E2F1 Regulates Adipocyte Differentiation and Adipogenesis by Activating ICAT

Novel insights into regulators and functional modulators of adipogenesis

Adipogenesis is a process that differentiates new adipocytes from precursor cells and is tightly regulated by several factors, including many transcription factors and various post-translational modifications. Recently, new roles of adipogenesis have been suggested in various diseases. However, the molecular mechanisms and functional modulation of these adipogenic genes remain poorly understood. This review summarizes the regulatory factors and modulators of adipogenesis and discusses future research directions to identify novel mechanisms regulating adipogenesis and the effects of adipogenic regulators in pathological conditions. The master adipogenic transcriptional factors PPARγ and C/EBPα were identified along with other crucial regulatory factors such as SREBP, Kroxs, STAT5, Wnt, FOXO1, SWI/SNF, KLFs, and PARPs. These transcriptional factors regulate adipogenesis through specific mechanisms, depending on the adipogenic stage. However, further studies related to the in vivo role of newly discovered adipogenic regulators and their function in various diseases are needed to develop new potent therapeutic strategies for metabolic diseases and cancer.

Transcriptomic analysis reveals regulation of adipogenesis via long non-coding RNA, alternative splicing, and alternative polyadenylation

Obesity is characterized by dysregulated adipogenesis that leads to increased number and/or size of adipocytes. Understanding the molecular mechanisms governing adipogenesis is therefore key to designing therapeutic interventions against obesity. In our study, we analyzed 3'-end sequencing data that we generated from human preadipocytes and adipocytes, as well as previously published RNA-seq datasets, to elucidate mechanisms of regulation via long non-coding RNA (lncRNA), alternative splicing (AS) and alternative polyadenylation (APA). We discovered lncRNAs that have not been previously characterized but may be key regulators of white adipogenesis. We also detected 100 AS events and, using motif enrichment analysis, identified RNA binding proteins (RBPs) that could mediate exon skipping-the most prevalent AS event. In addition, we show that usage of alternative poly(A) sites in introns or 3'-UTRs of key adipogenesis genes leads to isoform diversity, which can have significant biological consequences on differentiation efficiency. We also identified RBPs that may modulate APA and defined how 3'-UTR APA can regulate gene expression through gain or loss of specific microRNA binding sites. Taken together, our bioinformatics-based analysis reveals potential therapeutic avenues for obesity through manipulation of lncRNA levels and the profile of mRNA isoforms via alternative splicing and polyadenylation.

E2F transcription factor 5, a new regulator in adipogenesis to mediate the role of Krüppel-like factor 7 in chicken preadipocyte differentiation and proliferation

E2F transcription factor 5 (E2F5) gene is a transcription factor, plays an important role in the development of a variety of cells. E2F5 is expressed in human and mouse adipocytes, but its specific function in adipogenesis is unclear. Krüppel-like factor 7 (KLF7) facilitates proliferation and inhibits differentiation in chicken preadipocytes. Our previous KLF7 chromatin immunoprecipitation-sequencing analysis revealed a KLF7-binding peak in the 3' flanking region of the E2F5, indicating a regulatory role of KLF7 in this region. In the present study, we investigated E2F5 potential role, the overexpression and knockdown analyses revealed that E2F5 inhibited the differentiation and promoted the proliferation of chicken preadipocytes. Moreover, we identified enhancer activity in the 3' flanking region (nucleotides +22661/+22900) of E2F5 and found that KLF7 overexpression increased E2F5 expression and luciferase activity in this region. Deleting the putative KLF7-binding site eliminated the promoting effect of KLF7 overexpression on E2F5 expression. Further, E2F5 reversed the KLF7-induced decrease in preadipocyte differentiation and increase in preadipocyte proliferation. Taken together, our findings demonstrate that KLF7 inhibits differentiation and promotes proliferation in preadipocytes by enhancing E2F5 transcription.

Navigating Tumour Microenvironment and Wnt Signalling Crosstalk: Implications for Advanced Cancer Therapeutics

Cancer therapeutics face significant challenges due to drug resistance and tumour recurrence. The tumour microenvironment (TME) is a crucial contributor and essential hallmark of cancer. It encompasses various components surrounding the tumour, including intercellular elements, immune system cells, the vascular system, stem cells, and extracellular matrices, all of which play critical roles in tumour progression, epithelial-mesenchymal transition, metastasis, drug resistance, and relapse. These components interact with multiple signalling pathways, positively or negatively influencing cell growth. Abnormal regulation of the Wnt signalling pathway has been observed in tumorigenesis and contributes to tumour growth. A comprehensive understanding and characterisation of how different cells within the TME communicate through signalling pathways is vital. This review aims to explore the intricate and dynamic interactions, expressions, and alterations of TME components and the Wnt signalling pathway, offering valuable insights into the development of therapeutic applications.

GSK-3 inhibition reverts mesenchymal transition in primary human corneal endothelial cells

Human corneal endothelial cells are organized in a tight mosaic of hexagonal cells and serve a critical function in maintaining corneal hydration and clear vision. Regeneration of the corneal endothelial tissue is hampered by its poor proliferative capacity, which is partially retrieved in vitro, albeit only for a limited number of passages before the cells undergo mesenchymal transition (EnMT). Although different culture conditions have been proposed in order to delay this process and prolong the number of cell passages, EnMT has still not been fully understood and successfully counteracted. In this perspective, we identified herein a single GSK-3 inhibitor, CHIR99021, able to revert and avoid EnMT in primary human corneal endothelial cells (HCEnCs) from old donors until late passages in vitro (P8), as shown from cell morphology analysis (circularity). In accordance, CHIR99021 reduced expression of α-SMA, an EnMT marker, while restored endothelial markers such as ZO-1, Na⁺/K⁺ ATPase and N-cadherin, without increasing cell proliferation. A further analysis on RNA expression confirmed that CHIR99021 induced downregulation of EnMT markers (α-SMA and CD44), upregulation of the proliferation repressor p21 and revealed novel insights into the β-catenin and TGFβ pathways intersections in HCEnCs. The use of CHIR99021 sheds light on the mechanisms involved in EnMT, providing a substantial advantage in maintaining primary HCEnCs in culture until late passages, while preserving the correct morphology and phenotype. Altogether, these results bring crucial advancements towards the improvement of the corneal endothelial cells based therapy.

ICAT promotes colorectal cancer metastasis via binding to JUP and activating the NF-κB signaling pathway

Background

The inhibitor of β‐catenin and T‐cell factor (ICAT) is a direct negative regulator of the canonical Wnt signaling pathway, which is an attractive therapeutic target for colorectal cancer (CRC). Accumulating evidence suggests that ICAT interacts with other proteins to exert additional functions, which are not yet fully elucidated.

Methods

The overexpression of ICAT of CRC cells was conducted by lentivirus infection and plasmids transfection and verified by quantitative real‐time reverse transcription‐polymerase chain reaction (real‐time RT‐PCR) and Western blotting. The effect of ICAT on the mobility of CRC cells was assessed by wound healing assay and transwell assay in vitro and lung metastasis in vivo. New candidate ICAT‐interacting proteins were explored and verified using the STRING database, silver staining, co‐immunoprecipitation mass spectrometry analysis (Co‐IP/MS), and immunofluorescence (IF) staining analysis.

Result

Inhibitor of β‐catenin and T‐cell factor overexpression promoted in vitro cell migration and invasion and tumor metastasis in vivo. Co‐IP/MS analysis and STRING database analyses revealed that junction plakoglobin (JUP), a homolog of β‐catenin, was involved in a novel protein interaction with ICAT. Furthermore, JUP downregulation impaired ICAT‐induced migration and invasion of CRC cells. In addition, ICAT overexpression activated the NF‐κB signaling pathway, which led to enhanced CRC cell migration and invasion.

Conclusion

Inhibitor of β‐catenin and T‐cell factor promoted CRC cell migration and invasion by interacting with JUP and the NF‐κB signaling pathway. Thus, ICAT could be considered a protein diagnostic biomarker for predicting the metastatic ability of CRC.

The transcription factor E2F1 controls the GLP-1 receptor pathway in pancreatic β cells

The glucagon-like peptide 1 (Glp-1) has emerged as a hormone with broad pharmacological potential in type 2 diabetes (T2D) treatment, notably by improving β cell functions. The cell-cycle regulator and transcription factor E2f1 is involved in glucose homeostasis by modulating β cell mass and function. Here, we report that β cell-specific genetic ablation of E2f1 (E2f1β-/-) impairs glucose homeostasis associated with decreased expression of the Glp-1 receptor (Glp1r) in E2f1β-/- pancreatic islets. Pharmacological inhibition of E2F1 transcriptional activity in nondiabetic human islets decreases GLP1R levels and blunts the incretin effect of GLP1R agonist exendin-4 (ex-4) on insulin secretion. Overexpressing E2f1 in pancreatic β cells increases Glp1r expression associated with enhanced insulin secretion mediated by ex-4. Interestingly, ex-4 induces retinoblastoma protein (pRb) phosphorylation and E2f1 transcriptional activity. Our findings reveal critical roles for E2f1 in β cell function and suggest molecular crosstalk between the E2F1/pRb and GLP1R signaling pathways.

miR-10a-5p Inhibits the Differentiation of Goat Intramuscular Preadipocytes by Targeting KLF8 in Goats

Intramuscular fat contributes to the improvement of meat quality of goats. MicroRNAs (miRNAs) have been reported to regulate adipocyte differentiation and maturation. The aim of our study was to clarify whether miR-10a-5p regulates goat intramuscular preadipocyte (GIPC) differentiation and its direct downstream signaling pathway. GIPCs were isolated from longissimus dorsi, whose miR-10a-5p level was measured at different time point of differentiation induction. Adipogenic differentiation of the GIPCs was evaluated by Oil Red O and BODIPY staining, and the expression changes of adipogenic genes like ACC, ATGL, CEBPβ, PPARγ, etc. Related mechanisms were verified by qPCR, a bioinformatic analysis, a dual-luciferase reporter assay, overexpression, and siRNA transfection. Oil Red O and BODIPY staining both with adipogenic gene detection showed that miR-10a-5p suppressed the accumulation of lipid droplets in GIPCs and inhibited its differentiation. The dual-luciferase reporter assay experiment revealed that miR-10a-5p regulates GIPC differentiation by directly binding to KLF8 3’UTR to regulate its expression. Thus, the results indicated that miR-10a-5p inhibits GIPC differentiation by targeting KLF8 and supply a new target for fat deposition and meat quality improvement.

Oxysterol-binding protein-like 2 contributes to the developmental progression of preadipocytes by binding to β-catenin

Oxysterol-binding protein-like 2 (OSBPL2), also known as oxysterol-binding protein-related protein (ORP) 2, is a member of lipid transfer protein well-known for its role in regulating cholesterol homeostasis. A recent study reported that OSBPL2/ORP2 localizes to lipid droplets (LDs) and is associated with energy metabolism and obesity. However, the function of OSBPL2/ORP2 in adipocyte differentiation is poorly understood. Here, we report that OSBPL2/ORP2 contributes to the developmental progression of preadipocytes. We found that OSBPL2/ORP2 binds to β-catenin, a key effector in the Wnt signaling pathway that inhibits adipogenesis. This complex plays a role in regulating the protein level of β-catenin only in preadipocytes, not in mature adipocytes. Our data further indicated that OSBPL2/ORP2 mediates the transport of β-catenin into the nucleus and thus regulates target genes related to adipocyte differentiation. Deletion of OSBPL2/ORP2 markedly reduces β-catenin both in the cytoplasm and in the nucleus, promotes preadipocytes maturation, and ultimately leads to obesity-related characteristics. Altogether, we provide novel insight into the function of OSBPL2/ORP2 in the developmental progression of preadipocytes and suggest OSBPL2/ORP2 may be a potential therapeutic target for the treatment of obesity-related diseases.

Emerging Roles for the INK4a/ARF (CDKN2A) Locus in Adipose Tissue: Implications for Obesity and Type 2 Diabetes

Besides its role as a cell cycle and proliferation regulator, the INK4a/ARF (CDKN2A) locus and its associated pathways are thought to play additional functions in the control of energy homeostasis. Genome-wide association studies in humans and rodents have revealed that single nucleotide polymorphisms in this locus are risk factors for obesity and related metabolic diseases including cardiovascular complications and type-2 diabetes (T2D). Recent studies showed that both p16^INK4a-CDK4-E2F1/pRB and p19^ARF-P53 (p14^ARF in humans) related pathways regulate adipose tissue (AT) physiology and adipocyte functions such as lipid storage, inflammation, oxidative activity, and cellular plasticity (browning). Targeting these metabolic pathways in AT emerged as a new putative therapy to alleviate the effects of obesity and prevent T2D. This review aims to provide an overview of the literature linking the INK4a/ARF locus with AT functions, focusing on its mechanisms of action in the regulation of energy homeostasis.