Kallikrein 12 Regulates Innate Resistance of Murine Macrophages against Mycobacterium bovis Infection by Modulating Autophagy and Apoptosis

Abstract

Mycobacterium bovis (M. bovis) is a member of the Mycobacterium tuberculosis (Mtb) complex causing bovine tuberculosis (TB) and imposing a high zoonotic threat to human health. Kallikreins (KLKs) belong to a subgroup of secreted serine proteases. As their role is established in various physiological and pathological processes, it is likely that KLKs expression may mediate a host immune response against the M. bovis infection. In the current study, we report in vivo and in vitro upregulation of KLK12 in the M. bovis infection. To define the role of KLK12 in immune response regulation of murine macrophages, we produced KLK12 knockdown bone marrow derived macrophages (BMDMs) by using siRNA transfection. Interestingly, the knockdown of KLK12 resulted in a significant downregulation of autophagy and apoptosis in M. bovis infected BMDMs. Furthermore, we demonstrated that this KLK12 mediated regulation of autophagy and apoptosis involves mTOR/AMPK/TSC2 and BAX/Bcl-2/Cytochrome c/Caspase 3 pathways, respectively. Similarly, inflammatory cytokines IL-1β, IL-6, IL-12 and TNF-α were significantly downregulated in KLK12 knockdown macrophages but the difference in IL-10 and IFN-β expression was non-significant. Taken together, these findings suggest that upregulation of KLK12 in M. bovis infected murine macrophages plays a substantial role in the protective immune response regulation by modulating autophagy, apoptosis and pro-inflammatory pathways. To our knowledge, this is the first report on expression and the role of KLK12 in the M. bovis infection and the data may contribute to a new paradigm for diagnosis and treatment of bovine TB.

Mycobacterium tuberculosis infection increases the number of osteoclasts and inhibits osteoclast apoptosis by regulating TNF‑α‑mediated osteoclast autophagy

“…Recent studies have shown that autophagy plays an important role in diverse biological and pathological processes, including cell proliferation, differentiation, apoptosis, and carcinogenesis; however, little is known about the role of autophagy in the development of osteoarticular tuberculosis (18)(19)(20)(21). The present results demonstrated that the number of osteoclasts increased and autophagy was enhanced in the lesions of patients with osteoarticular tuberculosis compared with patients with OA.…”

The role of mitophagy in innate immune responses triggered by mitochondrial stress

“…A recent study reported that M. bovis infection upregulates the expression of the Kallikrein 12 (KLK12), and knockdown of KLK12 results in a significant downregulation of autophagy and apoptosis in M. bovis -infected BMDMs. Furthermore, KLK12-mediated regulation of apoptosis involves BAX/Bcl-2/cytochrome c/caspase 3 pathways [ 80 ]. Mycobacterium fortuitum infection induces Ca 2+ mobilization from the endoplasmic reticulum (ER) to mitochondria, leading to increased mitochondrial Ca 2+ load, MPTP opening, altered mitochondrial membrane potential (ΔΨm), cytochrome c release, and eventually activation of the caspase-9/− 3 mediated apoptosis in fish macrophage [ 81 ].…”

Guanylate-Binding protein 2b regulates the AMPK/mTOR/ULK1 signalling pathway to induce autophagy during Mycobacterium bovis infection

“…AMPK is a protein kinase that plays a major role in the regulation of the reprogramming of metabolism and cell growth, and its enzymatic activity is entirely dependent on the phosphorylation of the thr172α subunit [ 33 , 35 ]. AMPK inhibits mTOR activity by phosphorylating tuberous sclerosis syndrome 2, thereby promoting autophagy [ 36 ]. In addition, ULK1 is a homolog of yeast Atg1 kinase, which plays an important role in autophagy induction [ 37–39 ].…”

“…Numerous studies have elucidated the critical role of autophagy in the resistance to intracellular mycobacterial infection [ 29 , 36 ]. The experimental results reported above suggest that GBP2b promotes autophagy and that AMPK, which is a key protein in the regulation of the autophagic process, is also involved in the killing of intracellular M. bovis by macrophages [ 36 ].…”