Lichen Planopilaris and Pseudopelade of Brocq Involve Distinct Disease Associated Gene Expression Patterns by Microarray

Lichen planopilaris (LPP) and pseudopelade of Brocq (PPB) are two scarring alopecia diagnoses that often exhibit similar clinical features. Some suggest LPP and PPB are not distinct diseases, but rather different clinical presentations in a spectrum derived from the same underlying pathogenetic mechanism. We explored the degree of similarity between LPP and PPB gene expression patterns and the potential for common and unique gene pathway and gene activity in LPP and PPB using microarrays. Microarray analysis, using a 21K cDNA set was performed on pairs of biopsies obtained from affected and unaffected scalp of untreated patients (4 LPP and 4 PPB biopsy pairs). Diagnosis was confirmed by histopathology. Significantly differentially expressed genes were identified by analysis of microarray results in various data sets and screened for signaling pathway involvement. Selected genes were validated by quantitative PCR and immunohistology. The global gene expression profiles in LPP and PPB versus comparative intra-control scalp tissue were distinguishable by Significance Analysis of Microarrays (SAM). Specific genes, such as MMP11, were identified with significantly differential expression in association with LPP versus PPB. There was very limited commonality in the gene expression profiles between LPP and PPB. Our findings may have important implications for understanding the pathogenesis of LPP and PPB at the molecular level. Results suggest LPP and PPB involve different mechanisms of disease development and can be regarded as biologically distinct cicatricial alopecia diagnoses. Genes that we have identified may potentially be useful as markers of the respective diagnoses. Human LPP and PPB biopsies were collected from study volunteers in the Department of Dermatology and Skin Science, University of British Columbia. Only patients that had not been previously treated with any therapeutic approaches were approached. Patients were diagnosed with active phase LPP or PPB by clinical evaluation including a positive pull test when possible in those with LPP, and a possible pull test when possible in the case of PPB. Two tissue samples were then collected from each volunteer for laboratory analysis with one biopsy taken from the edge of an active lesion with perifollicular scale, with or without erythema, and the second biopsy from an unaffected region of scalp away from the lesional skin. Human Operon v.2.1 (21K) glass arrays were produced (based on human 70mers from Operon Biotechnologies Inc, Huntsville, AL) by the Microarray Facility of the Prostate Centre at Vancouver General Hospital, Vancouver, Canada [17, 18]. RNAs were amplified using the SenseAmp Plus kit (Genisphere Inc, Hatfield, PA). The calculated A 260/280 ratio was used to determine the appropriate amount of sense RNA for labeling. Total RNA from test samples and universal human reference RNA (Stratagene, Cedar Creek, TX) were differentially labeled with Cy5 and Cy3 respectively, with the 3DNA array detection 350 kit (Genisphere Inc, Hatfield, PA) and cohybridized to cDNA microarrays. Following overnight hybridization and washing, arrays were imaged using a ScanArray Express scanner (PerkinElmer, Boston, MA).