Lactate dehydrogenase activity drives hair follicle stem cell activation. Nat Cell Biol. 2017;19:1017-1026. [PMID: 28812580 PMCID: PMC5657543 DOI: 10.1038/ncb3575]

Small molecule agents against alopecia: Potential targets and related pathways

Alopecia has emerged as a global concern, extending beyond the middle-aged and elderly population and increasingly affecting younger individuals. Despite its growing prevalence, the treatment options and effective drugs for alopecia remain limited due to the incomplete understanding of its underlying mechanisms. Therefore, it is urgent to explore the pathogenesis of alopecia and discover novel and safer therapeutic agents. This review provided an overview of the prevailing clinical disorders of alopecia, and the key pathways and targets involved in hair growth process. Additionally, it discusses FDA-approved drugs and clinical candidates for the treatment of alopecia, and explores small molecule compounds with anti-alopecia potential in the drug discovery phase. These endeavors are expected to provide researchers with valuable scientific insights and practical information for anti-alopecia drug discovery.

Commensal microbe regulation of skin cells in disease

Human skin is the host to various commensal microbes that constitute a substantial microbial community. The reciprocal communication between these microbial inhabitants and host cells upholds both the morphological and functional attributes of the skin layers, contributing indispensably to microenvironmental and tissue homeostasis. Thus, disruption of the skin barrier or imbalances in the microbial communities can exert profound effects on the behavior of host cells. This influence, mediated by the microbes themselves or their metabolites, manifests in diverse outcomes. In this review, we examine existing knowledge to provide insight into the nuanced behavior exhibited by the microbiota on skin cells in health and disease states. These interactions provide insight into potential cellular targets for future microbiota-based therapies to prevent and treat skin disease.

Design, synthesis and biological evaluation of novel cyano-cinnamate derivatives as mitochondrial pyruvate carrier inhibitors

Mitochondrial pyruvate carrier (MPC) inhibitors promote the development of hair follicle stem cells without affecting normal cells, which is promising for the treatment of hair loss. Herein, a series of cyano-cinnamate derivatives of UK-5099 were designed and synthesized. All these new compounds have been tested for their ability to promote cellular lactate production in vitro. Compound 4i (LA content:0.322 μmol/106cell) showed better cellular lactate production activity than UK-5099 (LA content:0.185 μmol/106cell). Further compound 4i was also tested on shaved mice by topical treatment and promoted obvious hair growth on mice.

Coordinating energy metabolism and signaling pathways in epithelial self-renewal and differentiation

Epidermal stem cells (EPSCs) are essential for maintaining skin homeostasis and ensuring a proper wound healing. During in vitro cultivations, EPSCs give rise to transient amplifying progenitors and differentiated cells, finally forming a stratified epithelium that can be grafted onto patients. Epithelial grafts have been used in clinics to cure burned patients or patients affected by genetic diseases. The long-term success of these advanced therapies relies on the presence of a correct amount of EPSCs that guarantees long-term epithelial regeneration. For this reason, a deeper understanding of self-renewal and differentiation is fundamental to fostering their clinical applications.The coordination between energetic metabolism (e.g., glycolysis, tricarboxylic acid cycle, oxidative phosphorylation, and amino acid synthesis pathways), molecular signalling pathways (e.g., p63, YAP, FOXM1, AMPK/mTOR), and epigenetic modifications controls fundamental biological processes as proliferation, self-renewal, and differentiation. This review explores how these signalling and metabolic pathways are interconnected in the epithelial cells, highlighting the distinct metabolic demands and regulatory mechanisms involved in skin physiology.

Mitophagy Promotes Hair Regeneration by Activating Glutathione Metabolism

Mitophagy maintains tissue homeostasis by self-eliminating defective mitochondria through autophagy. How mitophagy regulates stem cell activity during hair regeneration remains unclear. Here, we found that mitophagy promotes the proliferation of hair germ (HG) cells by regulating glutathione (GSH) metabolism. First, single-cell RNA sequencing, mitochondrial probe, transmission electron microscopy, and immunofluorescence staining showed stronger mitochondrial activity and increased mitophagy-related gene especially Prohibitin 2 (Phb2) expression at early-anagen HG compared to the telogen HG. Mitochondrial inner membrane receptor protein PHB2 binds to LC3 to initiate mitophagy. Second, molecular docking and functional studies revealed that PHB2-LC3 activates mitophagy to eliminate the damaged mitochondria in HG. RNA-seq, single-cell metabolism, immunofluorescence staining, and functional validation discovered that LC3 promotes GSH metabolism to supply energy for promoting HG proliferation. Third, transcriptomics analysis and immunofluorescence staining indicated that mitophagy was down-regulated in the aged compared to young-mouse HG. Activating mitophagy and GSH pathways through small-molecule administration can reactivate HG cell proliferation followed by hair regeneration in aged hair follicles. Our findings open up a new avenue for exploring autophagy that promotes hair regeneration and emphasizes the role of the self-elimination effect of mitophagy in controlling the proliferation of HG cells by regulating GSH metabolism.

Ontogeny of Skin Stem Cells and Molecular Underpinnings

Skin stem cells (SCs) play a pivotal role in supporting tissue homeostasis. Several types of SCs are responsible for maintaining and regenerating skin tissue. These include bulge SCs and others residing in the interfollicular epidermis, infundibulum, isthmus, sebaceous glands, and sweat glands. The emergence of skin SCs commences during embryogenesis, where multipotent SCs arise from various precursor populations. These early events set the foundation for the diverse pool of SCs that will reside in the adult skin, ready to respond to tissue repair and regeneration demands. A network of molecular cues regulates skin SC behavior, balancing quiescence, self-renewal, and differentiation. The disruption of this delicate equilibrium can lead to SC exhaustion, impaired wound healing, and pathological conditions such as skin cancer. The present review explores the intricate mechanisms governing the development, activation, and differentiation of skin SCs, shedding light on the molecular signaling pathways that drive their fate decisions and skin homeostasis. Unraveling the complexities of these molecular drivers not only enhances our fundamental knowledge of skin biology but also holds promise for developing novel strategies to modulate skin SC fate for regenerative medicine applications, ultimately benefiting patients with skin disorders and injuries.

Altered neuronal lactate dehydrogenase A expression affects cognition in a sex- and age-dependent manner

The astrocyte-neuron lactate shuttle (ANLS) model posits that astrocyte-generated lactate is transported to neurons to fuel memory processes. However, neurons express high levels of lactate dehydrogenase A (LDHA), the rate-limiting enzyme of lactate production, suggesting a cognitive role for neuronally generated lactate. It was hypothesized that lactate metabolism in neurons is critical for learning and memory. Here transgenic mice were generated to conditionally induce or knockout (KO) the Ldha gene in CNS neurons of adult mice. High pattern separation memory was enhanced by neuronal Ldha induction in young females, and by neuronal Ldha KO in aged females. In older mice, Ldha induction caused cognitive deficits whereas Ldha KO caused cognitive improvements. Genotype-associated cognitive changes were often only observed in one sex or oppositely in males and females. Thus, neuronal-generated lactate has sex-specific cognitive effects, is largely indispensable at young age, and may be detrimental to learning and memory with aging.

Metabolic Recoding of NSUN2-Mediated m5C Modification Promotes the Progression of Colorectal Cancer via the NSUN2/YBX1/m5C-ENO1 Positive Feedback Loop

The RNA modification, 5-methylcytosine (m5C), has recently gained prominence as a pivotal post-transcriptional regulator of gene expression, intricately intertwined with various tumorigenic processes. However, the exact mechanisms governing m5C modifications during the onset and progression of colorectal cancer (CRC) remain unclear. Here, it is determined that the m5C methyltransferase NSUN2 exhibits significantly elevated expression and exerts an oncogenic function in CRC. Mechanistically, NSUN2 and YBX1 are identified as the "writer" and "reader" of ENO1, culminating in the reprogramming of the glucose metabolism and increased production of lactic acid in an m5C-dependent manner. The accumulation of lactic acid derived from CRC cells, in turn, activates the transcription of NSUN2 through histone H3K18 lactylation (H3K18la), and induces the lactylation of NSUN2 at the Lys356 residue (K356), which is crucial for capturing target RNAs. Together, these findings reveal an intriguing positive feedback loop involving the NSUN2/YBX1/m5C-ENO1 signaling axis, thereby bridging the connection between metabolic reprogramming and epigenetic remodeling, which may shed light on the therapeutic potential of combining an NSUN2 inhibitor with immunotherapy for CRC.

Molecular cascade reveals sequential milestones underlying hippocampal neural stem cell development into an adult state

Quiescent adult neural stem cells (NSCs) in the mammalian brain arise from proliferating NSCs during development. Beyond acquisition of quiescence, an adult NSC hallmark, little is known about the process, milestones, and mechanisms underlying the transition of developmental NSCs to an adult NSC state. Here, we performed targeted single-cell RNA-seq analysis to reveal the molecular cascade underlying NSC development in the early postnatal mouse dentate gyrus. We identified two sequential steps, first a transition to quiescence followed by further maturation, each of which involved distinct changes in metabolic gene expression. Direct metabolic analysis uncovered distinct milestones, including an autophagy burst before NSC quiescence acquisition and cellular reactive oxygen species level elevation along NSC maturation. Functionally, autophagy is important for the NSC transition to quiescence during early postnatal development. Together, our study reveals a multi-step process with defined milestones underlying establishment of the adult NSC pool in the mammalian brain.

Activation of the integrated stress response in human hair follicles

Unravelling how energy metabolism and stress responses are regulated in human scalp hair follicles could reveal novel insights into the controls of hair growth and provide new targets to manage hair loss disorders. The Mitochondrial Pyruvate Carrier (MPC) imports pyruvate, produced via glycolysis, into the mitochondria, fuelling the TCA cycle. Previous work has shown that MPC inhibition promotes lactate generation, which activates murine epithelial hair follicle stem cells (eHFSCs). However, by pharmacologically targeting the MPC in short-term human hair follicle ex vivo organ culture experiments using UK-5099, we induced metabolic stress-responsive proliferative arrest throughout the human hair follicle epithelium, including within Keratin 15+ eHFSCs. Through transcriptomics, MPC inhibition was shown to promote a gene expression signature indicative of disrupted FGF, IGF, TGFβ and WNT signalling, mitochondrial dysfunction, and activation of the integrated stress response (ISR), which can arrest cell cycle progression. The ISR, mediated by the transcription factor ATF4, is activated by stressors including amino acid deprivation and ER stress, consistent with MPC inhibition within our model. Using RNAScope, we confirmed the upregulation of both ATF4 and the highly upregulated ATF4-target gene ADM2 on human hair follicle tissue sections in situ. Moreover, treatment with the ISR inhibitor ISRIB attenuated both the upregulation of ADM2 and the proliferative block imposed via MPC inhibition. Together, this work reveals how the human hair follicle, as a complex and metabolically active human tissue system, can dynamically adapt to metabolic stress.

Autophagy Dysfunction: The Kernel of Hair Loss?

Autophagy is recognized as a crucial regulatory process, instrumental in the removal of senescent, dysfunctional, and damaged cells. Within the autophagic process, lysosomal digestion plays a critical role in the elimination of impaired organelles, thus preserving fundamental cellular metabolic functions and various biological processes. Mitophagy, a targeted autophagic process that specifically focuses on mitochondria, is essential for sustaining cellular health and energy balance. Therefore, a deep comprehension of the operational mechanisms and implications of autophagy and mitophagy is vital for disease prevention and treatment. In this context, we examine the role of autophagy and mitophagy during hair follicle cycles, closely scrutinizing their potential association with hair loss. We also conduct a thorough review of the regulatory mechanisms behind autophagy and mitophagy, highlighting their interaction with hair follicle stem cells and dermal papilla cells. In conclusion, we investigate the potential of manipulating autophagy and mitophagy pathways to develop innovative therapeutic strategies for hair loss.

Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices

Lineage plasticity-a state of dual fate expression-is required to release stem cells from their niche constraints and redirect them to tissue compartments where they are most needed. In this work, we found that without resolving lineage plasticity, skin stem cells cannot effectively generate each lineage in vitro nor regrow hair and repair wounded epidermis in vivo. A small-molecule screen unearthed retinoic acid as a critical regulator. Combining high-throughput approaches, cell culture, and in vivo mouse genetics, we dissected its roles in tissue regeneration. We found that retinoic acid is made locally in hair follicle stem cell niches, where its levels determine identity and usage. Our findings have therapeutic implications for hair growth as well as chronic wounds and cancers, where lineage plasticity is unresolved.

Histone lactylation bridges metabolic reprogramming and epigenetic rewiring in driving carcinogenesis: Oncometabolite fuels oncogenic transcription

Heightened lactate production in cancer cells has been linked to various cellular mechanisms such as angiogenesis, hypoxia, macrophage polarisation and T-cell dysfunction. The lactate-induced lactylation of histone lysine residues is noteworthy, as it functions as an epigenetic modification that directly augments gene transcription from chromatin. This epigenetic modification originating from lactate effectively fosters a reliance on transcription, thereby expediting tumour progression and development. Herein, this review explores the correlation between histone lactylation and cancer characteristics, revealing histone lactylation as an innovative epigenetic process that enhances the vulnerability of cells to malignancy. Moreover, it is imperative to acknowledge the paramount importance of acknowledging innovative therapeutic methodologies for proficiently managing cancer by precisely targeting lactate signalling. This comprehensive review illuminates a crucial yet inadequately investigated aspect of histone lactylation, providing valuable insights into its clinical ramifications and prospective therapeutic interventions centred on lactylation.

Glycolysis-Stimulated Esrrb Lactylation Promotes the Self-Renewal and Extraembryonic Endoderm Stem Cell Differentiation of Embryonic Stem Cells

Embryonic stem cells (ESCs) favor glycolysis over oxidative phosphorylation for energy production, and glycolytic metabolism is critical for pluripotency establishment, maintenance, and exit. However, an understanding of how glycolysis regulates the self-renewal and differentiation of ESCs remains elusive. Here, we demonstrated that protein lactylation, regulated by intracellular lactate, contributes to the self-renewal of ESCs. We further showed that Esrrb, an orphan nuclear receptor involved in pluripotency maintenance and extraembryonic endoderm stem cell (XEN) differentiation, is lactylated on K228 and K232. The lactylation of Esrrb enhances its activity in promoting ESC self-renewal in the absence of the LIF and XEN differentiation of ESCs by increasing its binding at target genes. Our studies reveal the importance of protein lactylation in the self-renewal and XEN differentiation of ESCs, and the underlying mechanism of glycolytic metabolism regulating cell fate choice.

Thermodynamically stable ionic liquid microemulsions pioneer pathways for topical delivery and peptide application

Copper peptides (GHK-Cu) are a powerful hair growth promoter with minimal side effects when compared with minoxidil and finasteride; however, challenges in delivering GHK-Cu topically limits their non-invasive applications. Using theoretical calculations and pseudo-ternary phase diagrams, we designed and constructed a thermodynamically stable ionic liquid (IL)-based microemulsion (IL-M), which integrates the high drug solubility of ILs and high skin permeability of microemulsions, thus improving the local delivery of copper peptides by approximately three-fold while retaining their biological function. Experiments in mice validated the effectiveness of our proposed IL-M system. Furthermore, the exact effects of the IL-M system on the expression of growth factors, such as vascular endothelial growth factor, were revealed, and it was found that microemulsion increased the activation of the Wnt/β-catenin signaling pathway, which includes factors involved in hair growth regulation. Overall, the safe and non-invasive IL microemulsion system developed in this study has great potential for the clinical treatment of hair loss.

Local and systemic mechanisms that control the hair follicle stem cell niche

Hair follicles are essential appendages of the mammalian skin, as hair performs vital functions of protection, thermoregulation and sensation. Hair follicles harbour exceptional regenerative abilities as they contain multiple somatic stem cell populations such as hair follicle stem cells (HFSCs) and melanocyte stem cells. Surrounding the stem cells and their progeny, diverse groups of cells and extracellular matrix proteins are organized to form a microenvironment (called 'niche') that serves to promote and maintain the optimal functioning of these stem cell populations. Recent studies have shed light on the intricate nature of the HFSC niche and its crucial role in regulating hair follicle regeneration. In this Review, we describe how the niche serves as a signalling hub, communicating, deciphering and integrating both local signals within the skin and systemic inputs from the body and environment to modulate HFSC activity. We delve into the recent advancements in identifying the cellular and molecular nature of the niche, providing a holistic perspective on its essential functions in hair follicle morphogenesis, regeneration and ageing.

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.

Metabolic regulation of the hallmarks of stem cell biology

Stem cells perform many different functions, each of which requires specific metabolic adaptations. Over the past decades, studies of pluripotent and tissue stem cells have uncovered a range of metabolic preferences and strategies that correlate with or exert control over specific cell states. This review aims to describe the common themes that emerge from the study of stem cell metabolism: (1) metabolic pathways supporting stem cell proliferation, (2) metabolic pathways maintaining stem cell quiescence, (3) metabolic control of cellular stress responses and cell death, (4) metabolic regulation of stem cell identity, and (5) metabolic requirements of the stem cell niche.

An AhR-Ovol1-Id1 regulatory axis in keratinocytes promotes skin homeostasis against atopic dermatitis

Skin is our outer permeability and immune defense barrier against myriad external assaults. Aryl hydrocarbon receptor (AhR) senses environmental factors and regulates barrier robustness and immune homeostasis. AhR agonist is in clinical trial for atopic dermatitis (AD) treatment, but the underlying mechanism of action remains ill-defined. Here we report OVOL1/Ovol1 as a conserved and direct transcriptional target of AhR in epidermal keratinocytes. We show that OVOL1/Ovol1 impacts AhR regulation of keratinocyte gene expression, and Ovol1 deletion in keratinocytes hampers AhR's barrier promotion function and worsens AD-like inflammation. Mechanistically, we identify Ovol1's direct downstream targets genome-wide, and provide in vivo evidence for Id1's critical role in barrier maintenance and disease suppression. Furthermore, our findings reveal an IL-1/dermal γδT cell axis exacerbating both type 2 and type 3 immune responses downstream of barrier perturbation in Ovol1 -deficient AD skin. Finally, we present data suggesting the clinical relevance of OVOL1 and ID1 function in human AD. Our study highlights a keratinocyte-intrinsic AhR-Ovol1-Id1 regulatory axis that promotes both epidermal and immune homeostasis against AD-like inflammation, implicating new therapeutic targets for AD.

The effect of oxygen supply using perfluorocarbon-based nanoemulsions on human hair growth

Hair dermal papilla cells (hDPCs) play a crucial role in hair growth and regeneration, and their function is influenced by nutrient and oxygen supply. A microenvironment with significantly low oxygen (O2) levels, known as anoxic conditions (<0.2%) due to oxygen deficiency, hinders hDPC promotion and retards hair regrowth. Here, a nanoemulsion (NE) based on perfluorooctyl bromide (PFOB), a member of the perfluorocarbon family, is presented to provide a sustainable O2 supply and maintain physical stability in vitro. The PFOB-NE has been shown to continuously release oxygen for 36 h, increasing and maintaining the O2 concentration in the anoxic microenvironment of up to 0.8%. This sustainable O2 supply using PFOB-NE has promoted hDPC growth and also induced a complex cascade of effects. These effects encompass regulation via inhibiting lactate accumulation caused via oxygen deficiency, increasing lactate dehydrogenase activity, and promoting the expression of genes, such as the hypoxia-inducible factor 1 family and NADPH oxidase 4 under anoxic conditions. Sustained O2 supply is shown to enhance human hair organ elongation approximately four times compared to the control under anoxic conditions. In conclusion, the perfluorocarbon-based NE containing oxygen proves to be an important strategic tool for improving hair growth and alleviating hair loss.

Autophagy induces hair follicle stem cell activation and hair follicle regeneration by regulating glycolysis

BACKGROUND

Hair follicle stem cells (HFSCs) typically remain quiescent and are activated only during the transition from telogen to anagen to ensure that the hair follicle enters a new cycle. The metabolic behavior of stem cells in tissues is regulated by macroautophagy/autophagy, and changes in HFSC metabolism directly affect their activation and maintenance. However, the role of autophagy in the regulation of HFSC metabolism and function remains unclear.

METHODS

Back skin samples were obtained from mice at different hair follicle cycle stages, and immunofluorescence staining was used to monitor autophagy in HFSCs. Mouse and human hair follicles were treated with rapamycin (Rapa, an autophagy activator) or 3-methyladenine (3-MA, an autophagy inhibitor). The effects of autophagy on the hair follicle cycle and HFSC were investigated by imaging, cell proliferation staining, and HFSC-specific marker staining. The influence and mechanism of autophagy on HFSC metabolism were explored using RNA sequencing, real-time polymerase chain reaction, immunohistochemical staining, and detection of lactate and glucose concentrations. Finally, the influence of autophagy-induced glycolysis on HFSC and the hair follicle cycle was verified by stem cell characteristics and in vivo functional experiments.

RESULTS

Autophagy in HFSC was highest during the transition from telogen to anagen. Inhibiting autophagy with 3-MA led to early entry into catagen and prolonged telogen, whereas Rapa promoted autophagy and hair growth. Autophagy activated HFSC by increasing the expression and activity of HFSC lactate dehydrogenase (Ldha), thereby transforming HFSC metabolism into glycolysis. Inhibition of Ldha expression counteracted the effects of autophagy.

CONCLUSIONS

Autophagy activated HFSC by promoting the transition from HFSC metabolism to glycolysis, ultimately initiating the hair follicle cycle and promoting hair growth.

Dietary Restriction Delays But Cannot Heal Irradiation-Induced Hair Graying by Preserving Hair Follicle Stem Cells in Quiescence

DNA damage represents one of the cell intrinsic causes of stem cell aging, which leads to differentiation-induced removal of damaged stem cells in skin and blood. Dietary restriction (DR) retards aging across various species, including several strains of laboratory mice. Whether, DR has the potential to ameliorate DNA damage-driven stem cell exhaustion remains incompletely understood. In this study, we show that DR strongly extends the time to hair graying in response to γ-irradiation (ionizing radiation [IR])-induced DNA damage of C57BL/6 J mice. The study shows that DR prolongs resting phase of hair follicles. DR-mediated prolongation of hair follicle stem cell (HFSC) quiescence blocks hair growth and prevents the depletion of HFSCs and ckit+ melanoblasts in response to IR. However, prolongation of HFSC quiescence also correlates with a suppression of DNA repair and cannot prevent melanoblast loss and hair graying in the long run, when hair cycling is reinitiated even after extended periods of time. Altogether, these results support a model indicating that nutrient deprivation can delay but not heal DNA damage-driven extinction of melanoblasts by stalling HFSCs in a prolonged state of quiescence coupled with inhibition of DNA repair. Disconnecting these two types of responses to DR could have the potential to delay stem cell aging.

Molecular mechanisms of cellular metabolic homeostasis in stem cells

Many tissues and organ systems have intrinsic regeneration capabilities that are largely driven and maintained by tissue-resident stem cell populations. In recent years, growing evidence has demonstrated that cellular metabolic homeostasis plays a central role in mediating stem cell fate, tissue regeneration, and homeostasis. Thus, a thorough understanding of the mechanisms that regulate metabolic homeostasis in stem cells may contribute to our knowledge on how tissue homeostasis is maintained and provide novel insights for disease management. In this review, we summarize the known relationship between the regulation of metabolic homeostasis and molecular pathways in stem cells. We also discuss potential targets of metabolic homeostasis in disease therapy and describe the current limitations and future directions in the development of these novel therapeutic targets.

Activation of mitochondrial aldehyde dehydrogenase 2 promotes hair growth in human hair follicles

INTRODUCTION

Hair loss is a common phenomenon associated with various environmental and genetic factors. Mitochondrial dysfunction-induced oxidative stress has been recognized as a crucial determinant of hair follicle (HF) biology. Aldehyde dehydrogenase 2 (ALDH2) mitigates oxidative stress by detoxifying acetaldehyde. This study investigated the potential role of ALDH2 modulation in HF function and hair growth promotion.

OBJECTIVES

To evaluate the effects of ALDH2 activation on oxidative stress in HFs and hair growth promotion.

METHODS

The modulatory role of ALDH2 on HFs was investigated using an ALDH2 activator. ALDH2 expression in human HFs was evaluated through in vitro immunofluorescence staining. Ex vivo HF organ culture was employed to assess hair shaft elongation, while the fluorescence probe 2',7'- dichlorodihydrofluorescein diacetate was utilized to detect reactive oxygen species (ROS). An in vivo mouse model was used to determine whether ALDH2 activation induces anagen.

RESULTS

During the anagen phase, ALDH2 showed significantly higher intensity than that in the telogen phase, and its expression was primarily localized along the outer layer of HFs. ALDH2 activation promoted anagen phase induction by reducing ROS levels and enhancing reactive aldehyde clearance, which indicated that ALDH2 functions as a ROS scavenger within HFs. Moreover, ALDH2 activation upregulated Akt/GSK 3β/β-catenin signaling in HFs.

CONCLUSIONS

Our findings highlight the hair growth promotion effects of ALDH2 activation in HFs and its potential as a promising therapeutic approach for promoting anagen induction.

Nanodrug Delivery Strategies to Signaling Pathways in Alopecia

Over 50% of the global population suffers from hair loss. The mixed results in the treatment of hair loss reveal the limitations of conventional commercial topical drugs. One the one hand, the definite pathogenesis of hair loss is still an enigma. On the other hand, targeted drug carriers ensure the drug therapeutic effect and low side effects. This review highlights the organization and overview of nine crucial signaling pathways associated with hair loss, as well as the development of nanobased topical delivery systems loading the clinical drugs, which will fuel emerging hair loss treatment strategies.

Dissolving microneedles for alopecia treatment

Alopecia is a treatable benign disease, however, approximately 15-30% of women and 50% of men suffer from alopecia, which greatly affects patient's self-esteem and quality of life. Currently, commercial products for alopecia treatment include topical minoxidil solution, oral finasteride tablets and oral baricitinib tablets. However, the barrier of stratum corneum, systemic adverse effects and poor cure rate limit the application of commercial products. Therefore, researchers investigated the mechanism of alopecia, and developed new drugs that could target lactate dehydrogenase-related pathways, remove excessive reactive oxygen in hair follicles, and reduce the escape of hair follicle stem cells, thus injecting new strength into the treatment of alopecia. Moreover, starting from improving drug stratum corneum penetration and reducing side effects, researchers have developed hair loss treatment strategies based on dissolved microneedles (MNs), such as drug powders/microparticles, nanoparticles, biomimetic cell membranes, phototherapy and magnetically responsive soluble microneedles, which show exciting alopecia treatment effects. However, there are still some challenges in the practical application of the current alopecia treatment strategy with soluble microneedles, and further studies are needed to accelerate its clinical translation.

Regulation of adult stem cell function by ketone bodies

Adult stem cells play key roles in tissue homeostasis and regeneration. Recent evidence suggests that dietary interventions can significantly impact adult stem cell function. Some of these effects depend on ketone bodies. Adult stem cells could therefore potentially be manipulated through dietary regimens or exogenous ketone body supplementation, a possibility with significant implications for regenerative medicine. In this review we discuss recent findings of the mechanisms by which ketone bodies could influence adult stem cells, including ketogenesis in adult stem cells, uptake and transport of circulating ketone bodies, receptor-mediated signaling, and changes to cellular metabolism. We also discuss the potential effects of ketone bodies on intracellular processes such as protein acetylation and post-transcriptional control of gene expression. The exploration of mechanisms underlying the effects of ketone bodies on stem cell function reveals potential therapeutic targets for tissue regeneration and age-related diseases and suggests future research directions in the field of ketone bodies and stem cells.

Fifty years of the mitochondrial pyruvate carrier: New insights into its structure, function, and inhibition

The mitochondrial pyruvate carrier (MPC) resides in the mitochondrial inner membrane, where it links cytosolic and mitochondrial metabolism by transporting pyruvate produced in glycolysis into the mitochondrial matrix. Due to its central metabolic role, it has been proposed as a potential drug target for diabetes, non-alcoholic fatty liver disease, neurodegeneration, and cancers relying on mitochondrial metabolism. Little is known about the structure and mechanism of MPC, as the proteins involved were only identified a decade ago and technical difficulties concerning their purification and stability have hindered progress in functional and structural analyses. The functional unit of MPC is a hetero-dimer comprising two small homologous membrane proteins, MPC1/MPC2 in humans, with the alternative complex MPC1L/MPC2 forming in the testis, but MPC proteins are found throughout the tree of life. The predicted topology of each protomer consists of an amphipathic helix followed by three transmembrane helices. An increasing number of inhibitors are being identified, expanding MPC pharmacology and providing insights into the inhibitory mechanism. Here, we provide critical insights on the composition, structure, and function of the complex and we summarize the different classes of small molecule inhibitors and their potential in therapeutics.

Neural stem cell metabolism revisited: a critical role for mitochondria

Metabolism has emerged as a key regulator of stem cell behavior. Mitochondria are crucial metabolic organelles that are important for differentiated cells, yet considered less so for stem cells. However, recent studies have shown that mitochondria influence stem cell maintenance and fate decisions, inviting a revised look at this topic. In this review, we cover the current literature addressing the role of mitochondrial metabolism in mouse and human neural stem cells (NSCs) in the embryonic and adult brain. We summarize how mitochondria are implicated in fate regulation and how substrate oxidation affects NSC quiescence. We further explore single-cell RNA sequencing (scRNA-seq) data for metabolic signatures of adult NSCs, highlight emerging technologies reporting on metabolic signatures, and discuss mitochondrial metabolism in other stem cells.

Psychological Stress-Induced Pathogenesis of Alopecia Areata: Autoimmune and Apoptotic Pathways

Alopecia areata (AA) is an autoimmune dermatological disease with multifactorial etiology and is characterized by reversible hair loss in patches. AA may be closely related to emotional stress and influenced by psychological factors as part of its pathophysiology; however, its etiology remains predominantly unknown. This review aimed to elucidate the association between AA occurrence and the neuropeptide substance P (SP) and corticotropin-releasing hormone (CRH), which are secreted during emotional stress, and have been understood to initiate and advance the etiopathogenesis of AA. Therefore, this review aimed to explain how SP and CRH initiate and contribute to the etiopathogenesis of AA. To assess the etiopathogenesis of AA, we conducted a literature search on PubMed and ClinicalTrials.gov. Overall, several authors described interactions between the hair follicles (HFs) and the stress-associated signaling substances, including SP and CRH, in the etiology of AA; this was attributed to the understanding in that AA can occur without the loss of HFs, similar to that observed in hereditary hair loss with age. Most studies demonstrated that the collapse of "immune privilege" plays a crucial role in the development and exacerbation of the AA; nonetheless, a few studies indicated that substances unrelated to autoimmunity may also cause apoptosis in keratocytes, leading to the development of AA. We investigated both the autoimmune and apoptotic pathways within the etiology of AA and assessed the potential interactions between the key substances of both pathways to evaluate potential therapeutic targets for the treatment of AA. Clinical trials of marketed/unreviewed intervention drugs for AA were also reviewed to determine their corresponding target pathways.

Novel recombinant R-spondin1 promotes hair regeneration by targeting the Wnt/β-catenin signaling pathway

Roof plate-specific spondin 1 (R-spondin1, RSPO1) is a Wnt/β-catenin signaling pathway activator that binds with Wnt ligands to stimulate the Wnt/β-catenin signaling pathway, which is key to hair regeneration. However, it is not clear whether recombinant RSPO1 (rRSPO1) affects hair regeneration. Here, we treat C57BL/6 male mice with rRSPO1 and investigate the expression of the Wnt/β-catenin signaling pathway and the activation of hair follicle stem cells in the dorsal skin. The mouse skin color score and hair-covered area are determined to describe hair growth, and the skin samples are subjected to H&E staining, western blot analysis and immunofluorescence staining to evaluate hair follicle development and the expressions of Wnt/β-catenin signaling pathway-related proteins. We find that rRSPO1 activates mouse hair follicle stem cells (mHFSCs) and accelerates hair regeneration. rRSPO1 increases the hair-covered area, the number of hair follicles, and the hair follicle diameter and length. Moreover, rRSPO1 enhances the activity of Wnt/β-catenin signaling pathway-related proteins and the expressions of HFSC markers, as well as mHFSC viability. These results indicate that subcutaneous injection of rRSPO1 can improve hair follicle development by activating the Wnt/β-catenin signaling pathway, thereby promoting hair regeneration. This study demonstrates that rRSPO1 has the potential to treat hair loss by activating the Wnt/β-catenin signaling pathway.

Traditional Chinese Medicine Shi-Bi-Man regulates lactic acid metabolism and drives hair follicle stem cell activation to promote hair regeneration

BACKGROUND

As a supplement for promoting hair health, Shi-Bi-Man (SBM) is a prescription comprising various traditional Chinese medicines. Though SBM has been reported to promote hair regeneration, its molecular mechanism remains unclear. Cynomolgus monkeys (Macaca fascicularis) are non-human primates with a gene expression profile similar to that of humans. The purpose of this research is to evaluate the effect of SBM on promoting hair regeneration in cynomolgus monkeys and to reveal the underlying mechanism.

METHODS

The effect of SBM on hair regeneration was observed by skin administration on 6 cynomolgus monkeys with artificial back shaving. The molecular mechanism of SBM was studied using single-cell RNA sequencing (scRNA-seq) in combination with quantitative polymerase chain reaction (qPCR) detection for gene transcription level, and immunofluorescence staining verification for protein level.

RESULTS

SBM significantly induced hair regeneration in cynomolgus monkeys, increased hair follicle number and facilitated hair follicle development. ScRNA-seq revealed an increase in the number of hair follicle stem cells (HFSCs) with a higher activation state, as evidenced by the higher expression of activation marker LDHA related to metabolism and the proliferation marker MKI67. Immunofluorescence analysis at the protein level and qPCR at the mRNA level confirmed the sequencing data. Cellchat analysis revealed an enrichment of ligand-receptor pairs involved in intercellular communication in Laminin-related pathways.

CONCLUSION

SBM significantly promotes hair regeneration in cynomolgus monkeys. Mechanically, SBM can up-regulate LDHA-mediated lactic acid metabolism and drive HFSC activation, which in turn promotes the proliferation and differentiation of HFSCs.

Lactate-dependent transcriptional regulation controls mammalian eye morphogenesis

Mammalian retinal metabolism favors aerobic glycolysis. However, the role of glycolytic metabolism in retinal morphogenesis remains unknown. We report that aerobic glycolysis is necessary for the early stages of retinal development. Taking advantage of an unbiased approach that combines the use of eye organoids and single-cell RNA sequencing, we identify specific glucose transporters and glycolytic genes in retinal progenitors. Next, we determine that the optic vesicle territory of mouse embryos displays elevated levels of glycolytic activity. At the functional level, we show that removal of Glucose transporter 1 and Lactate dehydrogenase A gene activity from developing retinal progenitors arrests eye morphogenesis. Surprisingly, we uncover that lactate-mediated upregulation of key eye-field transcription factors is controlled by the epigenetic modification of histone H3 acetylation through histone deacetylase activity. Our results identify an unexpected bioenergetic independent role of lactate as a signaling molecule necessary for mammalian eye morphogenesis.

Overview of the Circadian Clock in the Hair Follicle Cycle

The circadian clock adapts to the light-dark cycle and autonomously generates physiological and metabolic rhythmicity. Its activity depends on the central suprachiasmatic pacemaker. However, it also has an independent function in peripheral tissues such as the liver, adipose tissue, and skin, which integrate environmental signals and energy homeostasis. Hair follicles (HFs) maintain homeostasis through the HF cycle, which depends heavily on HF stem cell self-renewal and the related metabolic reprogramming. Studies have shown that circadian clock dysregulation in HFs perturbs cell cycle progression. Moreover, there is increasing evidence that the circadian clock exerts a significant influence on glucose metabolism, feeding/fasting, stem cell differentiation, and senescence. This suggests that circadian metabolic crosstalk plays an essential role in regulating HF regeneration. An improved understanding of the role of the circadian clock in HFs may facilitate the discovery of new drug targets for hair loss. Therefore, the present review provides a discussion of the relationship between the circadian clock and HF regeneration, mainly from the perspective of HF metabolism, and summarizes the current understanding of the mechanisms by which HFs function.

Cedrol-loaded dissolvable microneedles based on flexible backing for promoting hair growth

OBJECTIVES

The dissolvable microneedles loaded with cedrol based on flexible backing were developed to deliver cedrol directly and continuously to the dermis, where the drug concentration in the hair follicle can be increased locally.

METHODS

The tip-layer matrix solution was prepared by mixing cedrol and polyvinylpyrrolidone K25 (PVP K25), and the pedestal matrix solution was prepared with aqueous hyaluronic acid. The cedrol-loaded dissolvable microneedles (cedrol-DMNs) were prepared under vacuum conditions. The mechanical properties, pig skin penetration efficiency, in vitro cutaneous permeation test, and the amount of drug in the skin and receptor chamber were evaluated. Pharmacodynamical studies were performed with C57BL/6 mice.

RESULTS

The mechanical properties of cedrol-DMNs were good. In vitro cutaneous permeation tests and pharmacodynamical studies demonstrated that cedrol-DMN could efficiently deliver the drug to the deep dermis and effectively promote hair growth.

CONCLUSIONS

The cedrol-DMNs offer a promising strategy for treating patients suffering from hair loss.

LSD1 interacting with HSP90 promotes skin wound healing by inducing metabolic reprogramming of hair follicle stem cells through the c-MYC/LDHA axis

It has been demonstrated that hair follicle stem cells (HFSCs) can contribute to wound closure and repair. However, the specific mechanism remains unclear due to the complexity of the wound repair process. Lysine-specific demethylase 1 (LSD1), an important gene for the regulation of stem cell differentiation, has been reported to participate in wound healing regulation. Heat shock protein 90 (HSP90), a chaperone protein, is recently discovered to be a driver gene for wound healing. This study explored the molecular mechanisms by which the binding between LSD1 and HSP90 affects the role of HFSCs during skin wound healing. Following bioinformatics analysis, the key genes acting on HFSCs were identified. The expression of LSD1, HSP90, and c-MYC was found to be upregulated in differentiated HFSCs. Analysis of their binding affinity revealed that LSD1 interacted with HSP90 to enhance the stability of the transcription factor c-MYC. Lactate dehydrogenase A (LDHA) has been documented to be essential for HFSC activation. Therefore, we speculate that LDHA may induce the differentiation of HFSCs through glucose metabolism reprogramming. The results showed that c-MYC activated LDHA activity to promote glycolytic metabolism, proliferation, and differentiation of HFSCs. Finally, in vivo animal experiments further confirmed that LSD1 induced skin wound healing in mice via the HSP90/c-MYC/LDHA axis. From our data, we conclude that LSD1 interacting with HSP90 accelerates skin wound healing by inducing HFSC glycolytic metabolism, proliferation, and differentiation via c-MYC/LDHA axis.

The Potential Role of Exosomes in Aesthetic Plastic Surgery: A Review of Current Literature

Despite an increasing surge of exosome use throughout the aesthetic arena, a paucity of published exosome-based literature exists. Exosomes are membrane-bound extracellular vesicles derived from various cell types, exerting effects via intercellular communication and regulation of several signaling pathways. The purpose of this review was to summarize published articles elucidating mechanisms and potential applications, report available products and clinical techniques, and prompt further investigation of this emerging treatment within the plastic surgery community.

Methods

A literature review was performed using PubMed with keywords exosomes, secretomes, extracellular vesicles, plastic surgery, skin rejuvenation, scar revision, hair growth, body contouring, and breast augmentation. Publications from 2010 to 2021 were analyzed for relevance and level of evidence. A Google search identified exosome distributors, where manufacturing/procurement details, price, efficacy, and clinical indications for use were obtained by direct contact and summarized in table format.

Results

Exosomes are currently derived from bone marrow, placental, adipose, and umbilical cord tissue. Laboratory-based exosome studies demonstrate enhanced outcomes in skin rejuvenation, scar revision, hair restoration, and fat graft survival on the macro and micro levels. Clinical studies are limited to anecdotal results. Prices vary considerably from $60 to nearly $5000 based on company, source tissue, and exosome concentration. No exosome-based products are currently Food and Drug Administration-approved.

Conclusions

Administered alone or as an adjunct, current reports show promise in several areas of aesthetic plastic surgery. However, ongoing investigation is warranted to further delineate concentration, application, safety profile, and overall outcome efficacy.

Regulation of adult stem cell quiescence and its functions in the maintenance of tissue integrity

Adult stem cells are important for mammalian tissues, where they act as a cell reserve that supports normal tissue turnover and can mount a regenerative response following acute injuries. Quiescent stem cells are well established in certain tissues, such as skeletal muscle, brain, and bone marrow. The quiescent state is actively controlled and is essential for long-term maintenance of stem cell pools. In this Review, we discuss the importance of maintaining a functional pool of quiescent adult stem cells, including haematopoietic stem cells, skeletal muscle stem cells, neural stem cells, hair follicle stem cells, and mesenchymal stem cells such as fibro-adipogenic progenitors, to ensure tissue maintenance and repair. We discuss the molecular mechanisms that regulate the entry into, maintenance of, and exit from the quiescent state in mice. Recent studies revealed that quiescent stem cells have a discordance between RNA and protein levels, indicating the importance of post-transcriptional mechanisms, such as alternative polyadenylation, alternative splicing, and translation repression, in the control of stem cell quiescence. Understanding how these mechanisms guide stem cell function during homeostasis and regeneration has important implications for regenerative medicine.

Cellular rejuvenation: molecular mechanisms and potential therapeutic interventions for diseases

The ageing process is a systemic decline from cellular dysfunction to organ degeneration, with more predisposition to deteriorated disorders. Rejuvenation refers to giving aged cells or organisms more youthful characteristics through various techniques, such as cellular reprogramming and epigenetic regulation. The great leaps in cellular rejuvenation prove that ageing is not a one-way street, and many rejuvenative interventions have emerged to delay and even reverse the ageing process. Defining the mechanism by which roadblocks and signaling inputs influence complex ageing programs is essential for understanding and developing rejuvenative strategies. Here, we discuss the intrinsic and extrinsic factors that counteract cell rejuvenation, and the targeted cells and core mechanisms involved in this process. Then, we critically summarize the latest advances in state-of-art strategies of cellular rejuvenation. Various rejuvenation methods also provide insights for treating specific ageing-related diseases, including cellular reprogramming, the removal of senescence cells (SCs) and suppression of senescence-associated secretory phenotype (SASP), metabolic manipulation, stem cells-associated therapy, dietary restriction, immune rejuvenation and heterochronic transplantation, etc. The potential applications of rejuvenation therapy also extend to cancer treatment. Finally, we analyze in detail the therapeutic opportunities and challenges of rejuvenation technology. Deciphering rejuvenation interventions will provide further insights into anti-ageing and ageing-related disease treatment in clinical settings.

Mitochondrial pyruvate metabolism regulates the activation of quiescent adult neural stem cells

Cellular metabolism is important for adult neural stem/progenitor cell (NSPC) behavior. However, its role in the transition from quiescence to proliferation is not fully understood. We here show that the mitochondrial pyruvate carrier (MPC) plays a crucial and unexpected part in this process. MPC transports pyruvate into mitochondria, linking cytosolic glycolysis to mitochondrial tricarboxylic acid cycle and oxidative phosphorylation. Despite its metabolic key function, the role of MPC in NSPCs has not been addressed. We show that quiescent NSPCs have an active mitochondrial metabolism and express high levels of MPC. Pharmacological MPC inhibition increases aspartate and triggers NSPC activation. Furthermore, genetic Mpc1 ablation in vitro and in vivo also activates NSPCs, which differentiate into mature neurons, leading to overall increased hippocampal neurogenesis in adult and aged mice. These findings highlight the importance of metabolism for NSPC regulation and identify an important pathway through which mitochondrial pyruvate import controls NSPC quiescence and activation.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

STAT3 promotes a youthful epigenetic state in articular chondrocytes

Epigenetic mechanisms guiding articular cartilage regeneration and age-related disease such as osteoarthritis (OA) are poorly understood. STAT3 is a critical age-patterned transcription factor highly active in fetal and OA chondrocytes, but the context-specific role of STAT3 in regulating the epigenome of cartilage cells remain elusive. In this study, DNA methylation profiling was performed across human chondrocyte ontogeny to build an epigenetic clock and establish an association between CpG methylation and human chondrocyte age. Exposure of adult chondrocytes to a small molecule STAT3 agonist decreased DNA methylation, while genetic ablation of STAT3 in fetal chondrocytes induced global hypermethylation. CUT&RUN assay and subsequent transcriptional validation revealed DNA methyltransferase 3 beta (DNMT3B) as one of the putative STAT3 targets in chondrocyte development and OA. Functional assessment of human OA chondrocytes showed the acquisition of progenitor-like immature phenotype by a significant subset of cells. Finally, conditional deletion of Stat3 in cartilage cells increased DNMT3B expression in articular chondrocytes in the knee joint in vivo and resulted in a more prominent OA progression in a post-traumatic OA (PTOA) mouse model induced by destabilization of the medial meniscus (DMM). Taken together these data reveal a novel role for STAT3 in regulating DNA methylation in cartilage development and disease. Our findings also suggest that elevated levels of active STAT3 in OA chondrocytes may indicate an intrinsic attempt of the tissue to regenerate by promoting a progenitor-like phenotype. However, it is likely that chronic activation of this pathway, induced by IL-6 cytokines, is detrimental and leads to tissue degeneration.

SCD1 Sustains Homeostasis of Bulge Niche via Maintaining Hemidesmosomes in Basal Keratinocytes

Niche for stem cells profoundly influences their maintenance and fate during tissue homeostasis and pathological disorders; however, the underlying mechanisms and tissue-specific features remain poorly understood. Here, it is reported that fatty acid desaturation catabolized by stearoyl-coenzyme A desaturase 1 (SCD1) regulates hair follicle stem cells (HFSCs) and hair growth by maintaining the bulge, niche for HFSCs. Scd1 deletion in mice results in abnormal hair growth, an effect exerted directly on keratin K14⁺ keratinocytes rather than on HFSCs. Mechanistically, Scd1 deficiency impairs the level of integrin α6β4 complex and thus the assembly of hemidesmosomes (HDs). The disruption of HDs allows the aberrant activation of focal adhesion kinase and PI3K in K14⁺ keratinocytes and subsequently their differentiation and proliferation. The overgrowth of basal keratinocytes results in downward extension of the outer root sheath and interruption of bulge formation. Then, inhibition of PI3K signaling in Scd1^-/- mice normalizes the bulge, HFSCs, and hair growth. Additionally, supplementation of oleic acid to Scd1^-/- mice reestablishes HDs and the homeostasis of bulge niche, and restores hair growth. Thus, SCD1 is critical in regulating hair growth through stabilizing HDs in basal keratinocytes and thus sustaining bulge for HFSC residence and periodic activity.

Microneedle system for tissue engineering and regenerative medicine

Global increasing demand for high life quality and length facilitates the development of tissue engineering and regenerative medicine, which apply multidisciplinary theories and techniques to achieve the structural reconstruction and functional recovery of disordered or damaged tissues and organs. However, the clinical performances of adopted drugs, materials, and powerful cells in the laboratory are inescapably limited by the currently available technologies. To tackle the problems, versatile microneedles are developed as the new platform for local delivery of diverse cargos with minimal invasion. The efficient delivery, as well as painless and convenient procedure endow microneedles with good patient compliance in clinic. In this review, we first categorize different microneedle systems and delivery models, and then summarize their applications in tissue engineering and regenerative medicine mainly involving maintenance and rehabilitation of damaged tissues and organs. In the end, we discuss the advantages, challenges, and prospects of microneedles in depth for future clinical translations.

Role and Mechanisms of Phytochemicals in Hair Growth and Health

Hair health is associated with personal distress and psychological well-being. Even though hair loss (alopecia) does not affect humans' biological health, it affects an individual's social well-being. So, treatment for hair problems and improving hair health are obligatory. Several pharmacological and cosmeceutical treatment procedures are available to manage hair loss and promote growth. Several factors associated with hair health include genetics, disease or disorder, drugs, lifestyle, chemical exposure, and unhealthy habits such as smoking, diet, and stress. Synthetic and chemical formulations have side effects, so people are moving towards natural compounds-based remedies for their hair problems. The history of using phytochemicals for hair health has been documented anciently. However, scientific studies on hair loss have accelerated in recent decades. The current review summarizes the type of alopecia, the factor affecting hair health, alopecia treatments, phytochemicals' role in managing hair loss, and the mechanisms of hair growth-stimulating properties of phytochemicals. The literature survey suggested that phytochemicals are potent candidates for developing treatment procedures for different hair problems. Further detailed studies are needed to bring the scientific evidence to market.

Beyond metabolic waste: lysine lactylation and its potential roles in cancer progression and cell fate determination

BACKGROUND

Lactate is an important metabolite derived from glycolysis under physiological and pathological conditions. The Warburg effect reveals the vital role of lactate in cancer progression. Numerous studies have reported crucial roles for lactate in cancer progression and cell fate determination. Lactylation, a novel posttranslational modification (PTM), has provided a new opportunity to investigate metabolic epigenetic regulation, and studies of this process have been initiated in a wide range of cancer cells, cancer-associated immune cells, and embryonic stem cells.

CONCLUSION

Lactylation is a novel and interesting mechanism of lactate metabolism linked to metabolic rewiring and epigenetic remodeling. It is a potential and hopeful target for cancer therapy. Here, we summarize the discovery of lactylation, the mechanisms of site modification, and progress in research on nonhistone lactylation. We focus on the potential roles of lactylation in cancer progression and cell fate determination and the possible therapeutic strategies for targeting lysine lactylation. Finally, we suggest some future research topics on lactylation to inspire some interesting ideas.

Commensal microbiome promotes hair follicle regeneration by inducing keratinocyte HIF-1α signaling and glutamine metabolism

Tissue injury induces metabolic changes in stem cells, which likely modulate regeneration. Using a model of organ regeneration called wound-induced hair follicle neogenesis (WIHN), we identified skin-resident bacteria as key modulators of keratinocyte metabolism, demonstrating a positive correlation between bacterial load, glutamine metabolism, and regeneration. Specifically, through comprehensive multiomic analysis and single-cell RNA sequencing in murine skin, we show that bacterially induced hypoxia drives increased glutamine metabolism in keratinocytes with attendant enhancement of skin and hair follicle regeneration. In human skin wounds, topical broad-spectrum antibiotics inhibit glutamine production and are partially responsible for reduced healing. These findings reveal a conserved and coherent physiologic context in which bacterially induced metabolic changes improve the tolerance of stem cells to damage and enhance regenerative capacity. This unexpected proregenerative modulation of metabolism by the skin microbiome in both mice and humans suggests important methods for enhancing regeneration after injury.

The Association between Sugar-Sweetened Beverages and Male Pattern Hair Loss in Young Men

We performed this study to investigate the association between sugar-sweetened beverage (SSB) consumption and male pattern hair loss (MPHL) in young men. We conducted this cross-sectional study from January to April 2022 in mainland China. Young people aged 18-45 years (n = 1951) were recruited from 31 provinces in China. We used a self-reported online survey for data collection. We explored the associations between the amount/frequency of SSB consumption and MPHL by using a binary logistic regression model, with adjustments for sociodemographic, hair status, dietary intake, lifestyle, and psychological factors. Among the 1028 participants (27.8 ± 7.2 years) in the final analysis, we found that high SSB consumption is associated with a higher risk of MPHL. We recommend more support to decrease SSB consumption among young people to minimize negative health outcomes.

Regulation and function of the mammalian tricarboxylic acid cycle

The tricarboxylic acid (TCA) cycle, otherwise known as the Krebs cycle, is a central metabolic pathway that performs the essential function of oxidizing nutrients to support cellular bioenergetics. More recently, it has become evident that TCA cycle behavior is dynamic, and products of the TCA cycle can be co-opted in cancer and other pathologic states. In this review, we revisit the TCA cycle, including its potential origins and the history of its discovery. We provide a detailed accounting of the requirements for sustained TCA cycle function and the critical regulatory nodes that can stimulate or constrain TCA cycle activity. We also discuss recent advances in our understanding of the flexibility of TCA cycle wiring and the increasingly appreciated heterogeneity in TCA cycle activity exhibited by mammalian cells. Deeper insight into how the TCA cycle can be differentially regulated and, consequently, configured in different contexts will shed light on how this pathway is primed to meet the requirements of distinct mammalian cell states.

Extracellular serine empowers epidermal proliferation and psoriasis-like symptoms

The contribution of nutrient availability to control epidermal cell proliferation, inflammation, and hyperproliferative diseases remains unknown. Here, we studied extracellular serine and serine/glycine metabolism using human keratinocytes, human skin biopsies, and a mouse model of psoriasis-like disease. We focused on a metabolic enzyme, serine hydroxymethyltransferase (SHMT), that converts serine into glycine and tetrahydrofolate-bound one‑carbon units to support cell growth. We found that keratinocytes are both serine and glycine auxotrophs. Metabolomic profiling and hypoxanthine supplementation indicated that SHMT silencing/inhibition reduced cell growth through purine depletion, leading to nucleotide loss. In addition, topical application of an SHMT inhibitor suppressed both keratinocyte proliferation and inflammation in the imiquimod model and resulted in a decrease in psoriasis-associated gene expression. In conclusion, our study highlights SHMT2 activity and serine/glycine availability as an important metabolic hub controlling both keratinocyte proliferation and inflammatory cell expansion in psoriasis and holds promise for additional approaches to treat skin diseases.