The reduction of NLRX1 and its role in pulmonary aging

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PROJECT SUMMARY Biological aging of the pulmonary system is associated with structural changes that lead to a progressive decline in function, and the term “aging lung” is used to describe the organ in this stage of decline. With population rapidly aging, a thorough understanding of physiologic aging-related changes in the lung is imperative. We recently demonstrated a mitochondrial molecule, nucleotide-binding domain and leucine-rich- repeat-containing protein X1 (NLRX1) which has been identified as a negative regulator of mitochondrial antiviral signaling molecule (MAVS), plays a critical role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Because aging is a common risk factor for COPD, studies were undertaken to determine if NLRX1 is an important player in “aging lung.” Our preliminary studies revealed that (i) aging itself induced the reduction of NLRX1 at the level of gene and protein in murine lungs; (ii) the site of major reduction was in macrophages; and (iii) the lungs from 12-month-old (mo) NLRX1 null mutant (-/-) mice manifested enhanced characteristics of the “aging lung.” These features observed from NLRX1-/- mice included (a) activation of the inflammasome, (b) increased p53 signaling and its target molecule promyelocytic leukemia (PML; a well-known marker of cellular senescence), (c) decreased production of vascular endothelial growth factor (VEGF), a key regulator of pulmonary vasculature and cytoprotection and (d) enhancement of senile emphysema-like alveolar remodeling, all of which were modestly observed in lungs from wild type (WT) controls. In addition, we identified an unprecedented function of NLRX1 as an interacting molecule with PTEN-induced kinase 1 (PINK1), an essential regulator of mitochondrial quality control. The importance of NLRX1 in aging studies was evident in humans, revealing the expression of NLRX1 was significantly reduced in peripheral blood mononuclear cells from the elderly (age>65) compared to those from young controls (age<40). This constellation of findings led us to hypothesize that aging-induced reduction of NLRX1 plays a critical role in the aging of pulmonary system via, at least, mitochondrial dysfunction/molecular dysregulation. To test the hypothesis, we will utilize newly generated mice in which the NLRX1 gene can be null mutated or induced, respectively, in a temporospatial manner. Proposed aims driven by specific hypotheses are: Aim #1. Define the alteration of NLRX1 and its role(s) in pulmonary aging in vivo; Aim #2. Determine if restoring the expression of NLRX1 in vivo attenuates aging-related alterations in the pulmonary system; Aim #3. Characterize the mitochondrial dysfunction/molecular dysregulation in the lung with aging and define the role that NLRX1 plays in aging-related mitochondrial dysfunction/molecular dysregulation. To our best knowledge, NLRX1, an innate immune regulator, has never been studied in the context of aging. Its specific function(s) in macrophages, in spite of the importance of this cell type for tissue homeostasis with normal aging, have never been defined, either. The proposed aims will explore these unprecedented issues.