Study of the effect of survival promoted for the Mycobacterium leprae on the Schwann cell: analysis of the envolvement of the similar factors to the insulin (IGFs) and of way PI 3-K/Akt.
Leprosy is a chronic disease caused by Mycobacterium leprae, an obligate intracellular pathogen, which major target is the Schwann cell (SC) causing peripheralnerve functional loss and deformities. It is well known that intracellular pathogens block apoptotic pathways of the host cell preserving an appropriate niche for their survival andproliferation. Nevertheless, the M. leprae effects towards SC under stress conditions are still unknown. Initial results from our laboratory have shown that M. leprae promotes SCsurvival when these cells were kept under serum-free medium condition This survival effect was shown to depend on soluble factors secreted to culture medium by M. lepraetreated SC, and insulin-like growth factors ?I and -II (IGF-I and IGF-II) have been considered as possible candidates. Because these results were obtained using the human schwannoma cell line ST88-14, the first objective of the present work was toconfirm the M. leprae survival effect in primary human SC. For this, human primary SC with purity above 95% were plated in the absence of heregulin and forskolin and kept for24 or 48 hours in serum-free media with or without M. leprae treatment. Through trypan blue exclusion assay or propidium iodide labeling it was confirmed the M. leprae survivaleffect on primary cultures, as seen before with the schwannoma. The IGFs involvement on the survival effect of M. leprae was th en confirmed by survival experiments with theST88-14 lineage in the presence of neutralizing antibodies for IGF-I and IGF-II and their receptor IGF1-R. Moreover, higher levels of phosphorylated Akt were observed in M.leprae treated SC as compared to control cells, reinforcing the involvement of the PI 3- K/Akt anti-apoptotic signalling pathway in the M. leprae survival effect. Finally, it wasshown that this effect was M. leprae-specific, since other species of mycobacteria (Mycobacterium smegmatis and BCG) were unable to confer protection to SC againstapoptosis. These results suggest that M. leprae inhibits apoptotic pathways within SC through a novel strategy consisting of IGFs induction and subsequent PI 3-K/Aktactivation, guaranteeing an appropriated niche for its survival and replication early during infection.
Advisor:Maria Cristina Vidal Pessolani
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Keywords:Mycobacterium leprae Leprosy Schwann Cells Insulin Insulin-Like Growth Factor Binding Proteins
Date of Publication:03/28/2008