Structural Plasticity in Compensatory Lung Growth and Remodeling

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Project Summary Following loss of ~58% of lung units by right pneumonectomy (PNX) in adult canines, supra-threshold tissue and microvascular mechanical stress additively stimulate compensatory lung growth and remodeling (CLGR) of remaining lung units, leading to regeneration of alveolar tissue-capillaries and restoring ~50% of the lost function. This robust model of regeneration mimics the consequences of destructive lung disease, allowing exploration of adaptive mechanisms in the remaining functioning lung units capable of responding, irrespective of the specific pathology causing destruction. CLGR is plastic; supplementation of growth promoters, e.g., retinoic acid or erythropoietin (Epo), further enhances alveolar tissue-capillary formation in remaining lobes but has not further augmented lung function, indicating a structure-function discrepancy in response to exogenous stimulation. This may be because mechanically induced lung growth also increases oxidative stress, which in turn limits growth and remodeling; also newly added tissue-capillaries may distort architecture of the acinus, the fundamental unit of gas exchange, and detract from functional enhancement. Anti-oxidation may be a key factor in resolving the structure-function discrepancy. Oxidative stress, paracrine Epo signaling via its receptor (EpoR), and the circulating anti-oxidative factor αKlotho, are all persistently elevated during post-PNX CLGR. αKlotho acts upstream of EpoR to enhance EpoR cytoprotection in vitro, suggesting that αKlotho may also enhance angiogenic stimulation via the Epo-EpoR axis. We propose that optimal CLGR requires a balance between mechanical signals and cytoprotection, and concurrent αKlotho anti-oxidation may enhance EpoR-stimulated angiogenesis in CLGR. Aim 1 will test the hypothesis that αKlotho and EpoR mutually enhance each other to relieve oxidative stress in the lung, using mice with lung-specific conditional EpoR deletion ± genetic Klotho insufficiency, exposed to oxidant challenge. Aim 2 will test the hypothesis that αKlotho augments EpoR-mediated angiogenic stimulation and acinar remodeling in CLGR to facilitate translation of structural growth into functional gain. We will concurrently deliver nanoparticles containing EpoR and/or αKlotho cDNA to post-PNX young and adult canine lungs, to assess alveolar-capillary regrowth (in vivo CT and electron microscopy), angiogenic factor and progenitor cell distribution, stratified acinar architecture (microCT) and functional compensation. Finally, we will develop and compare (αKlotho+EpoR) cDNA treatment in PNX model with a canine unilateral elastase emphysema model characterized by reduced mechanical stress and elevated inflammatory oxidative stress. These issues of stratified acinar remodeling, growth-stimulation vs. cytoprotection balance, and overcoming structure-function discrepancy in CLGR, have not been examined; they directly impact any intervention aimed at promoting repair and regeneration of the native functioning lung units in destructive lung disease, e.g., emphysema or fibrosis as well as in transplanted or bioengineered lungs.