Mycobacterium leprae-induced Insulin-like Growth Factor I attenuates antimicrobial mechanisms, promoting bacterial survival in macrophages.

Mycobacterium leprae (ML), the etiologic agent of leprosy, can subvert macrophage antimicrobial activity by mechanisms that remain only partially understood. In the present study, the participation of hormone insulin-like growth factor I (IGF-I) in this phenomenum was investigated. Macrophages from the dermal lesions of the disseminated multibacillary lepromatous form (LL) of leprosy expressed higher levels of IGF-I than those from the self-limited paucibacillary tuberculoid form (BT). Higher levels of IGF-I secretion by ML-infected macrophages were confirmed in ex vivo and in vitro studies. Of note, the dampening of IGF-I signaling reverted the capacity of ML-infected human and murine macrophages to produce antimicrobial molecules and promoted bacterial killing. Moreover, IGF-I was shown to inhibit the JAK/STAT1-dependent signaling pathways triggered by both mycobacteria and IFN-γ most probably through its capacity to induce the suppressor of cytokine signaling-3 (SOCS3). Finally, these in vitro findings were corroborated by in vivo observations in which higher SOCS3 expression and lower phosphorylation of STAT1 levels were found in LL versus BT dermal lesions. Altogether, our data strongly suggest that IGF-I contributes to the maintenance of a functional program in infected macrophages that suits ML persistence in the host, reinforcing a key role for IGF-I in leprosy pathogenesis.

Mycobacterium leprae-induced insulin-like growth factor I attenuates antimicrobial mechanisms, promoting bacterial survival in macrophages

Mycobacterium leprae (ML), the etiologic agent of leprosy, can subvert macrophage antimicrobial activity by mechanisms that remain only partially understood. In the present study, the participation of hormone insulin-like growth factor I (IGF-I) in this phenomenum was investigated. Macrophages from the dermal lesions of the disseminated multibacillary lepromatous form (LL) of leprosy expressed higher levels of IGF-I than those from the self-limited paucibacillary tuberculoid form (BT). Higher levels of IGF-I secretion by ML-infected macrophages were confirmed in ex vivo and in vitro studies. Of note, the dampening of IGF-I signaling reverted the capacity of ML-infected human and murine macrophages to produce antimicrobial molecules and promoted bacterial killing. Moreover, IGF-I was shown to inhibit the JAK/STAT1-dependent signaling pathways triggered by both mycobacteria and IFN-γ most probably through its capacity to induce the suppressor of cytokine signaling-3 (SOCS3). Finally, these in vitro findings were corroborated by in vivo observations in which higher SOCS3 expression and lower phosphorylation of STAT1 levels were found in LL versus BT dermal lesions. Altogether, our data strongly suggest that IGF-I contributes to the maintenance of a functional program in infected macrophages that suits ML persistence in the host, reinforcing a key role for IGF-I in leprosy pathogenesis.

Participação do CD163 na via anti-inflamatória do polo lepromatoso da hanseníase / Involvement of CD163 in inflammatory pathway polo lepromatous leprosy

Estudos anteriores demonstraram que macrófagos de pacientes lepromatosos possuem um fenótipo regulador que contribui para a imunossupressão observada na hanseníase. IDO, CD86 e HLA-DR são moléculas altamente expressas por macrófagos de pacientes lepromatosos, como também o receptor “scavenger” CD163, regulado pela IL-10. Este trabalho foi realizado com o intuito de analisar a expressão de CD163 nas lesões cutâneas de pacientes polares da hanseníase e em monócitos infectados pelo Mycobacterium leprae (ML). Observamos um aumento de macrófagos CD163+IDO+ nas lesões e nas células isoladas do infiltrado inflamatório de pacientes LL. Ademais, durante o período de cultura de 6 dias dos macrófagos isolados das lesões lepromatosas, houve uma gradativa redução da expressão gênica de CD163, IDO e IL-10, assim como dos receptores de superfície CD163, CD209, HLA-DR, CD86 e CD14 observada por citometria de fluxo, fato que ocorreu concomitantemente com a saída de ML destas células. A expressão de células CD163+IDO+CD209+ aumentou em monócitos de indivíduos saudáveis, estimulados com ML irradiado obtido de extratos de lesão. Adição de citocalasina B na cultura de monócitos reduziu a expressão de CD163 nessas células, e, na presença de anti- CD163, a entrada de bactérias nos monócitos também foi reduzida. A adição da anti- IL-10 em cultura de monócitos de indivíduos sadios reduziu a expressão de CD163 até mesmo na presença do ML. Além disso, os níveis séricos de sCD163, IL-10 e heme estavam aumentados nos pacientes lepromatosos, em comparação com pacientes tuberculóides e indivíduos sadios, assim como os depósitos intracelulares de ferro. Estes resultados sugerem que o perfil de expressão de CD163 é importante na endocitose e sobrevivência do ML no polo lepromatoso da hanseníase.

Mycobacterium leprae intracellular survival relies on cholesterol accumulation in infected macrophages: a potential target for new drugs for leprosy treatment

We recently showed that Mycobacterium leprae (ML) is able to induce lipid droplet formation in infected macrophages. We herein confirm that cholesterol (Cho) is one of the host lipid molecules that accumulate in ML-infected macrophages and investigate the effects of ML on cellular Cho metabolism responsible for its accumulation. The expression levels of LDL receptors (LDL-R, CD36, SRA-1, SR-B1, and LRP-1) and enzymes involved in Cho biosynthesis were investigated by qRT-PCR and/or Western blot and shown to be higher in lepromatous leprosy (LL) tissues when compared to borderline tuberculoid (BT) lesions. Moreover, higher levels of the active form of the sterol regulatory element-binding protein (SREBP) transcriptional factors, key regulators of the biosynthesis and uptake of cellular Cho, were found in LL skin biopsies. Functional in vitro assays confirmed the higher capacity of ML-infected macrophages to synthesize Cho and sequester exogenous LDL-Cho. Notably, Cho colocalized to ML-containing phagosomes, and Cho metabolism impairment, through either de novo synthesis inhibition by statins or depletion of exogenous Cho, decreased intracellular bacterial survival. These findings highlight the importance of metabolic integration between the host and bacteria to leprosy pathophysiology, opening new avenues for novel therapeutic strategies to leprosy.