The Effect of Estrogen on Hepatic Fat Accumulation during Early Phase of Liver Regeneration after Partial Hepatectomy in Rats

HMGB2 Promotes De Novo Lipogenesis to Accelerate Hepatocyte Proliferation During Liver Regeneration

Liver regeneration is a well-orchestrated compensatory process that is regulated by multiple factors. We recently reported the importance of the chromatin protein, a high-mobility group box 2 (HMGB2) in mouse liver regeneration. However, the molecular mechanism remains unclear. In this study, we aimed to study how HMGB2 regulates hepatocyte proliferation during liver regeneration. Seventy-percent partial hepatectomy (PHx) was performed in wild-type (WT) and HMGB2-knockout (KO) mice, and the liver tissues were used for microarray, immunohistochemistry, quantitative polymerase chain reaction (qPCR), and Western blotting analyses. In the WT mice, HMGB2-positive hepatocytes colocalized with cell proliferation markers. In the HMGB2-KO mice, hepatocyte proliferation was significantly decreased. Oil Red O staining revealed the transient accumulation of lipid droplets at 12-24 hr after PHx in the WT mouse livers. In contrast, decreased amount of lipid droplets were found in HMGB2-KO mouse livers, and it was preserved until 36 hr. The microarray, immunohistochemistry, and qPCR results demonstrated that the expression of lipid metabolism-related genes was significantly decreased in the HMGB2-KO mouse livers. The in vitro experiments demonstrated that a decrease in the amount of lipid droplets correlated with decreased cell proliferation activity in HMGB2-knockdown cells. HMGB2 promotes de novo lipogenesis to accelerate hepatocyte proliferation during liver regeneration.

The crucial role of SETDB1 in structural and functional transformation of epithelial cells during regeneration after intestinal ischemia reperfusion injury

Su (var) 3-9, enhancer of seste, trithorax (SET)-domain bifurcated histone lysine methyltransferase (SETDB1) plays a crucial role in maintaining intestinal stem cell homeostasis; however, its physiological function in epithelial injury is largely unknown. In this study, we investigated the role of SETDB1 in epithelial regeneration using an intestinal ischemia/reperfusion injury (IRI) mouse model. Jejunum tissues were sampled after 75 min of ischemia followed by 3, 24, and 48 h of reperfusion. Morphological evaluations were performed using light microscopy and electron microscopy, and the involvement of SETDB1 in epithelial remodeling was investigated by immunohistochemistry. Expression of SETDB1 was increased following 24 h of reperfusion and localized in not only the crypt bottom but also in the transit amplifying zone and part of the villi. Changes in cell lineage, repression of cell adhesion molecule expression, and decreased histone H3 methylation status were detected in the crypts at the same time. Electron microscopy also revealed aberrant alignment of crypt nuclei and fusion of adjacent villi. Furthermore, increased SETDB1 expression and epithelial remodeling were confirmed with loss of stem cells, suggesting SETDB1 affects epithelial cell plasticity. In addition, crypt elongation and increased numbers of Ki-67 positive cells indicated active cell proliferation after IRI; however, the expression of PCNA was decreased compared to sham mouse jejunum. These morphological changes and the aberrant expression of proliferation markers were prevented by sinefungin, a histone methyltransferase inhibitor. In summary, SETDB1 plays a crucial role in changes in the epithelial structure after IRI-induced stem cell loss.

Estrogen regulates duodenal glucose absorption by affecting estrogen receptor-α on glucose transporters

The mechanisms of estrogen in glucose metabolism are well established; however, its role in glucose absorption remains unclear. In this study, we investigated the effects of estrogen on glucose absorption in humans, mice, and SCBN intestinal epithelial cells. We first observed a correlation between estrogen and blood glucose in young women and found that glucose tolerance was significantly less in the premenstrual phase than in the preovulatory phase. Similarly, with decreased serum estradiol levels in ovariectomized mice, estrogen receptors alpha (ERα) and beta (ERβ) in the duodenum were reduced, and weight and abdominal fat increased significantly. The expression of sodium/glucose cotransporter 1 (SGLT1) and glucose transporter 2 (GLUT2) and glucose absorption in the duodenum decreased significantly. Estrogen significantly upregulated SGLT1 and GLUT2 expression in SCBN cells. Silencing of ERα, but not ERβ, reversed this trend, suggesting that ERα may be key to estrogen-regulating glucose transporters. A mechanistic study revealed that downstream, estrogen regulates the protein kinase C (PKC) pathway. Overall, our findings indicate that estrogen promotes glucose absorption, and estrogen and ERα deficiency can inhibit SGLT1 and GLUT2 expression through the PKC signaling pathway, thereby reducing glucose absorption.

The IL-6/HO-1/STAT3 signaling pathway is implicated in the amelioration of acetaminophen-induced hepatic toxicity: A neonatal rat model

The widespread use of acetaminophen (APAP) in children as an over-the-counter treatment can cause acute liver failure through accidental overdose or ingestion. Therefore, the current research sought to investigate the function of hemin in mitigating the acute hepatotoxic effect of APAP in rat offspring. Thirty-two rats were assigned into four groups: control, hemin, APAP, and hemin/APAP groups. Liver enzymes were measured in serum along with oxidative stress indicators, tumor necrosis factor-α (TNF-α), interleukin-1beta (IL-1β), total nitrites (NOx), and caspase 3 in liver. Immunoblotting of heme oxygenase-1 (HO-1), interleukin-6 (IL-6), Janus kinase 2 (Jak2), and signal transducer and activator of transcription 3 (STAT3) was carried out. The Bax/Bcl2 mRNA expression ratio was determined. A histological study and an immunohistochemical study of phosphorylated STAT3 were also done. Hemin reduced liver enzymes, MDA, TNF-α, NOx, caspase 3, IL-1β, p-STAT3 expression, p-Jak2 expression, IL-6 expression, and Bax/Bcl2 mRNA expression ratio. In contrast, hemin increased GSH, TAC, and the expression of HO-1, improving the histopathological picture of liver tissue. Thus, hemin could ameliorate APAP-induced hepatic toxicity in rat offspring through anti-oxidant, anti-apoptotic, and anti-inflammatory actions with a possible role for the IL-6/HO-1/Jak2/STAT3 pathway.

Pivotal role of High-Mobility Group Box 2 in ovarian folliculogenesis and fertility

BACKGROUND

High-Mobility Group Box 1 (HMGB1) and HMGB2 are chromatin-associated proteins that belong to the HMG protein family, and are involved in the regulation of DNA transcription during cell differentiation, proliferation and regeneration in various tissues. However, the role of HMGB2 in ovarian folliculogenesis is largely unknown.

METHODS

We investigated the functional role of HMGB1 and HMGB2 in ovarian folliculogenesis and fertilization using C57BL/6 wild type (WT) and HMGB2-knockout (KO) mice. Ovarian tissues were obtained from WT and HMGB2-KO mice at postnatal days 0, 3, 7, and 2, 6 months of age, then performed immunohistochemistry, qPCR and Western blotting analyses. Oocyte fertilization capability was examined by natural breeding and in vitro fertilization experiments.

RESULTS

In HMGB2-KO mice, ovary weight was decreased due to reduced numbers of oocytes and follicles. Natural breeding and in vitro fertilization results indicated that HMGB2-KO mice are subfertile, but not sterile. Immunohistochemistry showed that oocytes expressed HMGB2, but not HMGB1, in neonatal and adult WT ovaries. Interestingly, in HMGB2-KO ovaries, a compensatory increase in HMGB1 was found in oocyte nuclei of neonatal and 2-month-old mice; however, this was lost at 6 months of age.

CONCLUSIONS

The depletion of HMGB2 led to alterations in ovarian morphology and function, suggesting that HMGB2 plays an essential role in ovarian development, folliculogenesis and fertilization.

Spatiotemporal expression of HMGB2 regulates cell proliferation and hepatocyte size during liver regeneration

Liver regeneration is an extraordinarily complex process involving a variety of factors; however, the role of chromatin protein in hepatocyte proliferation is largely unknown. In this study, we investigated the functional role of high-mobility group box 2 (HMGB2), a chromatin protein in liver regeneration using wild-type and HMGB2-knockout (KO) mice. Liver tissues were sampled after 70% partial hepatectomy (PHx), and analyzed by immunohistochemistry, western blotting and flow cytometry using various markers of cell proliferation. In WT mice, hepatocyte proliferation was strongly correlated with the spatiotemporal expression of HMGB2; however, cell proliferation was significantly delayed in hepatocytes of HMGB2-KO mice. Quantitative PCR demonstrated that cyclin D1 and cyclin B1 mRNAs were significantly decreased in HMGB2-KO mice livers. Interestingly, hepatocyte size was significantly larger in HMGB2-KO mice at 36-72 h after PHx, and these results suggest that hepatocyte hypertrophy appeared in parallel with delayed cell proliferation. In vitro experiments demonstrated that cell proliferation was significantly decreased in HMGB2-KO cells. A significant delay in cell proliferation was also found in HMGB2-siRNA transfected cells. In summary, spatiotemporal expression of HMGB2 is important for regulation of hepatocyte proliferation and cell size during liver regeneration.

Analysis of the relationship between serum alanine aminotransferase and body composition in Chinese women

Objective

To investigate the relationships between serum alanine aminotransferase (ALT) and body composition among postmenopausal women in China.

Methods

A cross‐sectional study was conducted with 776 postmenopausal women in China from May to July 2008. Clinical information was collected using a standardized questionnaire. Measures of body composition were obtained using dual X‐ray absorptiometry. Body lean mass and fat mass indices were calculated by dividing total body lean/fat weight (kg) by body height squared (kg/m²). Blood samples were collected to assess liver and renal functions and lipid profiles. Analysis of variance, Pearson correlations, and multiple regression were used to analyze the associations between serum ALT and body composition.

Results

We found negative relationships of serum ALT with age, menopause duration, and serum HDL‐C levels. Serum ALT was positively correlated with BMI, serum TG levels, and the lean mass index and fat mass index. In a multivariate model adjusted for age, menopause duration, serum TG, and HDL‐C levels, a 1‐unit increase in the fat mass index was associated with a 0.176 U/L increase in ALT (95% CI 0.020 to 0.050, P < 0.001).

Conclusion

Serum ALT was positively associated with the body fat mass index of postmenopausal women in China.

Role of JNK, ERK, and p38 MAPK signaling pathway in protective effect of sildenafil in cyclophosphamide-induced placental injury in rats

AIMS

Chemotherapeutic agents; cyclophosphamide (CYC) is used for treatment of cancer and autoimmune diseases. Grievously, CYC is non-selective as it affects both tumor and healthy cells resulting in systemic toxicity including placenta. The present study aimed to evaluate the effect of phosphodiesterase 5 inhibitor, sildenafil (Sild) on CYC-induced placental injury in rats.

MATERIALS AND METHODS

Thirty-two female Wister rats were randomly divided into 4 experimental groups. Group 1: control pregnant group; Group 2: Sild-treated pregnant rats; Group 3: pregnant rats received CYC; Group 4: pregnant rats received Sild and CYC. Placental malondialdehyde (MDA), total nitrite/nitrate (NOx), reduced glutathione (GSH), tumor necrosis factor-α (TNF-α), platelet growth factor (PlGF), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-regulated kinase (ERK) and cleaved caspase-3 were measured. Histological changes, Nuclear Factor kappa-light-chain-enhancer of activated B (NF-κB), Connexin 43 (GJA1) and proliferating cell nuclear antigen (PCNA) immuno-expressions were also evaluated.

KEY FINDINGS

CYC showed significant decrease in placental GSH, NOx, PlGF, GJA1 and PCNA immuno-expressions but significant increase in placental MDA, TNF-α, JNK, P38MAPK, ERK, caspase-3 and NF-kB immuno-expression. Sild showed significant improvement in all oxidative, inflammatory and apoptotic parameters.

SIGNIFICANCE

Sild is a promising protective drug against placental injury induced by CYC through antagonizing MAPK (JNK, ERK, and p38) signaling pathway with anti-oxidant, anti-inflammatory and anti-apoptotic effects.

Crucial role of high-mobility group box 2 in mouse ovarian follicular development through estrogen receptor beta

High-mobility group box 2 (HMGB2) is a chromatin-associated protein that is an important regulator of gene transcription, recombination, and repair processes. The functional importance of HMGB2 has been reported in various organs, including the testis, heart, and cartilage. However, its role in the ovary is largely unknown. In this study, ovary tissues from wild-type (WT) and HMGB2-knock-out (KO) mice were examined by histopathological staining and immunohistochemistry. The ovary size and weight were significantly lower in HMGB2-KO mice than in age-matched WT littermates. Histopathological analysis revealed ovarian atrophy and progressive fibrosis in 10-month-old HMGB2-KO mouse ovaries. Compared to age-matched WT mice, the numbers of oocytes and developing follicles were significantly decreased at 2 months of age and were completely depleted at 10 months of age in HMGB2-KO mice. Immunohistochemistry revealed the expression of HMGB2 in the granulosa cells of developing follicles, oocytes, some corpora lutea, and stromal cells. Importantly, HMGB2-positive cells were co-localized with estrogen receptor beta (ERβ), but not ERα. Estrogen response element-binding activity was demonstrated by southwestern histochemistry, and it was decreased in HMGB2-KO mouse ovaries. Cell proliferation activity was also decreased in HMGB2-KO mouse ovaries in parallel with the decreased folliculogenesis. These results indicated that the depletion of HMGB2 induced ovarian atrophy that was characterized by a decreased ovarian size and weight, progressive fibrosis, as well as decreased oocytes and folliculogenesis. In conclusion, we demonstrated the crucial role of HMGB2 in mouse ovarian folliculogenesis through ERβ expression.

Idebenone regulates sirt1/Nrf2/TNF-α pathway with inhibition of oxidative stress, inflammation, and apoptosis in testicular torsion/detorsion in juvenile rats

Testicular torsion is an emergency, mainly in newborn and adolescent males, resulting in testicular ischemia. The current study aimed to evaluate the effect of Idebenone (IDE) on testicular torsion/detorsion (T/D) in juvenile rats. Thirty-two rats were randomized into: (1) the sham group: rats received sham operations with no other interventions; (2) the IDE group: rats received idebenone (100 mg/kg, i. p) without T/D; (3) the T/D group: rats underwent torsion for 2 h and detorsion for 4 h; and (4) the IDE+ T/D group: rats received IDE 1 h before T/D. Testicular malondialdehyde (MDA), total nitrite/nitrate (NOx), total antioxidant capacity (TAC), tumor necrosis factor-α (TNF-α), caspase-3, sirtuin type 1 (Sirt1), serum interleukin-1β (IL-1β), total cholesterol, and testosterone were measured. Histological changes, nuclear factor (erythroid-derived 2)-like-2 factors (Nrf2), and proliferating cell nuclear antigen (PCNA) immuno-expressions were assessed. T/D displayed an increase in MDA, NOx, TNF-α, caspase-3, IL-1β, and total cholesterol with a significant decrease in TAC, Sirt1, and testosterone and strong positive Nrf2 and negative PCNA immuno-expressions. IDE could improve all oxidative, inflammatory, and apoptotic indicators. Therefore, IDE significantly reduced testicular ischemia-reperfusion injury in the juvenile rat testicular T/D model by limiting oxidative stress, inflammation, and apoptosis via the Sirt1/Nrf2/TNF-α pathway.

Depletion of high-mobility group box 2 causes seminiferous tubule atrophy via aberrant expression of androgen and estrogen receptors in mouse testis†

High-mobility group box 2, a chromatin-associated protein that interacts with deoxyribonucleic acid, is implicated in multiple biological processes, including gene transcription, replication, and repair. High-mobility group box 2 is expressed in several tissues, including the testis; however, its functional role is largely unknown. Here, we elucidated the role of high-mobility group box 2 in spermatogenesis. Paraffin-embedded testicular tissues were obtained from 8-week-old and 1-year-old wild-type and knock-out mice. Testis weight and number of seminiferous tubules were decreased, whereas atrophic tubules were increased in high-mobility group box 2-depleted mice. Immunohistochemistry revealed that atrophic tubules contained Sertoli cells, but not germ cells. Moreover, decreased cell proliferation and increased apoptosis were demonstrated in high-mobility group box 2-depleted mouse testis. To elucidate the cause of tubule atrophy, we examined the expression of androgen and estrogen receptors, and the results indicated aberrant expression of androgen receptor and estrogen receptor alpha in Sertoli and Leydig cells. Southwestern histochemistry detected decreased estrogen response element-binding sites in high-mobility group box 2-depleted mouse testis. High-mobility group box 1, which has highly similar structure and function as high-mobility group box 2, was examined by immunohistochemistry and western blotting, which indicated increased expression in testis. These findings indicate a compensatory increase in high-mobility group box 1 expression in high-mobility group box 2 knock-out mouse testis. In summary, depletion of high-mobility group box 2 induced aberrant expression of androgen receptor and estrogen receptor alpha, leading to decreased germ cell proliferation and increased apoptosis which resulted in focal seminiferous tubule atrophy.

Beyond the X Factor: Relevance of Sex Hormones in NAFLD Pathophysiology

Non-alcoholic fatty liver disease (NAFLD) is a major health issue worldwide, being frequently associated with obesity, unbalanced dietary regimens, and reduced physical activity. Despite their greater adiposity and reduced physical activity, women show a lower risk of developing NAFLD in comparison to men, likely a consequence of a sex-specific regulation of liver metabolism. In the liver, sex differences in the uptake, synthesis, oxidation, deposition, and mobilization of lipids, as well as in the regulation of inflammation, are associated with differences in NAFLD prevalence and progression between men and women. Given the major role of sex hormones in driving hepatic sexual dimorphism, this review will focus on the role of sex hormones and their signaling in the regulation of hepatic metabolism and in the molecular mechanisms triggering NAFLD development and progression.

Pemafibrate suppresses oxidative stress and apoptosis under cardiomyocyte ischemia-reperfusion injury in type 1 diabetes mellitus

Diabetes mellitus accelerates the hyperglycemia susceptibility-induced injury to cardiac cells. The activation of peroxisome proliferator-activated receptor α (PPARα) decreases ischemia-reperfusion (IR) injury in animals without diabetes. Therefore, the present study hypothesized that pemafibrate may exert a protective effect on the myocardium in vivo and in vitro. A type 1 diabetes mellitus (T1DM) rat model and H9c2 cells exposed to high glucose under hypoxia and reoxygenation treatments were used in the present study. The rat model and the cells were subsequently treated with pemafibrate. In the T1DM rat model, pemafibrate enhanced the expression of PPARα in the diabetic-myocardial ischemia-reperfusion injury (D-IRI) group compared with the D-IRI group. The infarct size in the D-IRI group was reduced following pemafibrate treatment relative to the untreated group. The disruption of the mitochondrial structure and myofibrils in the D-IRI group was partially recovered by pemafibrate. In addition, to evaluate the mechanism of action of pemafibrate in the treatment of diabetic myocardial IR injury, an in vitro model was established. PPARα protein expression levels were reduced in the high glucose and hypoxia/reoxygenation (H/R) groups compared with that in the control or high glucose-treated groups. Pemafibrate treatment significantly enhanced the ATP and superoxide dismutase levels, and reduced the mitochondrial reactive oxygen species and malondialdehyde levels compared with the high glucose combined with H/R group. Furthermore, pemafibrate inhibited the expression of cytochrome c and cleaved-caspase-3, indicating its involvement in the regulation of mitochondrial apoptosis. Pemafibrate also reduced the expression of nuclear factor-κB (NF-κB), the activation of which reversed the protective effects of pemafibrate on diabetic myocardial IR injury in vitro. Taken together, these results suggested that pemafibrate may activate PPARα to protect the T1DM rat myocardium against IR injury through inhibition of NF-κB signaling.

Non-alcoholic Fatty Liver Disease as a Canonical Example of Metabolic Inflammatory-Based Liver Disease Showing a Sex-Specific Prevalence: Relevance of Estrogen Signaling

There is extensive evidence supporting the interplay between metabolism and immune response, that have evolved in close relationship, sharing regulatory molecules and signaling systems, to support biological functions. Nowadays, the disruption of this interaction in the context of obesity and overnutrition underlies the increasing incidence of many inflammatory-based metabolic diseases, even in a sex-specific fashion. During evolution, the interplay between metabolism and reproduction has reached a degree of complexity particularly high in female mammals, likely to ensure reproduction only under favorable conditions. Several factors may account for differences in the incidence and progression of inflammatory-based metabolic diseases between females and males, thus contributing to age-related disease development and difference in life expectancy between the two sexes. Among these factors, estrogens, acting mainly through Estrogen Receptors (ERs), have been reported to regulate several metabolic pathways and inflammatory processes particularly in the liver, the metabolic organ showing the highest degree of sexual dimorphism. This review aims to investigate on the interaction between metabolism and inflammation in the liver, focusing on the relevance of estrogen signaling in counteracting the development and progression of non-alcoholic fatty liver disease (NAFLD), a canonical example of metabolic inflammatory-based liver disease showing a sex-specific prevalence. Understanding the role of estrogens/ERs in the regulation of hepatic metabolism and inflammation may provide the basis for the development of sex-specific therapeutic strategies for the management of such an inflammatory-based metabolic disease and its cardio-metabolic consequences.

Pregnancy facilitates maternal liver regeneration after partial hepatectomy

Liver resection induces robust liver regrowth or regeneration to compensate for the lost tissue mass. In a clinical setting, pregnant women may need liver resection without terminating pregnancy in some cases. However, how pregnancy affects maternal liver regeneration remains elusive. We performed 70% partial hepatectomy (PH) in nonpregnant mice and gestation day 14 mice, and histologically and molecularly compared their liver regrowth during the next 4 days. We found that compared with the nonpregnant state, pregnancy altered the molecular programs driving hepatocyte replication, indicated by enhanced activities of epidermal growth factor receptor and STAT5A, reduced activities of cMet and p70S6K, decreased production of IL-6, TNFα, and hepatocyte growth factor, suppressed cyclin D1 expression, increased cyclin A1 expression, and early activated cyclin A2 expression. As a result, pregnancy allowed the remnant hepatocytes to enter the cell cycle at least 12 h earlier, increased hepatic fat accumulation, and enhanced hepatocyte mitosis. Consequently, pregnancy ameliorated maternal liver regeneration following PH. In addition, a report showed that maternal liver regrowth after PH is driven mainly by hepatocyte hypertrophy rather than hyperplasia during the second half of gestation in young adult mice. In contrast, we demonstrate that maternal liver relies mainly on hepatocyte hyperplasia instead of hypertrophy to restore the lost mass after PH. Overall, we demonstrate that pregnancy facilitates maternal liver regeneration likely via triggering an early onset of hepatocyte replication, accumulating excessive liver fat, and promoting hepatocyte mitosis. The results from our current studies enable us to gain more insights into how maternal liver regeneration progresses during gestation.NEW & NOTEWORTHY We demonstrate that pregnancy may generate positive effects on maternal liver regeneration following partial hepatectomy, which are manifested by early entry of the cell cycle of remnant hepatocytes, increased hepatic fat accumulation, enhanced hepatocyte mitosis, and overall accelerated liver regrowth.