Role of Renin-Angiotensin-Aldosterone System during sarcoidosis granuloma formation

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Sarcoidosis is a pulmonary and systemic granulomatous disease of unknown cause. To better understand disease mechanisms, we have recently established a novel in vitro human granuloma model that shares many structural and molecular features of the disease in human tissues, yielding novel insights into mechanisms regulating early granuloma formation. In keeping with prior investigations and clinical experience linking sarcoidosis to elevated leves of angiotensin converting enzyme (ACE) in sarcoidosis tissues, molecular characterization of the sarcoidosis granuloma model indicates that macrophages participating in sarcoidosis granuloma formation are regulated by the renin-angiotensin-aldosterone system (RAAS). Our strong preliminary data shows that sarcoidosis macrophages produce aldosterone, a hormone that promotes inflammation through the activation of mineralocorticoid receptors (MRs); and we further show that suppression of the RAAS pathway (e.g., ACE inhibition) or inhibition of MRs attenuates granuloma formation. We hypothesize that RAAS promotes pathological granuloma formation in patients with sarcoidosis through activation of MRs. In the spirit of the R21 funding mechanisms, this project is highly innovative and has important beneficial implications for advancing our understanding of sarcoidosis disease mechanisms and for providing novel therapeutic targets and disease biomarkers. Aim 1 will determine if the balance between ACE1 and ACE2 (a suppressor of ACE1-mediated inflammation) regulates sarcoidosis granuloma formation by controlling angiotensin II levels and related angiotensin 1 receptor (ATR1) activation. We posit that the balance between ACE and ACE2 influences the formation of granulomas in sarcoidosis patients. Aim 2 will determine if aldosterone induced MR activation promotes NRF2/HO-1/STAT3 signaling to promote sarcoidosis granuloma formation, featuring polarization towards CD163 macrophages. These studies will determine if aldosterone promotes macrophage phagosome-activated signaling pathway NRF2/HO-1/STAT3 to polarize macrophages towards a CD163 expressing phenotype that is predisposed to aggregate and form granulomas. Aim 3 will be a pilot study designed to determine if aldosterone levels achieved in the in vitro granuloma model are predictive of pulmonary sarcoidosis disease progression. Currently, there are no reliable biomarkers predictive of sarcoidosis disease progression for prognostication and to guide therapy, and aldosterone is a viable candidate. The short-term goals of this are to advancing basic understanding of sarcoidosis disease mechanisms and to consider related therapeutic targets. Long-term aspirations of this project are to address current deficiencies in the field of sarcoidosis as relates to identifying novel disease-specific therapies (targeting granuloma formation), identifying novel biomarkers predictive of disease progression, and to ultimately determine if it is feasible to repurpose widely available RAAS modulating drugs (e.g., ACE, ATR1 and MR inhibitors) for the treatment of sarcoidosis.