Distinct hepatocyte identities in liver homeostasis and regeneration

Histone acetylation activated-IGF2BP3 regulates cyclin D1 mRNA stability to drive cell cycle transition and tumor progression of hepatocellular carcinoma

Insulin-like growth factor 2 mRNA binding protein 3 (IGF2BP3) is an oncofetal protein, is strongly associated with tumor initiation and progression due to its upregulation. However, the regulatory mechanisms driving IGF2BP3 upregulation and its contribution to the development and progression in hepatocellular carcinoma (HCC) remain unclear. In this study, we demonstrated that IGF2BP3 is re-expressed in HCC mouse models, with elevated levels correlating with a poor prognosis in patients with HCC. Our data revealed that histone acetylation at the IGF2BP3 promoter region drives transcription activation of IGF2BP3 in primary hepatocytes. Notably, histone acetylation and transcriptional reactivation of IGF2BP3 were observed in human HCC tissues as well. Mechanistically, IGF2BP3 knockdown modulated the cell cycle and cell proliferation by limiting G1/S phase transition, which is dependent on cyclin D1. We further showed that IGF2BP3 maintains CCND1 mRNA stability by directly interacting with its 3'UTR. Importantly, IGF2BP3 recruits the RNA stabilizer PABPC1 to potentiate CCND1 mRNA stability. These two proteins synergistically protect CCND1 mRNA from degradation. Furthermore, IGF2BP3-depleted HCC cells were unable to form tumors in the xenograft model. High IGF2BP3 and CCND1 levels predicted poor outcomes in patients. Collectively, our findings highlight the pivotal role of the IGF2BP3/cyclin D1 axis and reveal a new regulatory mechanism for IGF2BP3 re-expression via transcriptional activation during hepatocarcinogenesis. These results indicate that the IGF2BP3/CCND1 axis is a promising prognostic biomarker and potential therapeutic target for HCC.

Experimental Liver Surgery for Liver Research: Update, Choice and Translation

Experimental animal models of liver surgery are crucial for understanding human liver physiology and pathogenesis and identifying novel therapeutic modalities for liver disease. Herein, we update the brief summary of the most widely used experimental models and concepts in hepatic surgery, including hepatic ischemia/reperfusion, partial hepatectomy, liver transplantation, techniques and parameters of vascular perfusion of the liver, and using bile duct ligation as a model of cholestasis for the development of liver fibrosis. We focus on surgical aspects of available models for the study of various forms of liver disease. Furthermore, we summarize the translation of experimental liver surgery by highlighting surgical innovations, exploring key molecular mechanisms, and employing emerging treatment strategies.

Second harmonic generation microscopy reveals the spatial orientation of glutamine-potentiated liver regeneration after hepatectomy

BACKGROUND

Glutamine (Gln) is a critical amino acid for energy expenditure. It participates in extracellular matrix (ECM) formation and circulates in the hepatic parenchyma in a spatial-oriented manner. Posthepatectomy liver mass recovery poses a regenerative challenge. However, little is known about the role of Gln in liver regeneration, notably the spatial orientation in the remodeling process. This study aimed to elucidate Gln-potentiated liver regeneration and ECM remodeling after mass loss.

METHODS

We studied the regenerative process in hepatectomized mice supplemented with Gln. Second harmonic generation/two-photon excitation fluorescence microscopy, an artificial intelligence-assisted structure-based imaging, was used to demonstrate the spatial-oriented process in a hepatic acinus.

RESULTS

Gln promotes liver mass regrowth through the cell cycle, Gln metabolism, and adipogenesis pathways after hepatectomy. Ornithine transaminase, one of the upregulated enzymes, showed temporal, spatial, and functional correspondence with the regeneration process. Second harmonic generation/two-photon excitation fluorescence microscopy highlighted transient hepatic steatosis and ECM collagen synthesis, predominantly in the portal tract instead of the central vein area. Structural remodeling was also observed in the portal tract area.

CONCLUSIONS

Gln promotes liver regeneration through cellular proliferation and metabolic reprogramming after hepatectomy. Using structure-based imaging, we found that Gln potentiated hepatic steatosis and ECM collagen deposition predominantly in the portal tract area. These results highlighted the spatial orientation and mechanistic implications of Gln in liver regeneration.

Liver-specific actions of GH and IGF1 that protect against MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD; also known as nonalcoholic fatty liver disease) is a chronic condition associated with metabolic syndrome, a group of conditions that includes obesity, insulin resistance, hyperlipidaemia and cardiovascular disease. Primary growth hormone (GH) deficiency is associated with MASLD, and the decline in circulating levels of GH with weight gain might contribute to the development of MASLD. Raising endogenous GH secretion or administering GH replacement therapy in the context of MASLD enhances insulin-like growth factor 1 (IGF1) production and reduces steatosis and the severity of liver injury. GH and IGF1 indirectly control MASLD progression by regulating systemic metabolic function. Evidence supports the proposal that GH and IGF1 also have a direct role in regulating liver metabolism and health. This Review focuses on how GH acts on the hepatocyte in a sex-dependent manner to limit lipid accumulation, reduce stress, and promote survival and regeneration. In addition, we discuss how GH and IGF1 might regulate non-parenchymal cells of the liver to control inflammation and fibrosis, which have a major effect on hepatocyte survival and regeneration. Development of a better understanding of how GH and IGF1 coordinate the functions of specific, individual liver cell types might provide insight into the aetiology of MASLD initiation and progression and suggest novel approaches for the treatment of MASLD.

Mapping of mitogen and metabolic sensitivity in organoids defines requirements for human hepatocyte growth

Mechanisms underlying human hepatocyte growth in development and regeneration are incompletely understood. In vitro, human fetal hepatocytes (FH) can be robustly grown as organoids, while adult primary human hepatocyte (PHH) organoids remain difficult to expand, suggesting different growth requirements between fetal and adult hepatocytes. Here, we characterize hepatocyte organoid outgrowth using temporal transcriptomic and phenotypic approaches. FHs initiate reciprocal transcriptional programs involving increased proliferation and repressed lipid metabolism upon initiation of organoid growth. We exploit these insights to design maturation conditions for FH organoids, resulting in acquisition of mature hepatocyte morphological traits and increased expression of functional markers. During PHH organoid outgrowth in the same culture condition as for FHs, the adult transcriptomes initially mimic the fetal transcriptomic signatures, but PHHs rapidly acquire disbalanced proliferation-lipid metabolism dynamics, resulting in steatosis and halted organoid growth. IL6 supplementation, as emerged from the fetal dataset, and simultaneous activation of the metabolic regulator FXR, prevents steatosis and promotes PHH proliferation, resulting in improved expansion of the derived organoids. Single-cell RNA sequencing analyses reveal preservation of their fetal and adult hepatocyte identities in the respective organoid cultures. Our findings uncover mitogen requirements and metabolic differences determining proliferation of hepatocytes changing from development to adulthood.

Emerging roles of RNA-binding proteins in fatty liver disease

A rampant and urgent global health issue of the 21st century is the emergence and progression of fatty liver disease (FLD), including alcoholic fatty liver disease and the more heterogenous metabolism-associated (or non-alcoholic) fatty liver disease (MAFLD/NAFLD) phenotypes. These conditions manifest as disease spectra, progressing from benign hepatic steatosis to symptomatic steatohepatitis, cirrhosis, and, ultimately, hepatocellular carcinoma. With numerous intricately regulated molecular pathways implicated in its pathophysiology, recent data have emphasized the critical roles of RNA-binding proteins (RBPs) in the onset and development of FLD. They regulate gene transcription and post-transcriptional processes, including pre-mRNA splicing, capping, and polyadenylation, as well as mature mRNA transport, stability, and translation. RBP dysfunction at every point along the mRNA life cycle has been associated with altered lipid metabolism and cellular stress response, resulting in hepatic inflammation and fibrosis. Here, we discuss the current understanding of the role of RBPs in the post-transcriptional processes associated with FLD and highlight the possible and emerging therapeutic strategies leveraging RBP function for FLD treatment. This article is categorized under: RNA in Disease and Development > RNA in Disease.