Thymic stromal lymphopoietin induces adipose loss through sebum hypersecretion

5-Aminolevulinic Acid (5-ALA) Plays an Important Role in the Function of Innate Immune Cells

5-aminolevulinic acid (5-ALA) is an amino acid essential for the synthesis of heme, which is important for various cellular functions, including the mitochondrial electron transport chain. We previously established heterozygous knockout mice (Alas1+/-) for 5-ALA synthase 1 (ALAS1), the rate-limiting enzyme for 5-ALA synthesis, and reported that the mice developed non-obese insulin-resistant diabetes. In the present study, we used these mice to analyze the role of 5-ALA in the immune system. Using a lipopolysaccharide (LPS)-induced septic shock model, Alas1+/- mice showed reduced mortality compared to wild-type (WT) mice. In this model experiment, the plasma concentration of inflammatory cytokines such as tumor necrosis factor α (TNFα) and interleukin-6 (IL-6), and the chemokine monocyte chemoattractant protein-1 (MCP1) decreased in Alas1+/- mice compared that in WT mice, and inflammatory cell infiltration into the peritoneal cavity was also decreased. In ex vivo experiments, exogenous 5-ALA pretreatment enhanced LPS-induced TNFα and IL-6 production from peripheral blood leukocytes of Alas1+/- mice. Additionally, 5-ALA pretreatment enhanced LPS-induced activation of inflammatory cytokine genes in innate immune cells. Interestingly, the phagocytosis and reactive oxygen species (ROS) producing abilities of neutrophils were clearly hampered in Alas1+/- mice compared to WT mice, but after 2 weeks of 5-ALA administration to Alas1+/- mice, both abilities were significantly recovered up to the level in WT mice. These results reveal that 5-ALA is essential for the function of innate immune cells. Because 5-ALA can be supplemented orally, it has the potential to be used as a drug to restore innate immune function.

Standardized Assessment of Energy Excretion in Healthy Adults: A Novel Methodology

BACKGROUND

Accurate monitoring of energy balance is essential for effective weight management, but the role of energy excretion is often neglected.

OBJECTIVE

This study aimed to develop and validate a standardized method for assessing energy excretion using dye-labeled meal replacement bars with consistent and stable ingredients.

METHODS

We utilized baseline data from a registered cross-over trial involving twelve healthy adults (7 females, 5 males) with a body mass index of 18-25 kg/m2. Participants consumed dye-labeled meal replacement bars under a standardized protocol, and their feces and urine were collected for energy measurement using bomb calorimetry. Correlation analysis was conducted to explore associations between these variables.

RESULTS

The total energy excretion rate averaged 10.48% (SD 2.56%) of energy intake, with fecal and urinary excretion accounting for 7.95% (SD 2.67%) and 2.52% (SD 0.6%), respectively. Significant individual variability was observed, with total energy excretion ranging from 6.34% to 15.07%, resulting in a maximum difference of 209.64 kcal per day. Fecal energy excretion was positively correlated with fecal wet weight and energy density, while urinary energy excretion was associated with digestible energy.

CONCLUSIONS

This study presents a standardized and efficient methodology for accurately assessing energy excretion using dye-labeled replacement bars. The findings underscore the notable yet variable role of energy excretion in energy balance and suggest that this method could enhance the precision of future energy balance studies.

TRIAL REGISTRATION

Registered at chictr.org.cn as ChiCTR2000038421.

Thymic stromal lymphopoietin modulates T cell response and improves cardiac repair post-myocardial infarction

Background

The inflammatory response is associated with cardiac repair and ventricular remodeling after myocardial infarction (MI). The key inflammation regulatory factor thymic stromal lymphopoietin (TSLP) plays a critical role in various diseases. However, its role in cardiac repair after MI remains uncertain. In this study, we elucidated the biological function and mechanism of action of TSLP in cardiac repair and ventricular remodeling following MI.

Method and Result

Wild-type and TSLP receptor (TSLPR)-knockout (Crlf2-/-) mice underwent MI induction via ligation of the left anterior descending artery. TSLP expression was upregulated in the infarcted heart, with a peak observed on day 7 post-MI. TSLP expression was enriched in the cardiomyocytes of infarcted hearts and the highest expression of TSLPR was observed in dendritic cells. Crlf2-/- mice exhibited reduced survival and worsened cardiac function, increased interstitial fibrosis and cardiomyocyte cross-sectional area, and reduced CD31+ staining, with no change in the proportion of apoptotic cardiomyocytes within the border zone. Mechanistically, reduced Treg cell counts but increased myeloid cell infiltration and an increased ratio of Ly6Chigh/Ly6Clow monocyte were observed in the ani hearts of Crlf2-/- mice. Further, TSLP regulated CD4+ T cell activation and proliferation at baseline and after MI, with a greater impact on Treg cells than on conventional T cells. RNA-seq analysis revealed significant downregulation of genes involved in T cell activation and TCR signaling in the infarcted heart of Crlf2-/- mice compared with their WT counterparts.

Conclusion

Collectively, our data indicate a critical role for TSLP in facilitating cardiac repair and conferring protection against MI, primarily through regulating CD4+ T cell responses, which may provide a potential novel therapeutic approach for managing heart failure after MI.

CD4+ T Cells Occupy Perivascular and Perifollicular Niches in Healthy Human Skin

Regulatory T cells (Tregs) are specialised T lymphocytes that sit at the nexus of immune regulation and tissue repair. While it is appreciated that a substantial number of Tregs are present in healthy human skin, less is known about their microanatomic spatial localisation. Knowledge about the specialised niches that Tregs occupy may aid in rational drug development to treat dermatologic diseases. Thus, we performed multiplexed immunohistochemistry for CD4 and FOXP3 (the lineage-defining transcription factor of Tregs) on healthy skin sections obtained from eight different cutaneous sites, and quantified Tregs and Tcon in distinct regions. We found that Tregs (CD4+ FOXP3+) comprised roughly 20% of CD4+ T cells in skin and that Tregs and T-conventional cells (Tcon; CD4+ Foxp3-) are enriched in follicularly dense skin and show preferential accumulation in perivascular and perifollicular niches in the upper dermis. Additionally, male skin shows a significant increase in the numbers of Tregs and Tcon, while female skin shows a higher Tcon:Treg ratio. We also find that the frequency of skin Tregs declines over time. Overall, we conclude that the upper dermal perivascular region is a niche that supports the accumulation of CD4+ T cells in steady-state human skin.

A sensitive red/far-red photoswitch for controllable gene therapy in mouse models of metabolic diseases

Red light optogenetic systems are in high demand for the precise control of gene expression for gene- and cell-based therapies. Here, we report a red/far-red light-inducible photoswitch (REDLIP) system based on the chimeric photosensory protein FnBphP (Fn-REDLIP) or PnBphP (Pn-REDLIP) and their interaction partner LDB3, which enables efficient dynamic regulation of gene expression with a timescale of seconds without exogenous administration of a chromophore in mammals. We use the REDLIP system to establish the REDLIP-mediated CRISPR-dCas9 (REDLIPcas) system, enabling optogenetic activation of endogenous target genes in mammalian cells and mice. The REDLIP system is small enough to support packaging into adeno-associated viruses (AAVs), facilitating its therapeutic application. Demonstrating its capacity to treat metabolic diseases, we show that an AAV-delivered Fn-REDLIP system achieved optogenetic control of insulin expression to effectively lower blood glucose levels in type 1 diabetes model mice and control an anti-obesity therapeutic protein (thymic stromal lymphopoietin, TSLP) to reduce body weight in obesity model mice. REDLIP is a compact and sensitive optogenetic tool for reversible and non-invasive control that can facilitate basic biological and biomedical research.

A digital CRISPR-dCas9-based gene remodeling biocomputer programmed by dietary compounds in mammals

CRISPR-dCas9 (dead Cas9 protein) technology, combined with chemical molecules and light-triggered genetic switches, offers customizable control over gene perturbation. However, these simple ON/OFF switches cannot precisely determine the sophisticated perturbation process. Here, we developed a resveratrol and protocatechuic acid-programmed CRISPR-mediated gene remodeling biocomputer (REPACRISPR) for conditional endogenous transcriptional regulation of genes in vitro and in vivo. Two REPACRISPR variants, REPACRISPRi and REPACRISPRa, were designed for the logic control of gene inhibition and activation, respectively. We successfully demonstrated the digital computations of single or multiplexed endogenous gene transcription by using REPACRISPRa. We also established mathematical models to predict the dose-responsive transcriptional levels of a target endogenous gene controlled by REPACRISPRa. Moreover, high levels of endogenous gene activation in mice mediated by the AND logic gate demonstrated computational control of CRISPR-dCas9-based epigenome remodeling in mice. This CRISPR-based biocomputer expands the synthetic biology toolbox and can potentially advance gene-based precision medicine. A record of this paper's transparent peer review process is included in the supplemental information.

Mineralized aggregates based on native protein phase transition for non-destructive diagnosis of seborrheic skin by surface-enhanced Raman spectroscopy

The non-homeostasis of sebum secretion by the sebaceous glands in a complicated microenvironment dramatically impacts the skin health of many people in the world. However, the complexity and hydrophobicity of sebum mean a lack of diagnostic tools, which makes it challenging to determine the reason behind cortical imbalances. Herein, a biomimetic mineralized aggregates (PTL@Au and PTB@Au) strategy has been proposed, which could obtain molecular information about sebum by surface-enhanced Raman spectroscopy (SERS). The breaking of disulfide bonds leads to changes in hydrogen bonding, which transform the natural protein into amyloid-like phase transition protein with β-sheets. It provides sites for the nucleation and crystallization of gold nanocrystals to build mineralized aggregates. The mineralized aggregates show robust adhesion stability at the interfaces of different materials through hydrogen bonding and electrostatic interactions. The stabilization, hydrophobicity (contact angle: 134°), and optical transmission (75%) of the structure could result in superior SERS performance for sebum analysis. It should be noted that this enables the sebum detection of clinical samples while ensuring safety. Such generalized bionic mineralization construction and diagnosis methods also serve as an advanced paradigm for a range of biomedical applications.

Dietary lipid is largely deposited in skin and rapidly affects insulating properties

Skin has been shown to be a regulatory hub for energy expenditure and metabolism: mutations of skin lipid metabolism enzymes can change the rate of thermogenesis and susceptibility to diet-induced obesity. However, little is known about the physiological basis for this function. Here we show that the thermal properties of skin are highly reactive to diet: within three days, a high fat diet reduces heat transfer through skin. In contrast, a dietary manipulation that prevents obesity accelerates energy loss through skins. We found that skin was the largest target in a mouse body for dietary fat delivery, and that dietary triglyceride was assimilated both by epidermis and by dermal white adipose tissue. Skin from mice calorie-restricted for 3 weeks did not take up circulating lipids and showed a highly depleted stratum corneum. Dietary triglyceride acyl groups persist in skin for weeks after feeding. Using multi-modal lipid profiling, we have implicated both keratinocytes and sebocytes in the altered lipids which correlate with thermal function. In response to high fat feeding, wax diesters and ceramides accumulate, and triglycerides become more saturated. In contrast, in response to the dramatic loss of adipose tissue that accompanies restriction of the branched chain amino acid isoleucine, skin becomes more heat-permeable, resisting changes induced by Western diet feeding, with a signature of depleted signaling lipids. We propose that skin should be routinely included in physiological studies of lipid metabolism, given the size of the skin lipid reservoir and its adaptable functionality.

The role of cell-cell and cell-matrix junctional complexes in sebaceous gland homeostasis and differentiation

Sebaceous glands (SG) are essential for maintaining skin integrity, as their lipid-rich secretion (sebum) lubricates and protects the epidermis and hairs. In addition, these glands have an emerging role in immunomodulation and may affect whole-body energy metabolism, besides being an appealing model for research in topics as lipogenesis, stem cell biology and tumorigenesis. In spite of the increasing interest in studying SGs pathophysiology, sebocyte cell-cell and cell-matrix adhesion processes have been only superficially examined, and never in a systematic way. This is regrettable considering the key role of cellular adhesion in general, the specific expression pattern of indivdual junctional complexes, and the reports of structural changes in SGs after altered expression of adhesion-relevant proteins. Here, we review the available information on structural and functional aspects of cell-cell and cell-matrix junctions in sebocytes, and how these processes change under pathological conditions. This information will contribute for better understanding sebocyte differentiation and sebum secretion, and may provide hints for novel therapeutic strategies for skin diseases.

Immune infiltration analysis based on pyroptosis-related gene in metabolic dysfunction-associated fatty liver disease

Introduction

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a prevalent chronic disease that can involve pyroptosis. The primary objective of this study was to conduct a thorough and comprehensive analysis the pyroptosis-related genes in MAFLD.

Methods

We identified pyroptosis-related differentially expressed genes (PRDEGs) in both healthy individuals and MAFLD patients. Using various bioinformatic approaches, we conducted an immune infiltration analysis from multiple perspectives.

Results

A total of 20 pyroptosis-related LASSO genes were obtained, and 10 hub genes were used to do immune infiltration analysis. The hub genes were utilized in the construction of interaction networks between mRNA-miRNA and mRNA-TF. Immune characteristics analysis revealed multiple immune cell types significantly related to PRDEG expression, particularly genes HSP90AA1, TSLP, CDK9, and BRD4.

Conclusion

Pyroptosis-related immune infiltration might be a mechanism of MAFLD progression and offers a research direction for potential treatment techniques.

Thymic stromal lymphopoietin induces IL-4/IL-13 from T cells to promote sebum secretion and adipose loss

BACKGROUND

The cytokine TSLP promotes type 2 immune responses and can induce adipose loss by stimulating lipid loss from the skin through sebum secretion by sebaceous glands, which enhances the skin barrier. However, the mechanism by which TSLP upregulates sebaceous gland function is unknown.

OBJECTIVES

This study investigated the mechanism by which TSLP stimulates sebum secretion and adipose loss.

METHODS

RNA-sequencing analysis was performed on sebaceous glands isolated by laser capture microdissection and single-cell RNA-sequencing analysis was performed on sorted skin T cells. Sebocyte function was analyzed by histological analysis and sebum secretion in vivo and by measuring lipogenesis and proliferation in vitro.

RESULTS

This study found that TSLP sequentially stimulated the expression of lipogenesis genes followed by cell death genes in sebaceous glands to induce holocrine secretion of sebum. TSLP did not affect sebaceous gland activity directly. Rather, single-cell RNA-sequencing revealed that TSLP recruited distinct T-cell clusters that produce IL-4 and IL-13, which were necessary for TSLP-induced adipose loss and sebum secretion. Moreover, IL-13 was sufficient to cause sebum secretion and adipose loss in vivo and to induce lipogenesis and proliferation of a human sebocyte cell line in vitro.

CONCLUSIONS

This study proposes that TSLP stimulates T cells to deliver IL-4 and IL-13 to sebaceous glands, which enhances sebaceous gland function, turnover, and subsequent adipose loss.

A spatial portrait of the human sebaceous gland transcriptional program

Sebaceous glands (SG) and their oily secretion (sebum) are indispensable for maintaining skin structure and function, and their deregulation causes skin disorders including but not limited to acne. Recent studies also indicate that sebum may have important immunomodulatory activities and may influence whole-body energy metabolism. However, the progressive transcriptional changes of sebocytes that lead to sebum production have never been characterized in detail. Here, we exploited the high cellular resolution provided by sebaceous hyperplasia and integrated spatial transcriptomics, pseudo time analysis, RNA velocity, and functional enrichment to map the landscape of sebaceous differentiation. Our results were validated by comparison with published SG transcriptome data and further corroborated by assessing the protein expression pattern of a subset of the transcripts in the public repository Human Protein Atlas. Departing from four sebocyte differentiation stages generated by unsupervised clustering, we demonstrate consecutive modulation of cellular functions associable with specific gene sets, from cell proliferation and oxidative phosphorylation via lipid synthesis to cell death. Both validation methods confirmed the biological significance of our results. Our report is complemented by a freely available and browsable online tool. Our data provide the first high-resolution spatial portrait of the SG transcriptional landscape and deliver starting points for experimentally assessing novel candidate molecules for regulating SG homeostasis in health and disease.

TRPV3 promotes sebocyte inflammation via transcriptional modulating TLR2 in acne

Acne is a common chronic inflammatory disease of the pilosebaceous unit. Transient receptor potential vanilloid 3 (TRPV3) is an ion channel that is involved in inflammatory dermatosis development. However, the involvement of TRPV3 in acne-related inflammation remains unclear. Here, we used acne-like mice and human sebocytes to examine the role of TRPV3 in the development of acne. We found that TRPV3 expression increased in the skin lesions of Propionibacterium acnes (P. acnes)-injected acne-like mice and the facial sebaceous glands (SGs) of acne patients. TRPV3 promoted inflammatory cytokines and chemokines secretion in human sebocytes and led to neutrophil infiltration surrounding the SGs in acne lesions, further exacerbating sebaceous inflammation and participating in acne development. Mechanistically, TRPV3 enhanced TLR2 level by promoting transcriptional factor phosphorylated-FOS-like antigen-1 (p-FOSL1) expression and its binding to the TLR2 promoter, leading to TLR2 upregulation and downstream NF-κB signaling activation. Genetic or pharmacological inhibition of TRPV3 both alleviated acne-like skin inflammation in mice via the TLR2-NF-κB axis. Thus, our study revealed the critical role of TRPV3 in sebaceous inflammation and indicated its potential as an acne therapeutic target.

The microbiota and T cells non-genetically modulate inherited phenotypes transgenerationally

The host-microbiota relationship has evolved to shape mammalian physiology, including immunity, metabolism, and development. Germ-free models are widely used to study microbial effects on host processes such as immunity. Here, we find that both germ-free and T cell-deficient mice exhibit a robust sebum secretion defect persisting across multiple generations despite microbial colonization and T cell repletion. These phenotypes are inherited by progeny conceived during in vitro fertilization using germ-free sperm and eggs, demonstrating that non-genetic information in the gametes is required for microbial-dependent phenotypic transmission. Accordingly, gene expression in early embryos derived from gametes from germ-free or T cell-deficient mice is strikingly and similarly altered. Our findings demonstrate that microbial- and immune-dependent regulation of non-genetic information in the gametes can transmit inherited phenotypes transgenerationally in mice. This mechanism could rapidly generate phenotypic diversity to enhance host adaptation to environmental perturbations.

A case of type 2 diabetes mellitus with weight gain and worsening of glycemic management after tezepelumab administration for severe bronchial asthma

Some cases of bronchial asthma are refractory to conventional therapies. As the pathogenesis of bronchial asthma has been clarified, new treatments, such as bronchial thermoplasty and biological drugs, have been developed. Tezepelumab, an anti-thymic stromal lymphopoietin antibody, has been reported to inhibit the exacerbation of severe asthma; however, its adverse effects on glucose metabolism have not yet been reported. We encountered a case of weight gain and worsening glycemic management in a patient with type 2 diabetes and refractory bronchial asthma after the initiation of tezepelumab treatment. It has been reported that the overexpression of thymic stromal lymphopoietin in mice resulted in an enhanced release of free fatty acids from adipose tissues and the liver; thus, the administration of anti-thymic stromal lymphopoietin antibodies in the present case might have caused obesity, fatty liver and lower glucose tolerance.

AAV-delivered muscone-induced transgene system for treating chronic diseases in mice via inhalation

Gene therapies provide treatment options for many diseases, but the safe and long-term control of therapeutic transgene expression remains a primary issue for clinical applications. Here, we develop a muscone-induced transgene system packaged into adeno-associated virus (AAV) vectors (AAVMUSE) based on a G protein-coupled murine olfactory receptor (MOR215-1) and a synthetic cAMP-responsive promoter (PCRE). Upon exposure to the trigger, muscone binds to MOR215-1 and activates the cAMP signaling pathway to initiate transgene expression. AAVMUSE enables remote, muscone dose- and exposure-time-dependent control of luciferase expression in the livers or lungs of mice for at least 20 weeks. Moreover, we apply this AAVMUSE to treat two chronic inflammatory diseases: nonalcoholic fatty liver disease (NAFLD) and allergic asthma, showing that inhalation of muscone-after only one injection of AAVMUSE-can achieve long-term controllable expression of therapeutic proteins (ΔhFGF21 or ΔmIL-4). Our odorant-molecule-controlled system can advance gene-based precision therapies for human diseases.

Effects of energy loads on energy and nutrient absorption rates and gut microbiome in humans: A randomized crossover trial

OBJECTIVE

This study aimed to determine the effects of different energy loads on the gut microbiota composition and the rates of energy and nutrient excretion via feces and urine.

METHODS

A randomized crossover dietary intervention study was conducted with three dietary conditions: overfeeding (OF), control (CON), and underfeeding (UF). Ten healthy men were subjected to each condition for 8 days (4 days and 3 nights in nonlaboratory and laboratory settings each). The effects of dietary conditions on energy excretion rates via feces and urine were assessed using a bomb calorimeter.

RESULTS

Short-term energy loads dynamically altered the gut microbiota at the α-diversity (Shannon index), phylum, and genus levels (p < 0.05). Energy excretion rates via urine and urine plus feces decreased under OF more than under CON (urine -0.7%; p < 0.001, urine plus feces -1.9%; p = 0.049) and UF (urine -1.0%; p < 0.001, urine plus feces -2.1%; p = 0.031). However, energy excretion rates via feces did not differ between conditions.

CONCLUSIONS

Although short-term overfeeding dynamically altered the gut microbiota composition, the energy excretion rate via feces was unaffected. Energy excretion rates via urine and urine plus feces were lower under OF than under CON and UF conditions.

Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration

Hair follicles, which are connected to sebaceous glands in the skin, undergo cyclic periods of regeneration, degeneration, and rest throughout adult life in mammals. The crucial function of hair follicle stem cells is to maintain these hair growth cycles. Another vital aspect is the activity of melanocyte stem cells, which differentiate into melanin-producing melanocytes, contributing to skin and hair pigmentation. Sebaceous gland stem cells also have a pivotal role in maintaining the skin barrier by regenerating mature sebocytes. These stem cells are maintained in a specialized microenvironment or niche and are regulated by internal and external signals, determining their dynamic behaviors in homeostasis and hair follicle regeneration. The activity of these stem cells is tightly controlled by various factors secreted by the niche components around the hair follicles, as well as immune-mediated damage signals, aging, metabolic status, and stress. In this study, we review these diverse stem cell regulatory and related molecular mechanisms of hair regeneration and disease conditions. Molecular insights would provide new perspectives on the disease mechanisms as well as hair and skin disorder treatment.

CD36-SREBP1 Axis Mediates TSLP Production in Obesity-Exacerbated Atopic Dermatitis

Obesity is associated with an increased risk of atopic dermatitis (AD) and may accelerate its development. Keratinocyte dysfunction has been observed in obesity-related skin diseases, including psoriasis and acanthosis nigricans, but is not fully understood in AD. In this study, we found that high-fat diet-induced obesity exacerbated AD-like dermatitis in mice, with elevated inflammatory molecules and increased CD36-SREBP1-related fatty acid accumulation in the lesional skin. Blocking CD36 or SREBP1 with chemical inhibitors effectively alleviated AD-like inflammation, decreased fatty acid accumulation, and downregulated TSLP expression in obese calcipotriol (MC903)-treated mice. Moreover, palmitic acid treatment induced TSLP overexpression in keratinocytes through the activation of the CD36-SREBP1 signaling pathway. The chromatin immunoprecipitation assay further revealed increased binding of SREBP1 to the TSLP promoter region. Our findings provide compelling evidence that obesity triggers the activation of the CD36-SREBP1-TSLP axis in keratinocytes, leading to epidermal lipid disorders and the aggravation of AD-like inflammation. By targeting CD36 or SREBP1, future combination therapies or modified treatment strategies could be developed to help manage patients with both obesity and AD.

Skin-derived TSLP stimulates skin migratory dendritic cells to promote the expansion of regulatory T cells

Therapeutic strategies that enhance regulatory T (Treg) cell proliferation or suppressive function hold promise for the treatment of autoimmune and inflammatory diseases. We previously reported that the topical application of the vitamin D3 analog MC903 systemically expands Treg cells by stimulating the production of thymic stromal lymphopoietin (TSLP) from the skin. Using mice lacking TSLP receptor expression by dendritic cells (DCs), we hereby show that TSLP receptor signaling in DCs is required for this Treg expansion in vivo. Topical MC903 treatment of ear skin selectively increased the number of migratory DCs in skin-draining lymph nodes (LNs) and upregulated their expression of co-stimulatory molecules. Accordingly, DCs isolated from skin-draining LNs but not mesenteric LNs or spleen of MC903-treated mice showed an enhanced ability to promote Treg proliferation, which was driven by co-stimulatory signals through CD80/CD86 and OX40 ligand. Among the DC subsets in the skin-draining LNs of MC903-treated mice, migratory XCR1- CD11b+ type 2 and XCR1- CD11b- double negative conventional DCs promoted Treg expansion. Together, these data demonstrate that vitamin D3 stimulation of skin induces TSLP expression, which stimulates skin migratory DCs to expand Treg cells. Thus, topical MC903 treatment could represent a convenient strategy to treat inflammatory disorders by engaging this pathway.

Distinct mechanisms for sebaceous gland self-renewal and regeneration provide durability in response to injury

Sebaceous glands (SGs) release oils that protect our skin, but how these glands respond to injury has not been previously examined. Here, we report that SGs are largely self-renewed by dedicated stem cell pools during homeostasis. Using targeted single-cell RNA sequencing, we uncovered both direct and indirect paths by which resident SG progenitors ordinarily differentiate into sebocytes, including transit through a Krt5+PPARγ+ transitional basal cell state. Upon skin injury, however, SG progenitors depart their niche, reepithelialize the wound, and are replaced by hair-follicle-derived stem cells. Furthermore, following targeted genetic ablation of >99% of SGs from dorsal skin, these glands unexpectedly regenerate within weeks. This regenerative process is mediated by alternative stem cells originating from the hair follicle bulge, is dependent upon FGFR2 signaling, and can be accelerated by inducing hair growth. Altogether, our studies demonstrate that stem cell plasticity promotes SG durability following injury.

Biomimetic Gland Models with Engineered Stratagems

As extensively distributed tissues throughout the human body, glands play a critical role in various physiological processes. Therefore, the construction of biomimetic gland models in vitro has aroused great interest in multiple disciplines. In the biological field, the researchers focus on optimizing the cell sources and culture techniques to reconstruct the specific structures and functions of glands, such as the emergence of organoid technology. From the perspective of biomedical engineering, the generation of biomimetic gland models depends on the combination of engineered scaffolds and microfluidics, to mimic the in vivo environment of glandular tissues. These engineered stratagems endowed gland models with more biomimetic features, as well as a wide range of application prospects. In this review, we first describe the biomimetic strategies for constructing different in vitro gland models, focusing on the role of microfluidics in promoting the structure and function development of biomimetic glands. After summarizing several common in vitro models of endocrine and exocrine glands, the applications of gland models in disease modelling, drug screening, regenerative medicine, and personalized medicine are enumerated. Finally, we conclude the current challenges and our perspective of these biomimetic gland models.

Physiological protection against weight gain: evidence from overfeeding studies and future directions

Body weight is under physiological regulation. When body fat mass decreases, a series of responses are triggered to promote weight regain by increasing food intake and decreasing energy expenditure. Analogous, in response to experimental overfeeding, excessive weight gain is counteracted by a reduction in food intake and possibly by an increase in energy expenditure. While low blood leptin and other hormones defend against weight loss, the signals that oppose overfeeding-induced fat mass expansion are still unknown. In this article, we discuss insights gained from overfeeding interventions in humans and intragastric overfeeding studies in rodents. We summarize the knowledge on the relative contributions of energy intake, energy expenditure and energy excretion to the physiological defence against overfeeding-induced weight gain. Furthermore, we explore literature supporting the existence of unidentified endocrine and non-endocrine pathways that defend against weight gain. Finally, we discuss the physiological drivers of constitutional thinness and suggest that overfeeding of individuals with constitutional thinness represents a gateway to understand the physiology of weight gain resistance in humans. Experimental overfeeding, combined with modern multi-omics techniques, has the potential to unveil the long-sought signalling pathways that protect against weight gain. Discovering these mechanisms could give rise to new treatments for obesity. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

TMEM232 promotes the inflammatory response in atopic dermatitis via the nuclear factor-κB and signal transducer and activator of transcription 3 signalling pathways

BACKGROUND

Our group previously found that the transmembrane protein 232 (TMEM232) gene was associated with atopic dermatitis (AD) by genome-wide association study and fine mapping study. However, its function is unclear so far.

OBJECTIVES

To investigate the roles and mechanisms of TMEM232 in AD.

METHODS

The expression of TMEM232 was investigated in skin lesions of patients with AD, the MC903-induced AD mouse model, human primary keratinocytes and immortalized human keratinocyte cell line (HaCaT) cells stimulated with different inflammatory factors. The role of TMEM232 in AD was analysed in HaCaT cells and Tmem232 knockout (Tmem232-/-) mice. Tmem232-specific small interfering RNA (siRNA) was used to evaluate its therapeutic potential in the AD mouse model.

RESULTS

The expression of TMEM232 was significantly increased in skin lesions of patients with AD, the MC903-induced AD mouse model and human primary keratinocytes and HaCaT cells stimulated with different inflammatory factors compared with controls. In the presence of MC903, Tmem232-/- mice exhibited significantly reduced dermatitis severity, mast-cell infiltration in the back, and expression of T-helper (Th)1 and Th2-related inflammatory factors in skin tissue compared with wild-type mice. In vitro and in vivo experiments further showed that upregulation of TMEM232 in AD exacerbated the inflammation response through activating the pathway of nuclear factor-κB and signal transducer and activator of transcription (STAT) 3, and was regulated by the interleukin-4/STAT6 axis, which formed a self-amplifying loop. Finally, topical application of Tmem232 siRNA markedly ameliorated AD-like lesions in the AD model.

CONCLUSIONS

This study is the first to outline the function of TMEM232. It is involved in regulating inflammation in AD and may be a potential target for AD treatment.

Ovol1/2 loss-induced epidermal defects elicit skin immune activation and alter global metabolism

Skin epidermis constitutes the outer permeability barrier that protects the body from dehydration, heat loss, and myriad external assaults. Mechanisms that maintain barrier integrity in constantly challenged adult skin and how epidermal dysregulation shapes the local immune microenvironment and whole-body metabolism remain poorly understood. Here, we demonstrate that inducible and simultaneous ablation of transcription factor-encoding Ovol1 and Ovol2 in adult epidermis results in barrier dysregulation through impacting epithelial-mesenchymal plasticity and inflammatory gene expression. We find that aberrant skin immune activation then ensues, featuring Langerhans cell mobilization and T cell responses, and leading to elevated levels of secreted inflammatory factors in circulation. Finally, we identify failure to gain body weight and accumulate body fat as long-term consequences of epidermal-specific Ovol1/2 loss and show that these global metabolic changes along with the skin barrier/immune defects are partially rescued by immunosuppressant dexamethasone. Collectively, our study reveals key regulators of adult barrier maintenance and suggests a causal connection between epidermal dysregulation and whole-body metabolism that is in part mediated through aberrant immune activation.

Distinct mechanisms for sebaceous gland self-renewal and regeneration provide durability in response to injury

Sebaceous glands (SGs) release oils that protect our skin, but how these glands respond to injury has not been previously examined. Here, we report that SGs are largely self-renewed by dedicated stem cell pools during homeostasis. Using targeted single cell RNA-sequencing, we uncovered both direct and indirect paths by which these resident SG progenitors ordinarily differentiate into sebocytes, including transit through a PPARγ+Krt5+ transitional cell state. Upon skin injury, however, SG progenitors depart their niche, reepithelialize the wound, and are replaced by hair follicle-derived stem cells. Furthermore, following targeted genetic ablation of >99% of SGs from dorsal skin, these glands unexpectedly regenerate within weeks. This regenerative process is mediated by alternative stem cells originating from the hair follicle bulge, is dependent upon FGFR signaling, and can be accelerated by inducing hair growth. Altogether, our studies demonstrate that stem cell plasticity promotes SG durability following injury.

The microbiota and immune system non-genetically affect offspring phenotypes transgenerationally

The host-microbiota relationship has evolved to shape mammalian processes, including immunity, metabolism, and development 1-3 . Host phenotypes change in direct response to microbial exposures by the individual. Here we show that the microbiota induces phenotypic change not only in the individual but also in their succeeding generations of progeny. We found that germ-free mice exhibit a robust sebum secretion defect and transcriptional changes in various organs, persisting across multiple generations despite microbial colonization and breeding with conventional mice. Host-microbe interactions could be involved in this process, since T cell-deficient mice, which display defective sebum secretion 4 , also transgenerationally transmit their phenotype to progeny. These phenotypes are inherited by progeny conceived during in vitro fertilization using germ-free sperm and eggs, demonstrating that epigenetic information in the gametes is required for phenotypic transmission. Accordingly, small non-coding RNAs that can regulate embryonic gene expression 5 were strikingly and similarly altered in gametes of germ-free and T cell-deficient mice. Thus, we have uncovered a novel mechanism whereby the microbiota and immune system induce phenotypic changes in successive generations of offspring. This epigenetic form of inheritance could be advantageous for host adaptation to environmental perturbation, where phenotypic diversity can be introduced more rapidly than by genetic mutation.

Role of thymic stromal lymphopoietin in allergy and beyond

Thymic stromal lymphopoietin (TSLP) is a pleiotropic cytokine that acts on multiple cell lineages, including dendritic cells, T cells, B cells, neutrophils, mast cells, eosinophils and innate lymphoid cells, affecting their maturation, survival and recruitment. It is best known for its role in promoting type 2 immune responses such as in allergic diseases and, in 2021, a monoclonal antibody targeting TSLP was approved for the treatment of severe asthma. However, it is now clear that TSLP has many other important roles in a variety of settings. Indeed, several genetic variants for TSLP are linked to disease severity, and chromosomal alterations in TSLP are common in certain cancers, indicating important roles of TSLP in disease. In this Review, we discuss recent advances in TSLP biology, highlighting how it regulates the tissue environment not only in allergic disease but also in infectious diseases, inflammatory diseases and cancer. Encouragingly, therapies targeting the TSLP pathway are being actively pursued for several diseases.

Sebaceous immunobiology - skin homeostasis, pathophysiology, coordination of innate immunity and inflammatory response and disease associations

This review presents several aspects of the innovative concept of sebaceous immunobiology, which summarizes the numerous activities of the sebaceous gland including its classical physiological and pathophysiological tasks, namely sebum production and the development of seborrhea and acne. Sebaceous lipids, which represent 90% of the skin surface lipids in adolescents and adults, are markedly involved in the skin barrier function and perifollicular and dermal innate immune processes, leading to inflammatory skin diseases. Innovative experimental techniques using stem cell and sebocyte models have clarified the roles of distinct stem cells in sebaceous gland physiology and sebocyte function control mechanisms. The sebaceous gland represents an integral part of the pilosebaceous unit and its status is connected to hair follicle morphogenesis. Interestingly, professional inflammatory cells contribute to sebocyte differentiation and homeostasis, whereas the regulation of sebaceous gland function by immune cells is antigen-independent. Inflammation is involved in the very earliest differentiation changes of the pilosebaceous unit in acne. Sebocytes behave as potent immune regulators, integrating into the innate immune responses of the skin. Expressing inflammatory mediators, sebocytes also contribute to the polarization of cutaneous T cells towards the Th17 phenotype. In addition, the immune response of the perifollicular infiltrate depends on factors produced by the sebaceous glands, mostly sebaceous lipids. Human sebocytes in vitro express functional pattern recognition receptors, which are likely to interact with bacteria in acne pathogenesis. Sex steroids, peroxisome proliferator-activated receptor ligands, neuropeptides, endocannabinoids and a selective apoptotic process contribute to a complex regulation of sebocyte-induced immunological reaction in numerous acquired and congenital skin diseases, including hair diseases and atopic dermatitis.

The physiology of experimental overfeeding in animals

BACKGROUND

Body weight is defended by strong homeostatic forces. Several of the key biological mechanisms that counteract weight loss have been unraveled over the last decades. In contrast, the mechanisms that protect body weight and fat mass from becoming too high remain largely unknown. Understanding this aspect of energy balance regulation holds great promise for curbing the obesity epidemic. Decoding the physiological and molecular pathways that defend against weight gain can be achieved by an intervention referred to as 'experimental overfeeding'.

SCOPE OF THE REVIEW

In this review, we define experimental overfeeding and summarize the studies that have been conducted on animals. This field of research shows that experimental overfeeding induces a potent and prolonged hypophagic response that seems to be conserved across species and mediated by unidentified endocrine factors. In addition, the literature shows that experimental overfeeding can be used to model the development of non-alcoholic steatohepatitis and that forced intragastric infusion of surplus calories lowers survival from infections. Finally, we highlight studies indicating that experimental overfeeding can be employed to study the transgenerational effects of a positive energy balance and how dietary composition and macronutrient content might impact energy homeostasis and obesity development in animals.

MAJOR CONCLUSIONS

Experimental overfeeding of animals is a powerful yet underappreciated method to investigate the defense mechanisms against weight gain. This intervention also represents an alternative approach for studying the pathophysiology of metabolic liver diseases and the links between energy balance and infection biology. Future research in this field could help uncover why humans respond differently to an obesogenic environment and reveal novel pathways with therapeutic potential against obesity and cardiometabolic disorders.

Optimization of the extract from flower of Citrus aurantium L. var. amara Engl. and its inhibition of lipid accumulation

Flower of Citrus aurantium L. var. amara Engl. (CAVA) has been confirmed to have promising anti-obesity effects. However, the regulation of alkaloid extracts from flower of CAVA (Al) on lipid metabolism remain unknown. In this study, Al was optimized by ultrasound-assisted extraction using response surface methodology. The optimal conditions were ultrasonic time 72 min, ethanol concentration 78% and liquid/solid ratio 30 ml/g with the maximum alkaloid yield 5.66%. LC-MS assay indicated that the alkaloid compounds were enriched in Al after optimization. Nine alkaloid compounds were identified in Al by LC-MS assay and stachydrine, caffeine and cathine appeared as the major alkaloid compounds. Bioactivity assay showed that Al treatment significantly increased superoxide dismutase (SOD) activity, and reduced malonaldehyde (MDA) and reactive oxygen species (ROS) levels. Al administration also reversed oleic acid-induced hepatic steatosis in Hep G2 cells by inhibiting the expression of lipogenesis-signaling genes including fatty acid synthase (FAS), peroxisome proliferator-activated receptor subtype γ (PPARγ), uncoupling protein 2 (UCP2), and retinol binding protein (RBP4). However, OA-induced reduction of lipolysis-related gene carnitine palmitoyl transferase 1A (CPT1A) in Hep G2 cells was not improved by Al supplementation. Moreover, the increased SOD activity and decreased MDA and ROS contents were also observed in Caenorhabditis elegans by Al addition. Al intervention exhibited the ability to inhibit lipid accumulation in C. elegans by suppressing expression of lipid metabolism-related genes. These results suggested that the alkaloid extracts from the flower of CAVA showed great potential to regulate lipid metabolism. PRACTICAL APPLICATIONS: The extraction of alkaloid extracts from the flower of CAVA was optimized with a maximum yield of 5.66%. The regulatory effects and mechanisms of Al on lipid metabolism of Hep G2 cells and Caenorhabditis elegans were also investigated. More clinical studies are required to evaluate the potential of using alkaloids from the flower of CAVA as therapeutic agents against lipid metabolic disorders.

Obesity-Mediated Immune Modulation: One Step Forward, (Th)2 Steps Back

Over the past decades, the relationship between the immune system and metabolism has become a major research focus. In this arena of immunometabolism the capacity of adipose tissue to secrete immunomodulatory molecules, including adipokines, within the underlying low-grade inflammation during obesity brought attention to the impact obesity has on the immune system. Adipokines, such as leptin and adiponectin, influence T cell differentiation into different T helper subsets and their activation during immune responses. Furthermore, within the cellular milieu of adipose tissue nutrient availability regulates differentiation and activation of T cells and changes in cellular metabolic pathways. Upon activation, T cells shift from oxidative phosphorylation to oxidative glycolysis, while the differential signaling of the kinase mammalian target of rapamycin (mTOR) and the nuclear receptor PPARγ, amongst others, drive the subsequent T cell differentiation. While the mechanisms leading to a shift from the typical type 2-dominated milieu in lean people to a Th1-biased pro-inflammatory environment during obesity are the subject of extensive research, insights on its impact on peripheral Th2-dominated immune responses become more evident. In this review, we will summarize recent findings of how Th2 cells are metabolically regulated during obesity and malnutrition, and how these states affect local and systemic Th2-biased immune responses.

Alarmin Cytokines as Central Regulators of Cutaneous Immunity

Skin acts as the primary interface between the body and the environment. The skin immune system is composed of a complex network of immune cells and factors that provide the first line of defense against microbial pathogens and environmental insults. Alarmin cytokines mediate an intricate intercellular communication between keratinocytes and immune cells to regulate cutaneous immune responses. Proper functions of the type 2 alarmin cytokines, thymic stromal lymphopoietin (TSLP), interleukin (IL)-25, and IL-33, are paramount to the maintenance of skin homeostasis, and their dysregulation is commonly associated with allergic inflammation. In this review, we discuss recent findings on the complex regulatory network of type 2 alarmin cytokines that control skin immunity and highlight the mechanisms by which these cytokines regulate skin immune responses in host defense, chronic inflammation, and cancer.

Skin immunity: dissecting the complex biology of our body's outer barrier

Our skin contributes critically to health via its role as a barrier tissue, carefully regulating passage of key substrates while also providing defense against exogenous threats. Immunological processes are integral to almost every skin function and paramount to our ability to live symbiotically with skin commensal microbes and other environmental stimuli. While many parallels can be drawn to immunobiology at other mucosal sites, skin immunity demonstrates unique features that relate to its distinct topography, chemical composition and microbial ecology. Here we provide an overview of skin as an immune organ, with reference to the broader context of mucosal immunology. We review paradigms of innate as well as adaptive immune function and highlight how skin-specific structures such as hair follicles and sebaceous glands interact and contribute to these processes. Finally, we highlight for the mucosal immunology community a few emerging areas of interest for the skin immunity field moving forward.

Local hyperthermia therapy induces browning of white fat and treats obesity

Beige fat plays key roles in the regulation of systemic energy homeostasis; however, detailed mechanisms and safe strategy for its activation remain elusive. In this study, we discovered that local hyperthermia therapy (LHT) targeting beige fat promoted its activation in humans and mice. LHT achieved using a hydrogel-based photothermal therapy activated beige fat, preventing and treating obesity in mice without adverse effects. HSF1 is required for the effects since HSF1 deficiency blunted the metabolic benefits of LHT. HSF1 regulates Hnrnpa2b1 (A2b1) transcription, leading to increased mRNA stability of key metabolic genes. Importantly, analysis of human association studies followed by functional analysis revealed that the HSF1 gain-of-function variant p.P365T is associated with improved metabolic performance in humans and increased A2b1 transcription in mice and cells. Overall, we demonstrate that LHT offers a promising strategy against obesity by inducing beige fat activation via HSF1-A2B1 transcriptional axis.

Genetic variants affecting chemical mediated skin immunotoxicity

The skin is an immune-competent organ and this function may be impaired by exposure to chemicals, which may ultimately result in immune-mediated dermal disorders. Interindividual variability to chemical-induced skin immune reactions is associated with intrinsic individual characteristics and their genomes. In the last 30-40 years, several genes influencing susceptibility to skin immune reactions were identified. The aim of this review is to provide information regarding common genetic variations affecting skin immunotoxicity. The polymorphisms selected for this review are related to xenobiotic-metabolizing enzymes (CYPA1 and CYPB1 genes), antioxidant defense (GSTM1, GSTT1, and GSTP1 genes), aryl hydrocarbon receptor signaling pathway (AHR and ARNT genes), skin barrier function transepidermal water loss (FLG, CASP14, and SPINK5 genes), inflammation (TNF, IL10, IL6, IL18, IL31, and TSLP genes), major histocompatibility complex (MHC) and neuroendocrine system peptides (CALCA, TRPV1, ACE genes). These genes present variants associated with skin immune responses and diseases, as well as variants associated with protecting skin immune homeostasis following chemical exposure. The molecular and association studies focusing on these genetic variants may elucidate their functional consequences and contribution in the susceptibility to skin immunotoxicity. Providing information on how genetic variations affect the skin immune system may reduce uncertainties in estimating chemical hazards/risks for human health in the future.

Thymic stromal lymphopoietin controls hair growth

Skin tissue regeneration after injury involves the production and integration of signals by stem cells residing in hair follicles (HFSCs). Much remains unknown about how specific wound-derived factors modulate stem cell contribution to hair growth. We demonstrate that thymic stromal lymphopoietin (TSLP) is produced in response to skin injury and during the anagen phase of the hair cycle. Intradermal injection of TSLP promoted wound-induced hair growth (WIHG), whereas neutralizing TSLP receptor (TSLPR) inhibited WIHG. Using flow cytometry and fluorescent immunostaining, we found that TSLP promoted proliferation of transit-amplifying cells. Lgr5^CreER-mediated deletion of Tslpr in HFSCs inhibited both wound-induced and exogenous TSLP-induced hair growth. Our data highlight a novel function for TSLP in regulation of hair follicle activity during homeostasis and wound healing.

One Size Does Not Fit All: Diversifying Immune Function in the Skin

Our body's most outward facing epithelial barrier, the skin, serves as the frontline defense against myriad environmental assailants. To combat these motley threats, the skin has evolved a sophisticated immunological arsenal. In this article, I provide an overview of the skin's complex architecture and the distinct microniches in which immune cells reside and function. I review burgeoning literature on the synchronized immune, stromal, epithelial, and neuronal cell responses in healthy and inflamed skin. Next, I delve into the distinct requirement and mechanisms of long-term immune surveillance and tissue adaptation at the cutaneous frontier. Finally, by discussing the contributions of immune cells in maintaining and restoring tissue integrity, I underscore the constellation of noncanonical functions undertaken by the skin immune system. Just as our skin's immune system benefits from embracing diverse defense strategies, so, too, must we in the immunology research community support disparate perspectives and people from all walks of life.

Lipolysis: cellular mechanisms for lipid mobilization from fat stores

The perception that intracellular lipolysis is a straightforward process that releases fatty acids from fat stores in adipose tissue to generate energy has experienced major revisions over the last two decades. The discovery of new lipolytic enzymes and coregulators, the demonstration that lipophagy and lysosomal lipolysis contribute to the degradation of cellular lipid stores and the characterization of numerous factors and signalling pathways that regulate lipid hydrolysis on transcriptional and post-transcriptional levels have revolutionized our understanding of lipolysis. In this review, we focus on the mechanisms that facilitate intracellular fatty-acid mobilization, drawing on canonical and noncanonical enzymatic pathways. We summarize how intracellular lipolysis affects lipid-mediated signalling, metabolic regulation and energy homeostasis in multiple organs. Finally, we examine how these processes affect pathogenesis and how lipolysis may be targeted to potentially prevent or treat various diseases.