Mycobacterium leprae promotes Schwann cells survival through phosphatidilinositol 3-K/Akt signaling and NF-kappaB activation
1Rodrigues, L.S., 1Maeda, E.S., 3Pereira, R.M., 2Moreira, M.E.C., 3Lopes, U.G., 1Sarno, E.N., 1Pessolani, M.C.V.
1Cellular Microbiology Laboratory, Instituto Oswaldo Cruz, FIOCRUZ, Rio de Janeiro, BR; 2Experimental Medicine Laboratory, Instituto Nacional do Câncer, INCA, Rio de Janeiro, BR; 3Molecular Parasitology Laboratory, Instituto de Biofísica Carlos Chagas Filho, UFRJ, Rio de Janeiro, BR.
The lesions of the peripheral nervous are considered the most relevant symptoms of Leprosy, a chronic infectious disease caused by Mycobacterium leprae. The strategies employed by M. leprae to infect and multiply inside Schwann cells (SC) are, however poorly understood. In a previous study, we have shown that, similarly to other obligate intracellular pathogens, M. leprae promotes an anti-apoptotic effect on the host cell. In the present study, we further characterized the survival effect of M. leprae on Schwann cells. Human SC lineage ST88-14 was treated or not with the bacteria and incubated in serum-free RPMI medium to induce apoptosis. The cell viability was monitored by Tripan blue exclusion. After 48h incubation, cells treated with M. leprae shown 70-100% of survival, contrasting with 30-60% in the untreated cultures. M. leprae anti-apoptotic effect was shown to be dose-dependent. Reduction of cells undergoing apoptosis in cultures treated with M. leprae was also observed through DiOC6 staining by Flow Cytometry. In a next step the conditioned medium of cells treated with M. leprae was shown to mimic the anti-apoptotic effect of the bacteria, suggesting that soluble factors secreted by SC in response to M. leprae were involved in cell survival. One possible candidate for these soluble factors would be Insulin-Like Growth Factors, IGF-I and IGF-II. Recently, our laboratory demonstrated the expression of IGF-I and IGF-II on SC mediated by M. leprae. Literature data indicates that the linkage of IGF to especific receptor activates two signaling pathways: mitogen-activated protein kinases (MAPK) and phosphatidilinositol 3-kinase (PI 3-K), and this last one is envolved on apoptosis inhibition. To verify if M. leprae can mediate SC survival by PI 3-K pathway, we performed imunnodetection of phosphorilated Akt. We found that M. leprae promoted Akt activation in SC by phosphorilation of the Ser-473 residue and the highest expression of p-Akt could be seen at 48 hours of incubation. Finally, we showed that the pre-treatment of SC with NF-kappaB inhibitors, such as thalidomide, glyotoxin and SN50, completely abolished the anti-apoptotic effect of M. leprae. Altogether, our results suggest an important strategy for the successful colonization of M. leprae in the nerve, based on the survival maintenance of the host cell through induction of IGF production, PI 3-K/Akt signaling and NF-kB activation.
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