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J M Isaac

Publications and source records attributed to J M Isaac.

4 recordsLinked to original sources
PubMed1997

Distribution of epidermal growth factor receptor and ligands during bronchiolar epithelial repair from naphthalene-induced Clara cell injury in the mouse.

Clara cells are primary targets for metabolically activated pulmonary toxicants because they contain an abundance of the cytochrome P450 monooxygenases required for generation of toxic metabolites. The factors that regulate bronchiolar regeneration after Clara cell injury are not known. Previous studies of naphthalene-induced bronchiolar injury and repair in the mouse have shown that epithelial cell proliferation is maximal 1 to 2 days after injury and complete 4 days after injury. Proliferation is followed by epithelial re-differentiation (4 to 14 days). In this study, mice were treated with the environmental pollutant naphthalene to induce massive Clara cell injury. The distribution and abundance of three growth-regulatory peptides (epidermal growth factor receptor (EGFR), epidermal growth factor (EGF), and transforming growth factor (TGF)-alpha) was determined immunochemically during repair of this acute bronchiolar injury. EGFR and its ligands were detected at low levels in cells throughout the lung including peribronchiolar interstitial cells, blood vessels, and conducting airway epithelium. Immediately after naphthalene injury (1 to 2 days), EGFR, EGF, and TGF-alpha are expressed in increased abundance in squamous epithelial cells of the injury target zone, distal bronchioles. These immunopositive squamous cells are detected in clumps in the distal bronchioles at the time when cell proliferation is maximal. EGFR protein expression is decreased slightly 4 to 7 days after injury and continues to decrease below control levels of abundance 14 to 21 days after injury. This down-regulation of EGFR is not reflected in a corresponding decrease in EGF and TGF-alpha protein expression, indicating that control of cell proliferation is regulated at the receptor level. Co-localization of EGFR and bromodeoxyuridine-positive proliferating cells in the same bronchiole indicates that EGFR is up-regulated within the proliferative microenvironment as well as in specific proliferating cells within the injury target zone. The coincident localization within terminal bronchioles of EGFR, EGF, and TGF-alpha to groups of squamous epithelial cells 2 days after naphthalene injury suggests that these peptides are important in up-regulating cell proliferation after Clara cell injury in the mouse.

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PubMed1996

Repair of naphthalene-injured microdissected airways in vitro.

Nonciliated bronchiolar epithelial (Clara) cells, as both the primary target for metabolically activated pulmonary toxicants and the progenitor cell for repair after bronchiolar injury, are critical for distal airway epithelial function and regeneration. Previously, we described a model system whereby differentiated Clara cells can be maintained in culture using explants of microdissected distal airways. The purpose of this study is to establish whether distal airway explants can be used to study bronchiolar epithelial repair in vitro. Lungs from adult mice treated with naphthalene, a metabolically activated Clara cell cytotoxicant, or vehicle were inflated with agarose and distal airways were microdissected. Distal airway explants were cultured for up to 7 days in serum-free medium. Clara cells in explants from naphthalene-treated mice exhibited the characteristic cytotoxic responses previously reported in vivo when maintained in vitro: cell swelling, formation of cytoplasmic vacuoles, and exfoliation of injured cells into the airway lumen 1 to 2 days after injury (DAI). Epithelial cells squamated to cover the injured area 2 to 4 DAI. At 7 DAI, the epithelium generally consisted of cuboidal cells. Proliferating cells and marker proteins for differentiated Clara cells (Clara cell 10 kD secretory protein, or CC10, and cytochrome P450 monooxygenase isozyme 2B, or CYP2B) were detected immunochemically and their pattern of distribution during the injury and repair response in vitro paralleled the pattern of cell regeneration seen previously in vivo. We conclude that Clara cells in explants from defined regions of murine tracheobronchial airways can be used to study the early phases of the repair response to naphthalene injury, including differentiation and proliferation, in vitro.

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PubMed1995

Cellular response in naphthalene-induced Clara cell injury and bronchiolar epithelial repair in mice.

Clara cells, progenitors for bronchiolar epithelium, are also primary targets for metabolically activated pulmonary cytotoxicants and have an abundance of the cytochrome P-450 monooxygenases required for xenobiotic metabolism. To define the repair pattern after massive Clara cell injury, mice were treated with naphthalene, and lungs evaluated 1-14 days postinjury (DPI). Clara cells of terminal bronchioles were vacuolated and swollen 1 DPI, exfoliated 2 DPI, and resembled controls at 14 DPI. The volume fraction of vacuolated cells was highest 1 and 2 DPI and minimal at 5-7 DPI. The volume fraction of normal nonciliated cells decreased 40% at 1 DPI. Cell proliferation increased within epithelium and interstitium at 1 DPI, was maximal at 2 DPI, and at all other time points was similar to baseline levels. Expression of Clara cell differentiation markers was barely detectable in terminal bronchiolar epithelium at 1 and 2 DPI, clearly detectable at 4 DPI, and gradually returned to control levels at 5-14 DPI. We conclude that bronchiolar epithelial repair after naphthalene injury involves distinct phases of proliferation and differentiation, proliferation of cells that are not differentiated Clara cells, and interaction of multiple cell types including nontarget cells.

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