Preputial sebocyte 5alpha-reductase isoform specificity

Transcriptional Differences in Lipid-Metabolizing Enzymes in Murine Sebocytes Derived from Sebaceous Glands of the Skin and Preputial Glands

Sebaceous glands are adnexal structures, which critically contribute to skin homeostasis and the establishment of a functional epidermal barrier. Sebocytes, the main cell population found within the sebaceous glands, are highly specialized lipid-producing cells. Sebaceous gland-resembling tissue structures are also found in male rodents in the form of preputial glands. Similar to sebaceous glands, they are composed of lipid-specialized sebocytes. Due to a lack of adequate organ culture models for skin sebaceous glands and the fact that preputial glands are much larger and easier to handle, previous studies used preputial glands as a model for skin sebaceous glands. Here, we compared both types of sebocytes, using a single-cell RNA sequencing approach, to unravel potential similarities and differences between the two sebocyte populations. In spite of common gene expression patterns due to general lipid-producing properties, we found significant differences in the expression levels of genes encoding enzymes involved in the biogenesis of specialized lipid classes. Specifically, genes critically involved in the mevalonate pathway, including squalene synthase, as well as the sphingolipid salvage pathway, such as ceramide synthase, (acid) sphingomyelinase or acid and alkaline ceramidases, were significantly less expressed by preputial gland sebocytes. Together, our data revealed tissue-specific sebocyte populations, indicating major developmental, functional as well as biosynthetic differences between both glands. The use of preputial glands as a surrogate model to study skin sebaceous glands is therefore limited, and major differences between both glands need to be carefully considered before planning an experiment.

15-Lipoxygenase-2 expression in benign and neoplastic sebaceous glands and other cutaneous adnexa

15-Lipoxygenase-2 has a limited tissue distribution in epithelial tissues, with mRNA detected in skin, cornea, lung, and prostate. It was originally cloned from human hair rootlets. In this study the distribution of 15-lipoxygenase-2 was characterized in human skin using immunohistochemistry and in situ hybridization. Strong uniform 15-lipoxygenase-2 in situ hybridization (n = 6) and immunostaining (n = 16) were observed in benign cutaneous sebaceous glands, with expression in differentiated secretory cells. Strong 15-lipoxygenase-2 immunostaining was also observed in secretory cells of apocrine and eccrine glands. Variable reduced immunostaining was observed in skin-derived sebaceous neoplasms (n = 8). In the eyelid, Meibomian glands were uniformly negative for 15-lipoxygenase-2 in all cases examined (n = 9), and sebaceous carcinomas apparently derived from Meibomian glands were also negative (n = 12). The mechanisms responsible for differential expression in cutaneous sebaceous vs eyelid Meibomian glands remain to be established. In epidermis, positive immunostaining was observed in the basal cell layer in normal skin, whereas five examined basal cell carcinomas were negative. Thus, the strongest 15-lipoxygenase-2 expression is in the androgen regulated secretory cells of sebaceous, apocrine, and eccrine glands. This compares with the prostate, in which 15-lipoxygenase-2 is expressed in differentiated prostate secretory cells (and reduced in the majority of prostate adenocarcinomas). The product of 15-lipoxygenase-2, 15-hydroxyeicosatetraenoic acid, may be a ligand for the nuclear receptor peroxisome proliferator activated receptor-gamma, which is expressed in sebocytes, and contribute to secretory differentiation in androgen regulated tissues such as prostate and sebaceous glands.

Role of hormones in pilosebaceous unit development

Androgens are required for sexual hair and sebaceous gland development. However, pilosebaceous unit (PSU) growth and differentiation require the interaction of androgen with numerous other biological factors. The pattern of PSU responsiveness to androgen is determined in the embryo. Hair follicle growth involves close reciprocal epithelial-stromal interactions that recapitulate ontogeny; these interactions are necessary for optimal hair growth in culture. Peroxisome proliferator-activated receptors (PPARs) and retinoids have recently been found to specifically affect sebaceous cell growth and differentiation. Many other hormones such as GH, insulin-like growth factors, insulin, glucocorticoids, estrogen, and thyroid hormone play important roles in PSU growth and development. The biological and endocrinological basis of PSU development and the hormonal treatment of the PSU disorders hirsutism, acne vulgaris, and pattern alopecia are reviewed. Improved understanding of the multiplicity of factors involved in normal PSU growth and differentiation will be necessary to provide optimal treatment approaches for these disorders.