Hepatic-specific Pgc-1α ablation drives fibrosis in a MASH model.

BACKGROUND & AIMS: Metabolic dysfunction-associated steatohepatitis (MASH) is a growing cause of chronic liver disease, characterized by fat accumulation, inflammation and fibrosis, which development depends on mitochondrial dysfunction and oxidative stress. Highly expressed in the liver during fasting, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) regulates mitochondrial and oxidative metabolism. Given the relevant role of mitochondrial function in MASH, we investigated the relationship between PGC-1α and steatohepatitis. METHODS: We measured the hepatic expression of Pgc-1α in both MASH patients and wild-type mice fed a western diet (WD) inducing steatosis and fibrosis. We then generated a pure C57BL6/J strain loss of function mouse model in which Pgc-1α is selectively deleted in the liver and we fed these mice with a WD supplemented with sugar water that accurately mimics human MASH. RESULTS: We observed that the hepatic expression of Pgc-1α is strongly reduced in MASH, in both humans and mice. Moreover, the hepatic ablation of Pgc-1α promotes a considerable reduction of the hepatic mitochondrial respiratory capacity, setting up a bioenergetic harmful environment for liver diseases. Indeed, the lack of Pgc-1α decreases mitochondrial function and increases inflammation, fibrosis and oxidative stress in the scenario of MASH. Intriguingly, this profibrotic phenotype is not linked with obesity, insulin resistance and lipid disbalance. CONCLUSIONS: In a MASH model the hepatic ablation of Pgc-1α drives fibrosis independently from lipid and glucose metabolism. These results add a novel mechanistic piece to the puzzle of the specific and crucial role of mitochondrial function in MASH development.

Pivotal role of intestinal cholesterol and nuclear receptor LXR in metabolic liver steatohepatitis and hepatocarcinoma.

Hepatocellular carcinoma (HCC) incidence is continuously increasing worldwide, due to the rise of metabolic dysfunction-associated steatohepatitis (MASH) cases. Cholesterol is an essential driver of the metabolic dysregulations that promote HCC progression. Liver X Receptor (LXR) is a nuclear receptor best known for the regulation of lipid and cholesterol homeostasis, with a prominent function in the liver and in the intestine. Here, we aimed to explore whether modifications in intestinal lipid metabolism may contribute to the onset of HCC, particularly taking into account cholesterol metabolism and LXRs. To study the progression of MASH to HCC, we induced metabolic HCC in wild-type male mice and mice carrying an intestinal chronic activation of LXRα. Also, we analysed human hepatic transcriptome datasets. The increased consumption of fat and carbohydrates drives the intestinal activation of LXRα and accelerates the onset of the hepatic tumours. Chronic intestinal-specific activation of LXRα enhances HCC progression only in the presence of a high cholesterol intake. In HCC, despite the increased hepatic cholesterol content, LXR is not active, thus driving liver cancer development. Intriguingly, in line with these results in the mouse model, LXR transcriptome is also downregulated in human hepatocarcinoma and its expression level in liver tumours directly correlates with a decreased survival rate in patients. Overall, our findings establish the relevance of the intestine in influencing the susceptibility to MASH-HCC and point to intestinal LXRα activation as a driver of metabolic liver cancer in the presence of dietary cholesterol.

Intestinal Pgc1α ablation protects from liver steatosis and fibrosis.

Background & Aims: The gut-liver axis modulates the progression of metabolic dysfunction-associated steatotic liver disease (MASLD), a spectrum of conditions characterised by hepatic steatosis and a progressive increase of inflammation and fibrosis, culminating in metabolic dysfunction-associated steatohepatitis. Peroxisome proliferator-activated receptor-gamma coactivator 1α (Pgc1α) is a transcriptional co-regulator of mitochondrial activity and lipid metabolism. Here, the intestinal-specific role of Pgc1α was analysed in liver steatosis and fibrosis. Methods: We used a mouse model in which Pgc1α was selectively deleted from the intestinal epithelium. We fed these mice and their wild-type littermates a Western diet to recapitulate the major features of liver steatosis (after 2 months of diet) and metabolic dysfunction-associated steatohepatitis (after 4 months of diet). The chow diet was administered as a control diet. Results: In humans and mice, low expression of intestinal Pgc1α is inversely associated with liver steatosis, inflammation, and fibrosis. Intestinal disruption of Pgc1α impairs the transcription of a wide number of genes, including the cholesterol transporter Niemann-Pick C1-like 1 (Npc1l1), thus limiting the uptake of cholesterol from the gut. This results in a lower cholesterol accretion in the liver and a decreased production of new fatty acids, which protect the liver from lipotoxic lipid species accumulation, inflammation, and related fibrotic processes. Conclusions: In humans and mice, intestinal Pgc1α induction during Western diet may be another culprit driving hepatic steatosis and fibrosis. Here, we show that enterocyte-specific Pgc1α ablation protects the liver from steatosis and fibrosis by reducing intestinal cholesterol absorption, with subsequent decrease of cholesterol and de novo fatty acid accumulation in the liver. Impact and implications: Liver diseases result from several insults, including signals from the gut. Although the incidence of liver diseases is continuously increasing worldwide, effective drug therapy is still lacking. Here, we showed that the modulation of an intestinal coactivator regulates the liver response to a Western diet, by limiting the uptake of dietary cholesterol. This results in a lower accumulation of hepatic lipids together with decreased inflammation and fibrosis, thus limiting the progression of liver steatosis and fibrosis towards severe end-stage diseases.

Platelets from patients with visceral obesity promote colon cancer growth.

Several studies highlighted the importance of platelets in the tumor microenvironment due to their ability to interact with other cell types such as leukocytes, endothelial, stromal and cancer cells. Platelets can influence tumor development and metastasis formation through several processes consisting of the secretion of growth factors and cytokines and/or via direct interaction with cancer cells and endothelium. Patients with visceral obesity (VO) are susceptible to pro-thrombotic and pro-inflammatory states and to development of cancer, especially colon cancer. These findings provide us with the impetus to analyze the role of platelets isolated from VO patients in tumor growth and progression with the aim to explore a possible link between platelet activation, obesity and colon cancer. Here, using xenograft colon cancer models, we prove that platelets from patients with visceral obesity are able to strongly promote colon cancer growth. Then, sequencing platelet miRNome, we identify miR-19a as the highest expressed miRNA in obese subjects and prove that miR-19a is induced in colon cancer. Last, administration of miR-19a per se in the xenograft colon cancer model is able to promote colon cancer growth. We thus elect platelets with their specific miRNA abundance as important factors in the tumor promoting microenvironment of patients with visceral obesity.

Enterocyte superoxide dismutase 2 deletion drives obesity.

Compelling evidence support an involvement of oxidative stress and intestinal inflammation as early events in the predisposition and development of obesity and its related comorbidities. Here, we show that deficiency of the major mitochondrial antioxidant enzyme superoxide dismutase 2 (SOD2) in the gastrointestinal tract drives spontaneous obesity. Intestinal epithelium-specific Sod2 ablation in mice induced adiposity and inflammation via phospholipase A2 (PLA2) activation and increased release of omega-6 polyunsaturated fatty acid arachidonic acid. Remarkably, this obese phenotype was rescued when fed an essential fatty acid-deficient diet, which abrogates de novo biosynthesis of arachidonic acid. Data from clinical samples revealed that the negative correlation between intestinal Sod2 mRNA levels and obesity features appears to be conserved between mice and humans. Collectively, our findings suggest a role of intestinal Sod2 levels, PLA2 activity, and arachidonic acid in obesity presenting new potential targets of therapeutic interest in the context of this metabolic disorder.

let-7e downregulation characterizes early phase colonic adenoma in APCMin/+ mice and human FAP subjects.

The crypt-villus axis represents the essential unit of the small intestine, which integrity and functions are fundamental to assure tissue and whole-body homeostasis. Disruption of pathways regulating the fine balance between proliferation and differentiation results in diseases development. Nowadays, it is well established that microRNAs (miRNAs) play a crucial role in the homeostasis maintenance and perturbation of their levels may promote tumor development. Here, by using microarray technology, we analysed the miRNAs differentially expressed between the crypt and the villus in mice ileum. The emerged miRNAs were further validated by Real Time qPCR in mouse model (ApcMin/+), human cell lines and human tissue samples (FAP) of colorectal cancer (CRC). Our results indicated that miRNAs more expressed in the villi compartment are negatively regulated in tumor specimens, thus suggesting a close association between these microRNAs and the differentiation process. Particularly, from our analysis let-7e appeared to be a promising target for possible future therapies and a valuable marker for tumor staging, being upregulated in differentiated cells and downregulated in early-stage colonic adenoma samples.

Another One Bites the Gut: Nuclear Receptor LRH-1 in Intestinal Regeneration and Cancer.

The process of self-renewal in normal intestinal epithelium is characterized by a fine balance between proliferation, differentiation, migration, and cell death. When even one of these aspects escapes the normal control, cellular proliferation and differentiation are impaired, with consequent onset of tumorigenesis. In humans, colorectal cancer (CRC) is the main pathological manifestation of this derangement. Nowadays, CRC is the world's fourth most deadly cancer with a limited survival after treatment. Several conditions can predispose to CRC development, including dietary habits and pre-existing inflammatory bowel diseases. Given their extraordinary ability to interact with DNA, it is widely known that nuclear receptors play a key role in the regulation of intestinal epithelium, orchestrating the expression of a series of genes involved in developmental and homeostatic pathways. In particular, the nuclear receptor Liver Receptor Homolog-1 (LRH-1), highly expressed in the stem cells localized in the crypts, promotes intestine cell proliferation and renewal in both direct and indirect DNA-binding manner. Furthermore, LRH-1 is extensively correlated with diverse intestinal inflammatory pathways. These evidence shed a light in the dynamic intestinal microenvironment in which increased regenerative epithelial cell turnover, mutagenic insults, and chronic DNA damages triggered by factors within an inflammatory cell-rich microenvironment act synergistically to favor cancer onset and progression.

Intracoronary monocyte expression pattern and HDL subfractions after non-ST elevation myocardial infarction.

AIMS: Coronary artery disease (CAD) is described as a range of clinical conditions including myocardial infarction (MI) and unstable angina. Lipid and apolipoprotein profiles together with the study of cholesterol deposit and efflux serve to identify novel pre and post infarct scenarios for the treatment of these patients. In (non-ST elevation myocardial infarction) NSTEMI patients, we analysed both systemic and intracoronary serum ability to accept cholesterol as well as cholesterol efflux capacity (CEC) of monocytes in terms of expression of genes involved in the reverse cholesterol transport (RCT). METHODS AND RESULTS: While HDL-C quantity was similar between systemic and coronary arterial blood, in 21 NSTEMI patients we observed a significant reduction of the preß-HDL fraction and the levels of Apolipoproteins AI, AII, B and E in coronary versus systemic serum. These data are complemented with the observed reduction of CEC. On the contrary, compared to systemic arterial monocytes, in coronary microenvironment of NSTEMI patients after myocardial infarction, the monocytes exhibited a higher mRNA expression of nuclear receptor LXRα and its targets ABCA1 and APOE, which drive cholesterol efflux capacity. CONCLUSION: In this cross-sectional study we observe that in the immediate post infarction period, there is a spontaneous bona fide ligand-induced activation of the LXR driven cholesterol efflux capacity of intracoronary monocytes to overcome the reduced serum ability to accept cholesterol and to inhibit the post-infarction pro-inflammatory local microenvironment.

Increased risk of acute liver failure by pain killer drugs in NAFLD: Focus on nuclear receptors and their coactivators.

Non-alcoholic fatty liver disease (NAFLD) is a global condition characterized by an accumulation of lipids in the hepatocytes. NAFLD ranges from simple steatosis, a reversible and relatively benign condition, to fibrosis with non-alcoholic steatohepatitis (NASH), potentially leading to cirrhosis and hepatocarcinoma. NAFLD can increase the susceptibility to severe liver injury with eventual acute liver failure induced by specific hepatotoxic drugs, including acetaminophen (APAP), which is commonly used as analgesic and antipyretic. Although several animal models have been used to clarify the predisposing role of hepatic steatosis to APAP intoxication, the exact mechanism is still not clear. Here, we shed a light into the association between NAFLD and APAP toxicity by examining the peculiar role of nuclear receptor peroxisome proliferator-activated receptor α (PPARα) and coactivator peroxisome proliferator-activated receptor gamma coactivator 1-ß (PGC-1ß) in driving fatty acid metabolism, inflammation and mitochondria redox balance. The knowledge of the mechanism that exposes patients with NAFLD to higher risk of acute liver failure by pain killer drug is the first step to eventually claim for a reduction of the maximal diurnal dose of APAP for subjects with liver steatosis.

Hepatic microRNA Expression by PGC-1α and PGC-1ß in the Mouse.

The fine-tuning of liver metabolism is essential to maintain the whole-body homeostasis and to prevent the onset of diseases. The peroxisome proliferator-activated receptor-γ coactivators (PGC-1s) are transcriptional key players of liver metabolism, able to regulate mitochondrial function, gluconeogenesis and lipid metabolism. Their activity is accurately modulated by post-translational modifications. Here, we showed that specific PGC-1s expression can lead to the upregulation of different microRNAs widely implicated in liver physiology and diseases development and progression, thus offering a new layer of complexity in the control of hepatic metabolism.

PGC-1ß Induces Susceptibility To Acetaminophen-Driven Acute Liver Failure.

Acetaminophen (APAP) is a worldwide commonly used painkiller drug. However, high doses of APAP can lead to acute hepatic failure and, in some cases, death. Previous studies indicated that different factors, including life-style and metabolic diseases, could predispose to the risk of APAP-induced liver failure. However, the molecular process that could favor APAP hepatotoxicity remains understood. Here, we reported that a short-term high fat-enriched diet worsens APAP-induced liver damage, by promoting liver accumulation of lipids that induces the activation of peroxisome proliferator-activated receptor gamma coactivator 1-beta (PGC-1ß). Therefore, we challenged mice with hepatic-specific PGC-1ß overexpression on a chow diet with a subtoxic dose of APAP and we found that PGC-1ß overexpression renders the liver more sensitive to APAP damage, mainly due to intense oxidative stress, finally ending up with liver necrosis and mice death. Overall, our results indicated that during high fat feeding, PGC-1ß adversely influences the ability of the liver to overcome APAP toxicity by orchestrating different metabolic pathways that finally lead to fatal outcome.

PGC-1α induced browning promotes involution and inhibits lactation in mammary glands.

The PPARγ coactivator 1α (PGC-1α) is a transcriptional regulator of mitochondrial biogenesis and oxidative metabolism. Recent studies have highlighted a fundamental role of PGC-1α in promoting breast cancer progression and metastasis, but the physiological role of this coactivator in the development of mammary glands is still unknown. First, we show that PGC-1α is highly expressed during puberty and involution, but nearly disappeared in pregnancy and lactation. Then, taking advantage of a newly generated transgenic mouse model with a stable and specific overexpression of PGC-1α in mammary glands, we demonstrate that the re-expression of this coactivator during the lactation stage leads to a precocious regression of the mammary glands. Thus, we propose that PGC-1α action is non-essential during pregnancy and lactation, whereas it is indispensable during involution. The rapid preadipocyte-adipocyte transition, together with an increased rate of apoptosis promotes a premature mammary glands involution that cause lactation defects and pup growth retardation. Overall, we provide new insights in the comprehension of female reproductive cycles and lactation deficiency, thus opening new roads for mothers that cannot breastfeed.