Modulation of the Inflammatory Status of Macrophages and Their Paracrine Effect on the Sensitivity of Adipocytes to Insulin with Sirtuin and PPARγ Receptor Activators

Potentials of peroxisome proliferator-activated receptor (PPAR) α, β/δ, and γ: An in-depth and comprehensive review of their molecular mechanisms, cellular Signalling, immune responses and therapeutic implications in multiple diseases

Peroxisome proliferator-activated receptors (PPARs), ligand-activated transcription factors, have emerged as a key regulator of various biological processes, underscoring their relevance in the pathophysiology and treatment of numerous diseases. PPARs are primarily recognized for their critical role in lipid and glucose metabolism, which underpins their therapeutic applications in managing type 2 diabetes mellitus. Beyond metabolic disorders, they have gained attention for their involvement in immune modulation, making them potential targets for autoimmune-related inflammatory diseases. Furthermore, PPAR's ability to regulate proliferation, differentiation, and apoptosis has positioned them as promising candidates in oncology. Their anti-inflammatory and anti-fibrotic properties further highlight their potential in dermatological and cardiovascular conditions, where dysregulated inflammatory responses contribute to disease progression. Recent advancements have elucidated the molecular mechanisms of different PPAR isoforms, including their regulation of key signalling pathways such as NF-κB and MAPK, which are crucial in inflammation and cellular stress responses. Additionally, their interactions with co-factors and post-translational modifications further diversify their functional roles. The therapeutic potential of various PPAR agonists has been extensively explored, although challenges related to side effects and target specificity remain. This growing body of evidence underscores the significance of PPARs in understanding the molecular basis of diseases and advancing therapeutic interventions, paving way for targeted treatment approach across a wide spectrum of medical conditions. Here, we provide a comprehensive and detailed perspective of PPARs and their potential across different health conditions to advance our understanding, elucidate underlying mechanisms, and facilitate the development of potential treatment strategies.

Key genes and immune infiltration patterns and the clinical implications in psoriasis patients

BACKGROUND

Psoriasis is an immune-mediated skin disease, closely related to immune regulation. The aim was to understand the pathogenesis of psoriasis further, reveal potential therapeutic targets, and provide new clues for its diagnosis, treatment, and prevention.

MATERIALS AND METHODS

Expression profiling data were obtained from the Gene Expression Omnibus (GEO) database for skin tissues from healthy population and psoriasis patients. Differentially expressed genes (DEGs) were selected for Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) analysis separately. Machine learning algorithms were used to obtain characteristic genes closely associated with psoriasis. Receiver operating characteristic (ROC) curve was used to assess the diagnostic value of the characteristic genes for psoriasis. The Cell-type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT) algorithm was used to calculate the proportion of immune cell infiltration. Correlation analysis was used to characterize the connection between gene expression and immune cell, Psoriasis Area and Severity Index (PASI).

RESULTS

A total of 254 DEGs were identified in the psoriasis group, including 185 upregulated and 69 downregulated genes. GO was mainly enriched in cytokine-mediated signaling pathway, response to virus, and cytokine activity. KEGG was mainly focused on cytokine-cytokine receptor interaction and IL-17 signaling pathway. GSEA was mainly in chemokine signaling pathway and cytokine-cytokine receptor interaction. The machine learning algorithm screened nine characteristic genes C10orf99, GDA, FCHSD1, C12orf56, S100A7, INA, CHRNA9, IFI44, and CXCL9. In the validation set, the expressions of these nine genes increased in the psoriasis group, and the AUC values were all > 0.9, consistent with those of the training set. The immune infiltration results showed increased proportions of macrophages, T cells, and neutrophils in the psoriasis group. The characteristic genes were positively or negatively correlated to varying degrees with T cells and macrophages. Nine characteristic genes were highly expressed in the moderate to severe psoriasis group and positively correlated with PASI scores.

CONCLUSION

High levels of nine characteristic genes C10orf99, GDA, FCHSD1, C12orf56, S100A7, INA, CHRNA9, IFI44, and CXCL9 were risk factors for psoriasis, the differential expression of which was related to the regulation of immune system activity and PASI scores, affecting the proportions of different immune cells and promoting the occurrence and development of psoriasis.

The role of peroxisome proliferator-activated receptor γ in lipid metabolism and inflammation in atherosclerosis

Cardiovascular disease events are the result of functional and structural abnormalities in the arteries and heart. Atherosclerosis is the main cause and pathological basis of cardiovascular diseases. Atherosclerosis is a multifactorial disease associated with dyslipidemia, inflammation, and oxidative stress, among which dyslipidemia and chronic inflammation occur in all processes. Under the influence of lipoproteins, the arterial intima causes inflammation, necrosis, fibrosis, and calcification, leading to plaque formation in specific parts of the artery, which further develops into plaque rupture and secondary thrombosis. Foam cell formation from macrophages is an early event in the development of atherosclerosis. Lipid uptake causes a vascular inflammatory response, and persistent inflammatory infiltration in the lesion area further promotes the development of the disease. Inhibition of macrophage differentiation into foam cell and reduction of the level of proinflammatory factors in macrophages can effectively alleviate the occurrence and development of atherosclerosis. Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated nuclear receptor that plays an important antiatherosclerotic role by regulating triglyceride metabolism, lipid uptake, cholesterol efflux, macrophage polarity, and inhibiting inflammatory signaling pathways. In addition, PPARγ shifts its binding to ligands and co-activators or co-repressors of transcription of target genes through posttranslational modification, thereby affecting the regulation of its downstream target genes. Many ligand agonists have also been developed targeting PPARγ. In this review, we summarized the role of PPARγ in lipid metabolism and inflammation in development of atherosclerosis, the posttranslational regulatory mechanism of PPARγ, and further discusses the value of PPARγ as an antiatherosclerosis target.

Inonotsuoxide B regulates M1 to M2 macrophage polarization through sirtuin-1/endoplasmic reticulum stress axis

We explored the effect of tetracyclic triterpenoid inonotsuoxide B (IB) extracts of Inonotus obliquus on M1 to M2 macrophage polarization and its possible underlying mechanism. Lipopolysaccharide (LPS)-activated M1 macrophages exert pro-inflammatory effects and release inflammatory cytokines including interleukin (IL)-1β and tumor necrosis factor (TNF)-α. The model and various groups were treated with different IB concentrations (2.5, 5, and 10 μg/mL) to observe changes in the M1 and M2 phenotypes, gene expression of NAD-dependent deacetylase sirtuin-1 (Sirt1), and endoplasmic reticulum stress (ERS). SIRT1-siRNA and thapsigargin (TG), an ERS agonist, were used to examine the relationship between SIRT1/ERS and the effect of IB on M1 to M2 RAW264.7 macrophage phenotypic changes. We found that IB had no effect on RAW264.7 cell proliferation at 10 μg/mL. Increasing concentrations of IB (2.5, 5, and 10 μg/mL) decreased the number of phenotypic M1 macrophages and, consequently, decreased the release of the inflammatory cytokines, IL-1β and TNF-α. Furthermore, IB treatment increased the level of phenotypic M2 macrophages, which increased the release of anti-inflammatory cytokines such as arginase (Arg)-1 and found in inflammatory zone 1 (FIZZ1) in a dose-dependent manner. Further, we found that IB increased the expression of SIRT1 and inhibited that of ERS. Inhibition of Sirt1 expression by siRNA significantly increased that of ERS marker genes and IL1β. Excessive ERS levels inhibited the IB-induced transformation of phenotypic M1 macrophage to the M2 macrophage phenotype. Therefore, IB, an extract of I. obliquus, may regulate macrophage polarization through the SIRT1/ERS signaling pathway.

The role of peroxisome proliferator-activated receptors (PPAR) in immune responses

Peroxisome proliferator-activated receptors (PPARs) are fatty acid-activated transcription factors of nuclear hormone receptor superfamily that regulate energy metabolism. Currently, three PPAR subtypes have been identified: PPARα, PPARγ, and PPARβ/δ. PPARα and PPARδ are highly expressed in oxidative tissues and regulate genes involved in substrate delivery and oxidative phosphorylation (OXPHOS) and regulation of energy homeostasis. In contrast, PPARγ is more important in lipogenesis and lipid synthesis, with highest expression levels in white adipose tissue (WAT). In addition to tissues regulating whole body energy homeostasis, PPARs are expressed in immune cells and have an emerging critical role in immune cell differentiation and fate commitment. In this review, we discuss the actions of PPARs in the function of the innate and the adaptive immune system and their implications in immune-mediated inflammatory conditions.