Sebocyte Differentiation Research Articles

Endocrinology and immunology of acne: Two sides of the same coin.

Current experimental research on acne pathophysiology has revealed a more complicated background than the classically reported four-factor aetiology. Cells of the pilosebaceous unit, which represent the template for the development of acne lesions, seem to be parallelly affected by endocrinological/metabolic factors as well as inflammatory/immunological ones that cooperate in sebocyte differentiation and lipogenesis. Indeed, the unique programme of sebocyte terminal differentiation and death, the so called holocrine secretion, is influenced by inflammatory and metabolic (lipid) signalling with common denominator the selective regulation of peroxisome proliferator-activated receptors. Autophagy provides substrates for energy generation and biosynthesis of new cell structure proteins contributing to the normally increased sebaceous gland metabolic functions, which are also regulated by extracellular calcium signalling, essential lipids and hormones. The ultimate differentiation product of human sebocytes, sebum, co-regulates the inflammatory sebocyte status. Sebum composition is controlled among others by Propionibacterium acnes and other bacteria, sexual hormones, neuropeptides, endogenous opioids and environmental agents, which may function as endocrine disruptors. Diet may also be an important source of substrates for the synthesis of pro-inflammatory and anti-inflammatory sebaceous lipids. Sebum changes might induce inflammation and initiate underlying immune mechanisms leading to acne lesions. Current new therapeutic efforts on acne concentrate on anti-inflammatory/immunologically active concepts, which are able to regulate sebaceous lipogenesis. At last, current molecular studies based on published molecular data sets confirmed the major role of inflammation in acne development.

Acne as an altered dermato-endocrine response problem.

Acne is the most common skin disease in adolescent Westernized populations. Several data support the involvement of the mammalian target of rapamycin complex 1 (mTORC1) signalling in the interplay between androgens, insulin, insulin-like growth factor (IGF1) and high-glycaemic index diet in acne. The peroxisome proliferator-activated receptor γ (PPARγ) is involved in both differentiation and anti-inflammatory response. Low differentiated sebocytes showed decreased expression of PPARγ and increased level of insulin and IGF-1 receptors, resulting in the production of acne-like sebum and inflammatory mediators. In this viewpoint, we discuss how in acne the dysregulation of proliferation and differentiation processes in sebocytes and keratinocytes may be associated with altered response to androgens and other hormones, such as insulin or IGF-1. Moreover, we propose PPARγ modulation as an innovative therapeutic approach to normalize sebocyte differentiation process, interfering with the different mechanisms involved in altered pilosebaceous unit.

Network pharmacology-based identification for therapeutic mechanisms of Dangguikushen pill in acne vulgaris.

The Dangguikushen (DGKS) pill is a proprietary traditional Chinese medicine that has shown superior efficacy in the treatment of acne vulgaris for many years. A network pharmacology-based analysis was performed to explore the potential anti-acne compounds, core therapeutic targets, and the main pathways, involved in the DGKS pill bioactivity. The matching results between the predicted targets of the DGKS pill and the well-known targets of acne vulgaris were collected, followed by network establishment using protein-protein interaction (PPI) data. Cytoscape was utilized to analyze the network and screen the core targets. Furthermore, the Database for Annotation, Visualization and Integrated Discovery (DAVID), and ClueGO were used for the enrichment analysis of the Kyoto Encyclopedia of Genes and Genomics (KEGG) pathways and Gene Ontology biological processes (GO-BP). Finally, the "compound-target-pathway" network was constructed. This approach identified 19 active compounds, 46 therapeutic targets, and 12 core therapeutic targets of the DGKS pill. The biological processes were primarily related to reactive oxygen species (ROS) metabolic process, gland morphogenesis, and female gonad development. The DGKS pill was significantly associated with eight pathways including the PI3K-Akt, TNF, NF-kappa B, and p53 signaling pathways. DGKS pill might have a synergistic effect on the inhibition of excessive sebaceous lipogenesis and sebocyte differentiation, and likewise, anti-inflammatory effects via the different signaling pathways (PI3K-Akt, TNF, NF-kappa B, and p53).

Commentary on 'Sebocyte differentiation as a new target for acne therapy: an in vivo experience'.

Linked article: M. Ottaviani et al. J Eur Acad Dermatol Venereol 2020; 34: 1803–1814. https://doi.org/10.1111/jdv.16252.

Sebocyte differentiation as a new target for acne therapy: an invivo experience.

Acne, a disease of the sebaceous gland with multifactorial pathogenesis, affects more than 85% of adolescents. A better deepening of the mechanisms underlying the disease is needed to define effective and mechanism-targeted treatments. To understand whether the sebocyte differentiation process could be involved in the pathogenesis of the disease. Protein expressions were evaluated by Western blot analysis and ELISA; mRNA levels by real-time RT-PCR, lipid analysis and lipid peroxidation were performed by gas chromatography, mass spectrometry and spectrophotometric assay. In vitro, low differentiated SZ95 sebocyte expressed an up-modulation of genes involved in sebogenesis and a higher level of insulin receptor respect to differentiated cells, resulting in an increased response to insulin and in the production of acne-like sebum. The induction of SZ95 sebocyte differentiation by the peroxisome proliferator-activated receptor γ (PPARγ) modulator NAC-GED0507 reduced the response to insulin normalizing the sebum production and decreasing the release of proinflammatory mediators. In vivo treatment of acne patients with NAC-GED0507 1% gel ameliorated clinical manifestations and induced in sebum the expression of PPARγ, associated with the decrease in mammalian target of rapamycin activation and levels of inflammatory molecules, confirming the results obtained invitro. The study provides relevant insight into acne pathogenesis, identifying an alteration of sebocyte differentiation as pathogenetic basis of the disease and the induction of the differentiation process as a therapeutic target in acne therapy interfering with all pathogenic mechanisms.

GPR119 Is a Potent Regulator of Human Sebocyte Biology

We have shown previously that endocannabinoids promote sebaceous lipogenesis, and sebocytes are involved in the metabolism of the endocannabinoid-like substance oleoylethanolamide (OEA). OEA is an endogenous activator of GPR119, a recently deorphanized receptor, which currently is being investigated as a promising antidiabetic drug target. In this study, we investigated the effects of OEA as well as the expression and role of GPR119 in human sebocytes. We found that OEA promoted differentiation of human SZ95 sebocytes (elevated lipogenesis, enhanced granulation, and the induction of early apoptotic events), and it switched the cells to a proinflammatory phenotype (increased expression and release of several proinflammatory cytokines). Moreover, we could also demonstrate that GPR119 was expressed in human sebocytes, and its small interfering RNA-mediated gene silencing suppressed OEA-induced sebaceous lipogenesis, which was mediated via c-Jun N-terminal kinase, extracellular signal-regulated kinase 1/2, protein kinase B, and CRE-binding protein activation. Finally, our pilot data demonstrated that GPR119 was downregulated in the sebaceous glands of patients with acne, arguing that GPR119 signaling may indeed be disturbed in acne. Collectively, our findings introduce the OEA/GPR119 signaling as a positive regulator of sebocyte differentiation and highlight the possibility that dysregulation of this pathway may contribute to the development of seborrhea and acne.

879 Dynamic regulation of sebaceous gland stem cells during skin homeostasis and aging

Proper skin function depends upon sebaceous glands (SGs), which are typically paired appendages that release lipids onto the skin’s surface. SGs are subjected to complex regulation by diverse factors; however, it remains unclear how these factors act concurrently to regulate SG stem cells. Here, we provide functional evidence that SGs harbor distinct stem cell populations that replenish the gland from its proximal tip. These SG tip cells can be minimally defined as Lrig1+;PPARg+ or Lrig1+;AR+, while sebocyte differentiation is associated with a distinct K14:K5 to K14:K79 keratin shift. Ablation studies further suggest that individual sebaceous lobes do not sense the loss of their partners or neighbors. Rather, Notch signaling exerts dual contradicting effects on SGs, directly promoting sebocyte differentiation while simultaneously inhibiting SGs from a distance. Suppressing Notch in SG progenitors traps them in a hybrid state where stem cell markers become intermingled with sebocyte differentiation features, including nascent lipid droplet accumulation and K79 expression. Loss of K79 causes SG deterioration and also eyelid meibomian gland collapse, leading to corneal ulceration. Finally, to mimic the mutational status of aged, sun-exposed skin, we performed highly targeted sporadic Notch1 deletion in the adult epidermis and observed gradual SG expansion over time. This suggests that a common skin mutation incurred within one stem cell compartment can indirectly affect another during aging.

907 Propionibacterium acnes and peptidoglycan reduce lipidgenesis and change differentiation of SZ95 human sebocytes in vitro via aryl hydrocarbon receptor

Individual lesions in acne vulgaris exist spontaneous remission, which is related to shrunken and de-differential sebaceous gland (SGs) in comedone with unknown mechanisms. P. acnes stimulated by increased lipids from SGs plays key role in acne pathogenesis, while the relationship between the P. acnes and SGs is still a myth. We explored the action of P. acnes and peptidoglycan (PGN) on the effects of lipidgenesis and differentiation of cultured SZ95 human sebocytes. Firstly, we observed that both formaldehyde-inactivated P. acnes and PGN reduced Linoleic acid (LA) induced neutral lipid synthesis in SZ95 sebocytes, and GSEA analysis showed that the pathways of lipogenesis were downregulated ,but the pathways of keratinization were upregulated after P. acnes and PGN treatment respectively. Furthermore, expressions of keratin 7 and MUCIN1/EMA, markers of sebocytes differentiation, were decreased, while the terminal keratinocytes differentiation markers keratin 10 and involucrin were increased after P. acnes and PGN stimulation. Meanwhile, we also found P. acnes and PGN inhibit expressions of sebaceous differentiation-related antigens SREBP-1, FAS and PPAR-α. In addition, we proved both P. acnes and PGN could upregulate mRNA expression of CYP1A1, as well as a significantly induced translocation of AhR protein from cytoplasm into nucleus . after knocking out AhR gene the P. acnes and PGN induced changes of neutral lipid synthesis and related genes expressions in SZ95 were normalized. Our data proved evidences that P. acnes could reduce lipid synthesis and change differentiation of SZ95 sebocytes in vitro via activation of AhR signaling pathway, which is not only a motivator of acne initiation, but also a factor of acne remission.

Hydrogel from Acellular Porcine Adipose Tissue Accelerates Wound Healing by Inducing Intradermal Adipocyte Regeneration

As an important component of the skin, intradermal adipocytes are closely associated with skin homeostasis and wound healing. Although studies have focused on the role of fibroblasts, keratinocytes, and inflammatory cells in wound healing, the role of adipocytes has not been fully investigated. Here, we verified whether the induction of adipocyte regeneration in a wound bed can effectively promote wound healing, finding that the hydrogel from acellular porcine adipose tissue in combination with adipose-derived stem cells can induce in situ adipogenesis in the wound microenvironment. The newly regenerated adipocytes enhanced fibroblast migration, accelerated wound closing, and enhanced wound epithelialization. More importantly, newly formed intact skin structure was observed after treating the wound with adipose-derived stem cell-loaded hydrogel from acellular porcine adipose tissue. These results show that hydrogel from acellular porcine adipose tissue might substantially improve re-epithelialization, angiogenesis, and skin-appendage regeneration, making it a promising therapeutic biomaterial for skin wound healing.

The C/EBP\u03b2 LIP isoform rescues loss of C/EBP\u03b2 function in the mouse

The transcription factor C/EBPβ regulates hematopoiesis, bone, liver, fat, and skin homeostasis, and female reproduction. C/EBPβ protein expression from its single transcript occurs by alternative in-frame translation initiation at consecutive start sites to generate three isoforms, two long (LAP*, LAP) and one truncated (LIP), with the same C-terminal bZip dimerization domain. The long C/EBPβ isoforms are considered gene activators, whereas the LIP isoform reportedly acts as a dominant-negative repressor. Here, we tested the putative repressor functions of the C/EBPβ LIP isoform in mice by comparing monoallelic WT or LIP knockin mice with Cebpb knockout mice, in combination with monoallelic Cebpa mice. The C/EBPβ LIP isoform was sufficient to function in coordination with C/EBPα in murine development, adipose tissue and sebocyte differentiation, and female fertility. Thus, the C/EBPβ LIP isoform likely has more physiological functions than its currently known role as a dominant-negative inhibitor, which are more complex than anticipated.

Differentiation Model Establishment and Differentiation-Related Protein Screening in Primary Cultured Human Sebocytes.

Sebocyte differentiation is a continuous process, but its potential molecular mechanism remains unclear. We aimed to establish a novel sebocyte differentiation model using human primary sebocytes and to identify the expression profiles of differentiation-associated proteins. Primary human sebocytes were cultured on Sebomed medium supplemented with 2% serum for 7 days. Flow cytometry showed that S phase cells were decreased time-dependently, while G1 and subG1 (apoptosis) phase cells increased under serum starvation. Transmission electron microscopy and Oil Red O staining revealed a gradual increase of intracellular lipid accumulation. Expression of proliferation marker was diminished, while expression of differentiation, apoptosis, and lipogenic markers elevated gradually during 7-day culture. iTRAQ analysis identified 3582 expressed proteins in this differentiation model. Compared with day 0, number of differentially expressed proteins was 132, 54, 321, and 96 at days 1, 3, 5, and 7, respectively. Two overexpressed proteins (S100 calcium binding protein P and ferredoxin reductase) and 2 downexpressed proteins (adenosine deaminase and keratin 10) were further confirmed by Western blot and immunohistochemistry.

Heritability and GWAS Analyses of Acne in Australian Adolescent Twins.

Acne vulgaris is a skin disease with a multifactorial and complex pathology. While several twin studies have estimated that acne has a heritability of up to 80%, the genomic elements responsible for the origin and pathology of acne are still undiscovered. Here we performed a twin-based structural equation model, using available data on acne severity for an Australian sample of 4,491 twins and their siblings aged from 10 to 24. This study extends by a factor of 3 an earlier analysis of the genetic factors of acne. Acne severity was rated by nurses on a 4-point scale (1 = absent to 4 = severe) on up to three body sites (face, back, chest) and on up to three occasions (age 12, 14, and 16). The phenotype that we analyzed was the most severe rating at any site or age. The polychoric correlation for monozygotic twins was higher (r MZ = 0.86, 95% CI [0.81, 0.90]) than for dizygotic twins (r DZ = 0.42, 95% CI [0.35, 0.47]). A model that includes additive genetic effects and unique environmental effects was the most parsimonious model to explain the genetic variance of acne severity, and the estimated heritability was 0.85 (95% CI [0.82, 0.87]). We then conducted a genome-wide analysis including an additional 271 siblings - for a total of 4,762 individuals. A genome-wide association study (GWAS) scan did not detect loci associated with the severity of acne at the threshold of 5E-08 but suggestive association was found for three SNPs: rs10515088 locus 5q13.1 (p = 3.9E-07), rs12738078 locus 1p35.5 (p = 6.7E-07), and rs117943429 locus 18q21.2 (p = 9.1E-07). The 5q13.1 locus is close to PIK3R1, a gene that has a potential regulatory effect on sebocyte differentiation.

Delayed Hair Follicle Morphogenesis and Hair Follicle Dystrophy in a Lipoatrophy Mouse Model of Pparg Total Deletion

PPARγ regulates multiple aspects of skin physiology, including sebocyte differentiation, keratinocyte proliferation, epithelial stem cell survival, adipocyte biology, and inflammatory skin responses. However, the effects of its global deletion, namely of nonredundant key functions of PPARγ signaling in mammalian skin, are yet unknown because of embryonic lethality. Here, we describe the skin and hair phenotype of a whole-body PPARγ-null mouse (PpargΔ/Δ), obtained by preserving PPARγ expression in the placenta. PpargΔ/Δ mice exhibited total lipoatrophy and complete absence of sebaceous glands. Right after birth, hair follicle (HF) morphogenesis was transiently delayed, along with reduced expression of HF differentiation markers and of transcriptional regulators necessary for HF development. Later, adult PpargΔ/Δ mice developed scarring alopecia and severe perifollicular inflammation. Skin analyses in other models of lipodystrophy, AZIPtg/+ and Adipoq-Cretg/+Ppargfl/fl mice, coupled with skin graft experiments, showed that the early defects observed in hair morphogenesis were caused by the absence of adipose tissue. In contrast, the late alteration of HF cycleand appearance of inflammation were observed only in PpargΔ/Δ mice and likely were due to the lack sebaceous glands. Our findings underscore the increasing appreciation for the importance of adipose tissue-mediated signals in HF development and function.

245 Tight junction barriers in sebaceous glands are crucial for proper terminal differentiation of sebocytes

245 Tight junction barriers in sebaceous glands are crucial for proper terminal differentiation of sebocytes

Dermal Blimp1 Acts Downstream of Epidermal TGFβ and Wnt/β-Catenin to Regulate Hair Follicle Formation and Growth

B-lymphocyte-induced maturation protein 1 (Blimp1) is a transcriptional repressor that regulates cell growth and differentiation in multiple tissues, including skin. Although in the epidermis Blimp1 is important for keratinocyte and sebocyte differentiation, its role in dermal fibroblasts is unclear. Here we show that Blimp1 is dynamically regulated in dermal papilla cells during hair follicle (HF) morphogenesis and the postnatal hair cycle, preceding dermal Wnt/β-catenin activation. Blimp1 ablation in E12.5 mouse dermal fibroblasts delayed HF morphogenesis and growth and prevented new HF formation after wounding. By combining targeted quantitative PCR screens with bioinformatic analysis and experimental validation we demonstrated that Blimp1 is both a target and a mediator of key dermal papilla inductive signaling pathways including transforming growth factor-β and Wnt/β-catenin. Epidermal overexpression of stabilized β-catenin was able to override the HF defects in Blimp1 mutant mice, underlining the close reciprocal relationship between the dermal papilla and adjacent HF epithelial cells. Overall, our study reveals the functional role of Blimp1 in promoting the dermal papilla inductive signaling cascade that initiates HF growth.

889 Lemon myrtle: A new anti-seborrheic extract for multi-ethnic skins

Seborrhea is a common cosmetic issue that occurs when oversized sebaceous glands produce excessive amounts of sebum, giving the appearance of shiny and greasy skin. Sebum is made and secreted by sebaceous glands, via the differentiation and disintegration of fully mature sebocytes, a unique process termed holocrine secretion. Moreover, skin oiliness may vary according to diet, age, hot humid climates and ethnicity. Depending on new researches, ethnicity had no significant impact on level of residual skin surface components derived from sebum but, could affect sebum quality (composition and components oxidation). Convinced by the interest to act on the genesis of the sebum secretion mechanism, we have developed a new sebosuppressive agent able to modulate sebocytes differentiation, and also sebum quality. The natural Australian extract selected has been isolated from Backhousia citriodora (Lemon Myrtle leaf). Conforming its promise, Lemon myrtle extract tested on human sebocytes decrease by 32% Epithelial Membrane Antigen expression (marker of sebocyte differentiation) and so by 30% the lipid accumulation in the cytoplasm. Furthermore, two clinical studies validate Lemon Myrtle efficacy. On one hand, at 15 and 30 days, Lemon Myrtle treatment decreases significantly skin sebum content (-17% and -31% respectively) and thus surface covered by oily spots (-17% and -22% respectively). On the other hand, a sebum lipodimic analysis on ethnic volunteers (Caucasian, Asian and African-American) demonstrates that Lemon Myrtle regulates sebum composition and protects its components from oxidation. This natural extract has proven its efficiency to modulate human sebaceous terminal differentiation, characterized by cell changes, lipid droplets accumulation, nuclear degeneration and excess sebum production. Therefore, Lemon Myrtle extract is a promising sebo-regulator to act at the genesis of sebum production and to regulate sebum quality whatever the ethnicity.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-mediated deregulation of myeloid and sebaceous gland stem/progenitor cell homeostasis.

Studies of TCDD toxicitystimulated identification of the responsible aryl hydrocarbon receptor (AHR), a multifunctional, ligand-activated transcription factor of the basic helix-loop-helix/Per-Arnt-Sim family. Accumulating evidence suggests a role of this receptor in homeostasis of stem/progenitor cells, in addition to its known role in xenobiotic metabolism. (1) Regulation of myelopoiesis is complex. As one example, AHR-mediated downregulation of human CD34+ progenitor differentiation to monocytes/macrophages is discussed. (2) Accumulation of TCDD in sebum leads to deregulation of sebocyte differentiation via Blimp1-mediated inhibition of c-Myc signaling and stimulation of Wnt-mediated proliferation of interfollicular epidermis. The resulting sebaceous gland atrophy and formation of dermal cysts may explain the pathogenesis of chloracne, the hallmark of TCDD toxicity. (3) TCDD treatment of confluent liver stem cell-like rat WB-F344 cells leads to release from cell-cell contact inhibition via AHR-mediated crosstalk with multiple signaling pathways. Further work is needed to delineate AHR function in crosstalk with other signaling pathways.

Further Evidence of Sebaceous Differentiation Uniqueness: Holocrine Secretion of Sebocytes Is a Multistep, Cell-Specific Lysosomal DNase2-Mediated Mode of Programmed Cell Death

Holocrine secretion by sebocytes does not occur via increased cell volume, but rather from programmed DNA fragmentation and death, which differs from apoptosis. Moreover, it can be enhanced with increased rates of induced terminal sebocyte differentiation. Fischer etal. address the mode of holocrine sebocyte secretion, and they demonstrate that its mechanism differs from that of apoptosis, necroptosis, and cornification, being a multistep, cell-specific lysosomal DNase2-mediated mode of programmed cell death.

Effects of Isotretinoin on the Phosphoinositide-3-kinase/Akt/FoxO1 Pathway and Molecular Functions of SZ95 Sebocytes In vitro

Objective: For more than 3 decades, isotretinoin [13-cis retinoic acid (13-cis RA)] is established as the most potent oral treatment for severe acne. However, the molecular mechanisms of isotretinoin action have not been fully elucidated. Recently, we showed that insulin and insulin-like growth factor 1 (IGF-1) increase differentiation and decrease proliferation of SZ95 sebocytes in vitro via activation of the phosphoinositide 3-kinase (PI3K)/Akt/forkhead box-O1 (FoxO1) pathway. Furthermore, this pathway is activated in patient acne biopsies in vivo. Using SZ95 sebocytes as an in vitro model, the aim of this study was to investigate the effect of isotretinoin on PI3K pathway activation. Methods: SZ95 sebocytes were treated under light protection with 0.1 μM isotretinoin in the presence or absence of 1.0 and 0.1 μM IGF-1 or insulin or 50 μM LY294002 inhibitor in a time- dependent manner. The expression of p-Akt and its downstream target p-FoxO1 was analyzed by Western blot. FoxO transcriptional activity was measured by dual luciferase assay. Nuclear and cytoplasmic mobilization of FoxO1, p-FoxO1, and p-Akt were also determined by immunofluorescence microscopy.Proliferation of sebocytes was measured by [3H]-thymidine incorporation and sebocyte differentiation by oil red O staining. Results: We show that isotretinoin activates the PI3K/Akt pathway and decreases the nuclear content of FoxO1 and its transcriptional activity in sebocytes in vitro and in sebaceous gland biopsies from an isotretinoin-treated acne patient. Isotretinoin reduces the proliferation of IGF-1- or insulin-stimulated sebocytes more effectively than IGF-1 and insulin alone. However, it normalizes the increased lipid accumulation in IGF-1- or insulin-stimulated sebocytes via a PI3K-independent pathway. Conclusion: Our data from the SZ95 sebocyte in vitro model suggest that the potent therapeutic effect of isotretinoin in acne is not mediated via the PI3K/Akt/FoxO1 pathway.

Holocrine Secretion of Sebum Is a Unique DNase2-Dependent Mode of Programmed Cell Death

Sebaceous glands produce sebum via holocrine secretion, a largely uncharacterized mode of programmed cell death that contributes to the homeostasis and barrier function of the skin. To determine the mechanism of DNA degradation during sebocyte cell death, we have inactivated candidate DNA-degrading enzymes by targeted gene deletions in mice. DNase1 and DNase1-like 2 were dispensable for nuclear DNA degradation in sebocytes. By contrast, epithelial cell-specific deletion of lysosomal DNase2 blocked DNA degradation in these cells. DNA breakdown during sebocyte differentiation coincided with the loss of LAMP1 and was accelerated by the abrogation of autophagy, the central cellular program of lysosome-dependent catabolism. Suppression of DNA degradation by the deletion of DNase2 resulted in aberrantly increased concentrations of residual DNA and decreased amounts of the DNA metabolite uric acid in secreted sebum. These results define holocrine secretion as a DNase2-mediated form of programmed cell death and suggest that autophagy-dependent metabolism, DNA degradation, and the molecular composition of sebum are mechanistically linked.