Inactivation of autophagy leads to changes in sebaceous gland morphology and function

Abstract

We have reported recently that inactivation of the essential autophagy-related gene 7 (Atg7) in keratinocytes has little or no impact on morphology and function of the epidermal barrier in experimental animals. When these mice aged, mutant males, (Atg7 ΔKC), developed an oily coat. As the keratin 14 promoter driven cre/LoxP system inactivates floxed Atg7 in all keratin 14 (K14) expressing cells, including sebocytes, we investigated whether the oily hair phenotype was the consequence of changes in function of the skin sebaceous glands. Using an antibody to the GFP-LC3 fusion protein, autophagosomes were detected at the border of sebocyte disintegration in control but not in mutant animals, suggesting that autophagy was (a) active in normal sebaceous glands and (b) was inactivated in the mutant mice. Detailed analysis established that dorsal sebaceous glands were about twice as large in all Atg7 ΔKC mice compared to those of controls (Atg7 F/F), and their rate of sebocyte proliferation was increased. In addition, male mutant mice yielded twice as much lipid per unit hair as age-matched controls. Analysis of sebum lipids by thin layer chromatography revealed a 40% reduction in the proportion of free fatty acids (FFA) and cholesterol, and a 5-fold increase in the proportion of fatty acid methyl esters (FAME). In addition, the most common diester wax species (58-60 carbon atoms) were increased, while shorter species (54-55 carbon atoms) were under-represented in mutant sebum. Our data show that autophagy contributes to sebaceous gland function and to the control of sebum composition.

Cell death induced autophagy contributes to terminal differentiation of skin and skin appendages

“…In contrast, the SGls of the atg7 −/animals were enlarged and their sebum (SB) was of different opacity and granularity ( Figure 4E). This observation is consistent with the alterations of the sebum previously described in the absence of autophagy [34]. Most obvious, cell borders and nuclear remnants were still visible in the sebum.…”

“…Compared to controls, atg7 −/cells seemed to maintain their cytoplasm longer and obviously disintegrated later. Consequently, the ductal lumen in atg7-deficient SGl was occupied by more material (Figure S3A), a phenotype which has previously been characterized [34]. In atg7 −/glands, the nuclei of sebocytes were fully occupied with GFP without discernible vesicles (Figure 3Aii) and the chromatin was condensed and blebbing ( Figure 3Aii, high magnification).…”

Neuroendocrinology and neurobiology of sebaceous glands

“…Differentiation is evident by the accumulation of lipid droplets in sebocytes within the MZ, and dramatically increased cell size compared to the PZ (Figs 2A, C, D and ). Finally, the necrotic zone (NZ) is where terminally differentiated sebocytes release sebum by undergoing holocrine secretion, a process that resembles autophagic cell death (Brandes, Bertini & Smith, ; Mesquita‐Guimarãtes & Coimbra, ; Fischer et al ., ; Zouboulis, ; Rossiter et al ., ) (Figs 2A, B and ). The time taken for an undifferentiated sebocyte in the peripheral layer to differentiate fully is around 7–14 days, and is comparable between human and rodent SGs (Epstein & Epstein, ; Hamilton, ; Hamilton, Howard & Potten, ; Jung et al ., ).…”

“…Specifically, investigating the neuronal and neuroendocrine regulation of SGs promises to contribute further to fields of broad biological interest, such as maintenance of stem cell niches (Liao & Nguyen, ; Füllgrabe et al ., ; Kretzschmar et al ., ), tumour development and progression (Kyllo, Brady & Hurst, ; Quist et al ., ), lipid synthesis (Guy, Ridden & Kealey, ; Schneider & Paus, ; Jester, Potma & Brown, ), autophagy (Fischer et al ., ; Rossiter et al ., ), and interaction of the nervous system with cardinal signalling pathways in peripheral tissues, i.e. Hedgehog (Allen et al ., ; Brownell et al ., ), Wingless (Kretzschmar et al ., ; Lim et al ., ), and Hippo pathway signalling (Yosefzon et al ., ).…”

Do human dermal adipocytes switch from lipogenesis in anagen to lipophagy and lipolysis during catagen in the human hair cycle?

“…These can be complemented by confocal microscopy of human DAs cocultured with anagen/catagen HFs, and also live‐cell imaging using either deconvolution or super‐resolution microscopy coupled with correlative electron microscopy to detect early formation of ATG9 + autophagic vesicles . Other autophagy‐related techniques are comprehensively covered in including quantification of LC3B/p62 turnover using immunoblotting and detection of autophagolysosomes tagged with GFP labels …”