Abstract Rationale Bronchopulmonary dysplasia (BPD) is a leading cause of morbidity and mortality in preterm infants and is characterized by impaired alveolarization. CCN2 (connective tissue growth factor, CTGF) is a matrix-associated signaling modulator implicated in developmental and fibrotic lung diseases. However, its cell-specific role within alveolar epithelial cells (AEC) during postnatal lung development and injury remains poorly understood. Methods Conditional knockout mouse models were generated to delete Ccn2 globally (UbcCreERT2:Ccn2fl/fl), in alveolar type 1 (AT1; HopxCreERT2:Ccn2fl/fl), or alveolar type 2 (AT2; SftpcCreERT2:Ccn2fl/fl) cells. All lines were crossed with R26REYFP reporters for lineage tracing. Cre recombinase was induced by intraperitoneal tamoxifen injection on postnatal day (P) 0. Lung structure was quantified by mean linear intercept (MLI), and AEC subtypes were identified using immunofluorescence for HOPX (AT1) and SFTPC (AT2). A hyperoxia-induced BPD model (95% O2 exposure from P0–P5) was used to assess injury responses. Data are expressed as mean ± SEM and statistical analysis was performed using one-way ANOVA followed by Dunnett’s multiple comparison. Results AT1-specific Ccn2 deletion resulted in significant alveolar simplification (increased MLI) at P42 compared with wild-type littermates (WT vs. heterozygous vs. homozygous: 29.3±0.9 vs. 33.8±0.5 vs. 35.9±1.9; p 0.01), whereas AT2-specific deletion had no effect. Global loss of Ccn2 decreased AT1/AT2 cell ratios (Fig 1A) and AT1-specific Ccn2 deletion increased lineage-labeled AT2 cells (Fig 1B), indicating impaired AT1 differentiation and enhanced epithelial plasticity. Under hyperoxia conditions, AT1-specific Ccn2 deletion exacerbated alveolar simplification (WT vs. heterozygous vs. homozygous: 37.2±0.9 vs. 40.6±0.8 vs. 40.9±1.4; p 0.05). Hyperoxia exposure increased the proportion of lineage-labeled AT2 cells compared with normoxia controls; however, unlike under normoxia conditions, Ccn2 deletion did not further augment lineage-labeled AT2 cell during hyperoxia, suggesting that injury-induced epithelial remodeling may override CCN2-dependent differentiation effects. In contrast, AT2-specific deletion did not modify MLI or AT2 cell reprograming to AT1 cells in hyperoxia-induced injury. Global Ccn2 knockout was associated with increased mortality following hyperoxia exposure. Conclusions AT1-derived CCN2 is essential for postnatal alveolarization and maintenance of AT1 cell identity. CCN2 deficiency alters epithelial differentiation dynamics and worsens early alveolar injury following hyperoxia. These findings identify epithelial CCN2 as a critical regulator of alveolar maturation and a potential therapeutic target for preventing severe neonatal lung disease and BPD. This abstract is funded by: NIH-K08HL151760
Alapati et al. (Fri,) studied this question.