BNIP3 plays crucial roles in the differentiation and maintenance of epidermal keratinocytes

VAMP2 controls murine epidermal differentiation and carcinogenesis by regulation of nucleophagy

Differentiation of murine epidermal stem/progenitor cells involves the permanent withdrawal from the cell cycle, the synthesis of various protein and lipid components for the cornified envelope, and the controlled dissolution of cellular organelles and nuclei. Deregulated epidermal differentiation contributes to the development of various skin diseases, including skin cancers. With a genome-wide shRNA screen, we identified vesicle-associated membrane protein 2 (VAMP2) as a critical factor involved in skin differentiation. Deletion of VAMP2 leads to aberrant skin stratification and enucleation in vivo. With quantitative proteomics, we further identified an autophagy protein, focal adhesion kinase family interacting protein of 200 kDa (FIP200), as a binding partner of VAMP2. Additionally, we showed that both VAMP2 and FIP200 are critical for murine keratinocyte enucleation and epidermal differentiation. Loss of VAMP2 or FIP200 enhances cutaneous carcinogenesis in vivo. Together, our findings identify important molecular mechanisms underlying epidermal differentiation and skin tumorigenesis.

Hypoxic microenvironment promotes dermal fibroblast migration and proliferation via a BNIP3-autophagy pathway

Upon injury, nearby cells, including fibroblasts at the wound edge, are often found in a hypoxic microenvironment. Nevertheless, the influence of hypoxia on skin fibroblasts is poorly understood. Using previously established mouse full-thickness wounds, we show that Bcl-2 and adenovirus E1B 19-kDa interacting protein 3 (BNIP3) expression was significantly elevated at the wound edge, and hypoxia treatment enhanced BNIP3 expression in fibroblasts. Interestingly, BNIP3 promoted the migration and proliferation, as well as the activation of autophagy, in fibroblasts under hypoxia. The hypoxia-induced autophagy was found to induce the migration and proliferation of fibroblasts, a process that could be reversed by knocking down the autophagy-related gene for autophagy protein 5, ATG5. Furthermore, hypoxia-inducible factor 1 subunit alpha (HIF-1α) was significantly upregulated in fibroblasts under hypoxia treatment, and HIF-1α knockdown attenuated the hypoxia-induced expression of BNIP3 and the migration and proliferation of fibroblasts. Altogether, our results establish the hypoxia-BNIP3-autophagy signaling axis as a newly identified regulatory mechanism of skin fibroblast migration and proliferation upon wounding. Autophagy intervening might thus represent a promising therapeutic strategy for patients with chronic refractory wounds.

Mitochondrial protein BNIP3 regulates Chikungunya virus replication in the early stages of infection

Chikungunya virus (CHIKV) is a human pathogen causing outbreaks of febrile illness for which vaccines and specific treatments remain unavailable. Autophagy-related (ATG) proteins and autophagy receptors are a set of host factors that participate in autophagy, but have also shown to function in other unrelated cellular pathways. Although autophagy is reported to both inhibit and enhance CHIKV replication, the specific role of individual ATG proteins remains largely unknown. Here, a siRNA screen was performed to evaluate the importance of the ATG proteome and autophagy receptors in controlling CHIKV infection. We observed that 7 out of 50 ATG proteins impact the replication of CHIKV. Among those, depletion of the mitochondrial protein and autophagy receptor BCL2 Interacting Protein 3 (BNIP3) increased CHIKV infection. Interestingly, BNIP3 controls CHIKV independently of autophagy and cell death. Detailed analysis of the CHIKV viral cycle revealed that BNIP3 interferes with the early stages of infection. Moreover, the antiviral role of BNIP3 was found conserved across two distinct CHIKV genotypes and the closely related Semliki Forest virus. Altogether, this study describes a novel and previously unknown function of the mitochondrial protein BNIP3 in the control of the early stages of the alphavirus viral cycle.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Gasdermin A Is Required for Epidermal Cornification during Skin Barrier Regeneration and in an Atopic Dermatitis-Like Model

Atopic dermatitis is featured with impaired skin barrier. The stratum corneum and the intercellular tight junctions constitute the permeability barrier, which is essential to protect water loss in the host and prevent pathogen entry. The epidermal barrier is constantly renewed by differentiating keratinocytes through cornification, during which autophagy contributes to elimination of organelles and nucleus. The human GSDMA and its mouse homologs Gsdma1-3 are expressed in the suprabasal epidermis. Although a pyroptotic role of GSDMA/Gsdma1 in host defense against Streptococcus pyogenes has been reported, the physiological function of Gsdma1/a2/a3 in epidermal homeostasis remains elusive. Here, through repeated epidermal barrier disruption, we found that tight junction formation and stratum corneum maturation were defective in the Gsdma1/a3-deficient epidermis. Using comparative gene profiling analysis, mitochondrial respiration measurement, and in vivo tracing of mitophagy, our data indicate that Gsdma1/a3 activation leads to mitochondrial dysfunction and subsequently facilitates mitochondrial turnover and epidermal cornification. In calcipotriol (MC903)-induced atopic dermatitis-like animal model, we showed that Gsdma1/a3-deficiency selectively enhanced the T helper type 2 response. Remarkably, the GSDMA expression is reduced in the epidermis of patients with atopic dermatitis compared with that of normal individuals. Gsdma1/a3-deficiency might be involved in atopic dermatitis pathogenesis, likely through GSDMA-mediated epidermal differentiation and cornification.

The Notch pathway regulates autophagy after hypoxic-ischemic injury and affects synaptic plasticity

Following neonatal hypoxic-ischemia (HI) injury, it is crucial factor to reconstruct neural circuit and maintain neural network homeostasis for neurological recovery. A dynamic balance between the synthesis and degradation of synaptic protein is required for maintaining synaptic plasticity. Protein degradation is facilitated by autophagy. This study aimed to investigate the regulation of synaptic structural plasticity by the Notch pathway, by assessing changes in Notch pathway activation and their effects on synaptic proteins and autophagy after HI injury. The study involved 48 male newborn Yorkshire piglets, each weighing 1.0-1.5 kg and 3 days old. They were randomly assigned to two groups: the HI group and the Notch pathway inhibitor + HI group (n = 24 per group). Each group was further divided into six subgroups according to HI duration (n = 4 per group): a control subgroup, and 0-6, 6-12, 12-24, 24-48, and 48-72 h subgroups. The expression of Notch pathway-related proteins, including Notch1, Hes1, and Notch intracellular domains, increased following HI injury. The expression of autophagy proteins increased at 0-6 h and 6-12 h post-HI. The expression of synaptic proteins, such as postsynaptic density protein 95 (PSD95) and synaptophysin, increased 6-12 h and 12-24 h after HI, respectively. Notably, the increased expression of these proteins was reversed by a Notch pathway inhibitor. Transmission electron microscopy revealed the presence of autophagosome structures in synapses. These findings shed light on the underlying mechanisms of neurological recovery after HI injury and may provide insights into potential therapeutic targets for promoting neural circuit reconstruction and maintaining neural network homeostasis.

The outer mitochondrial membrane protein TMEM11 demarcates spatially restricted BNIP3/BNIP3L-mediated mitophagy

Mitochondria play critical roles in cellular metabolism and to maintain their integrity, they are regulated by several quality control pathways, including mitophagy. During BNIP3/BNIP3L-dependent receptor-mediated mitophagy, mitochondria are selectively targeted for degradation by the direct recruitment of the autophagy protein LC3. BNIP3 and/or BNIP3L are upregulated situationally, for example during hypoxia and developmentally during erythrocyte maturation. However, it is not well understood how they are spatially regulated within the mitochondrial network to locally trigger mitophagy. Here, we find that the poorly characterized mitochondrial protein TMEM11 forms a complex with BNIP3 and BNIP3L and co-enriches at sites of mitophagosome formation. We find that mitophagy is hyper-active in the absence of TMEM11 during both normoxia and hypoxia-mimetic conditions due to an increase in BNIP3/BNIP3L mitophagy sites, supporting a model that TMEM11 spatially restricts mitophagosome formation.

The Epidermal Keratinocyte as a Therapeutic Target for Management of Diabetic Wounds

Diabetes mellitus (DM) is an important cause of chronic wounds and non-traumatic amputation. The prevalence and number of cases of diabetic mellitus are increasing worldwide. Keratinocytes, the outermost layer of the epidermis, play an important role in wound healing. A high glucose environment may disrupt the physiologic functions of keratinocytes, resulting in prolonged inflammation, impaired proliferation, and the migration of keratinocytes and impaired angiogenesis. This review provides an overview of keratinocyte dysfunctions in a high glucose environment. Effective and safe therapeutic approaches for promoting diabetic wound healing can be developed if molecular mechanisms responsible for keratinocyte dysfunction in high glucose environments are elucidated.

Effects of Autophagy Modulators and Dioxin on the Expression of Epidermal Differentiation Proteins on Psoriasis-Like Keratinocytes in vitro and ex vivo

Objective

Psoriasis is a chronic inflammatory skin disorder associated with impairment of epidermal differentiation. Many signaling pathways, including those involved in aryl hydrocarbon receptor (AHR) and autophagy dysfunction, are reportedly associated with the pathogenesis of psoriasis. However, the discrete effects of dioxin via AHR activation or autophagy on the epidermal barrier remain unclear. In the current study, we evaluated the effects of autophagy modulators (chloroquine [CQ] and rapamycin) and the AHR agonist TCDD on the expression of epidermal barrier proteins in psoriasis-like keratinocytes and psoriasis lesional skin tissue culture.

Methods

Polycytokine-stimulated human keratinocytes and psoriasis skin biopsies were treated with TCDD, CQ, or rapamycin, and the expression of keratinocyte differentiation-related factors, such as S100A7, S100A8, HRNR, IVL, FLG, and KRT10, was examined by Western blotting or quantitative-polymerase chain reaction.

Results

TCDD upregulated S100A7 and S100A8 expression in polycytokine-stimulated HaCaT cells compared to that in unstimulated cells. CQ decreased HRNR, IVL, and KRT10 mRNA levels, while rapamycin increased HRNR, IVL, and KRT10 mRNA levels in HaCaT cells relative to that in unstimulated cells. Co-treatment with CQ reversed TCDD-induced elevation in FLG, HRNR, and IVL mRNA expression. In psoriasis skin tissue, TCDD induced the upregulation of HRNR, IVL, S100A7, and S100A8 compared with that in normal skin. In ex vivo cultures treated with CQ, IVL expression in psoriasis skin tissue was repressed compared to that in normal skin tissue.

Conclusion

Our data suggest that autophagy modulation or AHR activation affects processes involved in epidermal differentiation and relates to the pathogenesis of chronic inflammatory skin diseases with skin barrier abnormalities such as psoriasis.

Deletion of hypoxia-inducible factor prolyl 4-hydroxylase 2 in FoxD1-lineage mesenchymal cells leads to congenital truncal alopecia

Hypoxia-inducible factors (HIFs) induce numerous genes regulating oxygen homeostasis. As oxygen sensors of the cells, the HIF prolyl 4-hydroxylases (HIF-P4Hs) regulate the stability of HIFs in an oxygen-dependent manner. During hair follicle (HF) morphogenesis and cycling, the location of dermal papilla (DP) alternates between the dermis and hypodermis and results in varying oxygen levels for the DP cells. These cells are known to express hypoxia-inducible genes, but the role of the hypoxia response pathway in HF development and homeostasis has not been studied. Using conditional gene targeting and analysis of hair morphogenesis, we show here that lack of Hif-p4h-2 in Forkhead box D1 (FoxD1)-lineage mesodermal cells interferes with the normal HF development in mice. FoxD1-lineage cells were found to be mainly mesenchymal cells located in the dermis of truncal skin, including those cells composing the DP of HFs. We found that upon Hif-p4h-2 inactivation, HF development was disturbed during the first catagen leading to formation of epithelial-lined HF cysts filled by unorganized keratins, which eventually manifested as truncal alopecia. Furthermore, the depletion of Hif-p4h-2 led to HIF stabilization and dysregulation of multiple genes involved in keratin formation, HF differentiation, and HIF, transforming growth factor β (TGF-β), and Notch signaling. We hypothesize that the failure of HF cycling is likely to be mechanistically caused by disruption of the interplay of the HIF, TGF-β, and Notch pathways. In summary, we show here for the first time that HIF-P4H-2 function in FoxD1-lineage cells is essential for the normal development and homeostasis of HFs.

MiR-30a-5p Alters Epidermal Terminal Differentiation during Aging by Regulating BNIP3L/NIX-Dependent Mitophagy

Chronological aging is characterized by an alteration in the genes' regulatory network. In human skin, epidermal keratinocytes fail to differentiate properly with aging, leading to the weakening of the epidermal function. MiR-30a is particularly overexpressed with epidermal aging, but the downstream molecular mechanisms are still uncovered. The aim of this study was to decipher the effects of miR-30a overexpression in the human epidermis, with a focus on keratinocyte differentiation. We formally identified the mitophagy receptor BNIP3L as a direct target of miR-30a. Using a 3D organotypic model of reconstructed human epidermis overexpressing miR-30a, we observed a strong reduction in BNIP3L expression in the granular layer. In human epidermal sections of skin biopsies from donors of different ages, we observed a similar pattern of BNIP3L decreasing with aging. Moreover, human primary keratinocytes undergoing differentiation in vitro also showed a decreased expression of BNIP3L with age, together with a retention of mitochondria. Moreover, aging is associated with altered mitochondrial metabolism in primary keratinocytes, including decreased ATP-linked respiration. Thus, miR-30a is a negative regulator of programmed mitophagy during keratinocytes terminal differentiation, impairing epidermal homeostasis with aging.

Mitoptosis, Twenty Years After

In 1999 V. P. Skulachev proposed the term "mitoptosis" to refer to the programmed elimination of mitochondria in living cells. According to the initial thought, mitoptosis serves to protect cells from malfunctioning of the damaged mitochondria. At the same time, a new mechanism of the complete mitochondria elimination was found under the conditions of massive mitochondrial damage associated with oxidative stress. In this experimental model, mitochondrial cluster formation in the perinuclear region leads to the formation of "mitoptotic body" surrounded by a single-layer membrane and subsequent release of mitochondria from the cell. Later, it was found that mitoptosis plays an important role in various normal and pathological processes that are not necessarily associated with the mitochondrial damage. It was found that mitoptosis takes place during cell differentiation, self-maintenance of hematopoietic stem cells, metabolic remodelling, and elimination of the paternal mitochondria in organisms with the maternal inheritance of the mitochondrial DNA. Moreover, the associated with mitoptosis release of mitochondrial components into the blood may be involved in the transmission of signals between cells, but also leads to the development of inflammatory and autoimmune diseases. Mitoptosis can be attributed to the asymmetric inheritance of mitochondria in the division of yeast and some animal cells, when the defective mitochondria are transferred to one of the newly formed cells. Finally, a specific form of mitoptosis appears to be selective elimination of mitochondria with deleterious mutations in whole follicular ovarian cells in mammals. During formation of the primary follicle, the mitochondrial DNA copy number is significantly reduced. After division, the cells that receive predominantly mitochondria with deleterious mutations in their mtDNA die, thereby reducing the likelihood of transmission of these mutations to offspring. Further study of the mechanisms of mitoptosis in normal and pathological conditions is important both for understanding the processes of development and aging, and for designing therapeutic approaches for inflammatory, neurodegenerative and other diseases.

NIX initiates mitochondrial fragmentation via DRP1 to drive epidermal differentiation

The epidermis regenerates continually to maintain a protective barrier at the body’s surface composed of differentiating keratinocytes. Maturation of this stratified tissue requires that keratinocytes undergo wholesale organelle degradation upon reaching the outermost tissue layers to form compacted, anucleate cells. Through live imaging of organotypic cultures of human epidermis, we find that regulated breakdown of mitochondria is critical for epidermal development. Keratinocytes in the upper layers initiate mitochondrial fragmentation, depolarization, and acidification upon upregulating the mitochondrion-tethered autophagy receptor NIX. Depleting NIX compromises epidermal maturation and impairs mitochondrial elimination, whereas ectopic NIX expression accelerates keratinocyte differentiation and induces premature mitochondrial fragmentation via the guanosine triphosphatase (GTPase) DRP1. We further demonstrate that inhibiting DRP1 blocks NIX-mediated mitochondrial breakdown and disrupts epidermal development. Our findings establish mitochondrial degradation as a key step in terminal keratinocyte differentiation and define a pathway operating via the mitophagy receptor NIX in concert with DRP1 to drive epidermal morphogenesis.

Using live microscopy of human organotypic epidermis, Simpson et al. demonstrate how keratinocytes degrade their mitochondria in the upper tissue layers during their final stage of differentiation. By upregulating expression of the mitophagy receptor NIX, keratinocytes initiate DRP1- dependent mitochondrial fragmentation, a process critical for epidermal tissue maturation.

Autophagy Declines with Premature Skin Aging resulting in Dynamic Alterations in Skin Pigmentation and Epidermal Differentiation

Autophagy is a membrane traffic system that provides sustainable degradation of cellular components for homeostasis, and is thus considered to promote health and longevity, though its activity declines with aging. The present findings show deterioration of autophagy in association with premature skin aging. Autophagy flux was successfully determined in skin tissues, which demonstrated significantly decreased autophagy in hyperpigmented skin such as that seen in senile lentigo. Furthermore, an exacerbated decline in autophagy was confirmed in xerotic hyperpigmentation areas, accompanied by severe dehydration and a barrier defect, which showed correlations with skin physiological conditions. The enhancement of autophagy in skin ex vivo ameliorated skin integrity, including pigmentation and epidermal differentiation. The present results indicate that the restoration of autophagy can contribute to improving premature skin aging by various intrinsic and extrinsic factors via the normalization of protein homeostasis.

Cornification of nail keratinocytes requires autophagy for bulk degradation of intracellular proteins while sparing components of the cytoskeleton

Epidermal keratinocytes undergo cornification to form the cellular building blocks of hard skin appendages such as nails and the protective layer on the surface of the skin. Cornification requires the cross-linking of structural proteins and the removal of other cellular components to form mechanically rigid and inert corneocytes. Autophagy has been proposed to contribute to this intracellular remodelling process, but its molecular targets in keratinocytes, if any, have remained elusive. Here, we deleted the essential autophagy factor Atg7 in K14-positive epithelia of mice and determined by proteomics the impact of this deletion on the abundance of individual proteins in cornified nails. The genetic suppression of autophagy in keratinocytes resulted in a significant increase in the number of proteins that survived cornification and in alterations of their abundance in the nail proteome. A broad range of enzymes and other non-structural proteins were elevated whereas the amounts of cytoskeletal proteins of the keratin and keratin-associated protein families, cytolinker proteins and desmosomal proteins were either unaltered or decreased in nails of mice lacking epithelial autophagy. Among the various types of non-cytoskeletal proteins, the subunits of the proteasome and of the TRiC/CCT chaperonin were most strongly elevated in mutant nails, indicating a particularly important role of autophagy in removing these large protein complexes during normal cornification. Taken together, the results of this study suggest that autophagy is active during nail keratinocyte cornification and its substrate specificity depends on the accessibility of proteins outside of the cytoskeleton and their presence in large complexes.

Live imaging of alterations in cellular morphology and organelles during cornification using an epidermal equivalent model

The stratum corneum plays a crucial role in epidermal barrier function. Various changes occur in granular cells at the uppermost stratum granulosum during cornification. To understand the temporal details of this process, we visualized the cell shape and organelles of cornifying keratinocytes in a living human epidermal equivalent model. Three-dimensional time-lapse imaging with a two-photon microscope revealed that the granular cells did not simply flatten but first temporarily expanded in thickness just before flattening during cornification. Moreover, before expansion, intracellular vesicles abruptly stopped moving, and mitochondria were depolarized. When mitochondrial morphology and quantity were assessed, granular cells with fewer, mostly punctate mitochondria tended to transition to corneocytes. Several minutes after flattening, DNA leakage from the nucleus was visualized. We also observed extension of the cell-flattening time induced by the suppression of filaggrin expression. Overall, we successfully visualized the time-course of cornification, which describes temporal relationships between alterations in the transition from granular cells to corneocytes.

Epidermal and Dermal Hallmarks of Photoaging are Prevented by Treatment with Night Serum Containing Melatonin, Bakuchiol, and Ascorbyl Tetraisopalmitate: In Vitro and Ex Vivo Studies

INTRODUCTION

Photoaging is a complex process that is chiefly the result of oxidative stress caused by ultraviolet (UV)-generated reactive oxygen species. To counter this process, we developed a 3-in-1 night facial serum (3-in-1 NFS) containing a combination of direct and indirect antioxidants and polyphenols that is designed to attenuate UV-generated free radicals and stimulate dermal protein synthesis. In clinical trials 3-in-1 NFS improved the appearance of photoaged skin. In this study we sought to identify some of the main histologic changes responsible for this.

METHODS

We performed an immunolabeling analysis of some of the salient epidermal and dermal proteins in 3-in-1 NFS-treated primary epidermal keratinocytes (HEKs) and dermal fibroblasts (HDFs) in vitro, and in UV-exposed skin explants ex vivo. Numbers of apoptotic sunburn cells following exposure of 3-in-1 NFS-treated skin explants to UV radiation were also determined.

RESULTS

We demonstrate that 3-in-1 NFS increases levels of filaggrin and aquaporin 3 in HEKs, and levels of collagen I and collagen III in HDFs in vitro. Levels of precursor procollagen type I and tropoelastin were increased in ex vivo skin explants. Numbers of apoptotic sunburn cells were significantly reduced in UV-exposed skin explants. These effects were only observed with the combination of ingredients in 3-in-1 NFS, suggesting that they have a synergistic effect on photoaged skin biology.

CONCLUSION

Our results show that some of the histological hallmarks of photoaging are improved with the use of 3-in-1 NFS.

Involvement of autophagy in hypoxia-BNIP3 signaling to promote epidermal keratinocyte migration

BNIP3 is an atypical BH3-only member of the Bcl-2 family with pro-death, pro-autophagic, and cytoprotective functions, depending on the type of stress and cellular context. Recently, we demonstrated that BNIP3 stimulates the migration of epidermal keratinocytes under hypoxia. In the present study found that autophagy and BNIP3 expression were concomitantly elevated in the migrating epidermis during wound healing in a hypoxia-dependent manner. Inhibition of autophagy through lysosome-specific chemicals (CQ and BafA1) or Atg5-targeted small-interfering RNAs greatly attenuated the hypoxia-induced cell migration, and knockdown of BNIP3 in keratinocytes significantly suppressed hypoxia-induced autophagy activation and cell migration, suggesting a positive role of BNIP3-induced autophagy in keratinocyte migration. Furthermore, these results indicated that the accumulation of reactive oxygen species (ROS) by hypoxia triggered the activation of p38 and JNK mitogen-activated protein kinase (MAPK) in human immortalized keratinocyte HaCaT cells. In turn, activated p38 and JNK MAPK mediated the activation of BNIP3-induced autophagy and the enhancement of keratinocyte migration. These data revealed a previously unknown mechanism that BNIP3-induced autophagy occurs through hypoxia-induced ROS-mediated p38 and JNK MAPK activation and supports the migration of epidermal keratinocytes during wound healing.

High Glucose Suppresses Keratinocyte Migration Through the Inhibition of p38 MAPK/Autophagy Pathway

Wound healing is delayed frequently in patients with diabetes. Proper keratinocyte migration is an essential step during re-epithelialization. Impaired keratinocyte migration is a critical underlying factor responsible for the deficiency of diabetic wound healing, which is mainly attributed to the hyperglycemic state. However, the underlying mechanisms remain largely unknown. Previously, we demonstrated a marked activation of p38/mitogen-activated protein kinase (MAPK) pathway in the regenerated migrating epidermis, which in turn promoted keratinocyte migration. In the present study, we find that p38/MAPK pathway is downregulated and accompanied by inactivation of autophagy under high glucose (HG) environment. In addition, we demonstrate that inactivation of p38/MAPK and autophagy result in the inhibition of keratinocyte migration under HG environment, and the activating p38/MAPK by MKK6(Glu) overexpression rescues cell migration through an autophagy-dependent way. Moreover, diabetic wound epidermis shows a significant inhibition of p38/MAPK and autophagy. Targeting these dysfunctions may provide novel therapeutic approaches.

The neuroprotective mechanism of 2-arachidonoylglycerol 2-AG against non-caspase-dependent apoptosis in mice hippocampal neurons following MCAO

OBJECTIVE

In this study, the neuroprotective mechanism of 2-arachidonoylglycerol 2-AG against non-caspase-dependent apoptosis in mice hippocampal neurons following MCAO was investigated.

METHOD

One hundred and fifty healthy clean male C57BL/6 mice were randomly divided into 3 groups: sham group, model group and 2-AG treatment group, 50 mice in each group. A modified Zea Longa method was used to establish a model of middle cerebral artery occlusion (MCAO) in mice. The apoptosis rate and mitochondrial membrane potential of hippocampal nerve cells were measured by flow cytometry. The mRNA expressions of AIF, Endo G and BNIP3 in hippocampal tissues were determined by qPCR. Western blot was used to determine the protein expressions of AIF, Endo G and BNIP3 in the mitochondria of hippocampal tissue.

RESULTS

The apoptosis rate of hippocampal neurons in the group treated with 2-AG was significantly lower than that of the model (P<0.01), which indicated that 2-AG could inhibit the apoptosis of hippocampal neurons induced by MCAO. However, the mitochondrial membrane potential of hippocampal neurons in the group treated with 2-AG was significantly higher than that of the model (P<0.01), indicating that 2-AG could improve the mitochondrial membrane potential of hippocampal neurons in MCAO mice. Real-time quantitative PCR (qPCR) showed that 2-AG could inhibit the gene expressions of AIF, Endo G and BNIP3 in hippocampal tissues. Western blot results showed that 2-AG could inhibit the secretions of AIF, Endo G and BNIP3 into cytoplasm in mitochondria.

CONCLUSION

Endocannabinoids 2-AG had a protective effect on neurons injury, and the mechanism was possibly associated with the protection of the brain nerve cells in the hippocampus and the integrity of the mitochondrial function. Endocannabinoids 2-AG may inhibit the non-caspase-dependent apoptosis pathway, so as to exert its nerve protective effect.

Autophagy in malnutrition-associated dermatoses

Malnutrition-associated dermatoses including necrolytic migratory erythema (NME) and pellagra share common clinicopathological features; in particular, necrolytic changes in the upper epidermis. Here, we report the involvement of autophagy in the development of necrolysis in three patients with malnutrition-associated dermatoses. First, we examined an autophagy-specific molecule, microtubule-associated protein light chain 3 (LC3), using a monoclonal antibody. LC3 was strongly expressed in the granular layers of the active border, and less intensely observed in the perilesional areas. Little LC3 staining or only background levels were observed in control skin diseases including atopic dermatitis (n = 4), psoriasis vulgaris (n = 3), basal cell carcinoma with amyloid deposits (n = 3) and squamous cell carcinoma (n = 3). Electron microscopic observations revealed the presence of autophagosome-like structures in the necrolytic areas. No apoptotic signals were observed in the necrolytic lesion using the terminal deoxynucleotidyl transferase dUTP nick end labeling method. Epidermal Langerhans cells determined by anti-CD1a antibody were markedly decreased in number. Our observations suggest the possibility that malnutrition-associated necrolysis, as exemplified by NME and pellagra, may be induced by autophagy.

Role of Fibroblast Growth Factor Receptor 2b in the Cross Talk between Autophagy and Differentiation: Involvement of Jun N-Terminal Protein Kinase Signaling

Fibroblast growth factor receptor 2b (FGFR2b) is a receptor tyrosine kinase expressed exclusively in epithelial cells. We previously demonstrated that FGFR2b induces autophagy and that this process is required for the triggering of FGFR2b-mediated early differentiation of keratinocytes. However, the molecular mechanisms regulating this interplay remain to be elucidated. Since we have also recently shown that Jun N-terminal protein kinase 1 (JNK1) signaling is involved in FGFR2b-induced autophagy and a possible role of the JNK pathway in epidermal differentiation has been suggested (though it is still debated), we investigated here the cross talk between FGFR2b-mediated autophagy and differentiation, focusing on the downstream JNK signaling. Biochemical, molecular, and immunofluorescence approaches in 2-dimensional (2-D) keratinocyte cultures and three-dimensional (3-D) organotypic skin equivalents confirmed that FGFR2b overexpression increased both autophagy and early differentiation. The use of FGFR2b substrate inhibitors and the silencing of JNK1 highlighted that this signaling is required not only for autophagy but also for the triggering of early differentiation. In contrast, the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway did not appear to be involved in the two processes, and AKT signaling, whose activation contributes to the FGFR2b-mediated onset of keratinocyte differentiation, was not required for the triggering of autophagy. Overall, our results point to JNK1 as a signaling hub that regulates the interplay between FGFR2b-induced autophagy and differentiation.

MicroRNAs-103/107 Regulate Autophagy in the Epidermis

We have shown that microRNAs-103 and -107 (miRs-103/107) positively regulate end-stage autophagy by ensuring dynamin activity in cultured keratinocytes. Most work in end-stage autophagy has been conducted using in vitro model systems. In vivo regulation of end-stage autophagy in epidermis remains unknown. Here, we used antagomirs to subcutaneously knock down miR-107 in the skin; conversely, we delivered miR-107 mimic subcutaneously via in vivo transfection to increase this miR. We found that antagomir-107 treatment in epidermis: (i) depleted endogenous miR-107; (ii) increased GFP-LC3 puncta in epidermal basal layers of GFP-LC3 transgenic mice, indicative of an accumulation of autophagosomes; (iii) inhibited LC3 turnover and increased p62, suggesting an inhibition of autophagy flux; and (iv) increased phosphorylated dynamin (p-dynamin, an inactive form), a key enzyme in end-stage autophagy. Conversely, miR-107 mimic treatment in mouse epidermis: decreased GFP-LC3 puncta in basal layer, as well as p62 protein levels; and diminished p-dynamin, indicative of activation of this enzyme. In human epidermal keratinocytes, antagos-103/107 cause the formation of large vacuoles and an increase in p-dynamin, which can be rescued by inhibition of protein kinase C pathway. Collectively, these results suggest that the miR-103/107 family has a critical role in regulating end-stage autophagy in mouse epidermis via PLD1/2-protein kinase C-dynamin pathway.

The signaling involved in autophagy machinery in keratinocytes and therapeutic approaches for skin diseases

Autophagy is responsible for the lysosomal degradation of proteins, organelles, microorganisms and exogenous particles. Epidermis primarily consists of keratinocytes which functions as an extremely important barrier. Investigation on autophagy in keratinocytes has been continuously renewing, but is not so systematic due to the complexity of the autophagy machinery. Here we reviewed recent studies on the autophagy in keratinocyte with a focus on interplay between autophagy machinery and keratinocytes biology, and novel autophagy regulators identified in keratinocytes. In this review, we discussed the roles of autophagy in apoptosis, differentiation, immune response, survival and melanin metabolism, trying to reveal the possible involvement of autophagy in skin aging, skin disorders and skin color formation. Since autophagy routinely plays a double-edged sword role in various conditions, its functions in skin homeostasis and potential application as a therapeutic target for skin diseases remains to be clarified. Furthermore, more investigations are needed on optimizing designed strategies to inhibit or enhance autophagy for clinical efficacy.

Characterization of a new pathway that activates lumisterol in vivo to biologically active hydroxylumisterols

Using LC/qTOF-MS we detected lumisterol, 20-hydroxylumisterol, 22-hydroxylumisterol, 24-hydroxylumisterol, 20,22-dihydroxylumisterol, pregnalumisterol, 17-hydroxypregnalumisterol and 17,20-dihydroxypregnalumisterol in human serum and epidermis, and the porcine adrenal gland. The hydroxylumisterols inhibited proliferation of human skin cells in a cell type-dependent fashion with predominant effects on epidermal keratinocytes. They also inhibited melanoma proliferation in both monolayer and soft agar. 20-Hydroxylumisterol stimulated the expression of several genes, including those associated with keratinocyte differentiation and antioxidative responses, while inhibiting the expression of others including RORA and RORC. Molecular modeling and studies on VDRE-transcriptional activity excludes action through the genomic site of the VDR. However, their favorable interactions with the A-pocket in conjunction with VDR translocation studies suggest they may act on this non-genomic VDR site. Inhibition of RORα and RORγ transactivation activities in a Tet-on CHO cell reporter system, RORα co-activator assays and inhibition of (RORE)-LUC reporter activity in skin cells, in conjunction with molecular modeling, identified RORα and RORγ as excellent receptor candidates for the hydroxylumisterols. Thus, we have discovered a new biologically relevant, lumisterogenic pathway, the metabolites of which display biological activity. This opens a new area of endocrine research on the effects of the hydroxylumisterols on different pathways in different cells and the mechanisms involved.

BNIP3 upregulation via stimulation of ERK and JNK activity is required for the protection of keratinocytes from UVB-induced apoptosis

The human skin has an important role in barrier function. Ultraviolet rays (UV) from sunlight exposure can cause cell apoptosis in the skin epidermis, resulting in the disruption of the barrier. Previously, we have demonstrated that BNIP3 stimulates autophagy in epidermal keratinocytes and has a protective effect in these cells upon UVB irradiation. In this study, we found that the accumulation of reactive oxygen species (ROS) by UVB irradiation was sufficient to trigger the activation of JNK and ERK mitogen-activated protein kinase (MAPK) in human primary epidermal keratinocytes. In turn, activated JNK and ERK MAPK mediated the upregulation of BNIP3 expression. Treatment with an antioxidant reagent or a specific inhibitor of MAPK, U0126, and a JNK inhibitor significantly attenuated the expression of BNIP3 triggered by UVB, followed by the induction of cell death by apoptosis. Furthermore, UVB-induced apoptosis was significantly stimulated by chloroquine or bafilomycin A1, an inhibitor of autophagy. Moreover, BNIP3 was required for the degradation of dysfunctional mitochondria upon UVB irradiation. These data clearly indicated that BNIP3-induced autophagy, which occurs via UVB-generated ROS-mediated JNK and ERK MAPK activation, has a crucial role in the protection of the skin epidermis against UVB irradiation.

Constitutive Autophagy and Nucleophagy during Epidermal Differentiation

Epidermal keratinocytes migrate through the epidermis up to the granular layer where, on terminal differentiation, they progressively lose organelles and convert into anucleate cells or corneocytes. Our report explores the role of autophagy in ensuring epidermal function providing the first comprehensive profile of autophagy marker expression in developing epidermis. We show that autophagy is constitutively active in the epidermal granular layer where by electron microscopy we identified double-membrane autophagosomes. We demonstrate that differentiating keratinocytes undergo a selective form of nucleophagy characterized by accumulation of microtubule-associated protein light chain 3/lysosomal-associated membrane protein 2/p62 positive autolysosomes. These perinuclear vesicles displayed positivity for histone interacting protein, heterochromatin protein 1α, and localize in proximity with Lamin A and B1 accumulation, whereas in newborn mice and adult human skin, we report LC3 puncta coincident with misshaped nuclei within the granular layer. This process relies on autophagy integrity as confirmed by lack of nucleophagy in differentiating keratinocytes depleted from WD repeat domain phosphoinositide interacting 1 or Unc-51 like autophagy activating kinase 1. Final validation into a skin disease model showed that impaired autophagy contributes to the pathogenesis of psoriasis. Lack of LC3 expression in psoriatic skin lesions correlates with parakeratosis and deregulated expression or location of most of the autophagic markers. Our findings may have implications and improve treatment options for patients with epidermal barrier defects.

Nucleophagy: A New Look at Past Observations

Keratinization of the stratum corneum involves a highly choreographed sequence of events in which granular cells lose their nuclei and become desiccated corneocytes. Akinduro et al. detail the molecular machinery underlying removal of the nucleus (nucleophagy) during the final stages of keratinization. They provide evidence that nucleophagy is induced when the keratinocytes differentiate and that failure in the initiation of nucleophagy is associated with parakeratosis.

HPV16 E5 deregulates the autophagic process in human keratinocytes

Autophagy plays key roles during host defense against pathogens, but viruses have evolved strategies to block the process or to exploit it for replication and successful infection. The E5 oncoprotein of human papillomavirus type 16 (HPV16 E5) perturbs epithelial homeostasis down-regulating the expression of the keratinocyte growth factor receptor (KGFR/FGFR2b), whose signaling induces autophagy. Here we investigated the possible effects of 16E5 on autophagy in human keratinocytes expressing the viral protein. The 16E5 presence strongly inhibited the autophagic process, while forced expression and activation of KGFR counteracted this effect, demonstrating that the viral protein and the receptor exert opposite and interplaying roles not only on epithelial differentiation, but also in the control of autophagy. In W12 cells, silencing of the 16E5 gene in the context of the viral full length genome confirmed its role on autophagy inhibition. Finally, molecular approaches showed that the viral protein interferes with the transcriptional regulation of autophagy also through the impairment of p53 function, indicating that 16E5 uses parallel mechanisms for autophagy impairment. Overall our results further support the hypothesis that a transcriptional crosstalk among 16E5 and KGFR might be the crucial molecular driver of epithelial deregulation during early steps of HPV infection and transformation.

Establishment of Two Mouse Models for CEDNIK Syndrome Reveals the Pivotal Role of SNAP29 in Epidermal Differentiation

Loss-of-function mutations in the synaptosomal-associated protein 29 (SNAP29) gene cause the cerebral dysgenesis, neuropathy, ichthyosis, and keratoderma syndrome. In this study, we created total (Snap29(-/-)) as well as keratinocyte-specific (Snap29(fl/fl)/K14-Cre) Snap29 knockout mice. Both mutant mice exhibited a congenital distinct ichthyotic phenotype resulting in neonatal lethality. Mutant mice revealed acanthosis and hyperkeratosis as well as abnormal keratinocyte differentiation and increased proliferation. In addition, the epidermal barrier was severely impaired. These results indicate an essential role of SNAP29 in epidermal differentiation and barrier formation. Markedly decreased deposition of lamellar body contents in mutant mice epidermis and the observation of malformed lamellar bodies indicate severe impairments in lamellar body function due to the Snap29 knockout. We also found increased microtubule associated protein-1 light chain 3, isoform B-II levels, unchanged p62/SQSTM1 protein amounts, and strong induction of the endoplasmic reticulum stress marker C/EBP homologous protein in mutant mice. This emphasizes a role of SNAP29 in autophagy and endoplasmic reticulum stress. Our murine models serve as powerful tools for investigating keratinocyte differentiation processes and provide insights into the essential contribution of SNAP29 to epidermal differentiation.

Gene expression analysis of skin grafts and cultured keratinocytes using synthetic RNA normalization reveals insights into differentiation and growth control

Background

Keratinocytes (KCs) are the most frequent cells in the epidermis, and they are often isolated and cultured in vitro to study the molecular biology of the skin. Cultured primary cells and various immortalized cells have been frequently used as skin models but their comparability to intact skin has been questioned. Moreover, when analyzing KC transcriptomes, fluctuation of polyA+ RNA content during the KCs’ lifecycle has been omitted.

Results

We performed STRT RNA sequencing on 10 ng samples of total RNA from three different sample types: i) epidermal tissue (split-thickness skin grafts), ii) cultured primary KCs, and iii) HaCaT cell line. We observed significant variation in cellular polyA+ RNA content between tissue and cell culture samples of KCs. The use of synthetic RNAs and SAMstrt in normalization enabled comparison of gene expression levels in the highly heterogenous samples and facilitated discovery of differences between the tissue samples and cultured cells. The transcriptome analysis sensitively revealed genes involved in KC differentiation in skin grafts and cell cycle regulation related genes in cultured KCs and emphasized the fluctuation of transcription factors and non-coding RNAs associated to sample types.

Conclusions

The epidermal keratinocytes derived from tissue and cell culture samples showed highly different polyA+ RNA contents. The use of SAMstrt and synthetic RNA based normalization allowed the comparison between tissue and cell culture samples and thus proved to be valuable tools for RNA-seq analysis with translational approach. Transciptomics revealed clear difference both between tissue and cell culture samples and between primary KCs and immortalized HaCaT cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1671-5) contains supplementary material, which is available to authorized users.

Impairment of hypoxia-induced HIF-1α signaling in keratinocytes and fibroblasts by sulfur mustard is counteracted by a selective PHD-2 inhibitor

Skin exposure to sulfur mustard (SM) provokes long-term complications in wound healing. Similar to chronic wounds, SM-induced skin lesions are associated with low levels of oxygen in the wound tissue. Normally, skin cells respond to hypoxia by stabilization of the transcription factor hypoxia-inducible factor 1 alpha (HIF-1α). HIF-1α modulates expression of genes including VEGFA, BNIP3, and MMP2 that control processes such as angiogenesis, growth, and extracellular proteolysis essential for proper wound healing. The results of our studies revealed that exposure of primary normal human epidermal keratinocytes (NHEK) and primary normal human dermal fibroblasts (NHDF) to SM significantly impaired hypoxia-induced HIF-1α stabilization and target gene expression in these cells. Addition of a selective inhibitor of the oxygen-sensitive prolyl hydroxylase domain-containing protein 2 (PHD-2), IOX2, fully recovered HIF-1α stability, nuclear translocation, and target gene expression in NHEK and NHDF. Moreover, functional studies using a scratch wound assay demonstrated that the application of IOX2 efficiently counteracted SM-mediated deficiencies in monolayer regeneration under hypoxic conditions in NHEK and NHDF. Our findings describe a pathomechanism by which SM negatively affects hypoxia-stimulated HIF-1α signaling in keratinocytes and fibroblasts and thus possibly contributes to delayed wound healing in SM-injured patients that could be treated with PHD-2 inhibitors.

Analysis of genome-wide copy number variations in Chinese indigenous and western pig breeds by 60 K SNP genotyping arrays

Copy number variations (CNVs) represent a substantial source of structural variants in mammals and contribute to both normal phenotypic variability and disease susceptibility. Although low-resolution CNV maps are produced in many domestic animals, and several reports have been published about the CNVs of porcine genome, the differences between Chinese and western pigs still remain to be elucidated. In this study, we used Porcine SNP60 BeadChip and PennCNV algorithm to perform a genome-wide CNV detection in 302 individuals from six Chinese indigenous breeds (Tongcheng, Laiwu, Luchuan, Bama, Wuzhishan and Ningxiang pigs), three western breeds (Yorkshire, Landrace and Duroc) and one hybrid (Tongcheng×Duroc). A total of 348 CNV Regions (CNVRs) across genome were identified, covering 150.49 Mb of the pig genome or 6.14% of the autosomal genome sequence. In these CNVRs, 213 CNVRs were found to exist only in the six Chinese indigenous breeds, and 60 CNVRs only in the three western breeds. The characters of CNVs in four Chinese normal size breeds (Luchuan, Tongcheng and Laiwu pigs) and two minipig breeds (Bama and Wuzhishan pigs) were also analyzed in this study. Functional annotation suggested that these CNVRs possess a great variety of molecular function and may play important roles in phenotypic and production traits between Chinese and western breeds. Our results are important complementary to the CNV map in pig genome, which provide new information about the diversity of Chinese and western pig breeds, and facilitate further research on porcine genome CNVs.