MEOX2: A Critical Regulator of Alveolar Fibroblast Function

ABSTRACT: An in-depth understanding of the mechanisms that regulate alveolar septation and septal wall maturation will be re- quired to develop therapies for premature infants with Bronchopulmonary Dysplasia (BPD). We and others have begun to define changes in PDGFRa myo, lipo and matrix fibroblast (FB) function during alveolarization, homeostasis, regenera- tion, and fibrosis. Our long-term goal is elucidation of molecular regulators of FB functions and how diverse FBs support the alveolar niche. Our objective herein is to identify molecular mechanisms that result in functional changes in alveolar matrix FBs that regulate extra cellular matrix (ECM) organization and capillary network formation. Integration of tran- scriptomic datasets identified MEOX2 as a transcription factor of non-contractile fetal and postnatal alveolar FBs. Our preliminary data show that conditional inactivation of Meox2 in perinatal alveolar matrix FBs resulted in alveolar simpli- fication, gain of contractile FB function, and thickened interstitial ECM, comparable to findings in BPD and animal models of hyperoxia. Meox2 inactivation in alveolar matrix FBs also resulted in impaired capillary endothelial network for- mation, demonstrating a thus far unidentified role of alveolar FBs in postnatal angiogenesis. Inactivation of Meox2 re- sulted in an increase of ductal myo FB differentiation and gene expression analyses predict aberrant matrix synthesizing function in matrix FBs that is associated with abnormal vascular development and cell migration. The central hypothesis is that Meox2 directly regulates genes for matrix and myo FB function and their subsequent capacity to support vascular capillary formation. The rationale for this research is a new understanding of the regulation of matrix FB function and how these functionally different FB stages modify ECM and the FB-endothelial crosstalk. Aim 1 will test the hypothesis that MEOX2 regulates differentiation of myo and matrix FBs from a common mesenchymal progenitor. Using a new Meox2CreERT transgenic mouse we will identify lineage relationships and activation stages of alveolar FBs during normal and hyperoxia impaired alveolarization and identify direct MEOX2 target genes that regulate FB function. Aim 2 will test the hypothesis that MEOX2 regulates ECM composition, which is important for vascular network formation. We will gen- erate in vitro cell derived ECM from control and Meox2 deficient FBs and determine ECM composition, topography, and support of angiogenesis. Aim 3 will test the hypothesis that increased CXCL14 signaling from Meox2 deficient FBs to its receptor CXCR4 on capillary endothelial cells impairs postnatal capillary development. We will use in vivo and in vitro gain and loss of function analysis to determine the role of paracrine signaling from FBs to endothelial cells that direct angiogenesis. The proposed research is conceptually innovative, because we ask questions regarding FB plasticity and lineage specificity and define molecular players of the functional switches. The proposed research is scientifically innova- tive, because little is known about their ECM organizing function or their role in supporting capillary network formation. This contribution will be significant because it addresses 1) lack of knowledge of the function of the alveolar matrix FB; 2) identifies and validates the transcriptional network around Meox2 that regulates FB function.