Host-directed Therapy Alleviates Intracellular Mycobacterial Infection via Mediating Innate Immune Responses

Aims and objectives: Mycobacterium bovis (M. bovis) is the causative agent of bovine tuberculosis; however, it also causes infection in a wide range of hosts including human beings. Johne's disease (JD) is characterized by chronic granulomatous enteritis predominantly observed in ruminants, caused by Mycobacterium avium subsp. paratuberculosis (MAP). Autophagy is an innate immune defense mechanism for the control of intracellular bacteria, regulated by diverse signaling pathways. It plays a key role in the innate immune defense mechanism for controlling intracellular mycobacterium. Nilotinib, a tyrosine kinase inhibitor (TKI), has been studied extensively in various tumor models; however, no information exists about the pharmacological action of nilotinib in bacterial infections. We hypothesized to investigate the effect of nilotinib on the regulation of host innate immune responses against Mycobacterial infection. In addition, to devise best possible therapeutic remedy towards achieving the goal of mycobacterial diseases treatment based on molecular mechanism both in vitro and in vivo, which may provide useful strategy to treat animal's tuberculosis. Methods: In the current study, we conducted both in vitro and in vivo experiments to investigate the role of nilotinib in the regulation of autophagy. Western blot, confocal microscopy, electron microscopy and immunohistochemistry were performed to investigate the induction of autophagy upon nilotinib treatment during M. bovis infection. Gross and histological analysis were conducted to observe the effect of nilotinib on the development of lung's lesions in mice infected with M. bovis. CFU assay was performed to determine the effect of nilotinib on the intracellular growth of M. bovis. Results: We found that nilotinib improved the host immune responses by inhibiting intracellular survival and growth of both M. bovis and MAP. Nilotinib also attenuated PI3k/Akt/mTOR axis for the regulation of autophagic degradation of intracellular mycobacterium mediated by inhibition of Abelson (c-ABL) tyrosine kinase. In addition, nilotinib promoted ubiquitination of intracellular bacteria through activation of E3 ubiquitin ligase parkin. Similarly, lung tissue sections of nilotinib treated mice also showed high intensity of parkin protein post M. bovis infection. From in-vivo experiment, we found that nilotinib effectively controlled M. bovis growth and the severity of disease in infected mice. Conclusions: Altogether, our data shows that nilotinib regulates protective host innate immune responses against intracellular pathogen both in-vitro and in-vivo and can be exploited as a novel host-directed therapeutic agent in the control of M. bovis and MAP infections.