Stimulation of Autophagy by Soybean Lectin (SBL) And Its Antimycobacterial Response in Human Macrophages

Abstract

Host-directed therapy is considered a novel anti-TB strategy to tackle the ever-threatening global tuberculosis (TB) burden. In the past few years, autophagy has been one such strategy manipulated through various inducers to curtail the growth of intracellular Mycobacterium tuberculosis (M. tb). In the present study, the mechanism of action for the anti-tubercular role of soybean lectin (SBL), a lectin isolated from Glycine max (Soybean) has been investigated. SBL restricted intracellular mycobacterial growth by inducing autophagy in differentiated THP-1 (dTHP-1) cells. Mechanistic studies revealed that SBL exerts its antimycobacterial effect in P2RX7-NF-κB dependent manner through ROS generation in dTHP-1 cells. Further, the immunomodulatory effect of SBL in dTHP-1 cells was dissected. A significant increase in IL-6 expression was observed in uninfected and mycobacterial infected dTHP-1 cells through the P2RX7 mediated pathway via PI3K/Akt/CREB-dependent signalling after SBL treatment. Interestingly, the IL-6 receptor (IL-6Rα) was also remarkably expressed on the surface of SBL treated cells. Inhibition of IL-6 level using IL-6 neutralizing antibody or associated signalling significantly enhanced the mycobacterial load in SBL treated dTHP-1 cells, indicating the host defensive role of IL-6. Further, autocrine signalling of IL-6 through its receptor-induced Mcl-1 expression activates 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 dTHP-1 cells. In conclusion, 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 to control mycobacterial growth in macrophages. So this present study elucidated the mechanistic regulation of autophagy by SBL in dTHP-1 cells and highlighted the fact that triggering autophagy with natural compounds like SBL may be harnessed to develop better therapeutics against TB.