukocyte antigen and intracellular adhesion molecule-1 surface expression in malignant and nonmalignant human thyroid cells by cytokines in the context of extracellular matrix

Interactions between malignant cells and their environment are achieved via cell-surface receptors and adhesion molecules. The extracellular matrix (ECM) and ECM-bound cytokines modulate the expression of cell-surface molecules on target malignant cells, which may lead to changes in their susceptibility to cytolysis, in their ability to present antigens, and in the induction of local immune-cell activation and patrol. Eventually, these alterations may culminate in either the destruction, or escape and proliferation, of the tumor. We studied the effects of the ECM and its components in a "naive" form or following binding of the inflammatory cytokines interferon gamma (IFNgamma) and tumor necrosis factor alpha (TNFalpha) on the surface expression of human leukocyte antigen (HLA) class-I, HLA class-II (HLA-DR), and intracellular adhesion molecule-1 (ICAM-1), on nonmalignant and malignant thyroid cells. The basal expression of HLA class-I molecules was not significantly changed either by naive ECM and its components or by ECM-bound cytokines. ECM synergized with IFNgamma and TNFalpha in inducing HLA-DR molecules on nonmalignant and malignant thyrocytes, with higher HLA-DR levels on the malignant cells. The laminin component, in particular, synergized with IFNgamma. Basal ICAM-1 expression on nonneoplastic cells was not significantly affected by the cytokines when grown in the absence of ECM, but was significantly upregulated when cells were cultured on ECM. In contrast, in malignant thyrocyte cultures, ECM significantly attenuated IFNgamma- and TNFalpha-mediated enhancement of ICAM-1 expression. We concluded that signals derived from ECM-embedded cytokines participate in the regulation of key thyroid cell surface molecules and, thus, may affect the final outcome of human thyroid malignancies.

Characterization of prostaglandin endoperoxide H synthase-1 enzyme expression during differentiation of the megakaryocytic cell line MEG-01

OBJECTIVE

Because the prostaglandin endoperoxide H synthase-1 (PGHS-1)-dependent formation of thromboxane A(2) is an important modulator of platelet function, this pathway represents a pharmacologic target for the inhibition of platelet function by aspirin. The objective of our research was to study how PGHS-1 expression is regulated in platelets.

MATERIALS AND METHODS

Because platelets are anucleated, their protein content is a consequence of gene expression in precursor cells known as megakaryocytes. We used the immortalized human megakaryoblastic cell line MEG-01 as a model to study the expression of PGHS-1, because MEG-01 cells can be induced to differentiate into platelet-like structures by adding nanomolar concentrations of 12-0-tetradecanoylphorbol-13-acetate (TPA). We determined the expression profiles of PGHS-1 protein and mRNA in the cells comprising the three different populations of MEG-01 cultures: nucleated floating, nucleated attached, and platelet-like structures.

RESULTS

We determined that PGHS-1 protein levels were higher in the nucleated adherent population than in the nucleated floating population. PGHS-1 protein levels were greatest in the anucleated platelet-like population. In contrast, we found that PGHS-1 mRNA levels were highest in the cells that comprised the nucleated adherent population. Addition of TPA induced the expression of PGHS-1 protein and mRNA in all three populations but did not change the relationship of the amount of PGHS-1 protein or mRNA expressed in a given population relative to the other two fractions. We measured the expression of PGHS-1 protein on a cell-by-cell basis in the nucleated MEG-01 populations. We found that the percentage of MEG-01 cells expressing PGHS-1 protein in the adherent population was greater than in the floating population. We measured a time-dependent increase in the percentage of cells that expressed PGHS-1 over a period of 8 days after singular addition of TPA (1.6x10(-8)M). Importantly, we observed that TPA treatment stimulated floating MEG-01 to adhere to the surface of the tissue culture vessel and that, after such treatment, only floating MEG-01 cells suffered a compromised viability. We found that a high percentage of control cells expressed glycoprotein IIb/IIIa and that TPA treatment did not significantly alter this percentage. We did not detect glycoprotein Ib in control cells but did measure a slight increase in the percentage of MEG-01 cells that expressed this antigen in the TPA-treated population.

CONCLUSION

We established a correlation between the level of PGHS-1 expression and the overall level of differentiation of MEG-01 cells. PGHS-1 protein expression, which increases consistently over the full course of differentiation, now may be used as an additional and perhaps better index by which to survey megakaryocytes.

Primary megakaryocytes reveal a role for transcription factor NF-E2 in integrin alpha IIb beta 3 signaling

Platelet integrin alphaIIbbeta3 responds to intracellular signals by binding fibrinogen and triggering cytoskeletal reorganization, but the mechanisms of alphaIIbbeta3 signaling remain poorly understood. To better understand this process, we established conditions to study alphaIIbbeta3 signaling in primary murine megakaryocytes. Unlike platelets, these platelet precursors are amenable to genetic manipulation. Cytokine-stimulated bone marrow cultures produced three arbitrary populations of alphaIIbbeta3-expressing cells with increasing size and DNA ploidy: small progenitors, intermediate-size young megakaryocytes, and large mature megakaryocytes. A majority of the large megakaryocytes bound fibrinogen in response to agonists, while almost none of the smaller cells did. Fibrinogen binding to large megakaryocytes was inhibited by Sindbis virus-mediated expression of isolated beta3 integrin cytoplasmic tails. Strikingly, large megakaryocytes from mice deficient in the transcription factor NF-E2 failed to bind fibrinogen in response to agonists, despite normal surface expression of alphaIIbbeta3. Furthermore, while megakaryocytes from wild-type mice spread on immobilized fibrinogen and exhibited filopodia, lamellipodia and Rho-dependent focal adhesions and stress fibers, NF-E2-deficient megakaryocytes adhered poorly. These studies establish that agonist-induced activation of alphaIIbbeta3 is controlled by NF-E2-regulated signaling pathways that mature late in megakaryocyte development and converge at the beta3 cytoplasmic tail. Megakaryocytes provide a physiologically relevant and tractable system for analysis of bidirectional alphaIIbbeta3 signaling.

Megakaryocyte structure and function

Recent advances in the understanding of megakaryocyte (MK) function largely have been made through the careful observation of the morphological and structural events underlying MK development. Ultrastructural localization of enzymatic activities has facilitated the specific recognition of their committed diploid precursors. Observation of the sequential features of endomitosis demonstrates that although similar to normal mitosis, cell division aborts at the anaphase stage. The ability of thrombopoietin to induce the full maturation MKs in vitro not only facilitates platelet release but has increased our knowledge of various subcellular aspects of the phenomenon and eventually will improve the in vivo detection of the site of platelet formation and shedding. Finally, the structural and functional consequences of MK molecular dysfunction leading to thrombocytopenia or myelofibrosis can now be investigated because of the development of transgenic animal models. This review aims to incorporate these new findings within the classical knowledge of MK structure related to its function.