Introduction: Pediatric interstitial lung diseases (pILD) represent a heterogeneous group of rare and poorly defined disorders. Genetic abnormalities of surfactant proteins B (SP-B) and C (SP-C) have been shown to be related to these pathologies. However, variability in the lung disease phenotype suggests the involvement of other surfactant-associated genes. The aim of this study was to examined the contribution of TTF-1 (Thyroid Transcription Factor 1), a transcription factor especially involved in lung development in pILD.

Methods: TTF-1 gene sequencing was performed in two children presenting with hypotonia, pILD and hyptothyroidism without a known etiology. Surfactant proteins were assessed in bronchoalveolar lavage (BAL) fluid by western blot analysis using proSP-B, SP-B and proSP-C antibodies. TTF-1 mutated plasmids were realized by mutagenesis. SP-B/SP-C promoter analysis was realized in A549 cells using co-transfection experiment with SP-C and SP-B luciferase plasmids with wild type or mutated TTF-1 expression plasmids.

Results: Two new spontaneous TTF-1 mutations (M1 and M2) have been identified by sequencing in two patients (P1 and P2). The measurement of SP-B and SP-C promoter activation by plasmids encoding mutated TTF-1 (TTF-1M1 and TTF-1M2) revealed two different mecanisms. TTF-1M1 do not induces either SP- B or SP-C promoter activation and has a dominant negative effect on the wild type TTF-1. In contrast, TTF-1M2 activates SP-B and SP-C promoters Also, SP-C promoter activation was higher with TTF1M2 that the wild type TTF-1. BAL from P1 is characterized by a normal pattern of pro-SP-B and SP-B contents but exhibits an accumulation of pro-SP-C.

Conclusion: In this study, we identified and characterized two new TTF-1 mutations responsible for pILD with two different mecanisms.