Background: Lipid synthesis and storage are accomplished by lipid droplets (LDs). The perilipin family of LD-associated proteins, comprising 5 members (PLIN1-PLIN5), has been well characterized in adipocytes but not in sebocytes, epithelial cells in which LD formation is a key feature of the cellular differentiation.
Methods: Perilipin expression in the sebaceous gland cell line SZ95 and in human sebaceous glands was studied by qRT-PCR, Western blots, and immunohistochemistry. Lipid accumulation was evaluated by Nile red staining and mass spectrometry.
Results: PLIN2 and PLIN3 are the most abundant perilipins in undifferentiated sebocytes. Induction of lipogenesis by linoleic acid (LA) resulted in increased transcript levels of all perilipins except for PLIN3 and in a time-dependent increase of PLIN2 protein. Nile red staining revealed that siRNA-mediated downregulation of PLIN2 significantly impaired basal and LA-induced lipid accumulation. Mass spectrometry revealed PLIN2 deficiency to cause a reduction in the amount of several specific lipid fractions, including di- and triacyl-glycerol esters, phosphatidylcholine lipids, and ceramides in sebocytes under basal conditions. In contrast, PLIN2 downregulation exerted a statistically significant inhibitory effect only on the accumulation of specific LA-induced triglycerides. PLIN2-deficient mice showed normal morphology of sebaceous glands. However, their sebaceous glands were significantly reduced in size and showed less cell proliferation.
Conclusions: PLIN2 is the major perilipin regulated during sebocyte differentiation in vitro. PLIN2 is also important for sebaceous lipid accumulation in vitro and regulates sebaceous gland size in vivo.
General significance: Our study provides the first systematic analysis of LD-associated proteins in sebocytes.
Keywords: Lipid droplets; Perilipins; Sebaceous glands.
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