Peroxisomes in Sebaceous Glands: Biosynthetic Role and Hormonal Regulation

Abstract

Sebaceous glands specialize in the production of unique secretory lipids. The membrane fractions catalyzing the synthesis of some of these lipids sedimented between mitochondrial and endoplasmic reticulum fractions. Electron micrographs of avian uropygial glands taken in the 1970s reveal microperoxisome-like bodies and more recent results with stained glands clearly show the presence of peroxisomes. The bovine meibomian gland produces wax esters and sterol esters containing exclusively short (<C18) and long (>C18) acids, respectively. Experimental evidence suggest that wax esters are generated by enzymes located in the endoplasmic reticulum whereas the sterol esters are synthesized by peroxisomal enzymes. This compartmentation explains the striking differences in the acyl portion of the two classes of esters. Another example of peroxisomal synthesis of sebaceous gland lipids with pheromonal activity was recently discovered. Uropygial glands of female mallards produce wax esters during the entire year except during the mating season of April and May when they produce exclusively diesters of C8, C1(), and C12 3-hydroxy acids. The diesters are composed of n-components whereas branched acids dominate the acyl portion of tKe wax. Experiments with cell-free preparations from the glands showed that the 3-hydroxy acids are formed from the corresponding fatty acids by the action of a cyanide-insensitive and 02-dependent fatty acyl-CoA oxidase followed by hydration of the resulting double bond. This synthesis was catalyzed by a peroxisome-enriched fraction obtained by differential centrifugation and density gradient centrifugation. Injection of thyroxine and estradiol induced the synthesis of the diesters of 3-hydroxy acids in the uropygial glands of not only females but also males which do not ordinarily synthesize such esters at any time. The diester-producing males received female-like treatment from normal males. Light and electron microscopic examination of the glands showed that the hormone-induced synthesis of diesters was accompanied by proliferation of peroxisomes.