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Chronic signaling via the metabolic checkpoint kinase mTORC1 induces macrophage granuloma formation and marks sarcoidosis progression

ABSTRACT: Gene expression analysis of primary CSF1-deprived bone marrow-derived macrophages (BMDM) of Tsc2fl/fl LysM+/+ and TSC2fl/fl LysM+/cre mice Maintenance of tissue homeostasis requires a tight control of the in situ-proliferative capacity of tissue-resident macrophages. Here we show that specific deletion of Tsc2 in myeloid cells breaks quiescence and strongly induces macrophage proliferation and hypertrophy leading to granuloma formation in vivo in an mTORC1-dependent manner. Intriguingly, the growth factor CSF1 induces expression of cyclin-dependent kinase 4 (CDK4) via TSC2-mTORC1 to stimulate cell proliferation, while simultaneously NF-κB signaling and apoptosis are inhibited. Tsc2-deficient macrophages show constitutive CDK4 expression and enhanced M2-like polarization that is supported by a metabolic reprogramming towards increased glycolysis and mitochondrial metabolism. Strikingly, mTORC1 activation and macrophage proliferation are identified as a hallmark of the human granulomatous disease sarcoidosis and correlate with a clinically progressive disease outcome. In conclusion, TSC2-mTORC1 integrates macrophage quiescence, polarization, and metabolism to prevent granulomatous disease. Fundamentally, we show that the macrophage cell cycle is controlled by a growth factor-induced expression of CDK4.

ORGANISM(S): Mus musculus

PROVIDER: GSE77075 | GEO | 2017/01/03

SECONDARY ACCESSION(S): PRJNA309394

REPOSITORIES: GEO

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Project description:Background: Macrophage polarization programs, commonly referred to as âclassicalâ and âalternativeâ activation, are widely considered as distinct states that are exclusive of one another, and are associated with different functions such as inflammation and wound healing, respectively. In a number of disease contexts, such as traumatic brain injury (TBI), macrophage polarization influences the extent of pathogenesis, and efforts are underway to eliminate pathogenic subsets. However, previous studies have not distinguished whether the simultaneous presence of both classical and alternative activation signatures represents the admixture of differentially polarized macrophages, or if they have adopted a unique state characterized by components of both classical and alternative activation. Results: We analyzed the polarization of individual macrophages responding to TBI using single-cell RNA sequencing. Analysis of signature polarization genes revealed diverse activation states, including M(IL4), M(IL10), and M(LPS, IFNÎ³). However, the expression of a given polarization marker was no more likely than at random to predict simultaneous expression or repression of markers of another polarization program within the same cell, suggesting a lack of exclusivity in macrophage polarization states in vivo in TBI. Also unexpectedly, individual TBI macrophages simultaneously expressed high levels of signature polarization genes across two or three different polarization states, and in several distinct and seemingly incompatible combinations. Conclusions: Single-cell gene expression profiling demonstrated that monocytic macrophages in TBI are not comprised of distinctly polarized subsets, but are uniquely and broadly activated. TBI macrophage activation in vivo is deeply complex, with individual cells concurrently adopting both inflammatory and reparative features. These data provide physiologically relevant evidence that the early macrophage response to TBI is comprised of novel activation states that are discordant with the current paradigm of macrophage polarizationâa key consideration for therapeutic modulation. Monocyte derived macrophages were isolated from the ipsilateral hemisphere of mouse brains one day following traumatic brain injury elicited by control cortical impact in C57BL/6 adult male mice. Single-cells were isolated and processed for RNA sequencing using a Fluidigm C1 integrated fluidic circuit chip. 45 biological replicates were analyzed.

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Chronic signaling via the metabolic checkpoint kinase mTORC1 induces macrophage granuloma formation and marks sarcoidosis progression

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