Functioning of Mycobacterial Heat Shock Repressors Requires the Master Virulence Regulator PhoP

ABSTRACT A hallmark feature of Mycobacterium tuberculosis pathogenesis lies in the ability of the pathogen to survive within macrophages under a stressful environment. Thus, coordinated regulation of stress proteins is critically important for an effective adaptive response of M. tuberculosis, the failure of which results in elevated immune recognition of the tubercle bacilli with reduced survival during chronic infections. Here, we show that virulence regulator PhoP impacts the global regulation of heat shock proteins, which protect M. tuberculosis against stress generated by macrophages during infection. Our results identify that in addition to classical DNA-protein interactions, newly discovered protein-protein interactions control complex mechanisms of expression of heat shock proteins, an essential pathogenic determinant of M. tuberculosis. While the C-terminal domain of PhoP binds to its target promoters, the N-terminal domain of the regulator interacts with the C-terminal end of the heat shock repressors. Remarkably, our findings delineate a regulatory pathway which involves three major transcription factors, PhoP, HspR, and HrcA, that control in vivo recruitment of the regulators within the target genes and regulate stress-specific expression of heat shock proteins via protein-protein interactions. The results have implications on the mechanism of regulation of PhoP-dependent stress response in M. tuberculosis. IMPORTANCE The regulation of heat shock proteins which protect M. tuberculosis against stress generated by macrophages during infection is poorly understood. In this study, we show that PhoP, a virulence regulator of the tubercle bacilli, controls heat shock-responsive genes, an essential pathogenic determinant of M. tuberculosis. Our results unravel that in addition to classical DNA-protein interactions, complex mechanisms of regulation of heat shock-responsive genes occur through multiple protein-protein interactions. Together, these findings delineate a fundamental regulatory pathway where transcription factors PhoP, HspR, and HrcA interact with each other to control stress-specific expression of heat shock proteins.

The microcirculatory changes in patients with intermittent claudication after endovascular restoration of main blood flow to the extremity

The functional state of microvascular blood flow is the major pathogenic determinant in patients with intermittent claudication (IC). Revealing features of microcirculation (MC) shifts has been especially valuable after endovascular interventions. Purpose. To assess the alterations in MC profile after the restoration of main blood flow to affected extremity in patients with IC. Material and methods. MC was assessed by laser Doppler flowmehy in 37 patients before and 1 month after lower extremity angioplasty. Results. Restoration of main blood flow was associated with increased nutritional blood flow by 56.0 %, decreased arteriole-venule shunts by 30.7 % and venous congestion by 13.5 %. Conclusion. Endovascular interventions in patients with IC are associated with recovery of balance in MC processes.

Enterococcus faecalis and Dental Implants

Enterococcus faecalis appears in many tooth root infections and is not eliminated by root canal therapy. It can reside in tooth root canals and the surrounding bone. This species may vegetate in bone after extraction of an infected tooth and colonize a dental implant after placement in the healed site. A colonization may cause fixture loss or marginal bone loss. These colonizations are generally multibacterial and pathogenic properties can be shared via plasmids. However, E faecalis is not detectable with some culture techniques and thus can be missed. It is usually not a dominant species in these infections. Nonetheless, E faecalis may be a “keystone” player in dental implant bone loss or peri-implantitis. That is, E faecalis may be the pathogenic determinant for any particular peri-implantitis infection of a multiple-species infection.

Virulence Determinants in the PB2 Gene of a Mouse-Adapted H9N2 Virus

The molecular bases of adaptation and pathogenicity of H9N2 influenza virus in mammals are largely unknown. Here, we show that a mouse-adapted PB2 gene with a phenylalanine-to-leucine mutation (F404L) mainly contributes to enhanced polymerase activity, replication, and pathogenicity of H9N2 in mice and also increases the virulence of the H5N1 and 2009 pandemic H1N1 influenza viruses. Therefore, we defined a novel pathogenic determinant, providing further insights into the pathogenesis of influenza viruses in mammals.