Macrophage senescence as a driver of granuloma failure and progression to necrosis in TB and TB/HIV

Johns Hopkins University, Baltimore MD

Investigators

Abstract

ABSTRACT Understanding the fundamental mechanisms of granuloma breakdown and necrosis in pulmonary TB lesions is a key unmet need. Lung granulomatous lesions from human active TB lung lesions show prominent markers of cellular senescence in myeloid cells, but this aspect of granuloma breakdown has not been well-studied. In the B6.Sst1S mouse model (where granuloma failure also leads to necrosis) we have identified multiple senescence markers analogous to those seen in human TB. Senescent cells are non-replicating, long-lived cells which release signaling molecules (called the senescence-associated secretory phenotype, SASP) that are locally deleterious and promote tissue dysfunction. Our central premise is that non-controlling granulomas (both in predisposed humans and in the B6.Sst1S model) adopt a stress-induced senescence (SIS) phenotype during Mtb infection driven by (i) lipid peroxidation, (ii) Myc activation, and (iii) unresolving proteotoxic stress. These SIS Ms are (i) immunosuppressive (MDSC-like), (ii) long-lived and resistant to early death, and (iii) emit deleterious signals (eg SASP molecules) that inhibit T cell activation and promote recruitment of PMNs and immature Ms. Our data show that SIS-Ms display a Myc-driven phenotype with oxidative stress, dysregulated proteostasis, and hyperactivity of the IFN-I pathway. This fuels a self-sustained, escalating cycle that leads to necrosis occurs via a combination of ferroptotic-like death of SIS Ms and PMN-mediated damage. Underscoring the fact that senescent cells play a causal role in TB progression, we recently found that a 3-drug cocktail of senolytic drugs (dasatinib D, quercetin Q, and fisetin F)--designed to kill the deleterious senescent cells-- significantly reduces lung CFU counts and prolongs survival in Mtb-infected B6.Sst1S mice. Thus, studies of senescence in TB may offer a significant clinical payoff in the form of novel host-directed therapies (HDT) for TB. [NEW] In this application we will establish a detailed temporo-spatial understanding of SIS-Ms and surrounding cells using spatial transcriptomic in 2 species that progress to necrotic TB: B6.Sst1S mice and WT rabbits (Aim 1). We will exploit the new finding of successful HDT activity by a cocktail of 3 senolytic drugs by optimizing the 3 drugs and their interactions with Std-Tx (Aim 2). We will also explore the senescence-driven pathologic pathways in the setting of TB-SIV co-infection using non-human primates (Aim 3).