Adhesion of mycoplasmas to eukaryotic cells

Up-Regulation of miR-130b-3p Activates the PTEN/PI3K/AKT/NF-κB Pathway to Defense against Mycoplasma gallisepticum (HS Strain) Infection of Chicken

Mycoplasma gallisepticum (MG) is the pathogen of chronic respiratory disease (CRD), hallmarked by vigorous inflammation in chickens, causing the poultry industry enormous losses. miRNAs have emerged as important regulators of animal diseases. Previous miRNA sequencing data has demonstrated that miR-130b-3p is up-regulated in MG-infected chicken embryo lungs. Therefore, we aimed to investigate the function of miR-130b-3p in MG infection of chickens. RT-qPCR results confirmed that miR-130b-3p was up-regulated both in MG-infected chicken embryo lungs and chicken embryonic fibroblast cells (DF-1 cells). Furthermore, functional studies showed that overexpression of miR-130b-3p promoted MG-infected DF-1 cell proliferation and cell cycle, whereas inhibition of miR-130b-3p weakened these cellular processes. Luciferase reporter assay combined with gene expression data supported that phosphatase and tensin homolog deleted on chromosome ten (PTEN) was a direct target of miR-130b-3p. Additionally, overexpression of miR-130b-3p resulted in up-regulations of phosphatidylinositol-3 kinase (PI3K), serine/threonine kinase (AKT), and nuclear factor-κB (NF-κB), whereas inhibition of miR-130b-3p led to the opposite results. Altogether, upon MG infection, up-regulation of miR-130b-3p activates the PI3K/AKT/NF-κB pathway, facilitates cell proliferation and cell cycle via down-regulating PTEN. This study helps to understand the mechanism of host response to MG infection.

Delineation of immunodominant and cytadherence segment(s) of Mycoplasma pneumoniae P1 gene

BACKGROUND

Adhesion of Mycoplasma pneumoniae (M. pneumoniae) to host epithelial cells requires several adhesin proteins like P1, P30 and P116. Among these proteins, P1 protein has been inedited as one of the major adhesin and immunogenic protein present on the attachment organelle of M. pneumoniae. In the present study, we scanned the entire sequence of M. pneumoniae P1 protein to identify the immunodominant and cytadherence region(s). M. pneumoniae P1 gene was synthesized in four segments replacing all the UGA codons to UGG codons. Each of the four purified P1 protein fragment was analyzed for its immunogenicity with anti-M. pneumoniae M129 antibodies (Pab M129) and sera of M. pneumoniae infected patients by western blotting and ELISA. Antibodies were produced against all the P1 protein fragments and these antibodies were used for M. pneumoniae adhesion, M. pneumoniae adhesion inhibition and M. pneumoniae surface exposure assays using HEp-2 cells lines.

RESULTS

Our results show that the immunodominant regions are distributed throughout the entire length of P1 protein, while only the N- and C- terminal region(s) of P1 protein are surface exposed and block cytadhesion to HEp-2 cells, while antibodies to two middle fragments failed to block cytadhesion.

CONCLUSIONS

These results have important implications in designing strategies to block the attachment of M. pneumoniae to epithelial cells, thus preventing the development of atypical pneumonia.

Gordon memorial lecture: people, poultry and pathogenic mycoplasmas

Man in managing poultry for human benefit has found that his methods may precipitate or exacerbate certain diseases: among which are the mycoplasmosis of fowls and turkeys. Control measures for these conditions have therefore been sought and to make them effective it has been necessary to study the epidemiology, diagnosis and pathogenesis of these conditions. Much is now known about their epidemiology although certain aspects still require investigation. More sensitive and specific methods of diagnosis are also required and although it is possible to control these conditions by eradication the mycoplasmosis are still an economic problem. Under existing management systems, therefore, development and use of effective vaccines and additional drugs are essential. It is noteworthy that the pathogenesis of at least one of the avian mycoplasmosis is similar to human immune-complex disease. In further elucidation of this complex the fowl may be a useful experimental animal. Thus the association of people, poultry and pathogenic mycoplasmas not only involves attempts to control the pathogens in order to attain maximum production by poultry but also could include the utilisation of poultry and the pathogen in an attempt to elucidate some of the diseases of people.

Influence of cell shape and surface charge on attachment of Mycoplasma pneumoniae to glass surfaces

Attachment of Mycoplasma pneumoniae to glass is reduced in the presence of protein, and fatty acid-free bovine serum albumin is more effective than Cohn fraction V. Cultures in the early log phase (pH 7.45 to 7.25) and cultures in the stationary or decline phase (pH 6.9 to 6.4) were more sensitive to this inhibiting effect of protein-containing buffer. Treatment of the glass surface with bovine serum albumin, concanavalin A, or polylysine reduced attachment of the mycoplasma cells. The inhibiting effects of both proteins in buffer or on the glass surface could be overcome by the addition of glucose. Modification of the mycoplasma surface charge by blocking of carboxyl groups or neutralization of ionic lipids by tetracaine altered the attachment level, whereas fibronectin and its corresponding antiserum were without effect. The results suggest that the mycoplasma interaction with glass is a complex multifactorial process. In protein-free buffer both hydrophobic and electrostatic forces are involved; in protein-containing fluid, other factors seem to be involved. The energy required for this type of attachment could be necessary for maintenance of cell shape or synthesis of polypeptides.

Effects of ionophores and dicyclohexylcarbodiimide on Mycoplasma gallisepticum adherence to erythrocytes

To test the influence of the electrochemical ion gradient across mycoplasma membranes on the capacity of organisms to adhere to host cells, Mycoplasma gallisepticum cells were treated with valinomycin, carbonylcyanide m-chlorophenylhydrazone, and N,N'-dicyclohexylcarbodiimide (DCCD) singly or in combination. Uptake of [3H]tetraphenylphosphonium by the treated cells was employed as a measure of the effects of the ionophores on membrane potential. In the absence of K+, valinomycin increased, whereas carbonylcyanide m-chlorophenylhydrazone, and DCCD decreased [3H]tetraphenylphosphonium uptake. However, with a high level of K+ or with DCCD, uptake of [3H]tetraphenylphosphonium in the presence of valinomycin decreased below control levels, indicating that, generally, the ionophores affected membrane potential in the expected manner. The treated organisms were tested for their capacity to attach to glutaraldehyde-fixed human erythrocytes. DCCD was the best inhibitor of mycoplasma attachment, and in combination with valinomycin attachment, capacity decreased by about 40%. The combination of valinomycin plus carbonylcyanide m-chlorophenylhydrazone was less effective; it decreased attachment by about 15 to 25%. It was concluded that the dissipation of ion gradients across cell membranes decreases only partially mycoplasma adherence, in line with previous findings that isolated mycoplasma membranes retain the major part of the attachment capacity of intact cells.

Attachment of killed Mycoplasma gallisepticum cells and membranes to erythrocytes

To correlate viability with attachment capacity, Mycoplasma gallisepticum cell harvested at different growth phases and treated by various agents were tested for their capacity to attach to human erythrocytes. The results show that viability per se is not essential for M. gallisepticum attachment to erythrocytes, as cells killed by ultraviolet irradiation anmd membranes isolated by lysing M. gallisepticum cells by various means retained attachment capacity. However, treatment of the mycoplasmas by protein-denaturing agents, such as heart, glutaraldehyde, or prolonged exposure to low pH, drastically affected or even abolished attachment, supporting the protein nature of the mycoplasma membrane components responsible for specific binding to the sialoglycoprotein receptors on the erythrocytes.