A matrix metalloproteinase inhibitor promotes granuloma formation during the early phase of Mycobacterium tuberculosis pulmonary infection

Breaking the Cycle: Matrix Metalloproteinase Inhibitors as an Alternative Approach in Managing Tuberculosis Pathogenesis and Progression

Mycobacterium tuberculosis (Mtb) has long posed a significant challenge to global public health, resulting in approximately 1.6 million deaths annually. Pulmonary tuberculosis (TB) instigated by Mtb is characterized by extensive lung tissue damage, leading to lesions and dissemination within the tissue matrix. Matrix metalloproteinases (MMPs) exhibit endopeptidase activity, contributing to inflammatory tissue damage and, consequently, morbidity and mortality in TB patients. MMP activities in TB are intricately regulated by various components, including cytokines, chemokines, cell receptors, and growth factors, through intracellular signaling pathways. Primarily, Mtb-infected macrophages induce MMP expression, disrupting the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thereby impairing extracellular matrix (ECM) deposition in the lungs. Recent research underscores the significance of immunomodulatory factors in MMP secretion and granuloma formation during Mtb pathogenesis. Several studies have investigated both the activation and inhibition of MMPs using endogenous MMP inhibitors (i.e., TIMPs) and synthetic inhibitors. However, despite their promising pharmacological potential, few MMP inhibitors have been explored for TB treatment as host-directed therapy. Scientists are exploring novel strategies to enhance TB therapeutic regimens by suppressing MMP activity to mitigate Mtb-associated matrix destruction and reduce TB induced lung inflammation. These strategies include the use of MMP inhibitor molecules alone or in combination with anti-TB drugs. Additionally, there is growing interest in developing novel formulations containing MMP inhibitors or MMP-responsive drug delivery systems to suppress MMPs and release drugs at specific target sites. This review summarizes MMPs' expression and regulation in TB, their role in immune response, and the potential of MMP inhibitors as effective therapeutic targets to alleviate TB immunopathology.

KLK12 Regulates MMP-1 and MMP-9 via Bradykinin Receptors: Biomarkers for Differentiating Latent and Active Bovine Tuberculosis

It has been established that kallikrein12 (KLK12) expression is closely related to bovine tuberculosis (bTB) development. Herein, we sought to clarify the regulatory mechanism of KLK12 and its application in tuberculosis diagnosis. KLK12 knockdown macrophages were produced by siRNA transfection. Bradykinin receptors (BR, including B1R and B2R) were blocked with specific inhibitors. Mannose-capped lipoarabinomannan (ManLAM) was extracted from Mycobacterium bovis (M. bovis) and used to study the mechanism of KLK12 activation. In addition, we constructed different mouse models representing the latent and active stages of M. bovis infection. Mouse models and clinical serum samples were used to assess the diagnostic value of biomarkers. Through the above methods, we confirmed that KLK12 regulates MMP-1 and MMP-9 via BR. KLK12 upregulation is mediated by the M. bovis-specific antigen ManLAM. KLK12, MMP-1, and MMP-9 harbor significant value as serological markers for differentiating between latent and active bTB, especially KLK12. In conclusion, we identified a novel signaling pathway, KLK12/BR/ERK/MMPs, in M. bovis-infected macrophages, which is activated by ManLAM. From this signaling pathway, KLK12 can be used as a serological marker to differentiate between latent and active bTB. Importantly, KLK12 also has enormous potential for the clinical diagnosis of human tuberculosis (TB).

Neutrophil-Mediated Immunopathology and Matrix Metalloproteinases in Central Nervous System - Tuberculosis

Tuberculosis (TB) remains one of the leading infectious killers in the world, infecting approximately a quarter of the world’s population with the causative organism Mycobacterium tuberculosis (M. tb). Central nervous system tuberculosis (CNS-TB) is the most severe form of TB, with high mortality and residual neurological sequelae even with effective TB treatment. In CNS-TB, recruited neutrophils infiltrate into the brain to carry out its antimicrobial functions of degranulation, phagocytosis and NETosis. However, neutrophils also mediate inflammation, tissue destruction and immunopathology in the CNS. Neutrophils release key mediators including matrix metalloproteinase (MMPs) which degrade brain extracellular matrix (ECM), tumor necrosis factor (TNF)-α which may drive inflammation, reactive oxygen species (ROS) that drive cellular necrosis and neutrophil extracellular traps (NETs), interacting with platelets to form thrombi that may lead to ischemic stroke. Host-directed therapies (HDTs) targeting these key mediators are potentially exciting, but currently remain of unproven effectiveness. This article reviews the key role of neutrophils and neutrophil-derived mediators in driving CNS-TB immunopathology.

GSK-3α/β Activity Negatively Regulates MMP-1/9 Expression to Suppress Mycobacterium tuberculosis Infection

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection is the deadliest infectious disease and a global health problem. Macrophages (Mφs) and neutrophils that can phagocytose Mtb represent the first line of immune response to infection. Glycogen synthase kinase-3α/β (GSK-3α/β) represents a regulatory switch in host immune responses. However, the efficacy and molecular mechanisms of how GSK-3α/β interacts with Mtb infection in Mφs remain undefined. Here, we demonstrated that Mtb infection downregulated GSK-3α/β activity and promoted matrix metalloproteinase-1 (MMP-1) and MMP-9 expressions in Mφs derived from acute monocytic human leukemia THP-1 cells (THP-1-Mφs). We confirmed the upregulation of MMP-9 expression in tissues of TB patients compared with patients of chronic inflammation (CI). In THP-1-Mφs and C57BL/6 mice, GSK-3α/β inhibitor SB216763 significantly increased MMP-1/9 production and facilitated Mtb load, while MMP inhibitors blocked MMP-1/9 expression and Mtb infection. Consistently, GSK-3α/β silencing significantly increased MMP-1/9 expression and Mtb infection, while overexpression of GSK-3α/β and constitutive activated GSK-3α/β mutants significantly reduced MMP-1/9 expression and Mtb infection in THP-1-Mφs. MMP-1/9 silencing reduced Mtb infection, while overexpression of MMP-1/9 promoted Mtb infection in THP-1-Mφs. We further found that GSK-3α/β inhibition increased Mtb infection and MMP-1/9 expression was blocked by ERK1/2 inhibitor. Additionally, we showed that protein kinase C-δ (PKC-δ) and mammalian target of rapamycin (mTOR) reduced GSK-3α/β activity and promoted MMP-1/9 production in Mtb-infected THP-1-Mφs. In conclusion, this study suggests that PKC-δ-mTOR axis suppresses GSK-3α/β activation with acceleration of MMP-1/9 expression through phospho-ERK1/2. These results reveal a novel immune escape mechanism of Mtb and a novel crosstalk between these critical signaling pathways in anti-TB immunity.

Remodeling the matrix: doxycycline modulates tuberculosis immunopathology

Pulmonary cavitation is a hallmark of Mycobacterium tuberculosis (Mtb) infection that provides an immune-privileged niche for extracellular bacillary replication, which associates with increased transmission rates, drug resistance, and chronic lung dysfunction following antituberculous therapy (ATT). Inhibitors of matrix metalloproteinases (MMPs), which are induced by Mtb infection, have shown efficacy in preclinical models and improved microbiologic and immunopathologic outcomes. In this issue of the JCI, Hao Miow et al. performed a double-blind, randomized controlled trial exploring host-directed effects of the MMP inhibitor doxycycline versus placebo when added to standard ATT for pulmonary tuberculosis. Doxycycline treatment over two weeks durably modulated host blood transcription profiles, including the resolution of inflammatory gene programs. Reduced immunopathology markers in doxycycline-treated participants also included improved lung cavity volumes and lower MMP levels in blood and sputum. These findings provide mechanistic insight and momentum for using experimental medicine trials to develop host-directed therapies for tuberculosis.

Host-directed therapies targeting the tuberculosis granuloma stroma

Mycobacteria have co-evolved with their hosts resulting in pathogens adept at intracellular survival. Pathogenic mycobacteria actively manipulate infected macrophages to drive granuloma formation while subverting host cell processes to create a permissive niche. Granuloma residency confers phenotypic antimicrobial resistance by physically excluding or neutralising antibiotics. Host-directed therapies (HDTs) combat infection by restoring protective immunity and reducing immunopathology independent of pathogen antimicrobial resistance status. This review covers innovative research that has discovered ‘secondary’ symptoms of infection in the granuloma stroma are actually primary drivers of infection and that relieving these stromal pathologies with HDTs benefits the host. Advances in our understanding of the relationship between tuberculosis and the host vasculature, haemostatic system and extracellular matrix reorganisation are discussed. Preclinical and clinical use of HDTs against these stromal targets are summarised.

Matrix metalloproteinases: Expression, regulation and role in the immunopathology of tuberculosis

Mycobacterium tuberculosis (Mtb) leads to approximately 1.5 million human deaths every year. In pulmonary tuberculosis (TB), Mtb must drive host tissue destruction to cause pulmonary cavitation and dissemination in the tissues. Matrix metalloproteinases (MMPs) are endopeptidases capable of degrading all components of pulmonary extracellular matrix (ECM). It is well established that Mtb infection leads to upregulation of MMPs and also causes disturbance in the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thus altering the extracellular matrix deposition. In TB, secretion of MMPs is mainly regulated by NF-κB, p38 and MAPK signalling pathways. In addition, recent studies have demonstrated the immunomodulatory roles of MMPs in Mtb pathogenesis. Researchers have proposed a new regimen of improved TB treatment by inhibition of MMP activity to hinder matrix destruction and to minimize the TB-associated morbidity and mortality. The proposed regimen involves adjunctive use of MMP inhibitors such as doxycycline, marimastat and other related drugs along with front-line anti-TB drugs to reduce granuloma formation and bacterial load. These findings implicate the possible addition of economical and well-tolerated MMP inhibitors to current multidrug regimens as an attractive mean to increase the drug potency. Here, we will summarize the recent advancements regarding expression of MMPs in TB, their immunomodulatory role, as well as their potential as therapeutic targets to control the deadly disease.

Matrix Metalloproteinases in Pulmonary and Central Nervous System Tuberculosis-A Review

Tuberculosis (TB) remains the single biggest infectious cause of death globally, claiming almost two million lives and causing disease in over 10 million individuals annually. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes with various physiological roles implicated as key factors contributing to the spread of TB. They are involved in the breakdown of lung extracellular matrix and the consequent release of Mycobacterium tuberculosis bacilli into the airways. Evidence demonstrates that MMPs also play a role in central nervous system (CNS) tuberculosis, as they contribute to the breakdown of the blood brain barrier and are associated with poor outcome in adults with tuberculous meningitis (TBM). However, in pediatric TBM, data indicate that MMPs may play a role in both pathology and recovery of the developing brain. MMPs also have a significant role in HIV-TB-associated immune reconstitution inflammatory syndrome in the lungs and the brain, and their modulation offers potential novel therapeutic avenues. This is a review of recent research on MMPs in pulmonary and CNS TB in adults and children and in the context of co-infection with HIV. We summarize different methods of MMP investigation and discuss the translational implications of MMP inhibition to reduce immunopathology.

Matrix metalloproteinase-2 and matrix metalloproteinase-9 in mice with ocular toxocariasis

In ocular toxocariasis, Toxocara canis-induced inflammatory reaction can lead to eye destruction and granuloma, which is formed by immune cell infiltration and concurrent extensive remodeling tissue. Herein, the histomorphology of granuloma and proteinase production in the eye of T. canis-infected BALB/c mice were investigated. Pathological effects substantially increased after the infection culminated in a severe leukocyte infiltration and granuloma formation from days 4 to 56 post-inoculation. The matrix metalloproteinase (MMP)-2 and MMP-9 activities remarkably increased, compared with those of uninfected control, by gelatin zymography and Western blot analysis in ocular toxocariasis. Granuloma formation had a remarkably positive correlation with MMP-2 and MMP-9 levels. We suggested that T. canis larvae and leukocytes infiltrated from blood vessel both migrated into corpus adiposum orbitae. Activated leukocytes secreted MMP-2 and MMP-9, leading to fibronectin degradation. The imbalance of MMP-2/TIMP-2 and MMP-9/TIMP-1 may play a role in inflammatory cell infiltration and extracellular matrix degradation, forming granuloma, in ophthalmological pathogenesis of T. canis infection.

Elevated levels of matrix metalloproteinases reflect severity and extent of disease in tuberculosis-diabetes co-morbidity and are predominantly reversed following standard anti-tuberculosis or metformin treatment

Background

Matrix metalloproteinases (MMPs) are considered to be key mediators of tuberculosis (TB) pathology but their role in tuberculosis – diabetes comorbidity (TB-DM) is not well understood.

Methods

To study the association of MMP levels with severity and extent of disease as well as bacterial burden in TB-DM, we examined the systemic levels of MMP-1, − 2, − 3, − 7, − 8, − 9, − 10, − 12 and − 13 in individuals with TB-DM and compared them to those with TB alone (TB) or healthy controls (HC).

Results

Circulating levels of MMP-1, − 2, − 3, − 7, − 10 and − 12 were significantly higher in TB-DM compared to both TB and HC and MMP -13 levels were higher in comparison to HC alone. To understand the effect of standard anti-tuberculosis therapy (ATT) on these MMP levels in TB-DM, we measured the levels of MMPs at the end of treatment (post-treatment). Our findings indicate that ATT is associated with a significant reduction in the levels of MMP-1, − 2, − 3, − 8 and − 13 post-treatment. Moreover, the levels of MMP-1, − 2, − 3, − 9 and − 12 were significantly higher in TB-DM individuals with cavitary disease and/or bilateral disease at baseline but not post-treatment. Similarly, the levels of MMP -1, − 2, − 3 and − 8 exhibited a significant positive relationship with bacterial burden and HbA1c levels at baseline but not post-treatment. Within the TB-DM group, those known to be diabetic before incident TB (KDM) exhibited significantly higher levels of MMP-1, − 2, − 10 and − 12 at baseline and of MMP-1 and -3 post-treatment compared to those newly diagnosed with DM (NDM). Finally, KDM individuals on metformin treatment exhibited significantly lower levels of MMP-1, − 2, − 3, − 7, − 9 and − 12 at baseline and of MMP-7 post-treatment.

Conclusions

Our data demonstrate that systemic MMP levels reflect baseline disease severity and extent in TB-DM, differentiate KDM from NDM and are modulated by ATT and metformin therapy.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3246-y) contains supplementary material, which is available to authorized users.

Matrix metalloproteinase inhibitors enhance the efficacy of frontline drugs against Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) remains a grave threat to world health with emerging drug resistant strains. One prominent feature of Mtb infection is the extensive reprogramming of host tissue at the site of infection. Here we report that inhibition of matrix metalloproteinase (MMP) activity by a panel of small molecule inhibitors enhances the in vivo potency of the frontline TB drugs isoniazid (INH) and rifampicin (RIF). Inhibition of MMP activity leads to an increase in pericyte-covered blood vessel numbers and appears to stabilize the integrity of the infected lung tissue. In treated mice, we observe an increased delivery and/or retention of frontline TB drugs in the infected lungs, resulting in enhanced drug efficacy. These findings indicate that targeting Mtb-induced host tissue remodeling can increase therapeutic efficacy and could enhance the effectiveness of current drug regimens.

Mycobacterium tuberculosis (Mtb) continues to be the leading cause of death from a single infectious agent worldwide, leading to 1.8 million deaths in 2015. The long treatment required (6–9 months), with all of its incumbent problems, can promote the emergence of multidrug-resistant (MDR) TB strains, so strategies to shorten the treatment duration are in dire need. Mtb’s success as a pathogen hinges on its ability to remodel the host tissue, characterized by extracellular matrix (ECM) deposition and leaky vascularization. Here we report that inhibition of matrix metalloproteinases (MMPs) significantly enhances the potency of frontline TB antibiotics. These MMP inhibitors increase the relative proportion of healthy blood vessels versus leaky dysfunctional vessels at the infection site, and enhance drug delivery and/or retention. Our study highlights the potential of targeting Mtb-induced host tissue remodeling to enhance the efficacy of current frontline antibiotics. It also suggests an alternative therapeutic strategy to repair the leaky blood vessels in TB granulomas to enhance drug delivery. Repurposing of MMP inhibitors may hold the key to shortening TB treatments and combating the emergence of MDR strains.

Neutrophil Infiltration and Matrix Metalloproteinase-9 in Lacunar Infarction

We use the modified pial vessel disruption rat model to elucidate the cellular and molecular mechanisms of cavitation as it plays a role in lacunar infarction. Here we discuss the similarities between the genesis of pulmonary cavitation in various animal models and lacunar infarction in the cerebral cortex of rats. Both pathological processes involve the creation of a cavity surrounded by fibroblasts or reactive astrocytes. A crucial step in both, the lung and the cerebral cortex, appears to be the migration of neutrophils across the endothelial barrier into the parenchyma. In the lung and cerebral cortex this involves release of matrix metalloproteinase-9 (MMP-9). Inside the parenchyma neutrophils continue to release MMP-9. In both situations batimastat (BB-94) and minocycline reduce release of MMP-9 and prevent cavitation. In the cerebral cortex MMP-9 release by resident microglia plays an additional role. We therefore advance the hypothesis that cavitation in both tissues is driven by MMP-9 originating from invading neutrophils. Therapeutic intervention has to focus on these blood-borne intruder cells and specific MMP actions. Batimastat and its derivatives (marimastat, BB-1101, mCGS-27023-A, ilomastat, GM6001, CTK8G1150) are already in clinical or experimental use in humans for anti-cancer treatment, and these clinically relevant drugs could be repurposed to act as anti-inflammatory to counter neutrophil contribution to lung or cerebral cortex cavitation.

Mycobacterial Dormancy Systems and Host Responses in Tuberculosis

Tuberculosis (TB) caused by the intracellular pathogen, Mycobacterium tuberculosis (Mtb), claims more than 1.5 million lives worldwide annually. Despite promulgation of multipronged strategies to prevent and control TB, there is no significant downfall occurring in the number of new cases, and adding to this is the relapse of the disease due to the emergence of antibiotic resistance and the ability of Mtb to remain dormant after primary infection. The pathology of Mtb is complex and largely attributed to immune-evading strategies that this pathogen adopts to establish primary infection, its persistence in the host, and reactivation of pathogenicity under favorable conditions. In this review, we present various biochemical, immunological, and genetic strategies unleashed by Mtb inside the host for its survival. The bacterium enables itself to establish a niche by evading immune recognition via resorting to masking, establishment of dormancy by manipulating immune receptor responses, altering innate immune cell fate, enhancing granuloma formation, and developing antibiotic tolerance. Besides these, the regulatory entities, such as DosR and its regulon, encompassing various putative effector proteins play a vital role in maintaining the dormant nature of this pathogen. Further, reactivation of Mtb allows relapse of the disease and is favored by the genes of the Rtf family and the conditions that suppress the immune system of the host. Identification of target genes and characterizing the function of their respective antigens involved in primary infection, dormancy, and reactivation would likely provide vital clues to design novel drugs and/or vaccines for the control of dormant TB.

Transcriptomic Approaches in the Zebrafish Model for Tuberculosis-Insights Into Host- and Pathogen-specific Determinants of the Innate Immune Response

Mycobacterium marinum infection in zebrafish has become a well-established model of tuberculosis. Both embryonic and adult zebrafish infection studies have contributed to our knowledge of the development and function of tuberculous granulomas, which are typical of mycobacterial pathogenesis. In this review we discuss how transcriptome profiling studies have helped to characterize this infection process. We illustrate this using new RNA sequencing (RNA-Seq) data that reveals three main phases in the host response to M. marinum during the early stages of granuloma development in zebrafish embryos and larvae. The early phase shows induction of complement and transcription factors, followed by a relatively minor induction of pro-inflammatory cytokines within hours following phagocytosis of M. marinum. A minimal response is observed in the mid-phase, between 6 hours and 1day post infection, when the tissue dissemination of M. marinum begins. During subsequent larval development the granulomas expand and a late-phase response is apparent, which is characterized by progressively increasing induction of complement, transcription factors, pro-inflammatory cytokines, matrix metalloproteinases, and other defense and inflammation-related gene groups. This late-phase response shares common components with the strong and acute host transcriptome response that has previously been reported for Salmonella typhimurium infection in zebrafish embryos. In contrast, the early/mid-phase response to M. marinum infection, characterized by suppressed pro-inflammatory signaling, is strikingly different from the acute response to S. typhimurium infection. Furthermore, M. marinum infection shows a collective and strongly fluctuating regulation of lipoproteins, while S. typhimurium infection has pronounced effects on amino acid metabolism and glycolysis.

Trehalose 6,6-Dimycolate from Mycobacterium tuberculosis Induces Hypercoagulation

Tuberculosis (TB) remains a global health concern. Trehalose 6'6-dimycolate (TDM) activates innate inflammation and likely also stimulates chronic inflammation observed during disease progression. Noninfectious models using purified TDM oil/water emulsions elicit pathologic findings observed in patients with TB. We introduce a new TDM model that promotes inflammatory lung pathologic findings and vascular occlusion and hemorrhage. C57BL/6 and BALB/c mice were injected with 10 μg of i.p. TDM in light mineral oil (TDM-IP). At day 7, another injection of 10 μg of i.v. TDM in oil/water emulsion was given (TDM-IV). The i.p./i.v. TDM (TDM-IVIP) group was compared with mice injected once with i.v. or i.p. TDM. The responses to TDM-IP, TDM-IV, or TDM-IPIV were consistent between mouse strains. Mice that received TDM-IV and TDM-IPIV had inflammatory pathologic findings with increases in inflammatory and T-cell cytokines, and the TDM-IPIV group had further enhancement of IL-10 and granulocyte-macrophage colony-stimulating factor. The TDM-IPIV group had increased CD4(+) T cells in lung tissue, significantly increased coagulation, decreased clot formation time, and increased maximum clot firmness. Masson's trichrome staining revealed increased deposition of collagen in the occluded vasculature. TDM-IPIV promotes a hypercoagulopathy state, independent of inflammation. This new model argues that TDM is sufficient to generate the hypercoagulopathy observed in patients with TB.

Pathology and immune reactivity: understanding multidimensionality in pulmonary tuberculosis

Heightened morbidity and mortality in pulmonary tuberculosis (TB) are consequences of complex disease processes triggered by the causative agent, Mycobacterium tuberculosis (Mtb). Mtb modulates inflammation at distinct stages of its intracellular life. Recognition and phagocytosis, replication in phagosomes and cytosol escape induce tightly regulated release of cytokines [including interleukin (IL)-1, tumor necrosis factor (TNF), IL-10], chemokines, lipid mediators, and type I interferons (IFN-I). Mtb occupies various lung lesions at sites of pathology. Bacteria are barely detectable at foci of lipid pneumonia or in perivascular/bronchiolar cuffs. However, abundant organisms are evident in caseating granulomas and at the cavity wall. Such lesions follow polar trajectories towards fibrosis, encapsulation and mineralization or liquefaction, extensive matrix destruction, and tissue injury. The outcome is determined by immune factors acting in concert. Gradients of cytokines and chemokines (CCR2, CXCR2, CXCR3/CXCR5 agonists; TNF/IL-10, IL-1/IFN-I), expression of activation/death markers on immune cells (TNF receptor 1, PD-1, IL-27 receptor) or abundance of enzymes [arginase-1, matrix metalloprotease (MMP)-1, MMP-8, MMP-9] drive genesis and progression of lesions. Distinct lesions coexist such that inflammation in TB encompasses a spectrum of tissue changes. A better understanding of the multidimensionality of immunopathology in TB will inform novel therapies against this pulmonary disease.

Novel adjunctive therapies for the treatment of tuberculosis

Despite significant efforts to control tuberculosis (TB), the disease remains a major global threat, with an estimated 8.6 million new cases and 1.3 million deaths in 2012 alone. Significant treatment challenges include HIV co-infection, the dramatic rise of multidrug-resistant TB and the vast reservoir of latently infected individuals, who will develop active disease years after the initial infection. The long duration of chemotherapy also remains a major barrier to effective large scale treatment of TB. Significant advances are being made in the development of shorter and effective TB drug regimens and there is growing evidence that host-directed and "non-antimicrobial" pathogen-directed therapies, could serve as novel approaches to enhance TB treatments. This review highlights the rationale for using these therapies and summarizes some of the progress in this field.

Chemokines in tuberculosis: the good, the bad and the ugly

Mycobacterium tuberculosis (Mtb) infects about one-third of the world's population, with a majority of infected individuals exhibiting latent asymptomatic infection, while 5-10% of infected individuals progress to active pulmonary disease. Research in the past two decades has elucidated critical host immune mechanisms that mediate Mtb control. Among these, chemokines have been associated with numerous key processes that lead to Mtb containment, from recruitment of myeloid cells into the lung to activation of adaptive immunity, formation of protective granulomas and vaccine recall responses. However, imbalances in several key chemokine mediators can alter the delicate balance of cytokines and cellular responses that promote mycobacterial containment, instead precipitating terminal tissue destruction and spread of Mtb infection. In this review, we will describe recent insights in the involvement of chemokines in host responses to Mtb infection and Mtb containment (the good), chemokines contributing to inflammation during TB (the bad), and the role of chemokines in driving cavitation and lung pathology (the ugly).

Tuberculosis, pulmonary cavitation, and matrix metalloproteinases

Tuberculosis (TB), a chronic infectious disease of global importance, is facing the emergence of drug-resistant strains with few new drugs to treat the infection. Pulmonary cavitation, the hallmark of established disease, is associated with very high bacillary burden. Cavitation may lead to delayed sputum culture conversion, emergence of drug resistance, and transmission of the infection. The host immunological reaction to Mycobacterium tuberculosis is implicated in driving the development of TB cavities. TB is characterized by a matrix-degrading phenotype in which the activity of proteolytic matrix metalloproteinases (MMPs) is relatively unopposed by the specific tissue inhibitors of metalloproteinases. Proteases, in particular MMPs, secreted from monocyte-derived cells, neutrophils, and stromal cells, are involved in both cell recruitment and tissue damage and may cause cavitation. MMP activity is augmented by proinflammatory chemokines and cytokines, is tightly regulated by complex signaling paths, and causes matrix destruction. MMP concentrations are elevated in human TB and are closely associated with clinical and radiological markers of lung tissue destruction. Immunomodulatory therapies targeting MMPs in preclinical and clinical trials are potential adjuncts to TB treatment. Strategies targeting patients with cavitary TB have the potential to improve cure rates and reduce disease transmission.

Host-directed therapeutics for tuberculosis: can we harness the host?

Treatment of tuberculosis (TB) remains challenging, with lengthy treatment durations and complex drug regimens that are toxic and difficult to administer. Similar to the vast majority of antibiotics, drugs for Mycobacterium tuberculosis are directed against microbial targets. Although more effective drugs that target the bacterium may lead to faster cure of patients, it is possible that a biological limit will be reached that can be overcome only by adopting a fundamentally new treatment approach. TB regimens might be improved by including agents that target host pathways. Recent work on host-pathogen interactions, host immunity, and host-directed interventions suggests that supplementing anti-TB therapy with host modulators may lead to shorter treatment times, a reduction in lung damage caused by the disease, and a lower risk of relapse or reinfection. We undertook this review to identify molecular pathways of the host that may be amenable to modulation by small molecules for the treatment of TB. Although several approaches to augmenting standard TB treatment have been proposed, only a few have been explored in detail or advanced to preclinical and clinical studies. Our review focuses on molecular targets and inhibitory small molecules that function within the macrophage or other myeloid cells, on host inflammatory pathways, or at the level of TB-induced lung pathology.

Combination of gene expression patterns in whole blood discriminate between tuberculosis infection states

Background

Genetic factors are involved in susceptibility or protection to tuberculosis (TB). Apart from gene polymorphisms and mutations, changes in levels of gene expression, induced by non-genetic factors, may also determine whether individuals progress to active TB.

Methods

We analysed the expression level of 45 genes in a total of 47 individuals (23 healthy household contacts and 24 new smear-positive pulmonary TB patients) in Addis Ababa using a dual colour multiplex ligation-dependent probe amplification (dcRT-MLPA) technique to assess gene expression profiles that may be used to distinguish TB cases and their contacts and also latently infected (LTBI) and uninfected household contacts.

Results

The gene expression level of BLR1, Bcl2, IL4d2, IL7R, FCGR1A, MARCO, MMP9, CCL19, and LTF had significant discriminatory power between sputum smear-positive TB cases and household contacts, with AUCs of 0.84, 0.81, 0.79, 0.79, 0.78, 0.76, 0.75, 0.75 and 0.68 respectively. The combination of Bcl2, BLR1, FCGR1A, IL4d2 and MARCO identified 91.66% of active TB cases and 95.65% of household contacts without active TB. The expression of CCL19, TGFB1, and Foxp3 showed significant difference between LTBI and uninfected contacts, with AUCs of 0.85, 0.82, and 0.75, respectively, whereas the combination of BPI, CCL19, FoxP3, FPR1 and TGFB1 identified 90.9% of QFT^- and 91.6% of QFT⁺ household contacts.

Conclusions

Expression of single and especially combinations of host genes can accurately differentiate between active TB cases and healthy individuals as well as between LTBI and uninfected contacts.

Streptolysin-O/antibiotics adjunct therapy modulates site-specific expression of extracellular matrix and inflammatory genes in lungs of Rhodococcus equi infected foals

The addition of streptolysin-O (SLO) to the standard antibiotics regimen was shown to be superior to antibiotics alone after experimental infection of foals with Rhodoccocus equi (R. equi). The objective of this study is to investigate this response by determining the site-specific expression of extracellular matrix (ECM) and inflammatory response genes in biopsy samples taken from three distinct lung regions of the infected foals. Twenty-four foals were challenged by intrabronchial instillation of R. equi and assigned to four treatment groups: SLO/antibiotics adjunct therapy, antibiotics-only therapy (7.5 mg/kg clarithromycin and 5 mg/kg rifampin), SLO-only, and saline-only treatments. Treatments were administered twice daily for 16 days unless symptoms progressed to the point where the foals needed to be euthanized. Gene expressions were determined using custom-designed equine real-time qPCR arrays containing forty-eight genes from ECM remodeling and inflammation pathways. A non-parametric Wilcoxon signed-rank test for independent samples was applied to two pairs of time-matched comparison groups, SLO/antibiotics vs. antibiotics-only and SLO-only vs. saline-only, to document the significant differences in gene expressions within these groups. Several genes, MMP9, MMP2, TIMP2, COL1A1, COL12A1, ITGAL, ITGB1, FN1, CCL2, CCL3, CXCL9, TNFα, SMAD7, CD40, IL10, TGFB1, and TLR2, were significantly regulated compared to the unchallenged/untreated control foals. The results of this study demonstrate that enhancement of clinical responses by SLO is consistent with the changes in expression of critical genes in ECM remodeling and inflammatory response pathways.

Development of the first oligonucleotide microarray for global gene expression profiling in guinea pigs: defining the transcription signature of infectious diseases

Background

The Guinea pig (Cavia porcellus) is one of the most extensively used animal models to study infectious diseases. However, despite its tremendous contribution towards understanding the establishment, progression and control of a number of diseases in general and tuberculosis in particular, the lack of fully annotated guinea pig genome sequence as well as appropriate molecular reagents has severely hampered detailed genetic and immunological analysis in this animal model.

Results

By employing the cross-species hybridization technique, we have developed an oligonucleotide microarray with 44,000 features assembled from different mammalian species, which to the best of our knowledge is the first attempt to employ microarray to study the global gene expression profile in guinea pigs. To validate and demonstrate the merit of this microarray, we have studied, as an example, the expression profile of guinea pig lungs during the advanced phase of M. tuberculosis infection. A significant upregulation of 1344 genes and a marked down regulation of 1856 genes in the lungs identified a disease signature of pulmonary tuberculosis infection.

Conclusion

We report the development of first comprehensive microarray for studying the global gene expression profile in guinea pigs and validation of its usefulness with tuberculosis as a case study. An important gap in the area of infectious diseases has been addressed and a valuable molecular tool is provided to optimally harness the potential of guinea pig model to develop better vaccines and therapies against human diseases.

Doxycycline and HIV infection suppress tuberculosis-induced matrix metalloproteinases

RATIONALE

Tuberculosis kills more than 1.5 million people per year, and standard treatment has remained unchanged for more than 30 years. Tuberculosis (TB) drives matrix metalloproteinase (MMP) activity to cause immunopathology. In advanced HIV infection, tissue destruction is reduced, but underlying mechanisms are poorly defined and no current antituberculous therapy reduces host tissue damage.

OBJECTIVES

To investigate MMP activity in patients with TB with and without HIV coinfection and to determine the potential of doxycycline to inhibit MMPs and decrease pathology.

METHODS

Concentrations of MMPs and cytokines were analyzed by Luminex array in a prospectively recruited cohort of patients. Modulation of MMP secretion and Mycobacterium tuberculosis growth by doxycycline was studied in primary human cells and TB-infected guinea pigs.

MEASUREMENTS AND MAIN RESULTS

HIV coinfection decreased MMP concentrations in induced sputum of patients with TB. MMPs correlated with clinical markers of tissue damage, further implicating dysregulated protease activity in TB-driven pathology. In contrast, cytokine concentrations were no different. Doxycycline, a licensed MMP inhibitor, suppressed TB-dependent MMP-1 and -9 secretion from primary human macrophages and epithelial cells by inhibiting promoter activation. In the guinea pig model, doxycycline reduced lung TB colony forming units after 8 weeks in a dose-dependent manner compared with untreated animals, and in vitro doxycycline inhibited mycobacterial proliferation.

CONCLUSIONS

HIV coinfection in patients with TB reduces concentrations of immunopathogenic MMPs. Doxycycline decreases MMP activity in a cellular model and suppresses mycobacterial growth in vitro and in guinea pigs. Adjunctive doxycycline therapy may reduce morbidity and mortality in TB.

Phosphodiesterase-4 inhibition combined with isoniazid treatment of rabbits with pulmonary tuberculosis reduces macrophage activation and lung pathology

Tuberculosis (TB) is responsible for significant morbidity and mortality worldwide. Even after successful microbiological cure of TB, many patients are left with residual pulmonary damage that can lead to chronic respiratory impairment and greater risk of additional TB episodes due to reinfection with Mycobacterium tuberculosis. Elevated levels of the proinflammatory cytokine tumor necrosis factor-α and several other markers of inflammation, together with expression of matrix metalloproteinases, have been associated with increased risk of pulmonary fibrosis, tissue damage, and poor treatment outcomes in TB patients. In this study, we used a rabbit model of pulmonary TB to evaluate the impact of adjunctive immune modulation, using a phosphodiesterase-4 inhibitor that dampens the innate immune response, on the outcome of treatment with the antibiotic isoniazid. Our data show that cotreatment of M. tuberculosis infected rabbits with the phosphodiesterase-4 inhibitor CC-3052 plus isoniazid significantly reduced the extent of immune pathogenesis, compared with antibiotic alone, as determined by histologic analysis of infected tissues and the expression of genes involved in inflammation, fibrosis, and wound healing in the lungs. Combined treatment with an antibiotic and CC-3052 not only lessened disease but also improved bacterial clearance from the lungs. These findings support the potential for adjunctive immune modulation to improve the treatment of pulmonary TB and reduce the risk of chronic respiratory impairment.

MMPs in tuberculosis: granuloma creators and tissue destroyers

Most individuals infected with Mycobacterium tuberculosis develop a latent infection, which does not progress to active tuberculosis (TB). This occurs, in part, because infected macrophages recruit immune cells to form a granuloma, isolating the bacteria and preventing its spread. In some individuals, granulomas undergo necrosis and tissue destruction occurs, releasing the bacteria and allowing the development of active disease. In this issue of the JCI, Elkington et al. provide evidence that M. tuberculosis drives the expression of MMP-1, which in turn promotes the collagen breakdown that leads to alveolar destruction in TB. These findings identify putative therapeutic targets for the prevention of TB.

Mycobacterium bovis-BCG vaccination induces specific pulmonary transcriptome biosignatures in mice

Background

In the present study, we applied microarray technology to define biosignatures by microarray transcriptome analysis in lung and spleen samples after BCG vaccination and M. bovis infection of BALB/c mice. The aims were two-fold, namely to define biosignatures that could predict vaccine success before challenge, and biomarker patterns that correlated with anamnestic protective responses following exposure to virulent M. bovis. Further, these biosignatures should be detectable without in vitro antigenic challenge.

Principal Findings

After BCG vaccination, we defined a specific pulmonary gene expression signature related to the connective tissue development and function network that predicted vaccine success before M. bovis challenge. In addition, a Th17-related cytokine profile was found that correlated with vaccine-induced protective immunity following infection with virulent M. bovis in the lung as well as additional genes that were up-regulated in the spleens of vaccinated animals post-infection related to neutrophil biology and inflammation.

Conclusions

This study has therefore prioritized both biomarkers predicting vaccination success before challenge and bio-signatures that are potentially associated with protective immune responses that will be useful to evaluate future vaccine candidates.

Mycobacteria-induced granuloma necrosis depends on IRF-1

In a mouse model of mycobacteria-induced immunopathology, wild-type C57BL/6 (WT), IL-18-knockout (KO) and IFN-alphabeta receptor-KO mice developed circumscript, centrally necrotizing granulomatous lesions in response to aerosol infection with M. avium, whereas mice deficient in the IFN-gamma receptor, STAT-1 or IRF-1 did not exhibit granuloma necrosis. Comparative, microarray-based gene expression analysis in the lungs of infected WT and IRF-1-KO mice identified a set of genes whose differential regulation was closely associated with granuloma necrosis, among them cathepsin K, cystatin F and matrix metalloprotease 10. Further microarray-based comparison of gene expression in the lungs of infected WT, IFN-gamma-KO and IRF-1-KO mice revealed four distinct clusters of genes with variable dependence on the presence of IFN-gamma, IRF-1 or both. In particular, IRF-1 appeared to be directly involved in the differentiation of a type I immune response to mycobacterial infection. In summary, IRF-1, rather than being a mere transcription factor downstream of IFN-gamma, may be a master regulator of mycobacteria-induced immunopathology.

Synergistic up-regulation of epithelial cell matrix metalloproteinase-9 secretion in tuberculosis

Mycobacterium tuberculosis (MTb) kills approximately 2 million people each year. MTb must drive host tissue destruction to disseminate and also to cause pulmonary cavitation. Matrix metalloproteinase-9 (MMP-9, gelatinase B) is implicated in this Tb-related immunopathology. We demonstrate that conditioned media from MTb-infected monocytes (CoMTb), but not direct infection with MTb, up-regulates MMP-9 gene expression and secretion from primary human bronchial epithelial cells (NHBE). MMP-9 secretion was increased 8.7-fold by CoMTb (P < 0.05) as assayed by gelatin zymography. A549 and 16HBE14o epithelial cell MMP secretion was significantly less than primary NHBE secretion. MMP-9 secretion was decreased 53.2% by inhibition of the p38 mitogen-activated protein kinase (MAPK) by SB203580 (P < 0.01) and 48.3% by inhibition of extracellular signal-regulated kinase with PD98059 (P < 0.05). MMP-9 secretion was prostaglandin independent. TNF-alpha was necessary but not sufficient for MMP-9 up-regulation by the monocyte-epithelial cell network. Soluble factors derived from Tb culture synergized with TNF-alpha to increase MMP-9 secretion by NHBE 6-fold (P < 0.01 compared with either stimulus alone). Together, these data reveal a new mechanism by which host- and pathogen-derived factors act together in MTb infection to drive MAPK-dependent MMP-9 secretion from respiratory epithelial cells.

Role for matrix metalloproteinase 9 in granuloma formation during pulmonary Mycobacterium tuberculosis infection

Recent studies have shown that matrix metalloproteinases (MMPs) are induced by Mycobacterium tuberculosis during pulmonary infection. Here, expression of MMP-9 during pulmonary M. tuberculosis infection was characterized to determine whether its production correlated with disease resistance in vivo and to determine what role, if any, MMP-9 might have in granuloma formation. Following aerosol infection with M. tuberculosis, dissemination of bacilli occurred earlier in the C57BL/6 resistant mouse strain than in the susceptible CBA/J strain, as was evident from an increased number of bacteria in the blood, spleen, and liver at day 14 after infection. In addition, early dissemination of the bacilli was associated with early induction of protective immunity as assessed from gamma interferon levels. Nonspecific blocking of MMPs in C57BL/6 mice early during infection reduced hematogenous spread of the bacilli, suggesting that MMPs indeed play a role in facilitating dissemination, likely via extracellular matrix degradation. The concentration of active MMP-9, specifically, was greater in the lungs of C57BL/6 mice than in those of the CBA/J mice at day 28, thereby suggesting that MMP-9 is not one of the MMPs directly involved in promoting early dissemination of M. tuberculosis. Instead, however, histological lung sections and flow cytometric analysis of lung cells from MMP-9-knockout mice showed that MMP-9 is involved in macrophage recruitment and granuloma development. These combined data support the idea that early MMP activity is an essential component of resistance to pulmonary mycobacterial infection and that MMP-9, specifically, is required for recruitment of macrophages and tissue remodeling to allow for the formation of tight, well-organized granulomas.

A relevant enzyme in granulomatous reaction, active matrix metalloproteinase-9, found in bovine Echinococcus granulosus hydatid cyst wall and fluid

In addition to the ability of matrix metalloproteinases (MMP) to degrade components of the extracellular matrix and their involvement in pathology-related processes of tissue remodeling, they were recently reported to enhance inflammation by activation of proinflammatory cytokines, or their release from the cell surface. In the work reported here, proteolytic activity previously found for hydatid cysts was further characterized as MMP-9. Active host MMP-9 was found in walls and fluids of bovine hydatid cysts of Echinococcus granulosus in the environment of granulomatous reaction. Pooled walls and fluids of hydatid cysts obtained from infected cattle were processed. Strong proteolytic activity was detected by zymography. The proteolytic fraction was purified by anion exchange and gelatin-agarose affinity chromatography. Major proteinases of the purified fraction were subjected to mass spectrometry and their identities were further confirmed by Western blotting using commercial anti-human MMP-9 monoclonal antibodies. Two proteinases were characterized as latent and active forms of host MMP-9. Using the same antibody for immunoblot, activity was localized, in paraffin-embedded sections of the parasite and the local host environment, to epithelioid and giant multinucleated cells. It is proposed here that MMP-9 is secreted by specialized host cells of monocytic lineage (epithelioid/giant cells) as an effector, in an attempt to digest the persistent foreign body. In vivo activation of MMP-9 suggests its involvement in inflammatory reaction and in the chemotaxis of inflammatory cells to the cyst. However, E. granulosus can deal efficiently with MMP-9. Research is suggested into possible immune evasion mechanisms, including the secretion of an inhibitory molecule.

New insights into the function of granulomas in human tuberculosis

The human tuberculous granuloma provides the morphological framework for local immune processes central to the outcome of tuberculosis. This review article describes investigations on human lung granulomas aimed at better understanding the regional host response and counter-measures to Mycobacterium tuberculosis. These findings lead to a revised view of the regional immune response in human tuberculosis. Novel insights into this dynamic cross-talk form the basis of novel intervention strategies.

Alternative activation deprives macrophages of a coordinated defense program toMycobacterium tuberculosis

A potent Th1 immune response is critical to the control of tuberculosis. The impact of an additive Th2 response on the course of disease has so far been insufficiently characterized, despite increased morbidity after co-infection with Mycobacterium tuberculosis and Th2-eliciting helminths and possible involvement of Th2 polarization in reactivation of latent tuberculosis. Here, we describe the gene expression profile of murine bone marrow-derived macrophages alternatively activated by IL-4 in response to infection with M. tuberculosis. Comparison of transcriptional profiles of infected IL-4- and IFN-gamma-activated macrophages revealed delayed and partially diminished responses to intracellular bacteria in alternatively activated macrophages, characterized by reduced exposure to nitrosative stress and increased iron availability, respectively. Alternative activation of host macrophages correlated with elevated expression of the M. tuberculosis iron storage protein bacterioferritin as well as reduced expression of the mycobactin synthesis genes mbtI and mbtJ. The extracellular matrix-remodeling enzyme matrix metalloproteinase (MMP)-12 was induced in alternatively activated macrophages in vitro, and MMP-12-expressing macrophages were abundant at late, but not early, stages of tuberculosis in murine lungs. Our findings emphasize that alternative activation deprives macrophages of control mechanisms that limit mycobacterial growth in vivo, thus supporting intracellular persistence of M. tuberculosis.

Matrix metalloproteinases in destructive pulmonary pathology

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have a number of important physiological roles including remodelling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity may lead to tissue destruction. The biology of MMP and the role of these proteases in normal pulmonary immunity are reviewed, and evidence that implicates excess MMP activity in causing matrix breakdown in chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS), sarcoidosis, and tuberculosis is discussed. Evidence from both clinical studies and animal models showing that stromal and inflammatory cell MMP expression leads to immunopathology is examined, and the mechanisms by which excess MMP activity may be targeted to improve clinical outcomes are discussed.

The wound repair response controls outcome to cutaneous leishmaniasis

Chronic microbial infections are associated with fibrotic and inflammatory reactions known as granulomas showing similarities to wound-healing and tissue repair processes. We have previously mapped three leishmaniasis susceptibility loci, designated lmr1, -2, and -3, which exert their effect independently of T cell immune responses. Here, we show that the wound repair response is critically important for the rapid cure in murine cutaneous leishmaniasis caused by Leishmania major. Mice congenic for leishmaniasis resistance loci, which cured their lesions more rapidly than their susceptible parents, also expressed differentially genes involved in tissue repair, laid down more ordered collagen fibers, and healed punch biopsy wounds more rapidly. Fibroblast monolayers from these mice repaired in vitro wounds faster, and this process was accelerated by supernatants from infected macrophages. Because these effects are independent of T cell-mediated immunity, we conclude that the rate of wound healing is likely to be an important component of innate immunity involved in resistance to cutaneous leishmaniasis.

The paradox of matrix metalloproteinases in infectious disease

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that perform multiple roles in the normal immune response to infection. MMPs facilitate leucocyte recruitment, cytokine and chemokine processing, defensin activation and matrix remodelling. However, excess MMP activity following infection may lead to immunopathology that causes host morbidity or mortality and favours pathogen dissemination or persistence. Here, we review the normal functions of MMPs in immunity and then discuss viral and bacterial infections where excess MMP activity has been implicated in pathology, specifically examining HIV, HTLV-1, hepatitis B, endotoxin shock, Helicobacter pylori and Mycobacterium tuberculosis. Tissue destruction may be exacerbated further by bacterial-derived enzymes which activate the host pro-MMPs. Finally, the potential for therapeutic targeting of excess MMP activity in infection is considered.