Histone modifiers: Dynamic regulators of the cutaneous transcriptome

Saikosaponin A Recovers Impaired Filaggrin Levels in Inflamed Skin by Downregulating the Expression of FRA1 and c-Jun

Filaggrin (FLG) is an essential structural protein expressed in differentiated keratinocytes. Insufficient FLG expression contributes to the pathogenesis of chronic inflammatory skin diseases. Saikosaponin A (SSA), a bioactive oleanane-type triterpenoid, exerts anti-inflammatory activity. However, the effects of topically applied SSA on FLG expression in inflamed skin remain unclear. This study aimed to evaluate the biological activity of SSA in restoring reduced FLG expression. The effect of SSA on FLG expression in HaCaT cells was assessed through various biological methods, including reverse transcription PCR, quantitative real-time PCR, immunoblotting, and immunofluorescence staining. TNFα and IFNγ decreased FLG mRNA, cytoplasmic FLG protein levels, and FLG gene promoter-reporter activity compared to the control groups. However, the presence of SSA restored these effects. A series of FLG promoter-reporter constructs were generated to investigate the underlying mechanism of the effect of SSA on FLG expression. Mutation of the AP1-binding site (mtAP1) in the -343/+25 FLG promoter-reporter abrogated the decrease in reporter activities caused by TNFα + IFNγ, suggesting the importance of the AP1-binding site in reducing FLG expression. The SSA treatment restored FLG expression by inhibiting the expression and nuclear localization of FRA1 and c-Jun, components of AP1, triggered by TNFα + IFNγ stimulation. The ERK1/2 mitogen-activated protein kinase signaling pathway upregulates FRA1 and c-Jun expression, thereby reducing FLG levels. The SSA treatment inhibited ERK1/2 activation caused by TNFα + IFNγ stimulation and reduced the levels of FRA1 and c-Jun proteins in the nucleus, leading to a decrease in the binding of FRA1, c-Jun, p-STAT1, and HDAC1 to the AP1-binding site in the FLG promoter. The effect of SSA was evaluated in an animal study using a BALB/c mouse model, which induces human atopic-dermatitis-like skin lesions via the topical application of dinitrochlorobenzene. Topically applied SSA significantly reduced skin thickening, immune cell infiltration, and the expression of FRA1, c-Jun, and p-ERK1/2 compared to the vehicle-treated group. These results suggest that SSA can effectively recover impaired FLG levels in inflamed skin by preventing the formation of the repressor complex consisting of FRA1, c-Jun, HDAC1, and STAT1.

Identification of a signature of histone modifiers in kidney renal clear cell carcinoma

Kidney renal clear cell carcinoma (KIRC) is a cancer that is closely associated with epigenetic alterations, and histone modifiers (HMs) are closely related to epigenetic regulation. Therefore, this study aimed to comprehensively explore the function and prognostic value of HMs-based signature in KIRC. HMs were first obtained from top journal. Then, the mRNA expression profiles and clinical information in KIRC samples were downloaded from The Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) datasets. Cox regression analysis and least absolute shrinkage and selection operator (Lasso) analysis were implemented to find prognosis-related HMs and construct a risk model related to the prognosis in KIRC. Kaplan-Meier analysis was used to determine prognostic differences between high- and low-risk groups. Immune infiltration and drug sensitivity analysis were also performed between high- and low-risk groups. Eventually, 8 HMs were successfully identified for the construction of a risk model in KIRC. The results of the correlation analysis between risk signature and the prognosis showed HMs-based signature has good prognostic value in KIRC. Results of immune analysis of risk models showed there were significant differences in the level of immune cell infiltration and expression of immune checkpoints between high- and low-risk groups. The results of the drug sensitivity analysis showed that the high-risk group was more sensitive to several chemotherapeutic agents such as Sunitinib, Tipifarnib, Nilotinib and Bosutinib than the low-risk group. In conclusion, we successfully constructed HMs-based prognostic signature that can predict the prognosis of KIRC.

Noval advance of histone modification in inflammatory skin diseases and related treatment methods

Inflammatory skin diseases are a group of diseases caused by the disruption of skin tissue due to immune system disorders. Histone modification plays a pivotal role in the pathogenesis and treatment of chronic inflammatory skin diseases, encompassing a wide range of conditions, including psoriasis, atopic dermatitis, lupus, systemic sclerosis, contact dermatitis, lichen planus, and alopecia areata. Analyzing histone modification as a significant epigenetic regulatory approach holds great promise for advancing our understanding and managing these complex disorders. Additionally, therapeutic interventions targeting histone modifications have emerged as promising strategies for effectively managing inflammatory skin disorders. This comprehensive review provides an overview of the diverse types of histone modification. We discuss the intricate association between histone modification and prevalent chronic inflammatory skin diseases. We also review current and potential therapeutic approaches that revolve around modulating histone modifications. Finally, we investigated the prospects of research on histone modifications in the context of chronic inflammatory skin diseases, paving the way for innovative therapeutic interventions and improved patient outcomes.

Collagen synthesis in the skin: genetic and epigenetic aspects

One of the most important functions of the skin, mechanical, is provided by collagen fibers and their interaction with other elements of the extracellular matrix. Synthesis of collagen fibers is a complex multistep process. At each stage, disturbances may occur, leading, as a result, to a decrease in the mechanical properties of the connective tissue. In clinical practice, disorders of collagen synthesis are manifested through increased skin laxity and looseness and premature aging. In addition to the clinical presentation, it is important for the cosmetologist and dermatologist to understand the etiology and pathogenesis of collagenopathies. The present review summarizes and systematizes available information about the role of genetic and epigenetic factors in the synthesis of collagen fibers in the skin. Understanding the etiology of collagen synthesis disorders can allow doctors to prescribe pathogenetically grounded treatment with the most effective results and minimize adverse reactions.

FRA1:c-JUN:HDAC1 complex down-regulates filaggrin expression upon TNFα and IFNγ stimulation in keratinocytes

Filaggrin (FLG), an essential structural protein for skin barrier function, is down-regulated under chronic inflammatory conditions, leading to disruption of the skin barrier. However, the detailed molecular mechanisms of how FLG changes in the context of chronic inflammation are poorly understood. Here, we identified the molecular mechanisms by which inflammatory cytokines inhibit FLG expression in the skin. We found that the AP1 response element within the -343/+25 of the FLG promoter was necessary for TNFα + IFNγ-induced down-regulation of FLG promoter activity. Using DNA affinity precipitation assay, we observed that AP1 subunit composition binding to the FLG promoter was altered from c-FOS:c-JUN (at the early time) to FRA1:c-JUN (at the late time) in response to TNFα + IFNγ stimulation. Knockdown of FRA1 or c-JUN abrogated TNFα + IFNγ-induced FLG suppression. Histone deacetylase (HDAC) 1 interacted with FRA1:c-JUN under TNFα + IFNγ stimulation. Knockdown of HDAC1 abrogated the inhibitory effect of TNFα + IFNγ on FLG expression. The altered expression of FLG, FRA1, c-JUN, and HDAC1 was confirmed in mouse models of 2,4-dinitrochlorobenzene-induced atopic dermatitis and imiquimod-induced psoriasis. Thus, the current study demonstrates that TNFα + IFNγ stimulation suppresses FLG expression by promoting the FRA1:c-JUN:HDAC1 complex. This study provides insight into future therapeutic strategies targeting the FRA1:c-JUN:HDAC1 complex to restore impaired FLG expression in chronic skin inflammation.

Genetic and Epigenetic Aspects of Skin Collagen Fiber Turnover and Functioning

One of the most important functions of the skin, i.e., protection from mechanical damage, is ensured by collagen fibers and their interaction with other elements in the extracellular matrix. Collagen fiber turnover is a complex multi-stage process. At each stage, a disruption may occur, leading to a decrease in the mechanical properties of the connective tissue. Clinically, collagen formation disorders manifest themselves as increased flabbiness and looseness of the skin and as early signs of facial aging. In addition to the clinical picture, it is important for cosmetologists and dermatologists to understand the etiology and pathogenesis of collagenopathies. In our review, we summarized and systematized the available information concerning the role of genetic and epigenetic factors in skin collagen fiber turnover. Furthermore, we focused on the functions of different types of collagens present in the skin. Understanding the etiology of impaired collagen formation can allow doctors to prescribe pathogenetically based treatments, achieve the most effective results, and minimize adverse reactions.

Interrogating Epigenome toward Personalized Approach in Cutaneous Melanoma

Epigenetic alterations have emerged as essential contributors in the pathogenesis of various human diseases, including cutaneous melanoma (CM). Unlike genetic changes, epigenetic modifications are highly dynamic and reversible and thus easy to regulate. Here, we present a comprehensive review of the latest research findings on the role of genetic and epigenetic alterations in CM initiation and development. We believe that a better understanding of how aberrant DNA methylation and histone modifications, along with other molecular processes, affect the genesis and clinical behavior of CM can provide the clinical management of this disease a wide range of diagnostic and prognostic biomarkers, as well as potential therapeutic targets that can be used to prevent or abrogate drug resistance. We will also approach the modalities by which these epigenetic alterations can be used to customize the therapeutic algorithms in CM, the current status of epi-therapies, and the preliminary results of epigenetic and traditional combinatorial pharmacological approaches in this fatal disease.

Diacylglycerol Kinase Alpha in Radiation-Induced Fibrosis: Potential as a Predictive Marker or Therapeutic Target

Radiotherapy is an efficient tool in cancer treatment, but it brings along the risk of side effects such as fibrosis in the irradiated healthy tissue thus limiting tumor control and impairing quality of life of cancer survivors. Knowledge on radiation-related fibrosis risk and therapeutic options is still limited and requires further research. Recent studies demonstrated that epigenetic regulation of diacylglycerol kinase alpha (DGKA) is associated with radiation-induced fibrosis. However, the specific mechanisms are still unknown. In this review, we scrutinized the role of DGKA in the radiation response and in further cellular functions to show the potential of DGKA as a predictive marker or a novel target in fibrosis treatment. DGKA was reported to participate in immune response, lipid signaling, exosome production, and migration as well as cell proliferation, all processes which are suggested to be critical steps in fibrogenesis. Most of these functions are based on the conversion of diacylglycerol (DAG) to phosphatidic acid (PA) at plasma membranes, but DGKA might have also other, yet not well-known functions in the nucleus. Current evidence summarized here underlines that DGKA activation may play a central role in fibrosis formation post-irradiation and shows a potential of direct DGKA inhibitors or epigenetic modulators to attenuate pro-fibrotic reactions, thus providing novel therapeutic choices.

Histone H3K9 methylation is involved in temporomandibular joint osteoarthritis

The morbidity of temporomandibular joint osteoarthritis (TMJOA) increases with age. Condylar articular cartilage degradation, which causes TMJOA, is known to be involved in articular chondrocyte metabolic imbalances in the temporomandibular joint (TMJ) and in other joints of the body. Epigenetic regulation, such as the chemical modification of DNA and histones, is implicated in cartilage homeostasis. However, few studies have been conducted on the epigenetic regulation of condylar articular cartilage degradation. The present study investigated the regulation of histone H3 lysine 9 (H3K9) methylation and its effects on the pathogenesis of degenerative TMJ cartilage disorders. The histone H3K9 methylation level was decreased in degenerated condylar articular cartilage in aged mice. Treatment with chaetocin (a selective H3K9 methylation inhibitor) reduced cell viability and promoted caspase‑3/7 activity in ATDC5 mouse chondroprogenitor cells. The inhibition of H3K9 methylation increased matrix metalloproteinase (Mmp)1 and Mmp13 mRNA expression in these cells. Furthermore, the expression levels of Sox9 and collagen α1(II) (Col2a1) mRNA, which are anabolic factors for chondrogenic differentiation, were also decreased by treatment with chaetocin, which is an inhibitor of histone methyltransferases. These results indicated that histone H3K9 methylation regulates chondrocyte homeostasis in terms of cell growth, apoptosis and gene expression, and highlighted a possible future therapy option for TMJOA.

Epigenetic control in skin development, homeostasis and injury repair

Cell-type- and cell-state-specific patterns of covalent modifications on DNA and histone tails form global epigenetic profiles that enable spatiotemporal regulation of gene expression. These epigenetic profiles arise from coordinated activities of transcription factors and epigenetic modifiers, which result in cell-type-specific outputs in response to dynamic environmental conditions and signalling pathways. Recent mouse genetic and functional studies have highlighted the physiological significance of global DNA and histone epigenetic modifications in skin. Importantly, specific epigenetic profiles are emerging for adult skin stem cells that are associated with their cell fate plasticity and proper activity in tissue regeneration. We can now begin to draw a more comprehensive picture of how epigenetic modifiers orchestrate their cell-intrinsic role with microenvironmental cues for proper skin development, homeostasis and wound repair. The field is ripe to begin to implement these findings from the laboratory into skin therapies.

Epigenetic Regulation of Skin Cells in Natural Aging and Premature Aging Diseases

Skin undergoes continuous renewal throughout an individual’s lifetime relying on stem cell functionality. However, a decline of the skin regenerative potential occurs with age. The accumulation of senescent cells over time probably reduces tissue regeneration and contributes to skin aging. Keratinocytes and dermal fibroblasts undergo senescence in response to several intrinsic or extrinsic stresses, including telomere shortening, overproduction of reactive oxygen species, diet, and sunlight exposure. Epigenetic mechanisms directly regulate skin homeostasis and regeneration, but they also mark cell senescence and the natural and pathological aging processes. Progeroid syndromes represent a group of clinical and genetically heterogeneous pathologies characterized by the accelerated aging of various tissues and organs, including skin. Skin cells from progeroid patients display molecular hallmarks that mimic those associated with naturally occurring aging. Thus, investigations on progeroid syndromes strongly contribute to disclose the causal mechanisms that underlie the aging process. In the present review, we discuss the role of epigenetic pathways in skin cell regulation during physiologic and premature aging.

Dual inhibition of PI3K signaling and histone deacetylation halts proliferation and induces lethality in mantle cell lymphoma

The dysregulation of PI3K signaling has been implicated as an underlying mechanism associated with resistance to Bruton's tyrosine kinase inhibition by ibrutinib in both chronic lymphocytic leukemia and mantle cell lymphoma (MCL). Ibrutinib resistance has become a major unmet clinical need, and the development of therapeutics to overcome ibrutinib resistance will greatly improve the poor outcomes of ibrutinib-exposed MCL patients. CUDC-907 inhibits both PI3K and HDAC functionality to exert synergistic or additive effects. Therefore, the activity of CUDC-907 was examined in MCL cell lines and patient primary cells, including ibrutinib-resistant MCL cells. The efficacy of CUDC-907 was further examined in an ibrutinib-resistant MCL patient-derived xenograft (PDX) mouse model. The molecular mechanisms by which CUDC-907 dually inhibits PI3K and histone deacetylation were assessed using reverse protein array, immunoblotting, and chromatin immunoprecipitation (ChIP) coupled with sequencing. We showed evidence that CUDC-907 treatment increased histone acetylation in MCL cells. We found that CUDC-907 caused decreased proliferation and increased apoptosis in MCL in vitro and in vivo MCL models. In addition, CUDC-907 was effective in inducing lethality in ibrutinib-resistant MCL cells. Lastly, CUDC-907 treatment increased histone acetylation in MCL cells. Overall, these studies suggest that CUDC-907 may be a promising therapeutic option for relapsed or resistant MCL.

UV-induced DNA methyltransferase 1 promotes hypermethylation of tissue inhibitor of metalloproteinase 2 in the human skin

BACKGROUND

Ultraviolet (UV) radiation has been reported to influence epigenetic regulation by affecting the expression of genome regulators such as DNA methyltransferase 1 (DNMT1). DNMT1 is a "gene silencer," that is responsible for the maintenance of DNA methylation and contribution to de novo methylation. Implications of DNMT1's involvement in the expression of UV-induced proteins have been previously reported.

OBJECTIVE

To investigate for changes in DNA methylation-associated gene expressions by UV and to analyze the role of DNA methylation in the suppression of TIMP2 in UV-irradiated human skin.

METHODS

The expression of DNA methylation-associated proteins and TIMP2 were analyzed in UV-irradiated human skin in vivo and in human dermal fibroblasts in vitro. To investigate the relationship between DNMT1 and TIMP2, we assessed the effect of DNMT1 knockdown, inhibition and overexpression on TIMP2 levels in human dermal fibroblasts. Lastly, methylation-specific PCR was used to confirm increased DNA methylation in TIMP2 promoter in response to UV.

RESULTS

DNMT1 expression significantly increased whereas TIMP2 expression decreased in UV-irradiated human skin in vivo and in vitro. Downregulation of DNMT1 by knockdown or inhibition resulted in increased TIMP2 expression, whereas the overexpression of DNMT1 resulted in decreased TIMP2 expression. Lastly, methylation-specific PCR confirmed increased methylation on the CpG island residing in TIMP2 promoter in UV-irradiated human dermal fibroblasts.

CONCLUSION

These findings suggest that UV-induced expression of DNMT1 may be responsible for mediating DNA hypermethylation in TIMP2, and thus, silencing its expression, in UV-exposed human skin.