In addition to mTOR and JAK/STAT, NLRP3 inflammasome is another key pathway activated in sarcoidosis

Application of laboratory models for sarcoidosis research

This manuscript will review the implications and applications of sarcoidosis models towards advancing our understanding of sarcoidosis disease mechanisms, identification of biomarkers, and preclinical testing of novel therapies. Emerging disease models and innovative research tools will also be considered.

Simultaneous Assessment of mTORC1, JAK/STAT, and NLRP3 Inflammasome Activation Pathways in Patients with Sarcoidosis

The unknown etiology of sarcoidosis, along with the variability in organ involvement and disease course, complicates the effective treatment of this disease. Based on recent studies, the cellular inflammatory pathways involved in granuloma formation are of interest regarding possible new treatment options, such as the mechanistic (formerly mammalian) target of rapamycin complex 1 (mTORC1) pathway, the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, and the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3) inflammasome pathway. The aim of this study was to explore the potential coexpression of these three inflammatory pathways in patients with sarcoidosis and see whether possible differences were related to disease outcome. The tissue of 60 patients with sarcoidosis was used to determine the activity of these three signaling pathways using immunohistochemistry. The activation of NLRP3 was present in 85% of all patients, and the activation of mTORC1 and JAK/STAT was present in 49% and 50% of patients, respectively. Furthermore, the presence of NLRP3 activation at diagnosis was associated with a chronic disease course of sarcoidosis. Our finding of different new conceptual inflammatory tissue phenotypes in sarcoidosis could possibly guide future treatment studies using the available inhibitors of either NLRP3, JAK-STAT, and mTORC1 inhibitors in a more personalized medicine approach.

Novel insights in fibrotic pulmonary sarcoidosis

PURPOSE OF REVIEW

In chronic pulmonary sarcoidosis, the transition from the inflammatory to the fibrotic stage of the lungs occurs in about 10-20% of cases, eventually causing end-stage fibrotic disease. To date, pathogenetic mechanisms and clinical management remain challenging; thus, we highlight the recent evidence in pulmonary fibrotic processes, clinical signs for an early detection and the potential role of the current investigated antifibrotic agents and promising targeted therapies.

RECENT FINDINGS

Recent findings of relevant key cellular pathways can be considered as a glimmer of light in the complexity of sarcoidosis. In some patients, granulomas persist and serve as a nidus for fibrosis growth, sustained by several fibrosis-stimulating cytokines. Preclinical studies have detected profibrotic, antifibrotic and pleiotropic T cells as promoters of fibrosis. Epigenetics, genetics and transcriptomics research can lead to new target therapies. Antifibrotic drug nintedanib has shown a positive effect on non-idiopathic pulmonary fibrosis fibrotic lung diseases including fibrotic sarcoidosis; other antifibrotic drugs are under investigation.

SUMMARY

Pulmonary fibrosis strongly impacts the outcome of sarcoidosis, and a better understanding of the underlying pathogenic mechanisms can facilitate the development of novel treatments, improving clinical care and life expectancy of these patients. The greatest challenge is to investigate effective antifibrotic therapies once fibrosis develops. The role of these findings in fibrotic sarcoidosis can be translated into other interstitial lung diseases characterized by the coexistence of inflammatory and fibrotic processes.

Inflammatory Pathways in Sarcoidosis

Concepts regarding etiology and pathophysiology of sarcoidosis have changed remarkably within the past 5 years. Sarcoidosis is now viewed as a complex multi-causation disease related to a diverse collection of external environmental or infectious signals. It is generally accepted that the cause of sarcoidosis is unknown. Moreover, concepts of the inflammatory pathway have been modified by the realization that intrinsic genetic factors and innate immunity may modify adaptive immune responses to external triggers. With those potential regulatory pathways in mind, we will attempt to discuss the current understanding of the inflammatory response in sarcoidosis with emphasis on development of pulmonary granulomatous pathology. In that context, we will emphasize that both macrophages and T lymphocytes play key roles, with sometimes overlapping cytokine production (i.e., TNFα and IFN-γ) but also with unique mediators that influence the pathologic picture. Numerous studies have shown that in a sizable number of sarcoidosis patients, granulomas spontaneously resolve, usually within 3 years. Other sarcoidosis patients, however, may develop a chronic granulomatous disease which may subsequently lead to fibrosis. This chapter will outline our current understanding of inflammatory pathways in sarcoidosis which initiate and mediate granulomatous changes or onset of pulmonary fibrosis.