Canine Epidermal Keratinocytes (CPEK) Grown in Monolayer Are Not Representative of Normal Canine Keratinocytes for Permeability Studies: Pilot Studies

Canine progenitor epidermal keratinocytes (CPEK) are used as canine keratinocyte cell line. Their suitability for skin barrier studies is unknown. Measurement of transepithelial electric resistance (TEER) evaluates epithelial permeability. We compared TEER and tight junction (TJ) expression in CPEKs and normal keratinocytes (NK) harvested from biopsies of normal dogs. CPEKs and NK were grown until confluence (D0) and for 13 additional days. Slides were fixed on D0 and stained with ZO-1 and claudin-1 antibodies. Five images/antibody were taken, randomized and evaluated blindly by three investigators for intensity, staining location, granularity, and continuousness. Cell size and variability were evaluated. TEER increased overtime to 2000 Ohms/cm in NK, while remained around 100–150 Ohms/cm in CPEK. ANOVA showed significant effect of time (p < 0.0001), group (p < 0.0001) and group x time interaction (p < 0.0001) for TEER. Size of CPEKs was significantly (p < 0.0001) smaller and less variable (p = 0.0078) than NK. Intensity of claudin-1 staining was greater in CPEKs (p < 0.0001) while granularity was less in CPEKs (p = 0.0012). For ZO-1, cytoplasmic staining was greater in CPEK (p < 0.0001) while membrane continuousness of staining was greater in NK (p = 0.0002). We conclude that CPEKs grown in monolayer are not representative of NK for permeability studies.