Lack of the transcription factor hypoxia-inducible factor (HIF)-1α in macrophages accelerates the necrosis of Mycobacterium avium-induced granulomas

Accepted Manuscript

The establishment of mycobacterial infection is characterized by the formation of granulomas, which are well-organized aggregates of immune cells, namely, infected macrophages. The granuloma's main function is to constrain and prevent dissemination of the mycobacteria while focusing the immune response to a limited area. In some cases these lesions can grow progressively into large granulomas which can undergo central necrosis, thereby leading to their caseation. Macrophages are the most abundant cells present in the granuloma and are known to adapt under hypoxic conditions in order to avoid cell death. Our laboratory has developed a granuloma necrosis model that mimics the human pathology of Mycobacterium tuberculosis, using C57BL/6 mice infected intravenously with a low dose of a highly virulent strain of Mycobacterium avium. In this work, a mouse strain deleted of the hypoxia inducible factor 1a (HIF-1a) under the Cre-lox system regulated by the lysozyme M gene promoter was used to determine the relevance of HIF-1a in the caseation of granulomas. The genetic ablation of HIF-1a in the myeloid lineage causes the earlier emergence of granuloma necrosis and clearly induces an impairment of the resistance against M. avium infection coincident with the emergence of necrosis. The data provide evidence that granulomas become hypoxic before undergoing necrosis through the analysis of vascularization and quantification of HIF-1a in a necrotizing mouse model. Our results show that interfering with macrophage adaptation to hypoxia, such as through HIF-1a inactivation, accelerates granuloma necrosis.

Support from national funds through FCT/MEC (Fundação para a Ciência e a Tecnologia/Ministério da Educação e Ciência), when applicable cofunded by FEDER funds within the partnership agreement PT2020 related to the research unit number 4293; from “NORTE-07-0124-FEDER-000002-Host-Pathogen Interactions,” cofunded by Programa Operacional Regional do Norte (ON.2–O Novo Norte), under the Quadro de Referência Estratégico Nacional (QREN); and from HMSP-ICT/0024/2010. T.M.S. received postdoctoral grant ON2201310 from “NORTE-07-0124-FEDER-000002-Host-Pathogen Interactions,” cofunded by Programa Operacional Regional do Norte (ON.2–O Novo Norte), under the Quadro de Referência Estratégico Nacional (QREN). M.R. received Ph.D. grant SFRH/BD/89871/2012 from FCT, Portugal