SummaryRecent studies have implicated keratin 5 (KRT5)+ cells in repopulation of damaged lung tissue following severe H1N1 influenza virus infection. However, the origins of the cells repopulating the injured alveolar region remain controversial. We sought to determine the cellular dynamics of lung repair following influenza infection and define whether nascent KRT5+ cells repopulating alveolar epithelium were derived from pre-existing alveolar or airway progenitor cells. We found that the wound-healing response begins with proliferation of SOX2+ SCGB1A1− KRT5− progenitor cells in airways. These cells generate nascent KRT5+ cells as an early response to airway injury and yield progeny that colonize damaged alveolar parenchyma. Moreover, we show that local alveolar progenitors do not contribute to nascent KRT5+ cells after injury. Repopulation of injured airway and alveolar regions leads to proximalization of distal airways by pseudostratified epithelium and of alveoli by airway-derived epithelial cells that lack the normal characteristics of mature airway or alveolar epithelium.
Tissue fibrosis is a common pathological outcome of chronic disease that markedly impairs organ function leading to morbidity and mortality. In the lung, idiopathic pulmonary fibrosis (IPF) is an insidious and fatal interstitial lung disease associated with declining pulmonary function. Here, we show that alveolar type 2 (AT2) stem cells isolated from IPF lung tissue exhibit characteristic transcriptomic features of cellular senescence. We used conditional loss of Sin3a in adult mouse AT2 cells to initiate a program of p53-dependent cellular senescence, AT2 cell depletion, and spontaneous, progressive pulmonary fibrosis. We establish that senescence rather than loss of epithelial stem cells serves as a proximal driver of Tgfb activation and progressive fibrosis and show that either genetic or pharmacologic interventions targeting p53 activation, senescence, or downstream Tgfb activation, block fibrogenesis.
Mechanisms that regulate tissue-specific progenitors for maintenance and differentiation during development are poorly understood. Here, we demonstrate that the co-repressor protein Sin3a is crucial for lung endoderm development. Loss of Sin3a in mouse early foregut endoderm led to a specific and profound defect in lung development with lung buds failing to undergo branching morphogenesis and progressive atrophy of the proximal lung endoderm with complete epithelial loss at later stages of development. Consequently, neonatal pups died at birth due to respiratory insufficiency. Further analysis revealed that loss of Sin3a resulted in embryonic lung epithelial progenitor cells adopting a senescence-like state with permanent cell cycle arrest in G1 phase. This was mediated at least partially through upregulation of the cell cycle inhibitors Cdkn1a and Cdkn2c. At the same time, loss of endodermal Sin3a also disrupted cell differentiation of the mesoderm, suggesting aberrant epithelial-mesenchymal signaling. Together, these findings reveal that Sin3a is an essential regulator for early lung endoderm specification and differentiation.
We previously showed that maternal exposure to nicotine, alone or in combination with chlorpyrifos, caused an increase in glial fibrillary acidic protein (GFAP) immunostaining in the CA1 subfield of hippocampus and cerebellum in postnatal day (PND) 30 offspring. In the present study, PND 60 offspring were evaluated for histopathological and cholinergic effects following maternal exposure to nicotine and chlorpyrifos, alone and in combination. Timed-pregnant Sprague-Dawley rats (300-350 g) were treated daily with nicotine (1 mg/kg, s.c., in normal saline) or chlorpyrifos (0.1 mg/kg, dermal, in ethanol) or a combination of nicotine and chlorpyrifos from gestational days (GD) 4 to 20. Control animals were treated with saline and ethanol. On PND 60, the offspring were evaluated for cholinergic changes and pathological effects. Plasma butyrylcholinesterase (BChE) activity in the female offspring from chlorpyrifos treated mothers showed a significant increase (approximately 183% of control). Male offspring from mothers treated with either chlorpyrifos or nicotine alone showed a significant increase in the acetylcholinesterase (AChE) activity in the brainstem while female offspring from mothers treated with either nicotine or a combination of nicotine and chlorpyrifos showed a significant increase (approximately 134 and 126% of control, respectively) in AChE activity in the brainstem. No significant changes were observed in the ligand binding densities for alpha4beta2 and alpha7 nicotinic acetylcholine receptors in the cortex. Histopathological evaluation using cresyl violet staining showed a significant decrease in surviving Purkinje neurons in the cerebellum of the offspring from nicotine treated mothers. An increase in GFAP immunostaining in cerebellar white matter was observed in the offspring from the mothers treated with nicotine. These results suggest that maternal exposure to real-life levels of nicotine and/or chlorpyrifos causes differential regulation of brainstem AChE activity. Also, nicotine caused a decrease in the surviving neurons and an increased expression of GFAP in cerebellar white matter of the offspring on PND 60. These changes can lead to long-term neurological adverse health effects later in life.
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