Charles J. Roberge

Epidermis promotes dermal fibrosis: role in the pathogenesis of hypertrophic scars

Hypertrophic scarring is a pathological process characterized by fibroblastic hyperproliferation and by excessive deposition of extracellular matrix components. It has been hypothesized that abnormalities in epidermal–dermal crosstalk explain this pathology. To test this hypothesis, a tissue‐engineered model of self‐assembled reconstructed skin was used in this study to mimic interactions between dermal and epidermal cells in normal or pathological skin. These skin equivalents were constructed using three dermal cell types: normal wound (Wmyo) or hypertrophic wound (Hmyo) myofibroblasts and normal skin fibroblasts (Fb). Epidermis was reconstructed with normal skin keratinocytes (NK) or hypertrophic scar keratinocytes (HK). In the absence of keratinocytes, Hmyo formed a thicker dermis than Wmyo. When seeded with NK, the dermal thickness of Hmyo (121.2 ± 31.4 µm vs 196.2 ± 27.8 µm) and Fb (43.7 ± 7.1 µm vs 83.6 ± 16.3 µm) dermis was significantly (p < 0.05) reduced, while that of Wmyo (201.5 ± 15.7 µm vs 160.7 ± 21.1 µm) was increased. However, the presence of HK always induced significantly thicker dermis formation than observed with NK (Wmyo: 238.8 ± 25.9 µm; Hmyo: 145.5 ± 22.4 µm; Fb: 74.2 ± 11.2 µm). These results correlated with collagen and MMP‐1 secretion and with cell proliferation, which were increased when keratinocytes were added, except for the collagen secretion of Hmyo and Fb in the presence of NK. The level of dermal apoptosis was not different when epidermis was added to the dermis (<1% in each category). These observations strongly suggest that hypertrophic scar keratinocytes play a role in the development of pathological fibrosis by influencing the behaviour of dermal cells. Copyright

Activation of human neutrophils in vitro and dieldrin-induced neutrophilic inflammation in vivo

Many chemicals of environmental concern are known to alter the immune system and are considered toxic molecules because they affect immune cell functions. Inflammation related to environmental chemical exposure, however, is poorly documented, except that from air pollutants. In this study, we found that the organochlorine insecticide dieldrin could not alter the ability of human neutrophils to phagocytose opsonized sheep red blood cells at nonnecrotic concentrations (0.1, 1, 10, and 50 μM). However, dieldrin was found to increase human neutrophil superoxide production, RNA synthesis, and proinflammatory cytokine interleukin‐8 production. The normal apoptotic rate of neutrophils evaluated by both cytology and flow cytometry (CD‐16 staining) was not altered by dieldrin treatments, and this was correlated with its inability to inhibit spreading of neutrophils onto glass. Using the murine air pouch model, we found that dieldrin induces a neutrophilic inflammation. Taken together, these results demonstrated that dieldrin is a proinflammatory contaminant. To our knowledge, this is the first report establishing that dieldrin is a contaminant exhibiting proinflammatory properties. In addition, it is the first time that the murine air pouch model has been successfully used to confirm that a chemical of environmental concern can induce an inflammatory response in vivo.