Loss of GFI1 impairs pulmonary neuroendorine cell proliferation, but the neuroendocrine phenotype has limited impact on post-naphthalene airway repair

Abstract

Naphthalene exposure kills lung airway epithelial (Clara) cells, but is rapidly followed by Clara cell reconstitution coincident with proliferation of pulmonary neuroendocrine cells (PNEC). Although a role for mature PNEC in the reconstitution process has been excluded, the reconstituting progenitor cells have been suggested to enter a transient neuroendocrine (NE) differentiation phase before differentiating to Clara cells. Furthermore, these progenitors were suggested to be the target population for transformation to a NE tumor; small cell lung cancer (SCLC). Although the NE phenotype is central to SCLC oncogenesis, the relevance of NE differentiation to post naphthalene reconstitution remains to be determined. The Growth factor independent-1 (Gfi1) transcription factor is expressed in SCLC and is required for the NE differentiation of PNEC. Gfi1 À/À mice display a 70% reduction in airway cells that express NE markers, and cells that stain for NE markers show weak expression of some markers. Therefore, to determine the relevance of the NE phenotype to post-naphthalene reconstitution, we examined post-naphthalene reconstitution in Gfi1 À/À mice. Our analyses indicate that the post-naphthalene regeneration process includes both airway epithelial proliferation and apoptosis. Gfi1 deletion lowered both airway epithelial proliferation and apoptosis; however, the post-naphthalene rate of increase in growth and apoptosis was not significantly different between Gfi1 À/À mice and wild-type littermates. Moreover, the timing and extent of CC10 þ cell regeneration was unaffected by Gfi1 deletion. These data suggest that neither Gfi1 nor the NE phenotype play a dominant role in the regeneration process. However, the few Gfi1 À/À cells capable of NE differentiation show a significant reduction in post-naphthalene proliferation. The modest proliferation seen in Gfi1 À/À NE cells is consistent with the previously proposed role for Gfi1 in controlling neuroendocrine cancer growth.

Elf3 plays a role in regulating bronchiolar epithelial repair kinetics following Clara cell-specific injury

“…Regulation of gene expression is a very important aspect of many physiological and pathological processes, and there have only been few studies examining the role of various transcription factors in the pulmonary regenerative response to naphthalene-induced Clara cell damage. 4,6,9,33,40,41 In the present study, our findings suggest that Elf3 may play an important role in regulating airway epithelial repair kinetics, as the rate of bronchiolar epithelial cell proliferation and mitosis as well as Clara cell renewal was delayed in Elf3À/À mice after treatment with naphthalene. The absence of Elf3 appeared to have no observable effect on the extent of Clara cell injury in Elf3À/À mice, as there was no significant difference in the mean necrosis score between Elf3 þ / þ and Elf3À/À mice at any time point after naphthalene exposure.…”

“…After treatment with naphthalene, injured and necrotic Clara cells are replaced by other airway epithelial cells, which undergo dynamic changes in cell migration, proliferation, and differentiation. 1 Many different cell types have been shown to be involved in the process of airway epithelial regeneration following naphthalene-induced Clara cell ablation in mice, and those identified to date include: basal cells, 2,3 pulmonary neuroendocrine cells, [4][5][6] bronchioalveolar stem cells, 7,8 ciliated cells, 9,10 peribronchiolar interstitial cells, 11,12 and a pollutant-resistant sub-population of Clara cells that retain their expression of Clara cell 10-kDa secretory protein (CC10/CCSP), also known as variant CC10/CCSP-expressing (vCE) stem cells. [13][14][15] However, the role of various transcription factors in regulating the process of airway epithelial regeneration requires further investigation.…”

Targeted Disruption of NeuroD, a Proneural Basic Helix-Loop-Helix Factor, Impairs Distal Lung Formation and Neuroendocrine Morphology in the Neonatal Lung

“…Notably, we have recently shown that mice that are deficient in Gfi1, a determinant of neuroendocrine cell morphogenesis, display reduced airway cell proliferation after naphthalene injury (29). In order to connect the altered neuroendocrine developmental phenotype we observed in NeuroD deficient lungs with reduced epithelial proliferation, we examined whether overexpression of NeuroD in lung epithelial cells increased proliferation.…”

Lung Epithelial Progenitor Cells: Lessons from Development

“…regulate the transcription factors growth factor independent 1 (gfi1) and neurogenic differentiation 1 (neurod1) and subsequently the NE cell differentiation markers (calcitonin gene related peptide; also known as Calca) and uchl1 (ubiquitin carboxy-terminal hydrolase 1, also known as PGP9.5) (38). The retinoblastoma family proteins function to restrict the number of NE cells, although their exact role is currently ill defined (27,39).…”