Peroxisome proliferator-activated receptor α (PPARα) contributes to control of melanogenesis in B16 F10 melanoma cells

PPAR-γ in Melanoma and Immune Cells: Insights into Disease Pathogenesis and Therapeutic Implications

Changes in skin pigmentation, like hyperpigmentation or moles, can affect appearance and social life. Unlike locally containable moles, malignant melanomas are aggressive and can spread rapidly, disproportionately affecting younger individuals with a high potential for metastasis. Research has shown that the peroxisome proliferator-activated receptor gamma (PPAR-γ) and its ligands exhibit protective effects against melanoma. As a transcription factor, PPAR-γ is crucial in functions like fatty acid storage and glucose metabolism. Activation of PPAR-γ promotes lipid uptake and enhances sensitivity to insulin. In many cases, it also inhibits the growth of cancer cell lines, like breast, gastric, lung, and prostate cancer. In melanoma, PPAR-γ regulates cell proliferation, differentiation, apoptosis, and survival. During tumorigenesis, it controls metabolic changes and the immunogenicity of stromal cells. PPAR-γ agonists can target hypoxia-induced angiogenesis in tumor therapy, but their effects on tumors can be suppressive or promotional, depending on the tumor environment. Published data show that PPAR-γ-targeting agents can be effective in specific groups of patients, but further studies are needed to understand lesser-known biological effects of PPAR-γ and address the existing safety concerns. This review provides a summary of the current understanding of PPAR-γ and its involvement in melanoma.

Selective abrogation of S6K2 identifies lipid homeostasis as a survival vulnerability in MAPK inhibitor-resistant NRAS-mutant melanoma

Although oncogenic NRAS activates mitogen-activated protein kinase (MAPK) signaling, inhibition of the MAPK pathway is not therapeutically efficacious in NRAS-mutant (NRASMUT) tumors. Here, we report that selectively silencing the ribosomal protein S6 kinase 2 (S6K2) while preserving the activity of S6K1 perturbs lipid metabolism, enhances fatty acid unsaturation, and triggers lethal lipid peroxidation in NRASMUT melanoma cells that are resistant to MAPK inhibition. S6K2 depletion induces endoplasmic reticulum stress and peroxisome proliferator-activated receptor α (PPARα) activation, triggering cell death selectively in MAPK inhibitor-resistant melanoma. We found that combining PPARα agonists and polyunsaturated fatty acids phenocopied the effects of S6K2 abrogation, blocking tumor growth in both patient-derived xenografts and immunocompetent murine melanoma models. Collectively, our study establishes S6K2 and its effector subnetwork as promising targets for NRASMUT melanomas that are resistant to global MAPK pathway inhibitors.

Peroxisome proliferator-activated receptors: Key regulators of tumor progression and growth

One of the main causes of death on the globe is cancer. Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors, including PPARα, PPARδ and PPARγ, which are important in regulating cancer cell proliferation, survival, apoptosis, and tumor growth. Activation of PPARs by endogenous or synthetic compounds regulates tumor progression in various tissues. Although each PPAR isotype suppresses or promotes tumor development depending on the specific tissues or ligands, the mechanism is still unclear. PPARs are receiving interest as possible therapeutic targets for a number of disorders. Numerous clinical studies are being conducted on PPARs as possible therapeutic targets for cancer. Therefore, this review will focus on the existing and future uses of PPARs agonists and antagonists in treating malignancies. PubMed, Science Direct, and Scopus databases were searched regarding the effect of PPARs on various types of cancers until the end of May 2023. The results of the review articles showed the therapeutic influence of PPARs on a wide range of cancer on in vitro, in vivo and clinical studies. However, further experimental and clinical studies are needed to be conducted on the influence of PPARs on various cancers.

Phenylalanine Butyramide: A Butyrate Derivative as a Novel Inhibitor of Tyrosinase

Metabolites resulting from the bacterial fermentation of dietary fibers, such as short-chain fatty acids, especially butyrate, play important roles in maintaining gut health and regulating various biological effects in the skin. However, butyrate is underutilized due to its unpleasant odor. To circumvent this organoleptic unfavorable property, phenylalanine butyramide (PBA), a butyrate precursor, has been synthesized and is currently available on the market. We evaluated the inhibition of mushroom tyrosinase by butyrate and PBA through in vitro assays, finding IC50 values of 34.7 mM and 120.3 mM, respectively. Docking calculations using a homology model of human tyrosinase identified a putative binding mode of PBA into the catalytic site. The anti-aging and anti-spot efficacy of topical PBA was evaluated in a randomized, double-blind, parallel-arm, placebo-controlled clinical trial involving 43 women affected by photo-damage. The results of this study showed that PBA significantly improved skin conditions compared to the placebo and was well tolerated. Specifically, PBA demonstrated strong skin depigmenting activity on both UV and brown spots (UV: -12.7% and -9.9%, Bs: -20.8% and -17.7% after 15 and 30 days, respectively, p < 0.001). Moreover, PBA brightened and lightened the skin (ITA°: +12% and 13% after 15 and 30 days, respectively, p < 0.001). Finally, PBA significantly improved skin elasticity (Ua/Uf: +12.4% and +32.3% after 15 and 30 days, respectively, p < 0.001) and firmness (Uf: -3.2% and -14.9% after 15 and 30 days, respectively, p < 0.01).

Secondary glaucoma: Toward interventions based on molecular underpinnings

Glaucoma is a heterogeneous group of progressive diseases that leads to irreversible blindness. Secondary glaucoma refers to glaucoma caused by a known underlying condition. Pseudoexfoliation and pigment dispersion syndromes are common causes of secondary glaucoma. Their respective deposits may obstruct the trabecular meshwork, leading to aqueous humor outflow resistance, ocular hypertension, and optic neuropathy. There are no disease-specific interventions available for either. Pseudoexfoliation syndrome is characterized by fibrillar deposits (pseudoexfoliative material) on anterior segment structures. Over a decade of multiomics analyses taken together with the current knowledge on pseudoexfoliative glaucoma warrant a re-think of mechanistic possibilities. We propose that the presence of nucleation centers (e.g., vitamin D binding protein), crosslinking enzymes (e.g., transglutaminase 2), aberrant extracellular matrix, flawed endocytosis, and abnormal aqueous-blood barrier contribute to the formation of proteolytically resistant pseudoexfoliative material. Pigment dispersion syndrome is characterized by abnormal iridolenticular contact that disrupts iris pigment epithelium and liberates melanin granules. Iris melanogenesis is aberrant in this condition. Cytotoxic melanogenesis intermediates leak out of melanosomes and cause iris melanocyte and pigment epithelium cell death. Targeting melanogenesis can likely decrease the risk of pigmentary glaucoma. Skin and melanoma research provides insights into potential therapeutics. We propose that specific prostanoid agonists and fenofibrates may reduce melanogenesis by inhibiting cholesterol internalization and de novo synthesis. Additionally, melatonin is a potent melanogenesis suppressor, antioxidant, and hypotensive agent, rendering it a valuable agent for pigmentary glaucoma. In pseudoexfoliative glaucoma, where environmental insults drive pseudoexfoliative material formation, melatonin's antioxidant and hypotensive properties may offer adjunct therapeutic benefits. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Peroxisom proliferator-activated receptor-γ coactivator-1α in neurodegenerative disorders: A promising therapeutic target

Neurodegenerative disorders (NDDs) are characterized by progressive loss of selectively vulnerable neuronal populations and myelin sheath, leading to behavioral and cognitive dysfunction that adversely affect the quality of life. Identifying novel therapies that attenuate the progression of NDDs would be of significance. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a widely expressed transcriptional regulator, modulates the expression of genes engaged in mitochondrial biosynthesis, metabolic regulation, and oxidative stress (OS). Emerging evidences point to the strong connection between PGC-1α and NDDs, suggesting its positive impaction on the progression of NDDs. Therefore, it is urgent to gain a deeper and broader understanding between PGC-1α and NDDs. To this end, this review presents a comprehensive overview of PGC-1α, including its basic characteristics, the post-translational modulations, as well as the interacting transcription factors. Secondly, the pathogenesis of PGC-1α in various NDDs, such as Alzheimer's (AD), Parkinson's (PD), and Huntington's disease (HD) is briefly discussed. Additionally, this study summarizes the underlying mechanisms that PGC-1α is neuroprotective in NDDs via regulating neuroinflammation, OS, and mitochondrial dysfunction. Finally, we briefly outline the shortcomings of current NDDs drug therapy, and summarize the functions and potential applications of currently available PGC-1α modulators (activator or inhibitors). Generally, this review updates our insight of the important role of PGC-1α on the development of NDDs, and provides a promising therapeutic target/ drug for the treatment of NDDs.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

FZD1/KLF10-hsa-miR-4762-5p/miR-224-3p-circular RNAs axis as prognostic biomarkers and therapeutic targets for glioblastoma: a comprehensive report

BACKGROUND

The circular RNA (circRNA) plays a vital role in the pathogenesis of tumors as a competitive endogenous RNA (ceRNA). Given the high aggressiveness and fatality rate of glioblastoma (GBM) as well as poor prognosis, it is necessary to construct a circRNA-related ceRNA network for further studies on the mechanism of GBM and identify possible biomarkers as well as therapeutic drugs.

METHODS

Three datasets from the gene expression omnibus (GEO) database were downloaded to distinguish differential circRNAs, microRNAs, and messenger RNAs respectively in GBM. With the help of GEPIA2, circBank, CSCD, TargetScan, miRDB, and miRTarBase databases, we established a circRNAs-related ceRNA network in GBM. Functional enrichments were employed to profile the most relevant mRNAs to indirectly clarify the mechanisms of the ceRNA network. Based on the expression profile data and survival information of GBM patients from the GEO and the cancer genome atlas (TCGA) databases, we performed survival analysis to select prognostic mRNAs and constructed a novel circRNA-miRNA-mRNA central regulatory subnetwork. The DGIdb database was used to find potential drug-gene interactions.

RESULTS

The datasets obtained from the GEO and TCGA databases were analyzed, and 504 differentially expressed mRNAs (DEmRNAs), 71 differentially expressed microRNAs (DEmiRNAs), and 270 differentially expressed circRNAs (DEcircRNAs) were screened out. The novel ceRNA regulatory network included 22 circRNAs, 11 miRNAs, and 15 mRNAs. FZD1 and KLF10 were significantly correlated with the overall survival rate of patients with GBM (P < 0.05). The final survival subnetwork contained six circRNAs, two miRNAs, and two mRNAs. Two small-molecule compounds and one antibody could be used as therapeutic drugs for GBM. Interestingly, the Wnt signaling pathway appeared in both KEGG and GO functional terms.

CONCLUSIONS

Results of this study demonstrate that FZD1 and KLF10 may exert regulatory functions in GBM, and the ceRNA-mediated network could be a therapeutic strategy for GBM.

PPARs and the Kynurenine Pathway in Melanoma-Potential Biological Interactions

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in various physiological and pathological processes within the skin. PPARs regulate several processes in one of the most aggressive skin cancers, melanoma, including proliferation, cell cycle, metabolic homeostasis, cell death, and metastasis. In this review, we focused not only on the biological activity of PPAR isoforms in melanoma initiation, progression, and metastasis but also on potential biological interactions between the PPAR signaling and the kynurenine pathways. The kynurenine pathway is a major pathway of tryptophan metabolism leading to nicotinamide adenine dinucleotide (NAD+) production. Importantly, various tryptophan metabolites exert biological activity toward cancer cells, including melanoma. Previous studies confirmed the functional relationship between PPAR and the kynurenine pathway in skeletal muscles. Despite the fact this interaction has not been reported in melanoma to date, some bioinformatics data and biological activity of PPAR ligands and tryptophan metabolites may suggest a potential involvement of these metabolic and signaling pathways in melanoma initiation, progression, and metastasis. Importantly, the possible relationship between the PPAR signaling pathway and the kynurenine pathway may relate not only to the direct biological effect on melanoma cells but also to the tumor microenvironment and the immune system.

Highly Effective Protocol for Differentiation of Induced Pluripotent Stem Cells (iPS) into Melanin-Producing Cells

Melanin is a black/brown pigment present in abundance in human skin. Its main function is photo-protection of underlying tissues from harmful UV light. Natural sources of isolated human melanin are limited; thus, in vitro cultures of human cells may be a promising source of human melanin. Here, we present an innovative in vitro differentiation protocol of induced pluripotent stem cells (iPS) into melanin-producing cells, delivering highly pigmented cells in quantity and quality incomparably higher than any other methods previously described. Pigmented cells constitute over 90% of a terminally differentiated population and exhibit features characteristic for melanocytes, i.e., expression of specific markers such as MITF-M (microphthalmia-associated transcription factor isoform M), TRP-1 (tyrosinase-related protein 1), and TYR (tyrosinase) and accumulation of black pigment in organelles closely resembling melanosomes. Black pigment is unambiguously identified as melanin with features corresponding to those of melanin produced by typical melanocytes. The advantage of our method is that it does not require any sophisticated procedures and can be conducted in standard laboratory conditions. Moreover, our protocol is highly reproducible and optimized to generate high-purity melanin-producing cells from iPS cells; thus, it can serve as an unlimited source of human melanin for modeling human skin diseases. We speculate that FGF-8 might play an important role during differentiation processes toward pigmented cells.

Biophysical characterization of melanoma cell phenotype markers during metastatic progression

Melanoma is the most fatal form of skin cancer, with increasing prevalence worldwide. The most common melanoma genetic driver is mutation of the proto-oncogene serine/threonine kinase BRAF; thus, the inhibition of its MAP kinase pathway by specific inhibitors is a commonly applied therapy. However, many patients are resistant, or develop resistance to this type of monotherapy, and therefore combined therapies which target other signaling pathways through various molecular mechanisms are required. A possible strategy may involve targeting cellular energy metabolism, which has been recognized as crucial for cancer development and progression and which connects through glycolysis to cell surface glycan biosynthetic pathways. Protein glycosylation is a hallmark of more than 50% of the human proteome and it has been recognized that altered glycosylation occurs during the metastatic progression of melanoma cells which, in turn facilitates their migration. This review provides a description of recent advances in the search for factors able to remodel cell metabolism between glycolysis and oxidative phosphorylation, and of changes in specific markers and in the biophysical properties of cells during melanoma development from a nevus to metastasis. This development is accompanied by changes in the expression of surface glycans, with corresponding changes in ligand-receptor affinity, giving rise to structural features and viscoelastic parameters particularly well suited to study by label-free biophysical methods.

PPAR-α Modulators as Current and Potential Cancer Treatments

Cancer is one of the leading causes of mortality worldwide. PPAR modulators may hold great potential for the management of cancer patients. Indeed, PPARs are critical sensors and regulators of lipid, and they are able to promote eNOS activation, regulate immunity and inflammation response, and affect proliferation and differentiation of cancer cells. Cancer, a name given to a group of diseases, is characterized by multiple distinctive biological behaviors, including angiogenesis, abnormal cell proliferation, aerobic glycolysis, inflammation, etc. In the last decade, emerging evidence has shown that PPAR-α, a nuclear hormone receptor, can modulate carcinogenesis via exerting effects on one or several characteristic pathological behaviors of cancer. Therefore, the multi-functional PPAR modulators have substantial promise in various types of cancer therapies. This review aims to consolidate the functions of PPAR-α, as well as discuss the current and potential applications of PPAR-α agonists and antagonists in tackling cancer.

2,4-Dihydroxyphenyl-benzo[d]thiazole (MHY553), a synthetic PPARα agonist, decreases age-associated inflammatory responses through PPARα activation and RS scavenging in the skin

We previously reported that 2,4-dihydroxyphenyl-benzo[d]thiazole (MHY553) is a PPARα agonist, which has been shown to inhibit tyrosinase activity in murine melanocyte and alleviate hepatic steatosis in aged rats. This study investigated the effects of MHY553 on the age-related occurrence of inflammatory responses via the molecular modulation of the nuclear factor-κB (NF-κB) signaling pathway in the skin of aged rats and skin fibroblast cells. Moreover, we investigated the antioxidant effect of MHY553 via in vitro assays of reactive oxygen species (ROS) and peroxynitrite (ONOO^-) scavenging activities. We also scrutinized the ability of MHY553 as a PPARα activator in aged rat skin and H₂O₂-induced Hs27 fibroblast cells. In vivo experiments were performed in young, aged, and MHY553-fed aged rats (3 mg or 5 mg∙kg ^-1∙day ^-1 for 4 weeks). MHY553 dose-dependently scavenged ROS and ONOO^-. Furthermore, we found that MHY553 suppressed the NF-κB transcription factor and downregulated mitogen-activated protein kinase (MAPK)/activator protein-1 (AP-1) signaling. MHY553 also inhibited the expression of pro-inflammatory cytokines including COX-2, iNOS, IL-1β, and IL-6. Our findings indicate the MHY553 scavenges ROS/reactive nitrogen species and inhibits inflammatory cytokines through PPARα activation in the skin. Thus, these results suggest that MHY553 may be of therapeutic interest for protecting skin from oxidative stress-induced damage and intrinsic aging.

Melanoma-Time to fast or time to feast? An interplay between PPARs, metabolism and immunity

Development and progression of melanoma can be accelerated by intensification of particular metabolic pathways, such as aerobic glycolysis and avid amino acid catabolism, and is accompanied by aberrant immune responses within the tumor microenvironment. Contrary to other cancer types, melanoma reveals some unique tissue-specific features, such as melanogenesis, which is intertwined with metabolism. Nuclear peroxisome proliferator-activated receptors (PPARs) take part in regulation of systemic and cellular metabolism, inflammation and melanogenesis. They appear as a focal regulatory point for these three distinct processes by occupying the intersection among AMP-dependent protein kinase (AMPK), mammalian target of rapamycin (mTOR) and PPAR gamma coactivator 1-alpha (PGC-1α) signalling pathways. When deregulated, they may accelerate melanoma malignant growth. Presenting the contribution of PPARα and PPARγ in melanoma biology, we attempt to ask how two contrasting metabolic states: obesity and fasting, can change progression of the disease and possible outcome of the treatment. This short essay is aimed to provoke a discussion about some practical implications for melanoma prevention and treatment, especially: how metabolic manipulation may be exploited to overcome immunosuppression and support immune checkpoint blockade efficacy.

Bio-derived hydroxystearic acid ameliorates skin age spots and conspicuous pores

INTRODUCTION

We report on the preparation and efficacy of 10-hydroxystearic acid (HSA) that improves facial age spots and conspicuous pores.

METHODS

The hydration of oleic acid into HSA was catalyzed by the oleate hydratase from Escherichia coli. Following treatment with HSA, collagen type I and type III was assessed in primary human dermal fibroblasts together with collagen type III, p53 protein levels and sunburn cells (SBC) after UVB irradiation (1 J cm^-2 ) by immunohistochemistry on human ex vivo skin. UVB-induced expression of matrix metalloprotease-1 (MMP-1) was determined from full thickness skin by RT-qPCR. Modification of the fibroblast secretome by HSA was studied by mass-spectrometry-based proteomics. In a full-face, double blind, vehicle-controlled trial HSA was assessed for its effects on conspicuous facial pore size and degree of pigmentation of age spots in Caucasian women over an 8-week period.

RESULTS

HSA was obtained in enantiomeric pure, high yield (≥80%). Collagen type I and type III levels were dose-dependently increased (96% and 244%; P < 0.01) in vitro and collagen type III in ex vivo skin by +57% (P < 0.01) by HSA. HSA also inhibited UVB-induced MMP-1 gene expression (83%; P < 0.01) and mitigated SBC induction (-34% vs. vehicle control) and reduced significantly UV-induced p53 up-regulation (-46% vs. vehicle control; P < 0.01) in irradiated skin. HSA modified the fibroblast secretome with significant increases in proteins associated with the WNT pathway that could reduce melanogenesis and proteins that could modify dermal fibroblast activity and keratinocyte differentiation to account for the alleviation of conspicuous pores. Docking studies in silico and EC50 determination in reporter gene assays (EC50 5.5 × 10^-6  M) identified HSA as a peroxisomal proliferator activated receptor-α (PPARα) agonist. Clinically, HSA showed a statistically significant decrease of surface and volume of skin pores (P < 0.05) after 8 weeks of application and age spots became significantly less pigmented than the surrounding skin (contrast, P < 0.05) after 4 weeks.

CONCLUSION

HSA acts as a PPARα agonist to reduce the signs of age spots and conspicuous pores by significantly modulating the expression of p53, SBC, MMP-1 and collagen together with major changes in secreted proteins that modify keratinocyte, melanocyte and fibroblast cell behavior.

Quantitative analysis of melanin content in a three-dimensional melanoma cell culture

Reliable measurement of the amount of melanin produced by melanocytes is essential to study various skin disorders and to evaluate the efficacy of candidate reagents for such disorders or for whitening purposes. Conventional melanin quantification methods are based on absorption spectroscopy, which measures the melanin from lysed cells grown on two-dimensional (2D) surfaces. The 2D culture environment is intrinsically different from in vivo systems though, and therefore cells often lose their original phenotypes. Melanocytes in particular lose their ability to synthesize melanin, thereby requiring melanogenesis stimulators such as alpha-melanocyte stimulating hormone (α-MSH) to promote melanin synthesis. In this study, we compared melanin synthesis in B16 murine melanoma cells grown in 2D and three-dimensional culture environments. B16 cells instantly formed an aggregate in a hanging-drop culture, and synthesized melanin efficiently without treatment of α-MSH. We were able to measure the melanin secreted from a single melanocyte aggregate, indicating that our method enables non-invasive long-term monitoring of melanin synthesis and secretion in a high-throughput format. We successfully tested the developed platform by quantifying the depigmenting effects of arbutin and kojic acid.

Protective role of peroxisome proliferator-activated receptor α agonists in skin barrier and inflammation

Peroxisome proliferator-activated receptor α (PPARα) is one of the three isoforms of PPARs, which are ligand-activated nuclear transcription factors. PPARα is highly expressed in liver and its agonists are widely used to treat hyperlipidemia. Epidermal keratinocytes express all three isoforms (α, β/δ, and γ) of PPARs and PPARα is particularly important for regulating the epidermal barrier and inflammation. Agonistic ligation of PPARα protects the epidermal barrier function and inhibits the inflammatory response in dermatitis. In this review, we summarize recent topics on the role of PPARα in skin biology and discuss the potential use of topical PPARα agonists for treating atopic dermatitis and other eczemas.