4-(Benzyloxy)phenol-induced p53 exhibits antimycobacterial response triggering phagosome-lysosome fusion through ROS-dependent intracellular Ca2+ pathway in THP-1 cells

Drug-resistant tuberculosis (TB) outbreak has emerged as a global public health crisis. Therefore, new and innovative therapeutic options like host-directed therapies (HDTs) through novel modulators are urgently required to overcome the challenges associated with TB. In the present study, we have investigated the anti-mycobacterial effect of 4-(Benzyloxy)phenol. Cell-viability assay asserted that 50 μM of 4-(Benzyloxy)phenol was not cytotoxic to phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 (dTHP-1) cells. It was observed that 4-(Benzyloxy)phenol activates p53 expression by hindering its association with KDM1A. Increased ROS, intracellular Ca2+ and phagosome-lysosome fusion, were also observed upon 4-(Benzyloxy)phenol treatment. 4-(Benzyloxy)phenol mediated killing of intracellular mycobacteria was abrogated in the presence of specific inhibitors of ROS, Ca2+ and phagosome-lysosome fusion like NAC, BAPTA-AM, and W7, respectively. We further demonstrate that 4-(Benzyloxy)phenol mediated enhanced ROS production is mediated by acetylation of p53. Blocking of p53 acetylation by Pifithrin-α (PFT- α) enhanced intracellular mycobacterial growth by blocking the mycobactericidal effect of 4-(Benzyloxy)phenol. Altogether, the results showed that 4-(Benzyloxy)phenol executed its anti-mycobacterial effect by modulating p53-mediated ROS production to regulate phagosome-lysosome fusion through Ca2+ production.

Soybean lectin-triggered IL-6 secretion induces autophagy to kill intracellular mycobacteria through P2RX7 dependent activation of the JAK2/STAT3/Mcl-1 pathway

Cytokine therapy and cytokine-mediated autophagy have been used as prominent host-directed therapy (HDT) approaches to restrain M. tb growth in the host cell. In the present study, we have dissected the anti-tubercular activity of Soybean lectin (SBL) through cytokine-mediated autophagy induction in differentiated THP-1 (dTHP-1) cells. A significant increase in IL-6 expression was observed in both uninfected and mycobacteria infected dTHP-1 cells through the P2RX7 mediated pathway via PI3K/Akt/CREB-dependent signalling after SBL treatment. Inhibition of IL-6 level using IL-6 neutralizing antibody or associated signalling significantly enhanced the mycobacterial load in SBL-treated dTHP-1 cells. Further, autocrine signalling of IL-6 through its receptor-induced Mcl-1 expression activated autophagy via JAK2/STAT3 pathway, and inhibition of this pathway affected autophagy. Finally, blocking the IL-6-regulated autophagy through NSC 33994 (a JAK2 inhibitor) or S63845 (an Mcl-1 inhibitor) led to a notable increase in intracellular mycobacterial growth in SBL-treated cells. Taken together, these results indicate that SBL interacts with P2RX7 to regulate PI3K/Akt/CREB network to release IL-6 in dTHP-1 cells. The released IL-6, in turn, activates the JAK2/STAT3/Mcl-1 pathway upon interaction with IL-6Rα to modulate autophagy that ultimately controls mycobacterial growth in macrophages.

Ac-93,253 inhibits intracellular growth of mycobacteria in human macrophages by inducing apoptosis in mitochondrial-dependent manner

Recent studies suggest that apoptosis in macrophages plays a significant role in host defence against intracellular pathogens like viruses, fungi, protozoan, and bacteria, including Mycobacterium tuberculosis (M. tb). It is still unclear if micromolecules inducing apoptosis could be an attractive approach to combat the intracellular burden of M. tb. Hence, the present study has investigated the anti-mycobacterial effect of apoptosis mediated through phenotypic screening of micromolecules. Through MTT and trypan blue exclusion assay, 0.5 μM of Ac-93,253 was found to be non-cytotoxic even after 72 h of treatment in phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 (dTHP-1) cells. Significant regulation in the expression of various pro-apoptotic genes like Bcl-2, Bax, and Bad and the cleaved caspase 3 was observed upon treatment with a non-cytotoxic dose of Ac-93,253. Ac-93,253 treatment also leads to DNA fragmentation and increased phosphatidylserine accumulation in the plasma membrane's outer leaflet. Further, Ac-93,253 also effectively reduced the growth of mycobacteria in infected macrophages, Z-VAD-FMK a broad-range apoptosis inhibitor significantly brought back the mycobacterial growth in Ac-93,253 treated macrophages. These findings suggest apoptosis may be the probable effector response through which Ac-93,253 manifests its anti-mycobacterial property.

Involvement of epigenetics in affecting host immunity during SARS-CoV-2 infection

Coronavirus disease 19 (COVID-19) is caused by a highly contagious RNA virus Severe Acute Respiratory Syndrome coronavirus-2 (SARS-CoV-2), originated in December 2019 in Wuhan, China. Since then, it has become a global public health concern and leads the disease table with the highest mortality rate, highlighting the necessity for a thorough understanding of its biological properties. The intricate interaction between the virus and the host immune system gives rise to diverse implications of COVID-19. RNA viruses are known to hijack the host epigenetic mechanisms of immune cells to regulate antiviral defence. Epigenetics involves processes that alter gene expression without changing the DNA sequence, leading to heritable phenotypic changes. The epigenetic landscape consists of reversible modifications like chromatin remodelling, DNA/RNA methylation, and histone methylation/acetylation that regulates gene expression. The epigenetic machinery contributes to many aspects of SARS-CoV-2 pathogenesis, like global DNA methylation and receptor angiotensin-converting enzyme 2 (ACE2) methylation determines the viral entry inside the host, viral replication, and infection efficiency. Further, it is also reported to epigenetically regulate the expression of different host cytokines affecting antiviral response. The viral proteins of SARS-CoV-2 interact with various host epigenetic enzymes like histone deacetylases (HDACs) and bromodomain-containing proteins to antagonize cellular signalling. The central role of epigenetic factors in SARS-CoV-2 pathogenesis is now exploited as promising biomarkers and therapeutic targets against COVID-19. This review article highlights the ability of SARS-CoV-2 in regulating the host epigenetic landscape during infection leading to immune evasion. It also discusses the ongoing therapeutic approaches to curtail and control the viral outbreak.

ESAT-6 impedes IL-18 mediated phagosome lysosome fusion via microRNA-30a upon Calcimycin treatment in mycobacteria infected macrophages

The weaponry possessed by Mycobacterium tuberculosis (M. tb) in the form of immunodominant antigens hijack the host immune system to give a survival advantage to this intracellular fiend, but the mechanism of this control is not entirely known. Since we have previously reported the mechanism of autophagy inhibition by early secreted antigenic target 6 kDa (ESAT-6) through microRNA (miR)-30a-3p in Calcimycin treated differentiated THP-1 (dTHP-1) cells, the present study was undertaken to deduce the effect of miR-30a on the immunomodulatory profile of ESAT-6 treated cells and the mechanism involved thereof, if any. Initially, the effect of recombinant ESAT-6 (rESAT-6) on the immunomodulatory profile in Calcimycin-treated phorbol 12-myristate 13-acetate (PMA) dTHP-1 cells was checked. Later, transfection studies using miR-30a-3p inhibitor or -5p mimic highlighted the contrary roles of different arms of the same miRNA in regulating IL-18 response by ESAT-6 in dTHP-1 cells after Calcimycin treatment. By using either IL-18 neutralizing antibody or inhibitors of phosphoinositide 3-kinase (PI3K)/NF-κB/phagosome-lysosome fusion in the miRNA-30a transfected background, IL-18 mediated signaling and intracellular killing of mycobacteria was reversed in the presence of ESAT-6. Overall, the results of this study conclusively prove the contrary roles of miR-30a-3p and miR-30a-5p in regulating IL-18 signaling by ESAT-6 in dTHP-1 cells upon Calcimycin treatment that affected phagosome-lysosome fusion and intracellular survival of mycobacteria.

Soybean lectin induces autophagy through P2RX7 dependent activation of NF-κB-ROS pathway to kill intracellular mycobacteria

BACKGROUND

Host-directed therapy is considered a novel anti-tuberculosis strategy in tackling the tuberculosis burden through autophagy induction by various inducers to curtail the growth of intracellular Mycobacterium tuberculosis.

METHODS

In this study, we investigated the anti-tubercular role of soybean lectin, a lectin isolated from Glycine max (Soybean). Effect of SBL on intracellular mycobacterial viability through autophagy and the mechanism involved in differentiated THP-1 cells was studied using different experimental approaches.

RESULTS

We initially performed a time kinetic experiment with the non-cytotoxic dose of SBL (20 μg/ml) and observed autophagy induction after 24 h of treatment. Abrogation of autophagy in the presence of 3-MA and an increase in LC3 puncta formation upon Baf-A1 addition elucidated the specific effect on autophagy and autophagic flux. SBL treatment also led to autophagy induction in mycobacteria infected macrophages that restricted the intracellular mycobacterial growth, thus emphasizing the host defensive role of SBL induced autophagy. Mechanistic studies revealed an increase in P2RX7 expression, NF-κB activation and reactive oxygen species generation upon SBL treatment. Inhibition of P2RX7 expression suppressed NF-κB dependent ROS level in SBL treated cells. Moreover, SBL induced autophagy was abrogated in the presence of either different inhibitors or P2RX7 siRNA, leading to the reduced killing of intracellular mycobacteria.

CONCLUSION

Taken together, these results conclude that SBL induced autophagy exerts an anti-mycobacterial effect in P2RX7-NF-κB dependent manner through the generation of ROS.

GENERAL SIGNIFICANCE

This study has provided a novel anti-mycobacterial role of SBL, which may play an important role in devising new therapeutic interventions.

NSC 18725, a Pyrazole Derivative Inhibits Growth of Intracellular Mycobacterium tuberculosis by Induction of Autophagy

The increasing incident rates of drug-resistant tuberculosis (DR-TB) is a global health concern and has been further complicated by the emergence of extensive and total drug-resistant strains. Identification of new chemical entities which are compatible with first-line TB drugs, possess activity against DR-, and metabolically less active bacteria is required to tackle this epidemic. Here, we have performed phenotypic screening of a small molecule library against Mycobacterium bovis BCG and identified 24 scaffolds that exhibited MIC₉₉ values of at least 2.5 μM. The most potent small molecule identified in our study was a nitroso containing pyrazole derivative, NSC 18725. We observed a significant reduction in viable bacilli load of starved Mycobacterium tuberculosis upon exposure to NSC 18725. The action of NSC 18725 was “synergistic” with isoniazid (INH) and “additive” with other drugs in our checkerboard assays. Structure-activity relationship (SAR) studies of the parent compound revealed that pyrazole derivatives without a functional group at fourth position lacked anti-mycobacterial activity in vitro. The derivative with para-chlorophenyl substitution at the first position of the pyrazole ring was the most active scaffold. We also demonstrate that NSC 18725 is able to induce autophagy in differentiated THP-1 macrophages. The induction of autophagy by NSC 18725 is the major mechanism for the killing of intracellular slow and fast-growing mycobacteria. Taken together, these observations support the identification of NSC 18725 as an antimycobacterial compound, which synergizes with INH, is active against non-replicative mycobacteria and induces autophagy in macrophages.

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

ESAT-6 modulates Calcimycin-induced autophagy through microRNA-30a in mycobacteria infected macrophages

OBJECTIVE

Mycobacterium tuberculosis (M. tb) has a sumptuous repertoire of effector molecules to counter host defenses. Some of these antigens inhibit autophagy but the exact mechanism of this inhibition is poorly understood.

METHODS

Purified protein derivative (PPD) was fractionated using 10 (PPD 10, antigenic molecular weight > 10 kDa) and 3 (PPD 3, mol. weight > 3 kDa) kDa cutters. Effect of these fractions on Calcimycin-induced autophagy and intracellular mycobacterial viability was then studied using different experimental approaches.

RESULT

We found significant downregulation of autophagy by PPD 3 pre-treatment in Calcimycin-treated dTHP-1 cells compared to PPD 10. This reduction in autophagy also corroborated with the enhanced survival of mycobacteria in macrophages. We demonstrate that recombinant early secreted antigenic target 6 (rESAT-6) is responsible to inhibit Calcimycin-induced autophagy and enhance intracellular survival of mycobacteria. We also show that pre-treatment with rESAT-6 upregulates microRNA (miR)-30a-3p expression and vis-a-vis downregulates miR-30a-5p expression in Calcimycin-treated dTHP-1 cells. Transfection studies with either miR-30a-3p inhibitor or miR-30a-5p mimic clearly elucidated the opposing roles of miR-30a-3p and miR-30a-5p in rESAT-6 mediated mycobacterial survival through autophagy inhibition.

CONCLUSION

Taken together, our result evidently highlights that rESAT-6 enhances intracellular survival of mycobacteria by modulating miR-30a-3p and miR-30a-5p expression.

Calcimycin mediates mycobacterial killing by inducing intracellular calcium-regulated autophagy in a P2RX7 dependent manner

Phenotypic screening led to the identification of calcimycin as a potent inhibitor of Mycobacterium bovis BCG (M. bovis BCG) growth in vitro and in THP-1 cells. In the present study, we aim to decipher the mechanism of antimycobacterial activity of calcimycin. We noticed that treatment with calcimycin led to up-regulation of different autophagy markers like Beclin-1, autophagy-related gene (Atg) 7, Atg 3 and enhanced microtubule-associated protein 1A/1B-light chain 3-I (LC3-I) to LC3-II conversion in macrophages. This calcimycin-mediated killing of intracellular M. smegmatis and M. bovis BCG was abrogated in the presence of 3-methyladenine (3-MA). We also demonstrate that calcimycin binding with purinergic receptor P2X7 (P2RX7) led to increase in intracellular calcium level that regulates the extracellular release of ATP. ATP was able to regulate calcimycin-induced autophagy through P2RX7 in an autocrine fashion. Blocking of either P2RX7 expression by 1-[N,O-bis(5-Isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-phenylpiperazine (KN-62) or reducing intracellular calcium levels by 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra (acetoxy-methyl) ester (BAPTA-AM) abrogated the antimycobacterial activity of calcimycin. Taken together, these results showed that calcimycin exerts its antimycobacterial effect by regulating intracellular calcium-dependent ATP release that induces autophagy in a P2RX7 dependent manner.