The counter balancing of pro- and anti-inflammatory gene transcription is crucial for normal homeostasis after inflammatory lung injury induced by environmental toxicants and inflammatory agents. An aberrant regulation of this balance in the lung culminates in an unchecked inflammation and a failure to resolve tissue damage. Studies in this competing renewal will test the hypothesis that persistent inflammatory lung injury is the result of a shift within phagocytic cells in the balance between two crucial redox regulatory proteins, Fra-1/AP-1 and Nrf2. These transcription factors bind to DNA after heterodimerization with other binding partners and thereby regulate gene expression. During the previous grant-funding period, we showed that Fra-1 functioned as a crucial negative regulator of Nrf2-regulated cytoprotective gene expression containing the Nrf2-binding Anti- oxidant Response Element (ARE), often embedded with Fra-1/AP-1 binding sites. Fra-1 null mice are resistant to endotoxin-induced mortality and exhibit reduced levels of lung inflammation and injury and accelerated resolution of inflammation compared to wild-type mice. Endotoxin (LPS)-induced expression of Fra-1 largely occurs in alveolar macrophages, and in human lungs infected with E. coli ex vivo. Importantly, mice with myeloid-specific deletion of Fra-1 showed greater protection against endotoxin-induced mortality than wild-type mice. In preliminary mechanistic studies, we found reduced levels of endotoxin-induced NF-?B activation in Fra-1-deficient macrophages and an increased expression of TNFAIP3 (aka A20), a crucial bipartite ubiquitin-editing enzyme required for terminating uncontrolled activation of NF-?B, a crucial factor that regulates inflammation. Nrf2-deficient macrophages showed the opposite effects. These findings laid the foundation for the central concept in this project that Fra-1/Nrf2-balanced reciprocal signaling is essential for the resolution of lung injury mediated by ubiquitin-editing protein A20, essential for blunting inflammatory responses mediated by pro-inflammatory NF-KB. Additionally, we will address a novel concept that suppressing the function of Fra-1 while at the same time activating Nrf2 may be required for sustaining the anti-oxidative and anti-inflammatory effects of Nrf2, and accelerating resolution of lung injury. We will use multiple mechanistic approaches and tissue-specific knockout mouse models to test this hypothesis. Our specific objectives are: 1) To determine the mechanisms of the balance of Fra-1/Nrf2 reciprocal signaling in the regulation of endotoxin-induced A20 expression in lung macrophages, 2) To elucidate the pro-inflammatory role of myeloid-specific Fra-1 in the regulation of lung injury through the modulation of Nrf2-mediated A20 expression, and 3) To investigate the dual strategy of inactivating Fra-1 and concomitantly activating Nrf2 to accelerate resolution of inflammatory lung injury. The proposed studies will define whether a Fra-1 and Nrf2 imbalance is a causative factor in aberrant resolution of inflammatory lung injury and repair processes, and will lay the framework for drug development favoring resolution of inflammatory lung injury.
Changes in intracellular redox state (antioxidant and oxidant balance) and inflammatory state (pro- and anti-inflammatory mediators' balance) are critical for promoting host-defense functions and in maintaining lung homeostasis in response to various environmental and inflammatory agents. Redox imbalance and persistent inflammation generated can lead to chronic inflammation leading to impaired resolution after injury. The proposed studies in the grant will delineate the role of the balance of two b-ZIP transcription factors, Nrf2 and Fra-1, in phagocytes and how their interactions synchronize the resolution of lung inflammation. Additionally, the proposal tests utility of a novel dual strategy of Nrf2 activation and Fra-1 inactivation to accelerate the resolution of inflammatory lung injury caused by environmental toxins and inflammatory agents to therapeutically restore lung homeostasis
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