Rv3033, as an Emerging Anti-apoptosis Factor, Facilitates Mycobacteria Survival via Inhibiting Macrophage Intrinsic Apoptosis

Role of PE/PPE proteins of Mycobacterium tuberculosis in triad of host mitochondria, oxidative stress and cell death

The PE and PPE family proteins of Mycobacterium tuberculosis (Mtb) is exclusively found in pathogenic Mycobacterium species, comprising approximately 8-10 % of the Mtb genome. These emerging virulent factors have been observed to play pivotal roles in Mtb pathogenesis and immune evasion through various strategies. These immunogenic proteins are known to modulate the host immune response and cell-death pathways by targeting the powerhouse of the cell, the mitochondria to support Mtb survival. In this article, we are focused on how PE/PPE family proteins target host mitochondria to induce mitochondrial perturbations, modulate the levels of cellular ROS (Reactive oxygen species) and control cell death pathways. We observed that the time of expression of these proteins at different stages of infection is crucial for elucidating their impact on the cell death pathways and eventually on the outcome of infection. This article focuses on understanding the contributions of the PE/PPE proteins by unravelling the triad of host mitochondria, oxidative stress and cell death pathways that facilitate the Mtb persistence. Understanding the role of these proteins in host cellular pathways and the intricate mechanisms paves the way for the development of novel therapeutic strategies to combat TB infections.

A study of antigen selection by extracellular vesicles as vaccine candidates against Mycobacterium tuberculosis infection

Introduction. Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis (M. tb), remains a significant global public health concern. It is crucial to develop more effective vaccines for TB in order to achieve global control of the disease. Extracellular vesicles (EVs) are spherical membrane-bound structures released by pathogens and host cells. During the course of an infection, both pathogen- and host-derived EVs are produced and play important roles in determining the course of the infection. EVs offer intriguing tools as potential vaccines due to their ability to deliver multiple pathogen or host antigens.Hypothesis /Gap Statement. We hypothesized that EVs derived from M. tb and EVs from M. tb-infected macrophages may serve as potential vaccine candidates against M. tb infection.Aim. This study aims to compare the immunogenicity and immune protection between M. tb EVs and M. tb-infected macrophage-derived EVs.Methodology. In this study, EVs were extracted from culture supernatants of M. tb and M. tb-infected macrophages, respectively. Mass spectrometry was employed to explore the antigen composition of H37Rv-Mφ-EVs and H37Rv-EVs. Cytokine profiling and antibody response assays were used to analyse the immunogenicity offered by EVs. Additionally, we used histological examination to evaluate and protective efficacy of the EVs.Results. Our results demonstrated that mice immunized by EVs released from M. tb-infected macrophages induced stronger inflammatory cytokine response than M. tb. Moreover, EVs from M. tb-infected macrophages reinforced T-cell activation and antibody response compared to M. tb EVs. Proteomic analysis revealed that EVs from M. tb-infected macrophages containing immunodominant cargos have stronger binding ability with major histocompatibility complex molecules, which may contribute to the protection from M. tb infection. Indeed, immunization of EVs released from M. tb-infected macrophages significantly reduced the bacterial load and better protection against M. tb infection than EVs from M. tb. Importantly, the selected antigens (Ag85B, ESAT-6 and the Rv0580c) from EVs of M. tb-infected macrophages exhibited effective immunogenicity.Conclusion. Our results suggested that EVs derived from M. tb-infected macrophages might serve as a proper antigenic library for vaccine candidates against M. tb challenge.

Mycobacterial SapM hampers host autophagy initiation for intracellular bacillary survival via dephosphorylating Raptor

Secreted acid phosphatase (SapM) is an immunomodulator of Mycobacterium tuberculosis (Mtb) and consequently plays a crucial role in disease onset and development upon infection. Importantly, the virulence of SapM has rendered SapM an attractive target for drug development. However, the mechanism underlying the role of SapM in facilitating bacillary survival remains to be fully elucidated. In this context, the present study demonstrated that SapM hampered cellular autophagy to facilitate bacillary survival in mycobacterial-infected macrophages. Mechanically, SapM interacted with Raptor and was localized to the subcellular lysosomal organelle, causing the dephosphorylation of Raptor at the Ser792 position, resulting in mTORC1 hyperactivity and the subsequent autophagy inhibition. Consistent with this, SapM blocked the autophagy initiation and mitigated lung pathology in vivo. These findings highlighted the role of Raptor as a significant substrate of SapM for inhibiting autophagy, which is a novel clue for developing a treatment against tuberculosis.

Live Attenuated Vaccines against Tuberculosis: Targeting the Disruption of Genes Encoding the Secretory Proteins of Mycobacteria

Tuberculosis (TB), a chronic infectious disease affecting humans, causes over 1.3 million deaths per year throughout the world. The current preventive vaccine BCG provides protection against childhood TB, but it fails to protect against pulmonary TB. Multiple candidates have been evaluated to either replace or boost the efficacy of the BCG vaccine, including subunit protein, DNA, virus vector-based vaccines, etc., most of which provide only short-term immunity. Several live attenuated vaccines derived from Mycobacterium tuberculosis (Mtb) and BCG have also been developed to induce long-term immunity. Since Mtb mediates its virulence through multiple secreted proteins, these proteins have been targeted to produce attenuated but immunogenic vaccines. In this review, we discuss the characteristics and prospects of live attenuated vaccines generated by targeting the disruption of the genes encoding secretory mycobacterial proteins.

Pathogenicity and virulence of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, an infectious disease with one of the highest morbidity and mortality rates worldwide. Leveraging its highly evolved repertoire of non-protein and protein virulence factors, Mtb invades through the airway, subverts host immunity, establishes its survival niche, and ultimately escapes in the setting of active disease to initiate another round of infection in a naive host. In this review, we will provide a concise synopsis of the infectious life cycle of Mtb and its clinical and epidemiologic significance. We will also take stock of its virulence factors and pathogenic mechanisms that modulate host immunity and facilitate its spread. Developing a greater understanding of the interface between Mtb virulence factors and host defences will enable progress toward improved vaccines and therapeutics to prevent and treat tuberculosis.

Pgp3 protein of Chlamydia trachomatis inhibits apoptosis via HO-1 upregulation mediated by PI3K/Akt activation

As an obligate intracellular pathogen, Chlamydia trachomatis assumes various strategies to inhibit host cells apoptosis, thereby providing a suitable intracellular environment to ensure completion of the development cycle. In the current study, we revealed that Pgp3 protein, one of eight plasmid proteins of C. trachomatis that has been illustrated as the key virulence factor, increased HO-1 expression to suppress apoptosis, and downregulation of HO-1 with siRNA-HO-1 failed to exert anti-apoptosis activity of Pgp3 protein. Moreover, treatment of PI3K/Akt pathway inhibitor and Nrf2 inhibitor evidently reduced HO-1 expression and Nrf2 nuclear translocation was blocked by PI3K/Akt pathway inhibitor. These findings highlight that induction of HO-1 expression by Pgp3 protein is probably due to regulation of Nrf2 nuclear translocation activated by PI3K/Akt pathway, which provide clues on how C. trachomatis adjusts apoptosis.

Mycobacterium tuberculosis PE_PGRS1 promotes mycobacteria intracellular survival via reducing the concentration of intracellular free Ca2+ and suppressing endoplasmic reticulum stress

Mycobacterium tuberculosis (M. tuberculosis) is the causative agent of tuberculosis (TB). And the PE_PGRS family members of M. tuberculosis are closely associated with virulence and antigen presentation but with function largely elusive. PE_PGRS1(Rv0109) contained 7 Ca²⁺ binding domains of GGXGXD/NXUX (X is any amino acid), which can reduce intracellular Ca²⁺ surge. In addition, PE_PGRS1 can mitigate the activation of PERK branch in endoplasmic reticulum (ER) stress by down-regulating the expression of CHOP, Bip, p-PERK, p-eIF2α, and ATF4. Interestingly, we found that two splicing variations of Bax/Bcl-2, Baxβ, and Bcl-2α, were differentially expressed after infection with Ms_PE_PGRS1, and may be involved in the regulation of apoptosis. Hence, this study identified that PE_PGRS1 is a novel calcium-associated protein that can decrease intracellular Ca²⁺ levels and the PERK axis. And the weakening of the PERK-eIF2α-ATF4 axis reduces THP-1 macrophages apoptosis, promotes the survival of mycobacteria in macrophages.

Mycobacterium tuberculosis-macrophage interaction: Molecular updates

Mycobacterium tuberculosis (Mtb), the causative agent of Tuberculosis (TB), remains a pathogen of great interest on a global scale. This airborne pathogen affects the lungs, where it interacts with macrophages. Acidic pH, oxidative and nitrosative stressors, and food restrictions make the macrophage's internal milieu unfriendly to foreign bodies. Mtb subverts the host immune system and causes infection due to its genetic arsenal and secreted effector proteins. In vivo and in vitro research have examined Mtb-host macrophage interaction. This interaction is a crucial stage in Mtb infection because lung macrophages are the first immune cells Mtb encounters in the host. This review summarizes Mtb effectors that interact with macrophages. It also examines how macrophages control and eliminate Mtb and how Mtb manipulates macrophage defense mechanisms for its own survival. Understanding these mechanisms is crucial for TB prevention, diagnosis, and treatment.

Mycobacterium tuberculosis Rv0790c inhibits the cellular autophagy at its early stage and facilitates mycobacterial survival

Rv0790c is predicted to be a conserved hypothetical protein encoded by Mycobacterium tuberculosis (Mtb). However, its function in Mtb infection remains largely unknown. In this study, we found that Rv0790c promoted bacillary survival of M. smegmatis (Ms), both in vitro and in vivo. The bacillary burden of Ms exogenously expressing Rv0790c increased, whereas in Rv0790c-knockouts the bacillary burden decreased in infected macrophages. Multiple cellular processes were analyzed to explore the underlying mechanisms. We found that neither inflammatory regulation nor apoptotic induction were responsible for the promotion of bacillary survival mediated by Rv0790c. Interestingly, we found that Rv0790c facilitates mycobacterial survival through cellular autophagy at its early stage. Immunoprecipitation assay of autophagy initiation-related proteins indicated that Rv0790c interacted with mTOR and enhanced its activity, as evidenced by the increased phosphorylation level of mTOR downstream substrates, ULK-1, at Ser757 and P70S6K, at Thr389. Our study uncovers a novel autophagy suppressor encoded by mycobacterial Rv0790c, which inhibits the early stage of cellular autophagy induction upon Mtb infection and takes an important role in maintaining intracellular mycobacterial survival. It may aid in understanding the mechanism of Mtb evasion of host cellular degradation, as well as hold the potential to develop new targets for the prevention and treatment of tuberculosis.

Mycobacterium tuberculosis Rv2387 Facilitates Mycobacterial Survival by Silencing TLR2/p38/JNK Signaling

Mycobacterium tuberculosis (Mtb) can evade antimicrobial immunity and persist within macrophages by interfering with multiple host cellular functions through its virulence factors, causing latent tuberculosis. The Rv2387 protein has been identified as a putative effector that potentially participates in Mtb pathogenicity. To explore the role of the Rv2387 protein in host–mycobacteria interactions, we established recombinant M. smegmatis strains and RAW264.7 cell lines that stably express the Rv2387 protein. We found that this protein suppresses mycobacteria infection-induced macrophage apoptosis by inactivating caspase-3/-8, thus facilitating the intracellular survival of mycobacteria. In addition, Rv2387 inhibits the production of inflammatory cytokines in macrophages by specifically suppressing TLR2-dependent stimulation of p38 and JNK MAPK pathways. Moreover, we further determined that the Rv2387 protein conferred a growth advantage over recombinant M. smegmatis and suppressed the inflammatory response in a mouse infection model. Overall, these data suggested that Rv2387 facilitates mycobacteria to escape host immunity and might be an essential virulence factor in Mtb.

Enterococcus faecalis shifts macrophage polarization toward M1-like phenotype with an altered cytokine profile

Background: The macrophage is an innate immune defense cell involved in pathogen recognition and clearance.

Aim: In view of the diversity of the macrophage phenotype and function, the present study investigated how Enterococcus faecalis infection affects the differentiation, phenotype and cytokine profile of macrophages.

Methods: Murine bone marrow-derived stem cells were co-cultured with E. faecalis before and after differentiation. Macrophage M0 polarization towards M1 or M2 was initiated at day 6 by addition of LPS and INF-γ, or IL-4 and IL-13, respectively.

Results: E. faecalis did not inhibit macrophage differentiation and were identified within macrophages. Viability of the macrophages infected with E. faecalis prior to differentiation was enhanced, evidenced by apoptosis inhibition, as was expression of CD38 and IRF5 proteins, indicators of M1-like polarization. These M1-like macrophages expressed an aberrant cytokine mRNA profile, with reduction in inflammatory cytokines IL-1β and IL-12 and increase in regulatory cytokine IL-10. No changes in TNF-α or TGF-β1 were detected, compared with the control groups. This atypical M1-like phenotype was retained even upon stimulation with growth factors that normally trigger their development into M2 macrophages.

Conclusions: These findings suggested that E. faecalis infection of bone marrow-derived stem cells during differentiation into macrophages induces an atypical M1-like phenotype associated with intracellular bacterial survival.

Impact of knockdown LincRNA-Cox2 on apoptosis of macrophage infected with Bacillus Calmette-Guérin

Mycobacterium tuberculosis (Mtb)-induced apoptosis of alveolar macrophages plays an important role in the pathogenesis of tuberculosis. Previous studies indicated that massive LncRNAs could deteriorate MTB invasion or latent infection by regulating macrophage's apoptosis. However, whether LincRNA-Cox2 is involved in apoptosis of macrophage infected with Mtb is unclear. In this study, we found Bacillus Calmette-Guerin(BCG)infection induced cell apoptosis with a increasing LincRNA-Cox2 expression in RAW264.7 cells. Furthermore, the activation of TLR signal pathway elevated the expression of lincRNA-Cox2. In this regard, we used small interfering RNA to explore the role of LincRNA-Cox2 on regulating apoptosis of RAW264.7 cells infected with BCG. The results showed that si-LincRNA-Cox2 was capable of increased the expression of apoptosis-associated proteins and accumulation of ROS in BCG-infected RAW264.7 cells. Mechanically, si-LincRNA-Cox2 facilitated BCG-induced macrophage apoptosis by activating the intrinsic apoptotic pathway as well as increased the genes expression of PERK/eIF2α/CHOP. These results provide novel insights into host-pathogen interactions and highlight the potential role of LincRNA-Cox2 in regulating apoptosis induced by BCG-infection.

Tuberculosis vaccination needs to avoid 'decoy' immune reactions

Current search for a new effective vaccine against tuberculosis involves selected antigens, vectors and adjuvants. These are being evaluated usually by their booster inoculation following priming with Bacillus Calmette-Guerin. The purpose of this article is to point out, that despite being attenuated of virulence, priming with BCG may still involve immune mechanisms, which are not favourable for protection against active disease. It is postulated, that the responsible 'decoy' constituents selected during the evolution of pathogenic tubercle bacilli may be involved in the evasion from bactericidal host resistance and stimulate immune responses of a cytokine phenotype, which lead to the transition from latent closed granulomas to reactivation with infectious lung cavities. The decoy mechanisms appear as favourable for most infected subjects but leading in a minority of cases to pathology which can effectively transmit the infection. It is proposed that construction and development of new vaccine candidates could benefit from avoiding decoy-type immune mechanisms.

Host Cell Targets of Released Lipid and Secreted Protein Effectors of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is a very successful pathogen, strictly adapted to humans and the cause of tuberculosis. Its success is associated with its ability to inhibit host cell intrinsic immune responses by using an arsenal of virulence factors of different nature. It has evolved to synthesize a series of complex lipids which form an outer membrane and may also be released to enter host cell membranes. In addition, secreted protein effectors of Mtb are entering the host cell cytosol to interact with host cell proteins. We briefly discuss the current model, involving the ESX-1 type seven secretion system and the Mtb lipid phthiocerol dimycoserosate (PDIM), of how Mtb creates pores in the phagosomal membrane to allow Mtb proteins to access to the host cell cytosol. We provide an exhaustive list of Mtb secreted proteins that have effector functions. They modify (mostly inhibit but sometimes activate) host cell pathways such as: phagosome maturation, cell death, cytokine response, xenophagy, reactive oxygen species (ROS) response via NADPH oxidase 2 (NOX2), nitric oxide (NO) response via NO Synthase 2 (NOS2) and antigen presentation via MHC class I and class II molecules. We discuss the host cell targets for each lipid and protein effector and the importance of the Mtb effector for virulence of the bacterium.

Intelligent Mechanisms of Macrophage Apoptosis Subversion by Mycobacterium

Macrophages are one of the first innate defense barriers and play an indispensable role in communication between innate and adaptive immune responses, leading to restricted Mycobacterium tuberculosis (Mtb) infection. The macrophages can undergo programmed cell death (apoptosis), which is a crucial step to limit the intracellular growth of bacilli by liberating them into extracellular milieu in the form of apoptotic bodies. These bodies can be taken up by the macrophages for the further degradation of bacilli or by the dendritic cells, thereby leading to the activation of T lymphocytes. However, Mtb has the ability to interplay with complex signaling networks to subvert macrophage apoptosis. Here, we describe the intelligent strategies of Mtb inhibition of macrophages apoptosis. This review provides a platform for the future study of unrevealed Mtb anti-apoptotic mechanisms and the design of therapeutic interventions.

Effects of autophagy on apoptosis of articular chondrocytes in adjuvant arthritis rats

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease that eventually leads to joint deformities and loss of joint function. Previous studies have demonstrated a close relationship between autophagy and the development of RA. Although autophagy and apoptosis are two different forms of programmed death, the relationship between them in relation to RA remains unclear. In this study, we explored the effect of autophagy on apoptosis of articular chondrocytes in vivo and in vitro. Adjuvant arthritis (AA) and acid‐induced primary articular chondrocyte apoptosis were used as in vivo and in vitro models, respectively. Articular chondrocyte autophagy and apoptosis were both observed dynamically in AA rat articular cartilage at different stages (15 days, 25 days and 35 days). Moreover, chondrocyte apoptosis and articular cartilage injury in AA rats were increased by the autophagy inhibitor 3‐methyladenine (3‐MA) and decreased by the autophagy activator rapamycin. In addition, pre‐treatment with 3‐MA increased acid‐induced chondrocyte apoptosis, while pre‐treatment with rapamycin reduced acid‐induced chondrocyte apoptosis in vitro. These results suggest that autophagy might be a potential target for the treatment of RA.