Nuclear receptor 4A1 (NR4A1) silencing protects hepatocyte against hypoxia-reperfusion injury in vitro by activating liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling

Exploring the impact of the PNPLA3 I148M variant on primary human hepatic stellate cells using 3D extracellular matrix models

BACKGROUND & AIMS

The PNPLA3 rs738409 C>G (encoding for I148M) variant is a risk locus for the fibrogenic progression of chronic liver diseases, a process driven by hepatic stellate cells (HSCs). We investigated how the PNPLA3 I148M variant affects HSC biology using transcriptomic data and validated findings in 3D-culture models.

METHODS

RNA sequencing was performed on 2D-cultured primary human HSCs and liver biopsies of individuals with obesity, genotyped for the PNPLA3 I148M variant. Data were validated in wild-type (WT) or PNPLA3 I148M variant-carrying HSCs cultured on 3D extracellular matrix (ECM) scaffolds from human healthy and cirrhotic livers, with/without TGFB1 or cytosporone B (Csn-B) treatment.

RESULTS

Transcriptomic analyses of liver biopsies and HSCs highlighted shared PNPLA3 I148M-driven dysregulated pathways related to mitochondrial function, antioxidant response, ECM remodelling and TGFB1 signalling. Analogous pathways were dysregulated in WT/PNPLA3-I148M HSCs cultured in 3D liver scaffolds. Mitochondrial dysfunction in PNPLA3-I148M cells was linked to respiratory chain complex IV insufficiency. Antioxidant capacity was lower in PNPLA3-I148M HSCs, while reactive oxygen species secretion was increased in PNPLA3-I148M HSCs and higher in bioengineered cirrhotic vs. healthy scaffolds. TGFB1 signalling followed the same trend. In PNPLA3-I148M cells, expression and activation of the endogenous TGFB1 inhibitor NR4A1 were decreased: treatment with the Csn-B agonist increased total NR4A1 in HSCs cultured in healthy but not in cirrhotic 3D scaffolds. NR4A1 regulation by TGFB1/Csn-B was linked to Akt signalling in PNPLA3-WT HSCs and to Erk signalling in PNPLA3-I148M HSCs.

CONCLUSION

HSCs carrying the PNPLA3 I148M variant have impaired mitochondrial function, antioxidant responses, and increased TGFB1 signalling, which dampens antifibrotic NR4A1 activity. These features are exacerbated by cirrhotic ECM, highlighting the dual impact of the PNPLA3 I148M variant and the fibrotic microenvironment in progressive chronic liver diseases.

IMPACT AND IMPLICATIONS

Hepatic stellate cells (HSCs) play a key role in the fibrogenic process associated with chronic liver disease. The PNPLA3 genetic mutation has been linked with increased risk of fibrogenesis, but its role in HSCs requires further investigation. Here, by using comparative transcriptomics and a novel 3D in vitro model, we demonstrate the impact of the PNPLA3 genetic mutation on primary human HSCs' behaviour, and we show that it affects the cell's mitochondrial function and antioxidant response, as well as the antifibrotic gene NR4A1. Our publicly available transcriptomic data, 3D platform and our findings on NR4A1 could facilitate the discovery of targets to develop more effective treatments for chronic liver diseases.

M1 linear ubiquitination of LKB1 inhibits vascular endothelial cell injury in atherosclerosis through activation of AMPK

Endothelial cell injury is confirmed to be the initial step in the atherosclerosis (AS) process. Here, we tried to elucidate the role of liver kinase B1 (LKB1) and adenosine phosphate protein kinase (AMPK) in modulating vascular endothelial cells (VECs) in AS. High-fat feed (HFD)-induced AS rat models were prepared and treated with AMPK activator A-769662 alone or combined with chloroquine. An analysis of VEC injury, inflammation response, and autophagy followed it. The M1 linear ubiquitination of LKB1 was assessed by co-immunoprecipitation. The interaction between LKB1 and AMPK was analyzed. Primary aortic VECs were isolated and induced by LPS to verify the effects of LKB1 and AMPK on VEC injury in AS. Activation of AMPK reduced the VEC injury and inflammatory response of VECs and promoted autophagy caused by AS. LKB1 could regulate the activation of AMPK in AS. M1 linear ubiquitination enhanced LKB1 activity and increased AMPK activation to protect against VEC injury in AS, which was validated by in vitro experiments. Our current study highlighted that M1 linear ubiquitination of LKB1 may induce the activation of LKB1 to activate AMPK, which inhibited VEC injury in AS.

NR4A1 Aggravates Myocardial Ischaemia-Reperfusion Injury by Inhibiting OPA1-Mediated Mitochondrial Fusion

Mitochondrial fusion is an important process that protects the myocardium. However, mitochondrial fusion is often inhibited in myocardial ischaemia-reperfusion injury (IR). The upstream mechanism of this effect is unclear. Nuclear receptor subfamily 4 group A member 1 (NR4A1) can aggravate myocardial IR and increase the level of oxidative stress, thereby affecting mitochondrial function and morphology. Inhibiting NR4A1 can improve oxidative stress levels and mitochondrial function and morphology, thereby reducing IR. Downregulating NR4A1 increases the expression level of the mitochondrial fusion-related protein optic atrophy 1 (OPA1), which is associated with these benefits. Inhibiting OPA1 expression with MYLS22 abrogates the effects of NR4A1 downregulation on IR. Furthermore, NR4A1 disrupts mitochondrial dynamics and activates the STING and NF-κB pathways. Insufficient mitochondrial fusion and increased apoptosis and inflammatory reactions worsen irreversible damage to cardiomyocytes. In conclusion, NR4A1 can exacerbate IR by inhibiting OPA1, causing mitochondrial damage.

The nuclear receptor subfamily 4 group A1 in human disease

Nuclear receptor 4A1 (NR4A1), a member of the NR4A subfamily, acts as a gene regulator in a wide range of signaling pathways and responses to human diseases. Here, we provide a brief overview of the current functions of NR4A1 in human diseases and the factors involved in its function. A deeper understanding of these mechanisms can potentially improve drug development and disease therapy.

An update on the molecular mechanism and pharmacological interventions for Ischemia-reperfusion injury by regulating AMPK/mTOR signaling pathway in autophagy

AMP-activated protein kinase (5'-adenosine monophosphate-activated protein kinase, AMPK)/mammalian target of rapamycin (mTOR) is an important signaling pathway maintaining normal cell function and homeostasis in vivo. The AMPK/mTOR pathway regulates cellular proliferation, autophagy, and apoptosis. Ischemia-reperfusion injury (IRI) is secondary damage that frequently occurs clinically in various disease processes and treatments, and the exacerbated injury during tissue reperfusion increases disease-associated morbidity and mortality. IRI arises from multiple complex pathological mechanisms, among which cell autophagy is a focus of recent research and a new therapeutic target. The activation of AMPK/mTOR signaling in IRI can modulate cellular metabolism and regulate cell proliferation and immune cell differentiation by adjusting gene transcription and protein synthesis. Thus, the AMPK/mTOR signaling pathway has been intensively investigated in studies focused on IRI prevention and treatment. In recent years, AMPK/mTOR pathway-mediated autophagy has been found to play a crucial role in IRI treatment. This article aims to elaborate the action mechanisms of AMPK/mTOR signaling pathway activation in IRI and summarize the progress of AMPK/mTOR-mediated autophagy research in the field of IRI therapy.