Growth hormone stimulates proliferation of old-aged regenerating liver through forkhead box m1b

Insulin-like Growth Factor-1 Levels Reflect Muscle and Bone Health and Determine Complications and Mortality in Decompensated Cirrhosis

Background

The growth hormone-insulin-like growth factor (GH-IGF-1) axis and its impairment with sarcopenia, frailty, bone health, complications, and prognosis are not well characterized in cirrhosis.

Methods

We investigated the adult decompensated cirrhosis out-patients at a tertiary care institute between 2021 and 2023 for serum GH and IGF-1 levels, and associated them with sarcopenia (CT-SMI in cm2/m2), liver frailty index (LFI), osteodystrophy (DEXA), clinical decompensations (overall, ascites, encephalopathy, infection, and bleed), and survival up to 180 days.

Results

One-hundred-seventy-two patients, 95% males, aged 46.5 years (median). logIGF-1 levels were negatively associated with sarcopenia, osteodystrophy, LFI, CTP, and MELD-Na score (P < 0.05 each). Patients with low IGF-1 levels had a higher incidence of complications (overall, ascites and encephalopathy) than those with intermediate, and high IGF-1 levels (P < 0.05 each). Both logIGF-1 (AUC: 0.686) and MELD (AUC: 0.690) could predict 180-day mortality (P < 0.05, each). Adding logIGF-1 with MELDNa further improved discriminative accuracy of MELDNa (AUC: 0.729) P < 0.001. The increase in IGF-1 on follow-up was associated with better survival and fewer complications.

Conclusion

Reduced IGF-1 levels reflect sarcopenia, frailty, and osteodystrophy in cirrhosis. Low IGF-1 are associated with severity, development of decompensations, and mortality.

Transcriptional control of a stem cell factor nucleostemin in liver regeneration and aging

Nucleostemin (NS) plays a role in liver regeneration, and aging reduces its expression in the baseline and regenerating livers following 70% partial hepatectomy (PHx). Here we interrogate the mechanism controlling NS expression during liver regeneration and aging. The NS promoter was analyzed by TRANSFAC. Functional studies were performed using cell-based luciferase assay, endogenous NS expression in Hep3B cells, mouse livers with a gain-of-function mutation of C/EBPα (S193D), and mouse livers with C/EBPα knockdown. We found a CAAT box with four C/EBPα binding sites (-1216 to -735) and a GC box with consensus binding sites for c-Myc, E2F1, and p300-associated protein complex (-633 to -1). Age-related changes in NS expression correlated positively with the expression of c-Myc, E2F1, and p300, and negatively with that of C/EBPα and C/EBPβ. PHx upregulated NS expression at 1d, coinciding with an increase in E2F1 and a decrease in C/EBPα. C/EBPα bound to the consensus sequences found in the NS promoter in vitro and in vivo, inhibited its transactivational activity in a binding site-dependent manner, and decreased the expression of endogenous NS in Hep3B cells. In vivo activation of C/EBPα by the S193D mutation resulted in a 4th-day post-PHx reduction of NS, a feature shared by 16-m/o livers. Finally, C/EBPα knockdown increased its expression in aged (24-m/o) livers under both baseline and regeneration conditions. This study reports the C/EBPα suppression of NS expression in aged livers, providing a new perspective on the mechanistic orchestration of tissue homeostasis in aging.

Proteomic and metabolomic analysis of GH deficiency-induced NAFLD in hypopituitarism: insights into oxidative stress

Objective

Individuals with hypopituitarism (HPs) have an increased risk of developing non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH) due to growth hormone deficiency (GHD). We aimed to investigate the possible mechanisms underlying the relationship between GHD and NAFLD using proteomic and metabolomic insights.

Methods

Serum metabolic alternations were assessed in male HPs using untargeted metabolomics. A rat model of HP was established through hypophysectomy, followed by recombinant human growth hormone (rhGH) intervention. The mechanisms underlying GHD-mediated NAFLD were elucidated through the application of label-free proteomics and phosphorylation proteomics.

Results

Metabolomic analysis revealed that biomarkers of mitochondrial dysfunction and oxidative stress, such as alanine, lactate, and creatine, were significantly elevated in HPs compared to age-matched controls. In rats, hypophysectomy led to marked hepatic steatosis, lipid peroxidation, and reduced glutathione (GSH), which were subsequently modulated by rhGH replacement. Proteomic analysis identified cytochrome P450s, mitochondrial translation elongation, and PPARA activating genes as the major distinguishing pathways in hypophysectomized rats. The processes of fatty acid transport, synthesis, oxidation, and NADP metabolism were tightly described. An enhanced regulation of peroxisome β-oxidation and ω-oxidation, together with a decreased NADPH regeneration, may exacerbate oxidative stress. Phosphoproteome data showed downregulation of JAK2-STAT5B and upregulation of mTOR signaling pathway.

Conclusions

This study identified proteo-metabolomic signatures associated with the development of NAFLD in pituitary GHD. Evidence was found of oxidative stress imbalance resulting from abnormal fatty acid oxidation and NADPH regeneration, highlighting the role of GH deficiency in the development of NAFLD.

Granulocyte colony-stimulating factor with or without stem or progenitor cell or growth factors infusion for people with compensated or decompensated advanced chronic liver disease

BACKGROUND

Advanced chronic liver disease is characterised by a long compensated phase followed by a rapidly progressive 'decompensated' phase, which is marked by the development of complications of portal hypertension and liver dysfunction. Advanced chronic liver disease is considered responsible for more than one million deaths annually worldwide. No treatment is available to specifically target fibrosis and cirrhosis; liver transplantation remains the only curative option. Researchers are investigating strategies to restore liver functionality to avoid or slow progression towards end-stage liver disease. Cytokine mobilisation of stem cells from the bone marrow to the liver could improve liver function. Granulocyte colony-stimulating factor (G-CSF) is a 175-amino-acid protein currently available for mobilisation of haematopoietic stem cells from the bone marrow. Multiple courses of G-CSF, with or without stem or progenitor cell or growth factors (erythropoietin or growth hormone) infusion, might be associated with accelerated hepatic regeneration, improved liver function, and survival.

OBJECTIVES

To evaluate the benefits and harms of G-CSF with or without stem or progenitor cell or growth factors (erythropoietin or growth hormone) infusion, compared with no intervention or placebo in people with compensated or decompensated advanced chronic liver disease.

SEARCH METHODS

We searched the Cochrane Hepato-Biliary Group Controlled Trials Register, CENTRAL, MEDLINE, Embase, three other databases, and two trial registers (October 2022) together with reference-checking and web-searching to identify additional studies. We applied no restrictions on language and document type.

SELECTION CRITERIA

We only included randomised clinical trials comparing G-CSF, independent of the schedule of administration, as a single treatment or combined with stem or progenitor cell infusion, or with other medical co-interventions, with no intervention or placebo, in adults with chronic compensated or decompensated advanced chronic liver disease or acute-on-chronic liver failure. We included trials irrespective of publication type, publication status, outcomes reported, or language.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane procedures. All-cause mortality, serious adverse events, and health-related quality of life were our primary outcomes, and liver disease-related morbidity, non-serious adverse events, and no improvement of liver function scores were our secondary outcomes. We undertook meta-analyses, based on intention-to-treat, and presented results using risk ratios (RR) for dichotomous outcomes and the mean difference (MD) for continuous outcomes, with 95% confidence intervals (CI) and I2 statistic values as a marker of heterogeneity. We assessed all outcomes at maximum follow-up. We determined the certainty of evidence using GRADE, evaluated the risk of small-study effects in regression analyses, and conducted subgroup and sensitivity analyses.

MAIN RESULTS

We included 20 trials (1419 participants; sample size ranged from 28 to 259), which lasted between 11 and 57 months. Nineteen trials included only participants with decompensated cirrhosis; in one trial, 30% had compensated cirrhosis. The included trials were conducted in Asia (15), Europe (four), and the USA (one). Not all trials provided data for our outcomes. All trials reported data allowing intention-to-treat analyses. The experimental intervention consisted of G-CSF alone or G-CSF plus any of the following: growth hormone, erythropoietin, N-acetyl cysteine, infusion of CD133-positive haemopoietic stem cells, or infusion of autologous bone marrow mononuclear cells. The control group consisted of no intervention in 15 trials and placebo (normal saline) in five trials. Standard medical therapy (antivirals, alcohol abstinence, nutrition, diuretics, β-blockers, selective intestinal decontamination, pentoxifylline, prednisolone, and other supportive measures depending on the clinical status and requirement) was administered equally to the trial groups. Very low-certainty evidence suggested a decrease in mortality with G-CSF, administered alone or in combination with any of the above, versus placebo (RR 0.53, 95% CI 0.38 to 0.72; I2 = 75%; 1419 participants; 20 trials). Very low-certainty evidence suggested no difference in serious adverse events (G-CSF alone or in combination versus placebo: RR 1.03, 95% CI 0.66 to 1.61; I2 = 66%; 315 participants; three trials). Eight trials, with 518 participants, reported no serious adverse events. Two trials, with 165 participants, used two components of the quality of life score for assessment, with ranges from 0 to 100, where higher scores indicate better quality of life, with a mean increase from baseline of the physical component summary of 20.7 (95% CI 17.4 to 24.0; very low-certainty evidence) and a mean increase from baseline of the mental component summary of 27.8 (95% CI 12.3 to 43.3; very low-certainty evidence). G-CSF, alone or in combination, suggested a beneficial effect on the proportion of participants who developed one or more liver disease-related complications (RR 0.40, 95% CI 0.17 to 0.92; I2 = 62%; 195 participants; four trials; very low-certainty evidence). When we analysed the occurrences of single complications, there was no suggestion of a difference between G-CSF, alone or in combination, versus control, in participants in need of liver transplantation (RR 0.85, 95% CI 0.39 to 1.85; 692 participants; five trials), in the development of hepatorenal syndrome (RR 0.65, 95% CI 0.33 to 1.30; 520 participants; six trials), in the occurrence of variceal bleeding (RR 0.68, 95% CI 0.37 to 1.23; 614 participants; eight trials), and in the development of encephalopathy (RR 0.56, 95% CI 0.31 to 1.01; 605 participants; seven trials) (very low-certainty evidence). The same comparison suggested that G-CSF reduces the development of infections (including sepsis) (RR 0.50, 95% CI 0.29 to 0.84; 583 participants; eight trials) and does not improve liver function scores (RR 0.67, 95% CI 0.53 to 0.86; 319 participants; two trials) (very low-certainty evidence).

AUTHORS' CONCLUSIONS

G-CSF, alone or in combination, seems to decrease mortality in people with decompensated advanced chronic liver disease of whatever aetiology and with or without acute-on-chronic liver failure, but the certainty of evidence is very low because of high risk of bias, inconsistency, and imprecision. The results of trials conducted in Asia and Europe were discrepant; this could not be explained by differences in participant selection, intervention, and outcome measurement. Data on serious adverse events and health-related quality of life were few and inconsistently reported. The evidence is also very uncertain regarding the occurrence of one or more liver disease-related complications. We lack high-quality, global randomised clinical trials assessing the effect of G-CSF on clinically relevant outcomes.

Liver Regeneration: Changes in Oxidative Stress, Immune System, Cytokines, and Epigenetic Modifications Associated with Aging

The regenerative capacity of the liver decreases with increase in age. In recent years, studies in mice have found that the regenerative capacity of the liver is associated with changes in the immune system of the liver, cytokines in the body, aging-related epigenetic modifications in the cell, and intracellular signaling pathways. In the immune system of the aging liver, monocytes and macrophages play an important role in tissue repair. During tissue repair, monocytes and macrophages undergo a series of functional and phenotypic changes to initiate and maintain tissue repair. Studies have discovered that knocking out macrophages in the liver during the repair phase results in significant impairment of liver regeneration. Furthermore, as the body ages, the secretion and function of cytokines undergo a series of changes. For example, the levels of interleukin-6, transforming growth factor-alpha, hepatocyte growth factor, and vascular endothelial growth factor undergo changes that alter hepatocyte regulation, thereby affecting its proliferation. In addition, body aging is accompanied by cellular aging, which leads to changes in gene expression and epigenetic modifications. Additionally, this in turn causes alterations in cell function, morphology, and division and affects the regenerative capacity of the liver. As the body ages, the activity of associated functional proteins, such as CCAAT-enhancer-binding proteins, p53, and switch/sucrose nonfermentable complex, changes in the liver, leading to alterations in several signaling pathways, such as the Hippo, PI3K-Akt, mTOR, and STAT3 pathways. Therefore, in recent years, research on aging and liver regeneration has primarily focused on the immune system, signaling pathways, epigenetic changes of senescent cells, and cytokine secretion in the liver. Hence, this review details the roles of these influencing factors in liver regeneration and impact of aging-related factors.

Roles of FoxM1-driven basal β-cell proliferation in maintenance of β-cell mass and glucose tolerance during adulthood

Aims/Introduction

Whether basal β‐cell proliferation during adulthood is involved in maintaining sufficient β‐cell mass, and if so, the molecular mechanism(s) underlying basal β‐cell proliferation remain unclear. FoxM1 is a critical transcription factor which is known to play roles in ‘adaptive’ β‐cell proliferation, which facilitates rapid increases in β‐cell mass in response to increased insulin demands. Therefore, herein we focused on the roles of β‐cell FoxM1 in ‘basal’ β‐cell proliferation under normal conditions and in the maintenance of sufficient β‐cell mass as well as glucose homeostasis during adulthood.

Materials and Methods

FoxM1 deficiency was induced specifically in β‐cells of 8‐week‐old mice, followed by analyzing its short‐ (2 weeks) and long‐ (10 months) term effects on β‐cell proliferation, β‐cell mass, and glucose tolerance.

Results

FoxM1 deficiency suppressed β‐cell proliferation at both ages, indicating critical roles of FoxM1 in basal β‐cell proliferation throughout adulthood. While short‐term FoxM1 deficiency affected neither β‐cell mass nor glucose tolerance, long‐term FoxM1 deficiency suppressed β‐cell mass increases with impaired insulin secretion, thereby worsening glucose tolerance. In contrast, the insulin secretory function was not impaired in islets isolated from mice subjected to long‐term β‐cell FoxM1 deficiency. Therefore, β‐cell mass reduction is the primary cause of impaired insulin secretion and deterioration of glucose tolerance due to long‐term β‐cell FoxM1 deficiency.

Conclusions

Basal low‐level proliferation of β‐cells during adulthood is important for maintaining sufficient β‐cell mass and good glucose tolerance and β‐cell FoxM1 underlies this mechanism. Preserving β‐cell FoxM1 activity may prevent the impairment of glucose tolerance with advancing age.

Evolutionarily conserved transcription factors as regulators of longevity and targets for geroprotection

Aging is the single largest risk factor for many debilitating conditions, including heart diseases, stroke, cancer, diabetes, and neurodegenerative disorders. While far from understood in its full complexity, it is scientifically well-established that aging is influenced by genetic and environmental factors, and can be modulated by various interventions. One of aging's early hallmarks are aberrations in transcriptional networks, controlling for example metabolic homeostasis or the response to stress. Evidence in different model organisms abounds that a number of evolutionarily conserved transcription factors, which control such networks, can affect lifespan and healthspan across species. These transcription factors thus potentially represent conserved regulators of longevity and are emerging as important targets in the challenging quest to develop treatments to mitigate age-related diseases, and possibly even to slow aging itself. This review provides an overview of evolutionarily conserved transcription factors that impact longevity or age-related diseases in at least one multicellular model organism (nematodes, flies, or mice), and/or are tentatively linked to human aging. Discussed is the general evidence for transcriptional regulation of aging and disease, followed by a more detailed look at selected transcription factor families, the common metabolic pathways involved, and the targeting of transcription factors as a strategy for geroprotective interventions.

Aged-related Function Disorder of Liver is Reversed after Exposing to Young Milieu via Conversion of Hepatocyte Ploidy

Previous study showed that senescent hepatocytes from aged liver could be rejuvenated after repopulated in the young recipient liver. The proliferative capacity of hepatocytes was restored with the senescence reversal. However, it is unknown whether metabolic and homeostatic function of aged liver, as well as age-dependent liver steatosis could be rejuvenated or alleviated. Here, we found that senescent hepatocytes from aged liver were rejuvenated after exposing to young blood. An autonomous proliferation of senescent hepatocytes which resulting in ploidy reversal might be the underlying mechanism of senescent reversal. After performing 2/3 partial hepatectomy (2/3PHx) in young blood exposed old liver, delayed DNA synthesis of senescent hepatocytes was rescued and the number of BrdU positive hepatocytes was restored from 4.39±2.30% to 17.85±3.21%, similarly to that in the young mice at 36 hours post 2/3PHx. Moreover, Cyclin A2 and Cyclin E1 overexpression of hepatocytes in aged liver facilitating the G1/S phase transition was contributed to enhance liver regeneration. Furthermore, lipid droplet spread widely in the elderly human liver and old mouse liver, but this aged-associated liver steatosis was alleviated as senescence reversal. Collectively, our study provides new thoughts for effectively preventing age-related liver diseases.

Growth Hormone Stops Excessive Inflammation After Partial Hepatectomy, Allowing Liver Regeneration and Survival Through Induction of H2-Bl/HLA-G

BACKGROUND AND AIMS

Growth hormone (GH) is important for liver regeneration after partial hepatectomy (PHx). We investigated this process in C57BL/6 mice that express different forms of the GH receptor (GHR) with deletions in key signaling domains.

APPROACH AND RESULTS

PHx was performed on C57BL/6 mice lacking GHR (Ghr^-/- ), disabled for all GH-dependent Janus kinase 2 signaling (Box1^-/- ), or lacking only GH-dependent signal transducer and activator of transcription 5 (STAT5) signaling (Ghr391^-/- ), and wild-type littermates. C57BL/6 Ghr^-/- mice showed striking mortality within 48 hours after PHx, whereas Box1^-/- or Ghr391^-/- mice survived with normal liver regeneration. Ghr^-/- mortality was associated with increased apoptosis and elevated natural killer/natural killer T cell and macrophage cell markers. We identified H2-Bl, a key immunotolerance protein, which is up-regulated by PHx through a GH-mediated, Janus kinase 2-independent, SRC family kinase-dependent pathway. GH treatment was confirmed to up-regulate expression of the human homolog of H2-Bl (human leukocyte antigen G [HLA-G]) in primary human hepatocytes and in the serum of GH-deficient patients. We find that injury-associated innate immune attack by natural killer/natural killer T cell and macrophage cells are instrumental in the failure of liver regeneration, and this can be overcome in Ghr^-/- mice by adenoviral delivery of H2-Bl or by infusion of HLA-G protein. Further, H2-Bl knockdown in wild-type C57BL/6 mice showed elevated markers of inflammation after PHx, whereas Ghr^-/- backcrossed on a strain with high endogenous H2-Bl expression showed a high rate of survival following PHx.

CONCLUSIONS

GH induction of H2-Bl expression is crucial for reducing innate immune-mediated apoptosis and promoting survival after PHx in C57BL/6 mice. Treatment with HLA-G may lead to improved clinical outcomes following liver surgery or transplantation.

Liver regeneration in aged mice: new insights

The regenerative capacity of the liver after resection is reduced with aging. Recent studies on rodents revealed that both intracellular and extracellular factors are involved in the impairment of liver mass recovery during aging. Among the intracellular factors, age-dependent decrease of BubR1 (budding uninhibited by benzimidazole-related 1), YAP (Yes-associated protein) and SIRT1 (Sirtuin-1) have been associated to dampening of tissue reconstitution and inhibition of cell cycle genes following partial hepatectomy. Extra-cellular factors, such as age-dependent changes in hepatic stellate cells affect liver regeneration through inhibition of progenitor cells and reduction of liver perfusion. Furthermore, chronic release of pro-inflammatory proteins by senescent cells (SASP) affects cell proliferation suggesting that senescent cell clearance might improve tissue regeneration. Accordingly, young plasma restores liver regeneration in aged animals through autophagy re-establishment. This review will discuss how intracellular and extracellular factors cooperate to guarantee a proper liver regeneration and the possible causes of its impairment during aging. The possibility that an improvement of the liver regenerative capacity in elderly might be achieved through elimination of senescent cells via autophagy or by administration of direct mitogenic agents devoid of cytotoxicity will also be entertained.

Outcomes after multiple courses of granulocyte colony-stimulating factor and growth hormone in decompensated cirrhosis: A randomized trial

Decompensated cirrhosis (DC) carries a high mortality. Liver transplantation (LT) is the treatment of choice; however, the limited availability of donor organs has resulted in high waitlist mortality. The present study investigated the impact of multiple courses of granulocyte-colony stimulating factor (G-CSF) with or without growth hormone (GH) in these patients. Sixty-five patients with DC were randomized to standard medical therapy (SMT) plus G-CSF 3 monthly plus GH daily (group A; n = 23) or SMT plus G-CSF (group B; n = 21) or SMT alone (group C; n = 21). The primary outcome was transplant-free survival (TFS) at 12 months. Secondary outcomes were mobilization of CD34⁺ cells at day 6 and improvement in clinical scores, liver stiffness, nutrition, episodes of infection, and quality of life (QOL) at 12 months. There was significantly better 12-month TFS in groups A and B than in group C (P = 0.001). At day 6 of therapy, CD34⁺ cells increased in groups A and B compared to baseline (P < 0.001). There was a significant decrease in clinical scores, improvement in nutrition, better control of ascites, reduction in liver stiffness, lesser infection episodes, and improvement in QOL scores in groups A and B at 12 months as compared to baseline (P < 0.05). The therapies were well tolerated.

CONCLUSION

Multiple courses of G-CSF improved 12-month TFS, mobilized hematopoietic stem cells, improved disease severity scores, nutrition, fibrosis, QOL scores, ascites control, reduced infections, and the need for LT in patients with DC. However, the use of GH was not found to have any additional benefit. (Hepatology 2017).

Engineered fibroblast growth factor 19 protects from acetaminophen-induced liver injury and stimulates aged liver regeneration in mice

The liver displays a remarkable regenerative capacity triggered upon tissue injury or resection. However, liver regeneration can be overwhelmed by excessive parenchymal destruction or diminished by pre-existing conditions hampering repair. Fibroblast growth factor 19 (FGF19, rodent FGF15) is an enterokine that regulates liver bile acid and lipid metabolism, and stimulates hepatocellular protein synthesis and proliferation. FGF19/15 is also important for liver regeneration after partial hepatectomy (PH). Therefore recombinant FGF19 would be an ideal molecule to stimulate liver regeneration, but its applicability may be curtailed by its short half-life. We developed a chimaeric molecule termed Fibapo in which FGF19 is covalently coupled to apolipoprotein A-I. Fibapo retains FGF19 biological activities but has significantly increased half-life and hepatotropism. Here we evaluated the pro-regenerative activity of Fibapo in two clinically relevant models where liver regeneration may be impaired: acetaminophen (APAP) poisoning, and PH in aged mice. The only approved therapy for APAP intoxication is N-acetylcysteine (NAC) and no drugs are available to stimulate liver regeneration. We demonstrate that Fibapo reduced liver injury and boosted regeneration in APAP-intoxicated mice. Fibapo improved survival of APAP-poisoned mice when given at later time points, when NAC is ineffective. Mechanistically, Fibapo accelerated recovery of hepatic glutathione levels, potentiated cell growth-related pathways and increased functional liver mass. When Fibapo was administered to old mice prior to PH, liver regeneration was markedly increased. The exacerbated injury developing in these mice upon PH was attenuated, and the hepatic biosynthetic capacity was enhanced. Fibapo reversed metabolic and molecular alterations that impede regeneration in aged livers. It reduced liver steatosis and downregulated p21 and hepatocyte nuclear factor 4 α (Hnf4α) levels, whereas it stimulated Foxm1b gene expression. Together our findings indicate that FGF19 variants retaining the metabolic and growth-promoting effects of this enterokine may be valuable for the stimulation of liver regeneration.

The Role of Growth Hormone and Insulin-Like Growth Factor-I in the Liver

Adult growth hormone deficiency (GHD) is characterized by metabolic abnormalities associated with visceral obesity, impaired quality of life, and increased mortality. Patients with adult GHD show increased prevalence of non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH), and growth hormone (GH) replacement therapy has been shown to improve these conditions. It has also been demonstrated that a decrease in the GH insulin-like growth factor-I (IGF-I) axis is closely associated with the progression of general NAFLD, suggesting a physiological role of these hormones for the maintenance of the liver. NASH histologically demonstrates inflammation, necrosis, and fibrosis, in addition to steatosis (and is a serious disease because it can progress to liver cirrhosis and hepatocellular carcinoma in a subset of cases). While fibrosis determines the prognosis of the patient, efficacious treatment for fibrosis is crucial; however, it has not yet been established. Recent studies have clarified the essential roles of GH and IGF-I in the liver. GH profoundly reduces visceral fat, which plays an important role in the development of NAFLD. Furthermore, GH directly reduces lipogenesis in the hepatocytes. IGF-I induces cellular senescence and inactivates hepatic stellate cells, therefore ameliorating fibrosis. IGF-I treatment has been shown to improve animal models of NASH and cirrhosis, suggesting potential clinical applications of IGF-I in these conditions. In this review, I will focus on the important roles of GH and IGF-I in the liver, their underlying mechanisms, and their potential therapeutic applications.

Insulin-Like Growth Factor-1 Deficiency and Cirrhosis Establishment

Cirrhosis represents the final stage of chronic liver damage, which can be due to different factors such as alcohol, metabolic syndrome with liver steatosis, autoimmune diseases, drugs, toxins, and viral infection, among others. Nowadays, cirrhosis is an important health problem and it is an increasing cause of morbidity and mortality, being the 14th most common cause of death worldwide. The physiopathological pathways that lead to fibrosis and finally cirrhosis partly depend on the etiology. Nevertheless, some common features are shared in this complex mechanism. Recently, it has been demonstrated that cirrhosis is a dynamic process that can be altered in order to delay or revert fibrosis. In addition, when cirrhosis has been established, insulin-like growth factor-1 (IGF-1) deficiency or reduced availability is a common condition, independently of the etiology of chronic liver damage that leads to cirrhosis. IGF-1 deprivation seriously contributes to the progressive malnutrition of cirrhotic patient, increasing the vulnerability of the liver to establish an inflammatory and oxidative microenvironment with mitochondrial dysfunction. In this context, IGF-1 deficiency in cirrhotic patients can justify some of the common characteristics of these individuals. Several studies in animals and humans have been done in order to test the replacement of IGF-1 as a possible therapeutic option, with promising results.

Impairment of Host Liver Repopulation by Transplanted Hepatocytes in Aged Rats and the Release by Short-Term Growth Hormone Treatment

Hepatocyte transplantation is an alternative to whole liver transplantation. Yet, efficient liver repopulation by transplanted hepatocytes is low in livers of old animals. This restraint might be because of the poor proliferative capacity of aged donor hepatocytes or the regenerative impairment of the recipient livers. The age-dependent liver repopulation by transplanted wild-type hepatocytes was investigated in juvenile and senescent rats deficient in dipeptidyl-peptidase IV. Repopulation was quantified by flow cytometry and histochemical estimation of dipeptidyl-peptidase IV enzyme activity of donor cells in the negative host liver. As a potential pathway involved, expression of cell cycle proteins was assessed. Irrespective of the age of the donor hepatocytes, large cell clusters appeared in juvenile, but only small clusters in senescent host livers. Because juvenile and senescent donor hepatocytes were likewise functional, host-derived factor(s) impaired senescent host liver repopulation. Growth hormone levels were significantly higher in juvenile than in senescent rats, suggesting that growth hormone might promote host liver repopulation. Indeed, short-term treatment with growth hormone augmented senescent host liver repopulation involving the growth hormone-mediated release of the transcriptional blockade of genes associated with cell cycle progression. Short-term growth hormone substitution might improve liver repopulation by transplanted hepatocytes, thus augmenting the therapeutic benefit of clinical hepatocyte transplantation in older patients.

Bile acid signaling and liver regeneration

The liver is able to regenerate itself in response to partial hepatectomy or liver injury. This is accomplished by a complex network of different cell types and signals both inside and outside the liver. Bile acids (BAs) are recently identified as liver-specific metabolic signals and promote liver regeneration by activating their receptors: Farnesoid X Receptor (FXR) and G-protein-coupled BA receptor 1 (GPBAR1, or TGR5). FXR is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. FXR promotes liver regeneration after 70% partial hepatectomy (PHx) or liver injury. Moreover, activation of FXR is able to alleviate age-related liver regeneration defects. Both liver- and intestine-FXR are activated by BAs after liver resection or injury and promote liver regeneration through distinct mechanism. TGR5 is a membrane-bound BA receptor and it is also activated during liver regeneration. TGR5 regulates BA hydrophobicity and stimulates BA excretion in urine during liver regeneration. BA signaling thus represents a novel metabolic pathway during liver regeneration. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Human early liver regeneration after hepatectomy in patients with hepatocellular carcinoma: special reference to age

BACKGROUND AND AIMS

This study was conducted to clarify the effects of age on human liver regeneration.

PATIENTS AND METHODS

Thirty major hepatectomies, equal to or more than two segmentectomies for hepatocellular carcinoma, were performed. Ages ranged from 37 to 85 years and five octogenarians were included. The early regenerative index was defined: (liver volume after 7 days after hepatectomy - estimated remnant liver volume before hepatectomy)/estimated remnant liver volume, using three-dimensional computed tomographic volumetry. Farnesoid X receptor and forkhead box m1 expression in the liver, which has been reported to age-related decrease of liver regeneration in animal model, were examined using real-time polymerase chain reaction. The patients were divided into two groups: low early regenerative index (n = 15), early regenerative index less than 55% and high early regenerative index (n = 15), early regenerative index equal to or more than 55%.

RESULTS

The mean early regenerative index was 57%. Age (R (2) = 0.274, P = 0.003) and estimated blood loss (R (2) = 0.134, P = 0.0466) were inversely correlated with the early regenerative index, and the expression of farnesoid X receptor and forkhead box m1 was not. The incidence of post-hepatectomy liver failure in the low early regenerative index group was higher than that in the high early regenerative index group (P = 0.0421).

CONCLUSIONS

Age and intraoperative blood loss are inversely correlated with early liver regeneration in humans. In elderly patients, massive blood loss should be avoided in view of liver regeneration.

Aging and regeneration in vertebrates

Aging is marked by changes that affect organs and resident stem cell function. Shorting of telomeres, DNA damage, oxidative stress, deregulation of genes and proteins, impaired cell-cell communication, and an altered systemic environment cause the eventual demise of cells. At the same time, reparative activities also decline. It is intriguing to correlate aging with the decline of regenerative abilities. Animal models with strong regenerative capabilities imply that aging processes might not be affecting regeneration. In this review, we selectively present age-dependent changes in stem/progenitor cells that are vital for tissue homeostasis and repair. In addition, the aging effect on regeneration following injury in organs such as lung, skeletal muscle, heart, nervous system, cochlear hair, lens, and liver are discussed. These tissues are also known for diseases such as heart attack, stroke, cognitive impairment, cataract, and hearing loss that occur mostly during aging in humans. Conclusively, vertebrate regeneration declines with age with the loss of stem/progenitor cell function. Future studies on improving the function of stem cells, along with studies in fish and amphibians where regeneration does not decline with age, will undoubtedly provide insights into both processes.

Lixisenatide treatment for older patients with type 2 diabetes mellitus uncontrolled on oral antidiabetics: meta-analysis of five randomized controlled trials

AIM

Evaluate the efficacy and safety of lixisenatide, a once-daily prandial glucagon-like peptide-1 receptor agonist, in older patients with type 2 diabetes mellitus (T2DM) insufficiently controlled on oral antidiabetics (OADs).

METHODS

A meta-analysis was conducted on data from older patients (≥65 years) from five of the GetGoal trials, in which patients with T2DM were treated with lixisenatide 20 µg once daily or placebo, as an add-on to OADs. The primary endpoint in all trials was change from baseline at week 24 in glycated hemoglobin (HbA1c). Other endpoints included changes in post-prandial plasma glucose (PPG), fasting plasma glucose (FPG) and weight. Composite and safety endpoints were also analyzed.

RESULTS

A total of 501 patients aged ≥65 years were included in this meta-analysis: 304 received lixisenatide plus OADs and 197 received placebo as add-on to OADs. Lixisenatide as an add-on to OADs significantly reduced HbA1c, PPG, FPG and weight, with placebo-corrected treatment effects at week 24 of -0.54% (p<0.0001), -126 mg/dL (p<0.0001), -13 mg/dL (p=0.0005) and -0.90 kg (p=0.0021), respectively. Patients receiving lixisenatide plus OADs were significantly more likely to achieve composite (HbA1c levels<7%, HbA1c levels<7% and no symptomatic hypoglycemia, and HbA1c levels<7%, no weight gain and no symptomatic hypoglycemia) and safety endpoints than those receiving placebo plus OADs. Symptomatic hypoglycemia was experienced by 8.55% and 3.55% of patients in the lixisenatide plus OADs and placebo plus OADs groups, respectively (p=0.0276), although no serious hypoglycemic episodes were reported.

CONCLUSIONS

Lixisenatide plus OADs improved glycemic control in older patients inadequately controlled on OADs compared with placebo plus OADs. Lixisenatide is well tailored to the pathophysiology of T2DM in older patients.

GH administration rescues fatty liver regeneration impairment by restoring GH/EGFR pathway deficiency

GH pathway has been shown to play a major role in liver regeneration through the control of epidermal growth factor receptor (EGFR) activation. This pathway is down-regulated in nonalcoholic fatty liver disease. Because regeneration is known to be impaired in fatty livers, we wondered whether a deregulation of the GH/EGFR pathway could explain this deficiency. Hepatic EGFR expression and triglyceride levels were quantified in liver biopsies of 32 obese patients with different degrees of steatosis. We showed a significant inverse correlation between liver EGFR expression and the level of hepatic steatosis. GH/EGFR down-regulation was also demonstrated in 2 steatosis mouse models, a genetic (ob/ob) and a methionine and choline-deficient diet mouse model, in correlation with liver regeneration defect. ob/ob mice exhibited a more severe liver regeneration defect after partial hepatectomy (PH) than methionine and choline-deficient diet-fed mice, a difference that could be explained by a decrease in signal transducer and activator of transcription 3 phosphorylation 32 hours after PH. Having checked that GH deficiency accounted for the GH signaling pathway down-regulation in the liver of ob/ob mice, we showed that GH administration in these mice led to a partial rescue in hepatocyte proliferation after PH associated with a concomitant restoration of liver EGFR expression and signal transducer and activator of trnascription 3 activation. In conclusion, we propose that the GH/EGFR pathway down-regulation is a general mechanism responsible for liver regeneration deficiency associated with steatosis, which could be partially rescued by GH administration.

Chronic inflammation induces telomere dysfunction and accelerates ageing in mice

Chronic inflammation is associated with normal and pathological ageing. Here we show that chronic, progressive low-grade inflammation induced by knockout of the nfkb1 subunit of the transcription factor NF-κB induces premature ageing in mice. We also show that these mice have reduced regeneration in liver and gut. nfkb1(-/-) fibroblasts exhibit aggravated cell senescence because of an enhanced autocrine and paracrine feedback through NF-κB, COX-2 and ROS, which stabilizes DNA damage. Preferential accumulation of telomere-dysfunctional senescent cells in nfkb1(-/-) tissues is blocked by anti-inflammatory or antioxidant treatment of mice, and this rescues tissue regenerative potential. Frequencies of senescent cells in liver and intestinal crypts quantitatively predict mean and maximum lifespan in both short- and long-lived mice cohorts. These data indicate that systemic chronic inflammation can accelerate ageing via ROS-mediated exacerbation of telomere dysfunction and cell senescence in the absence of any other genetic or environmental factor.

Non-viral FoxM1 gene delivery to hepatocytes enhances liver repopulation

Hepatocyte transplantation as a substitute strategy of orthotopic liver transplantation is being studied for treating end-stage liver diseases. Several technical hurdles must be overcome in order to achieve the therapeutic liver repopulation, such as the problem of insufficient expansion of the transplanted hepatocytes in recipient livers. In this study, we analyzed the application of FoxM1, a cell-cycle regulator, to enhance the proliferation capacity of hepatocytes. The non-viral sleeping beauty (SB) transposon vector carrying FoxM1 gene was constructed for delivering FoxM1 into the hepatocytes. The proliferation capacities of hepatocytes with FoxM1 expression were examined both in vivo and in vitro. Results indicated that the hepatocytes with FoxM1 expression had a higher proliferation rate than wild-type (WT) hepatocytes in vitro. In comparison with WT hepatocytes, the hepatocytes with FoxM1 expression had an enhanced level of liver repopulation in the recipient livers at both sub-acute injury (fumaryl acetoacetate hydrolase (Fah)^–/– mice model) and acute injury (2/3 partial hepatectomy mice model). Importantly, there was no increased risk of tumorigenicity with FoxM1 expression in recipients even after serial transplantation. In conclusion, expression of FoxM1 in hepatocytes enhanced the capacity of liver repopulation without inducing tumorigenesis. FoxM1 gene delivered by non-viral SB vector into hepatocytes may be a viable approach to promote therapeutic repopulation after hepatocyte transplantation.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

The role of CUGBP1 in age-dependent changes of liver functions

Aging liver is characterized by alterations of liver biology and by a reduction of many functions which are important for the maintenance of body homeostasis. The main dysfunctions include appearance of enlarged hepatocytes, impaired liver regeneration after partial hepatectomy (PH), development of hepatic steatosis, reduction of secretion of proteins and alterations in the hepatic sinusoid. RNA binding proteins are involved in the regulation of gene expression in all tissues including regulation of biological processes in the liver. This review is focused on the role of a conserved, multi-functional RNA-binding protein, CUGBP1, in the development of aging phenotype in the liver. CUGBP1 has been identified as a protein which binds to RNA CUG repeats expanded in Myotonic Dystrophy type 1 (DM1). CUGBP1 is highly expressed in the liver and regulates translation of proteins which are critical for maintenance of liver functions. In livers of young mice, CUGBP1 forms complexes with eukaryotic translation initiation factor eIF2 and supports translation of C/EBPβ and HDAC1 proteins, which are involved in liver growth, differentiation and liver cancer. Aging changes several signaling pathways which lead to the elevation of the CUGBP1-eIF2α complex and to an increase of translation of C/EBPβ and HDAC1. These proteins form multi-protein complexes with additional transcription factors and with chromatin remodeling proteins causing epigenetic alterations of gene expression in livers of old mice. It appears that CUGBP1-mediated translational elevation of HDAC1 is one of the key events in the epigenetic changes in livers of old mice, leading to the development of age-associated dysfunctions of the liver. This review will also discuss a possible role of CUGBP1 in liver dysfunction in patients affected with DM1.

Hypoxia-induced pulmonary arterial smooth muscle cell proliferation is controlled by forkhead box M1

Pulmonary arterial hypertension (PAH) is a devastating disease, and no effective treatments are available. Hypoxia-induced pulmonary artery remodeling, including smooth muscle cell proliferation, contributes to PAH, but the exact mechanisms underlying this abnormal process are largely undefined. The forkhead box M1 (FoxM1) transcription factor regulates cancer cell growth by modulating gene expression critical for cell cycle progression. Here, we report for the first time, to the best of our knowledge, a novel function of FoxM1 in the hypoxia-stimulated proliferation of human pulmonary artery smooth muscle cells (HPASMCs). Exposure to hypoxia caused a marked up-regulation of FoxM1 gene expression, mainly at the transcription level, and this induction correlated with HPASMC cell proliferation. The knockdown of FoxM1 inhibited the hypoxia-stimulated proliferation of HPASMCs. We found that the knockdown of HIF-2α, but not HIF-1α, diminished FoxM1 induction in response to hypoxia. However, the knockdown of FoxM1 did not alter expression levels of HIF-2α or HIF-1α, suggesting that HIF-2α is an upstream regulator of FoxM1. Furthermore, the knockdown of FoxM1 prevented the hypoxia-induced expression of aurora A kinase and cyclin D1. Collectively, our results suggest that hypoxia induces FoxM1 gene expression in an HIF-2α-dependent pathway, thereby promoting HPASMC proliferation.

A mouse model of accelerated liver aging caused by a defect in DNA repair

The liver changes with age, leading to an impaired ability to respond to hepatic insults and increased incidence of liver disease in the elderly. Therefore, there is critical need for rapid model systems to study aging-related liver changes. One potential opportunity is murine models of human progerias or diseases of accelerated aging. Ercc1(-/Δ) mice model a rare human progeroid syndrome caused by inherited defects in DNA repair. To determine whether hepatic changes that occur with normal aging occur prematurely in Ercc1(-/Δ) mice, we systematically compared liver from 5-month-old progeroid Ercc1(-/Δ) mice to old (24-36-month-old) wild-type (WT) mice. Both displayed areas of necrosis, foci of hepatocellular degeneration, and acute inflammation. Loss of hepatic architecture, fibrosis, steatosis, pseudocapillarization, and anisokaryosis were more dramatic in Ercc1(-/Δ) mice than in old WT mice. Liver enzymes were significantly elevated in serum of Ercc1(-/Δ) mice and old WT mice, whereas albumin was reduced, demonstrating liver damage and dysfunction. The regenerative capacity of Ercc1(-/Δ) liver after partial hepatectomy was significantly reduced. There was evidence of increased oxidative damage in Ercc1(-/Δ) and old WT liver, including lipofuscin, lipid hydroperoxides and acrolein, as well as increased hepatocellular senescence. There was a highly significant correlation in genome-wide transcriptional changes between old WT and 16-week-old, but not 5-week-old, Ercc1(-/Δ) mice, emphasizing that the Ercc1(-/Δ) mice acquire an aging profile in early adulthood.

CONCLUSION

There are strong functional, regulatory, and histopathological parallels between accelerated aging driven by a DNA repair defect and normal aging. This supports a role for DNA damage in driving aging and validates a murine model for rapidly testing hypotheses about causes and treatment for aging-related hepatic changes.

Type 2 diabetes and the aging pancreatic beta cell

The incidence of and susceptibility to Type 2 diabetes increases with age, but the underlying mechanism(s) within beta cells that contribute to this increased susceptibility have not been fully elucidated. Here we review how aging affects the proliferative and regenerative capacity of beta cells and how this impacts beta cell mass. In addition we review changes that occur in beta cell function with age. Although we focus on the different rodent models that have provided insight into the characteristics of the aging beta cell, the limited knowledge from non-rodent models is also reviewed. Further studies are needed in order to identify potential beta cell targets for preventing or slowing the progression of diabetes that occurs with age.

Liver regeneration and aging: a current perspective

Many organ systems exhibit significant age-related deficits, but, based on studies in old rodents and elderly humans, the liver appears to be relatively protected from such changes. A remarkable feature of the liver is its capacity to regenerate its mass following partial hepatectomy. Reports suggests that aging compromises the liver's regenerative capacity, both in the rate and to the extent the organ's original volume is restored. There has been modest definitive information as to which cellular and molecular mechanisms regulating hepatic regeneration are affected by aging. Changes in hepatic sensitivity to growth factors, for example, epidermal growth factor (EGF), appear to influence regeneration in old animals. Studies have demonstrated (a) a 60% decline in EGF binding to hepatocyte plasma membranes, (b) reduced expression of the hepatic high affinity EGF receptor and (c) a block between G1 and S-phases of the cell cycle in old rats following EGF stimulation. Recent studies suggest that reduced phosphorylation and dimerization of the EGF receptor, critical steps in the activation of the extracellular signal-regulated kinase pathway and subsequent cell proliferation are responsible. Other studies have demonstrated that aging affects the upregulation of a Forkhead Box transcription factor, FoxM1B, which is essential for growth hormone-stimulated liver regeneration in hepatectomized mice. Aging appears to compromise liver regeneration by influencing several pathways, the result of which is a reduction in the rate of regeneration, but not in the capacity to restore the organ to its original volume.

Nuclear bile acid receptor FXR in the hepatic regeneration

The liver can fully regenerate itself by a compensatory regrowth in response to partial hepatectomy or injury. This process consists of a variety of well-orchestrated phases and is mediated by many signals. Farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Bile acids are FXR physiological ligands. As a metabolic regulator, FXR plays key roles in regulating metabolism of bile acids, lipids and glucose. Recently, bile acid/FXR signaling pathway is shown to be required for normal liver regeneration. Furthermore, FXR promotes liver repair after injury and activation of FXR is able to alleviate age-related defective liver regeneration. These novel findings suggest that FXR-mediated bile acid signaling is an integrated component of normal liver regeneration machinery, and also highlight the potential use of FXR ligands to promote liver regeneration after segmental liver transplantation or resection of liver tumors. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Hierarchies of transcriptional regulation during liver regeneration

The remarkable capacity of the liver to regenerate after severe injury or disease has excited interest for centuries. The goal of harnessing this process in treatment of liver disease, and the appreciation of the parallels between regeneration and tumor development in the liver, remain a major driver for research in this area. Studies of liver regeneration as a model system offer a view of intricate and precisely timed regulatory pathways that drive the process toward completion. Successful regeneration of the liver mass demands a hierarchal and well-controlled balance between proliferative and metabolic functions, which is orchestrated by signaling and regulation of transcription factors. Control and regulation of these cascades of transcriptional activities, necessary for induction, renewal, and cessation of liver growth, are the focus of this chapter.

GH receptor plays a major role in liver regeneration through the control of EGFR and ERK1/2 activation

GH is a pleiotropic hormone that plays a major role in proliferation, differentiation, and metabolism via its specific receptor. It has been previously suggested that GH signaling pathways are required for normal liver regeneration but the molecular mechanisms involved have yet to be determined. The aim of this study was to identify the mechanisms by which GH controls liver regeneration. We performed two thirds partial hepatectomies in GH receptor (GHR)-deficient mice and wild-type littermates and showed a blunted progression in the G(1)/S transition phase of the mutant hepatocytes. This impaired liver regeneration was not corrected by reestablishing IGF-1 expression. Although the initial response to partial hepatectomy at the priming phase appeared to be similar between mutant and wild-type mice, cell cycle progression was significantly blunted in mutant mice. The main defect in GHR-deficient mice was the deficiency of the epidermal growth factor receptor activation during the process of liver regeneration. Finally, among the pathways activated downstream of GHR during G(1) phase progression, namely Erk1/2, Akt, and signal transducer and activator of transcription 3, we only found a reduced Erk1/2 phosphorylation in mutant mice. In conclusion, our results demonstrate that GH signaling plays a major role in liver regeneration and strongly suggest that it acts through the activation of both epidermal growth factor receptor and Erk1/2 pathways.

The influence of donor age on liver regeneration and hepatic progenitor cell populations

BACKGROUND

Recent reports suggest that donor age might have a major impact on recipient outcome in adult living donor liver transplantation (LDLT), but the reasons underlying this effect remain unclear. The aims of this study were to compare liver regeneration between young and aged living donors and to evaluate the number of Thy-1+ cells, which have been reported to be human hepatic progenitor cells.

METHODS

LDLT donors were divided into 2 groups (Group O, donor age ≥ 50 years, n = 6 and Group Y, donor age ≤ 30 years, n = 9). The remnant liver regeneration rates were calculated on the basis of computed tomography volumetry on postoperative days 7 and 30. Liver tissue samples were obtained from donors undergoing routine liver biopsy or patients undergoing partial hepatectomy for metastatic liver tumors. Thy-1+ cells were isolated and counted using immunomagnetic activated cell sorting (MACS) technique.

RESULTS

Donor liver regeneration rates were significantly higher in young donors compared to old donors (P = .042) on postoperative day 7. Regeneration rates were significantly higher after right lobe resection compared to rates after left lobe resection. The MACS findings showed that the number of Thy-1+ cells in the human liver consistently tended to decline with age.

CONCLUSION

Our study revealed that liver regeneration is impaired with age after donor hepatectomy, especially after right lobe resection. The declining hepatic progenitor cell population might be one of the reasons for impaired liver regeneration in aged donors.

Elevated interferon gamma signaling contributes to impaired regeneration in the aged liver

Our previous study on immune-related changes in the aged liver described immune cell infiltration and elevation of inflammation with age. Levels of interferon (IFN)-γ, a known cell cycle inhibitor, were elevated in the aging liver. Here, we determine the role played by IFN-γ in the delayed regenerative response observed in the aged livers. We observed elevated IFN signaling in both aged hepatocytes and regenerating livers post-partial hepatectomy. In vivo deletion of the major IFN-γ producers-the macrophages and the natural killer cells, leads to a reduction in the IFN-γ levels accompanied with the restoration of the DNA synthesis kinetics in the aged livers. Eighteen-month-old IFN-γ-/- mice livers, upon resection, exhibited an earlier entry into the cell cycle compared with age-matched controls. Thus, our study strongly suggests that an age-related elevation in inflammatory conditions in the liver often dubbed as "inflammaging" has a detrimental effect on the regenerative response.

Mechanisms in the adaptation of maternal β-cells during pregnancy

Pancreatic β-cell mass adapts to changing insulin demands in the body. One of the most amazing reversible β-cell adaptations occurs during pregnancy and postpartum conditions. During pregnancy, the increase in maternal insulin resistance is compensated by maternal β-cell hyperplasia and hyperfunctionality to maintain normal blood glucose. Although the cellular mechanisms involved in maternal β-cell expansion have been studied in detail in rodents, human studies are very sparse. A summary of these studies in rodents and humans is described below. Since β-cell mass expands during pregnancy, unraveling the endocrine/paracrine/autocrine molecular mechanisms responsible for these effects can be of great importance for predicting and treating gestational diabetes and for finding new cues that induce β-cell regeneration in diabetes. In addition to the well known implication of lactogens during maternal β-cell expansion, additional participants are being discovered such as serotonin and HGF. Transcription factors, such as hepatocyte nuclear factor-4α and the forkhead box protein-M1, and cell cycle regulators, such as menin, p27 and p18, are important intracellular signals responsible for these effects. In this article, we summarize and discuss novel studies uncovering molecular mechanisms involved in the maternal β-cell adaptive expansion during pregnancy.

Cascades of transcription regulation during liver regeneration

An increasing demand for new strategies in cancer prevention and regenerative medicine requires a better understanding of molecular mechanisms that control cell proliferation in tissue-specific manner. Regenerating liver is a unique model allowing use of biochemical, genetic, and engineering tools to uncover molecular mechanisms and improve treatment of hepatic cancers, liver failure, and fibrotic disease. Molecular mechanisms of liver regeneration involve extra- and intracellular factors to activate transcription of genes normally silenced in quiescent liver. While many upstream signaling pathways of the regenerating liver have been extensively studied, our knowledge of the downstream effectors, transcription factors (TFs), remains limited. This review describes consecutive engagement of pre-existing and de novo synthesized TFs, as cascades that regulate expression of growth-related and metabolic genes during liver regeneration after partial hepatectomy in mice. Several previously recognized regulators of regenerating liver are described in the light of recently identified co-activator and co-repressor complexes that interact with primary DNA-binding TFs. Published results of gene expression and chromatin immunoprecipitation analyses, as well as studies of transgenic mouse models, are used to emphasize new potential regulators of transcription during liver regeneration. Finally, a more detailed description of newly identified transcriptional regulators of liver regeneration illustrates the tightly regulated balance of proliferative and metabolic responses to partial hepatectomy.

Serotonin reverts age-related capillarization and failure of regeneration in the liver through a VEGF-dependent pathway

The function of the liver is well-preserved during the aging process, although some evidence suggests that liver regeneration might be impaired with advanced age. We observed a decreased ability of the liver to restore normal volume after partial hepatectomy in elderly mice, and we identified a pathway that rescued regeneration and was triggered by serotonin. 2,5-dimethoxy-4-iodoamphetamine (DOI), a serotonin receptor agonist, reversed the age-related pseudocapillarization of old liver and improved hepatosinusoidal blood flow. After hepatectomy, the open fenestrae were associated with a restored attachment of platelets to endothelium and the initiation of a normal regenerative response, including the up-regulation of essential growth mediators and serotonin receptors. In turn, hepatocyte proliferation recovered along with regain of liver volume and animal survival. DOI operates through the release of VEGF, and its effects could be blocked with anti-VEGF antibodies both in vitro and in vivo. These results suggest that pseudocapillarization in the aged acts as a barrier to liver regeneration. DOI breaks this restraint through an endothelium-dependent mechanism driven by VEGF. This pathway highlights a target for reversing the age-associated decline in the capacity of the liver to regenerate.

Epigenetic changes play critical role in age-associated dysfunctions of the liver

CCAAT/Enhancer Binding Proteins family proteins are important regulators of liver functions. Here, we show the critical role of C/EBPα-mediated chromatin remodeling in the age-associated dysfunctions of the liver and in the maintenance of physiological homeostasis. Because ph-S193 isoform of C/EBPα is increased in livers of old mice, we have generated C/EBPα-S193D knockin mice, which mimic the ph-S193 isoform of C/EBPα. Analyses of these mice showed that the S193D mutation causes chromatin remodeling leading to histological appearance of 'foci-like' nodules, which are also observed in livers of old mice. These 'foci-like' structures contain K9 trimethylated histone H3, a marker of heterochromatin. The increase of heterochromatin regions in S193D mice correlates with the elevation of S193D-C/EBPα-HDAC1 complexes and with dys-regulation of gene expression including epigenetic silencing of cyclin D1 and D2 promoters and the inhibition of liver proliferation. The elimination of C/EBPα-HDAC1 complexes in S193D mice by inhibition of HDAC1 corrects chromatin structure and normalizes expression of cyclin D1 and D2. We found that epigenetic dys-regulation is also associated with the elevation of C/EBPβ and with the increase of C/EBPα/β heterodimers in S193D mice. The C/EBPα/β heterodimers activate transcription of Glut4 and increase the levels of Glut4. As the result, S193D livers have accelerated uptake of glucose and accumulation of glycogen in the liver. Thus, this study demonstrates that the phosphorylation of C/EBPα at S193 leads to the appearance of heterochromatin regions, which correlates with the development of age-related dysfunctions of the liver.

RhGH attenuates ischemia injury of intrahepatic bile ducts relating to liver transplantation

BACKGROUND

To study the effect of rhGH administration on intrahepatic cholangiocytes relating to liver transplantation with ischemia of hepatic artery, and ultimately, clarify pathologic mechanism of the injury.

METHODS

Rat orthotopic autologous liver transplantation was performed first. Three hours later, the rats were grouped as followed: HAL (hepatic artery ligation) group; HAL + rhGH (hepatic artery ligation followed by rhGH administration) group; CON (without hepatic artery ligation) group. Specimen was collected after 7 d. ALT and ALP of serum were measured. The pathologic changes of bile ducts of liver tissue were observed. The number of bile ducts and blood vessels in portal area were counted. Immunochemistry for VEGF, VEGFR-2, VEGFR-3, GHR, and IGF-1R of intrahepatic cholangiocytes was performed. Cholangiocytes apoptosis was evaluated by TUNEL analysis. Cholangiocytes proliferation was evaluated by PCNA immunolabeling.

RESULTS

ALT and ALP of HAL + rhGH group were significantly ameliorated compared with untreated animals (P < 0.05). ALT and ALP of HAL group were significantly higher compared with CON group (P < 0.05). In HAL group, the main injury of bile ducts was not reversible, whereas it was reversible in CON and rhGH groups. In HAL group, the number of bile ducts in portal area decreased, while the number of bile ducts not accompanying blood vessels increased (P < 0.05). In rhGH group, the number of bile ducts in portal area increased, while the number of bile ducts accompanying blood vessels increased compared with HAL group (P < 0.05). The expression of VEGF, VEGFR-2, VEGFR-3, GHR, and IGF-1R was significantly lower in HAL group than in CON group (P < 0.05). Following administration of rhGH to HAL rats, the expression of VEGF, VEGFR-2, VEGFR-3, IGF-1R, and GHR was significantly higher (P < 0.05). Administration of rhGH prevented increase in cholangiocytes apoptosis induced by HAL (P < 0.05). Administration of rhGH promoted increase in cholangiocytes proliferation held by HAL (P < 0.05).

CONCLUSIONS

Administration of rhGH appears to attenuate ischemia injury of intrahepatic bile ducts relating to liver transplantation. This function is partly related to the capacity that rhGH inhibits the apoptosis of intrahepatic cholangiocytes and prompts the proliferation and angiogenesis by increasing the expression of VEGF, VEGFR2, VEGFR3, GHR, and IGF1-R.

Farnesoid X receptor alleviates age-related proliferation defects in regenerating mouse livers by activating forkhead box m1b transcription

Elucidating the mechanism of liver regeneration could lead to life-saving therapy for a large number of patients, especially elderly patients, after segmental liver transplantation or resection of liver tumors. The forkhead box m1b (Foxm1b) transcription factor is required for normal liver regeneration. Here we report that Foxm1b is the first direct farnesoid X receptor (FXR) target gene known to be involved in cell cycle regulation and that aging regenerating livers have delayed activation of FXR, which results in defective induction of Foxm1b and thereby contributes to defective liver regeneration. An inverted repeat 0 (IR-0) FXR response element, acting as an enhancer in intron 3 of the Foxm1b gene, was identified by a combination of transcriptional reporter, electrophoretic mobility shift, and chromatin immunoprecipitation assays. Diminished FXR binding to the IR-0 element was found in aging regenerating livers. FXR activation by a novel ligand in aging livers induced Foxm1b expression and elevated hepatocyte DNA replication to about 70% of the levels found in young regenerating livers, which were specifically suppressed by hepatic expression of anti-Foxm1b short hairpin RNA.

CONCLUSION

Our results have revealed Foxm1b as the first known direct FXR target gene involved in cell cycle regulation and have demonstrated that defective activation of FXR could be an intrinsic defect in aging regenerating livers. Activation of FXR alone is largely able to alleviate age-related liver regeneration defects. These findings highlight FXR as a potential target of drug design for promoting liver regeneration in older subjects.

Gestational diabetes mellitus resulting from impaired beta-cell compensation in the absence of FoxM1, a novel downstream effector of placental lactogen

OBJECTIVE

The objectives of the study were to determine whether the cell cycle transcription factor, FoxM1, is required for glucose homeostasis and beta-cell mass expansion in maternal islets during pregnancy and whether FoxM1 is essential for placental lactogen (PL)-induced beta-cell proliferation.

RESEARCH DESIGN AND METHODS

beta-Cell mass, beta-cell proliferation, and glucose homeostasis were assessed in virgin, pregnant, and postpartum mice with a pancreas-wide Foxm1 deletion (FoxM1(Deltapanc)). Wild-type islets were cultured with or without PL and examined for Foxm1 induction. Transgenic mice overexpressing PL in beta-cells were bred with FoxM1(Deltapanc) mice, and beta-cell proliferation was examined.

RESULTS

Foxm1 was upregulated in maternal islets during pregnancy. In contrast to controls, beta-cell proliferation did not increase in pregnant FoxM1(Deltapanc) females. Mutant islets showed increased Menin and nuclear p27. FoxM1(Deltapanc) females developed gestational diabetes mellitus as pregnancy progressed. After parturition, euglycemia was restored in FoxM1(Deltapanc) females, but islet size was significantly reduced. Strikingly, beta-cell mass was normal in postpartum FoxM1(Deltapanc) pancreata due to a combination of increased beta-cell size and islet neogenesis. Evidence for neogenesis included increased number of endocrine clusters, increased proportion of smaller islets, and increased neurogenin 3 or insulin expression in cells adjacent to ducts. PL induced Foxm1 expression in cultured islets, and FoxM1 was essential for PL-mediated increases in beta-cell proliferation in vivo.

CONCLUSIONS

FoxM1 is essential for beta-cell compensation during pregnancy. In the absence of increased beta-cell proliferation, neogenesis is induced in postpartum FoxM1(Deltapanc) pancreata. Our results suggest that FoxM1 functions downstream of PL to mediate its effects on beta-cell proliferation.

GSK3beta and aging liver

The loss of regenerative capacity of tissues is one of the major characteristics of aging. Liver represents a powerful system for investigations of mechanisms by which aging reduces regenerative capacity of tissues. The studies within last five years revealed critical role of epigenetic silencing in the inhibition of liver proliferation in old mice. These studies have shown that a number of cell cycle proteins are silenced in livers of old mice by C/EBPα-HDAC1-Brm complex and that old liver fails to reduce the complex and activate these genes in response to proliferative stimulus such as partial hepatectomy. The complex modifies histone H3 on the promoters of c-myc and FoxM1B in the manner which prevents expression of these genes. Despite this progress, little is known about mechanisms by which aging causes this epigenetic silencing. We have recently discovered signal transduction pathways which operate upstream of the C/EBPα-HDAC1-Brm complex. These pathways involve communications of growth hormone, GSK3β and cyclin D3. In addition to the liver, GH-GSK3β-cyclin D3 pathway is also changed with age in lung, brain and adipose tissues. We suggest that other age-associated alterations in these tissues might be mediated by the reduced levels of GSK3β and by elevation of cyclin D3. In this review, we summarize these new data and discuss the role of such alterations in the development of aging phenotype in the liver and in other tissues.

Aging and liver regeneration

The loss of regenerative capacity is the most dramatic age-associated alteration in the liver. Although this phenomenon was reported over 50 years ago, the molecular basis for the loss of regenerative capacity of aged livers has not been fully elucidated. Aging causes alterations of several signal-transduction pathways and changes in the expression of CCAAT/enhancer-binding protein (C/EBP) and chromatin-remodeling proteins. Consequently, aging livers accumulate a multi-protein C/EBPalpha-Brm-HDAC1 complex that occupies and silences E2F-dependent promoters, reducing the regenerative capacity of livers in older mice. Recent studies have provided evidence for the crucial role of epigenetic silencing in the age-dependent inhibition of liver proliferation. This review focuses on mechanisms of age-dependent inhibition of liver proliferation and approaches for correcting liver regeneration in the elderly.

The age-associated decline of glycogen synthase kinase 3beta plays a critical role in the inhibition of liver regeneration

Aging reduces the regenerative capacities of many tissues. In this paper, we show a critical role of the glycogen synthase kinase 3beta (GSK3beta)-cyclin D3 pathway in the loss of the regenerative capacity of the liver. In young animals, high levels of growth hormone (GH) increase expression of GSK3beta, which associates with cyclin D3 and triggers degradation of cyclin D3. In livers of old mice, the GSK3beta promoter is repressed by C/EBPbeta-histone deacetylase 1 (HDAC1) complexes, leading to the reduction of GSK3beta. The treatment of old mice with GH increases expression of GSK3beta via removal of the C/EBPbeta-HDAC1 complexes from the GSK3beta promoter. We found that the GSK3beta-cyclin D3 pathway is also altered in young GH-deficient Little mice and that treatment of Little mice with GH corrects the GSK3beta-cyclin D3 pathway. We present evidence that GSK3beta regulates liver proliferation by controlling growth-inhibitory activity of C/EBPalpha. The downregulation of GSK3beta in young mice inhibits liver proliferation after partial hepatectomy via the cyclin D3-C/EBPalpha pathway, while the elevation of GSK3beta in old mice accelerates liver proliferation. Thus, this paper shows that GSK3beta is a critical regulator of liver proliferation and that the reduction of GSK3beta with age causes the loss of regenerative capacities of the liver.