Retinoid metabolism is altered in human and mouse cicatricial alopecia

Abstract

C57BL/6 mice develop dermatitis and scarring alopecia resembling human cicatricial alopecias (CAs), particularly the central centrifugal CA (CCCA) type. To evaluate the role of retinoids in CA, the expression of retinoid metabolism components were examined in these mice with mild, moderate, or severe CA compared with hair cycle-matched mice with no disease. Two feeding studies were conducted with dams fed either NIH 31 diet (study 1) or AIN93G diet (study 2). Adult mice were fed AIN93M diet with 4 (recommended), 28, or 56 IU vitamin A g(-1) diet. Feeding the AIN93M diet to adults increased CA frequency over NIH 31 fed mice. Increased follicular dystrophy was seen in study 1 and increased dermal scars in study 2 in mice fed the 28 IU diet. These results indicate that retinoid metabolism is altered in CA in C57BL/6J mice that require precise levels of dietary vitamin A. Human patients with CCCA, pseudopelade (end-stage scarring), and controls with no alopecia were also studied. Many retinoid metabolism proteins were increased in mild CCCA, but were undetectable in pseudopelade. Studies to determine whether these dietary alterations in retinoid metabolism seen in C57BL/6J mice are also involved in different types of human CA are needed.

Figure 1. Immunoreactivity of DHRS9 increased in C57BL/6J mice with mild dermatitis and biopsies from human patients with CCCA, but was reduced in mice with severe disease and biopsies from human patients with pseudopelade

Immunohistochemistry was performed with an antibody against DHRS9 in dorsal skin from chow fed B6 mice with no disease (a, n=18), mild disease (c, n=6), severe disease (e, n=38), biopsies from patients with no alopecia (b, normal Caucasian skin adjacent to Pilar Cyst removed by excision n=2, Tinea capitus from African American n=1), CCCA (d, n=14), or pseudopelade (f, n=3). B and f are from Caucasian patients, while d is from an African American patient. Bar = 101 μM for main picture and 10.1 μM for insets.

Figure 2. CRABP2 and RARA were increased in C57BL/6J mice with cicatricial alopecia

Immunohistochemistry was performed with antibodies against CRABP2 (a,c,e), and RARA (b,d,f), in mice with no disease (a,b), mild disease (c,d), or severe disease (e,f). Bar = 101 μM for main picture and 10.1 μM for insets.

Figure 3. Overview of retinoid metabolism and how these proteins changed during the progression of cicatricial alopecia

The left shows a schematic of RA synthesis, degradation, and signalling pathways in B6 mice. The right shows a summary of IHC results in chow fed B6 mice with no (control), mild, moderate, or severe disease. Immunoreactivity intensity ranges from dark to light; very strong (maroon), strong (red), moderate (hot pink), mild (pink), or undetectable (white). CL= companion layer, PM= premedulla.

Figure 4. Cicatrical alopecia was altered by dietary vitamin A and wax stripping

The percent of mice with hair loss (a) was determined by visual inspection in B6 mice fed 4 (open bars), 28 (closed bars), or 56 (hatched bars) IU vitamin A/g diet. H&E slides were then scored for % of hair follicles in anagen (b) and telogen (c), % of follicular dystrophy (d), % granulomas (e), and % of dermal scars (f). * Significant effect of wax stripping as analyzed by chi square (p<0.05), # significant diet effect in the wax stripped mice (p<0.05). Results with different letters are significantly different from each other in mice with hair loss (p<0.05). e) r = −0.86, p<0.001. n=9–10 study 1, n=8–19 study 2.

Figure 5. Dietary vitamin A altered liver and skin retinoids differently in the various studies

Liver retinol (a), liver retinyl palmitate (b), skin retinol (c), and skin retinyl esters (d) were analyzed by HPLC in study 1 (open bars, n=9–10), study 2 with no wax stripping (closed bars, n=8–19), and study 2 with wax stripping (hatched bars, n=10–16). *Significant study effect (p< 0.001 in a, and p< 0.05 in c), # significant effect of wax stripping (p < 0.005), results with different letters are significantly different from each other (p<0.05).