To divide or not to divide: revisiting liver regeneration

Multiscale 3D genome organization underlies duck fatty liver with no adipose inflammation or serious injury

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease. Little is known about how gene expression and chromatin structure are regulated in NAFLD due to lack of suitable model. Ducks naturally develop fatty liver similar to serious human non-alcoholic fatty liver (NAFL) without adipose inflammation and liver fibrosis, thus serves as a good model for investigating molecular mechanisms of adipose metabolism and anti-inflammation. Here, we constructed a NAFLD model without adipose inflammation and liver fibrosis in ducks. By performing dynamic pathological and transcriptomic analyses, we identified critical genes involving in regulation of the NF-κB and MHCII signaling, which usually lead to adipose inflammation and liver fibrosis. We further generated dynamic three-dimensional chromatin maps during liver fatty formation and recovery. This showed that ducks enlarged hepatocyte cell nuclei to reduce inter-chromosomal interaction, decompress chromatin structure, and alter strength of intra-TAD and loop interactions during fatty liver formation. These changes partially contributed to the tight control the NF-κB and the MHCII signaling. Our analysis uncovers duck chromatin reorganization might be advantageous to maintain liver regenerative capacity and reduce adipose inflammation. These findings shed light on new strategies for NAFLD control.

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 molecular circadian rhythms regulating the cell cycle

The circadian clock controls the expression of a large proportion of protein-coding genes in mammals and can modulate a wide range of physiological processes. Recent studies have demonstrated that disruption or dysregulation of the circadian clock is involved in the development and progression of several diseases, including cancer. The cell cycle is considered to be the fundamental process related to cancer. Accumulating evidence suggests that the circadian clock can control the expression of a large number of genes related to the cell cycle. This article reviews the mechanism of cell cycle-related genes whose chromatin regulatory elements are rhythmically occupied by core circadian clock transcription factors, while their RNAs are rhythmically expressed. This article further reviews the identified oscillatory cell cycle-related genes in higher organisms such as baboons and humans. The potential functions of these identified genes in regulating cell cycle progression are also discussed. Understanding how the molecular clock controls the expression of cell cycle genes will be beneficial for combating and treating cancer.

Phenotypic characterization of liver tissue heterogeneity through a next-generation 3D single-cell atlas

Three-dimensional (3D) geometrical models are potent tools for quantifying complex tissue features and exploring structure-function relationships. However, these models are generally incomplete due to experimental limitations in acquiring multiple (> 4) fluorescent channels in thick tissue sections simultaneously. Indeed, predictive geometrical and functional models of the liver have been restricted to few tissue and cellular components, excluding important cellular populations such as hepatic stellate cells (HSCs) and Kupffer cells (KCs). Here, we combined deep-tissue immunostaining, multiphoton microscopy, deep-learning techniques, and 3D image processing to computationally expand the number of simultaneously reconstructed tissue structures. We then generated a spatial single-cell atlas of hepatic architecture (Hep3D), including all main tissue and cellular components at different stages of post-natal development in mice. We used Hep3D to quantitatively study 1) hepatic morphodynamics from early post-natal development to adulthood, and 2) the effect on the liver's overall structure when changing the hepatic environment after removing KCs. In addition to a complete description of bile canaliculi and sinusoidal network remodeling, our analysis uncovered unexpected spatiotemporal patterns of non-parenchymal cells and hepatocytes differing in size, number of nuclei, and DNA content. Surprisingly, we found that the specific depletion of KCs results in morphological changes in hepatocytes and HSCs. These findings reveal novel characteristics of liver heterogeneity and have important implications for both the structural organization of liver tissue and its function. Our next-gen 3D single-cell atlas is a powerful tool to understand liver tissue architecture, opening up avenues for in-depth investigations into tissue structure across both normal and pathological conditions.

Study of laser fluorescence spectroscopy in livers of rats with hypothermic ischemia

PURPOSE

After partial hepatectomy (PH), the remaining liver (RL) undergoes regenerative response proportional to the host. Limited literature exists on hepatic viability after tissue injury during hypothermic preservation. Spectroscopy measures cellular fluorescence and is explored for tissue characterization and parameter investigation. This study aimed to assess fluorescence analysis (spectroscopy) in evaluating liver viability and its relationship with hepatic tissue regeneration 24 hours after PH. Additionally, we analyzed liver regeneration in RL after 70% partial hepatectomy under hypothermic conditions with laser irradiation.

METHODS

Fifty-six Wistar rats were divided into four groups: total non-perfused liver (control), total perfused liver, partial hepatectomy "in situ", and partial hepatectomy "ex situ". Tissue analysis was performed at 0 and 24 hours using spectroscopy with laser devices emitting at 532 (green) and 405 nm (violet).

RESULTS

Spectroscopy identified tissue viability based on consistent results with Ki67 staining. The fluorescence spectra and Ki67 analysis displayed similar patterns, linking proliferative activity and absorption intensity.

CONCLUSIONS

Fluorescence spectroscopy proves to be promising for real-time analysis of cellular activity and viability. Metabolic activity was observed in groups of live animals and hypothermically preserved samples, indicating cellular function even under blood deprivation and hypothermic conditions.

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

Future medicine: from molecular pathways to the collective intelligence of the body

The remarkable anatomical homeostasis exhibited by complex living organisms suggests that they are inherently reprogrammable information-processing systems that offer numerous interfaces to their physiological and anatomical problem-solving capacities. We briefly review data suggesting that the multiscale competency of living forms affords a new path for biomedicine that exploits the innate collective intelligence of tissues and organs. The concept of tissue-level allostatic goal-directedness is already bearing fruit in clinical practice. We sketch a roadmap towards 'somatic psychiatry' by using advances in bioelectricity and behavioral neuroscience to design methods that induce self-repair of structure and function. Relaxing the assumption that cellular control mechanisms are static, exploiting powerful concepts from cybernetics, behavioral science, and developmental biology may spark definitive solutions to current biomedical challenges.

Regenerative potential of multinucleated cells: bone marrow adiponectin-positive multinucleated cells take the lead

BACKGROUND

Polyploid cells can be found in a wide evolutionary spectrum of organisms. These cells are assumed to be involved in tissue regeneration and resistance to stressors. Although the appearance of large multinucleated cells (LMCs) in long-term culture of bone marrow (BM) mesenchymal cells has been reported, the presence and characteristics of such cells in native BM and their putative role in BM reconstitution following injury have not been fully investigated.

METHODS

BM-derived LMCs were explored by time-lapse microscopy from the first hours post-isolation to assess their colony formation and plasticity. In addition, sub-lethally irradiated mice were killed every other day for four weeks to investigate the histopathological processes during BM regeneration. Moreover, LMCs from GFP transgenic mice were transplanted to BM-ablated recipients to evaluate their contribution to tissue reconstruction.

RESULTS

BM-isolated LMCs produced mononucleated cells with characteristics of mesenchymal stromal cells. Time-series inspections of BM sections following irradiation revealed that LMCs are highly resistant to injury and originate mononucleated cells which reconstitute the tissue. The regeneration process was synchronized with a transient augmentation of adipocytes suggesting their contribution to tissue repair. Additionally, LMCs were found to be adiponectin positive linking the observations on multinucleation and adipogenesis to BM regeneration. Notably, transplantation of LMCs to myeloablated recipients could reconstitute both the hematopoietic system and BM stroma.

CONCLUSIONS

A population of resistant multinucleated cells reside in the BM that serves as the common origin of stromal and hematopoietic lineages with a key role in tissue regeneration. Furthermore, this study underscores the contribution of adipocytes in BM reconstruction.

Liver cell therapies: cellular sources and grafting strategies

The liver has a complex cellular composition and a remarkable regenerative capacity. The primary cell types in the liver are two parenchymal cell populations, hepatocytes and cholangiocytes, that perform most of the functions of the liver and that are helped through interactions with non-parenchymal cell types comprising stellate cells, endothelia and various hemopoietic cell populations. The regulation of the cells in the liver is mediated by an insoluble complex of proteins and carbohydrates, the extracellular matrix, working synergistically with soluble paracrine and systemic signals. In recent years, with the rapid development of genetic sequencing technologies, research on the liver's cellular composition and its regulatory mechanisms during various conditions has been extensively explored. Meanwhile breakthroughs in strategies for cell transplantation are enabling a future in which there can be a rescue of patients with end-stage liver diseases, offering potential solutions to the chronic shortage of livers and alternatives to liver transplantation. This review will focus on the cellular mechanisms of liver homeostasis and how to select ideal sources of cells to be transplanted to achieve liver regeneration and repair. Recent advances are summarized for promoting the treatment of end-stage liver diseases by forms of cell transplantation that now include grafting strategies.

Physics-based tissue simulator to model multicellular systems: A study of liver regeneration and hepatocellular carcinoma recurrence

We present a multiagent-based model that captures the interactions between different types of cells with their microenvironment, and enables the analysis of the emergent global behavior during tissue regeneration and tumor development. Using this model, we are able to reproduce the temporal dynamics of regular healthy cells and cancer cells, as well as the evolution of their three-dimensional spatial distributions. By tuning the system with the characteristics of the individual patients, our model reproduces a variety of spatial patterns of tissue regeneration and tumor growth, resembling those found in clinical imaging or biopsies. In order to calibrate and validate our model we study the process of liver regeneration after surgical hepatectomy in different degrees. In the clinical context, our model is able to predict the recurrence of a hepatocellular carcinoma after a 70% partial hepatectomy. The outcomes of our simulations are in agreement with experimental and clinical observations. By fitting the model parameters to specific patient factors, it might well become a useful platform for hypotheses testing in treatments protocols.

Surgical Models of Liver Regeneration in Pigs: A Practical Review of the Literature for Researchers

The remarkable capacity of regeneration of the liver is well known, although the involved mechanisms are far from being understood. Furthermore, limits concerning the residual functional mass of the liver remain critical in both fields of hepatic resection and transplantation. The aim of the present study was to review the surgical experiments regarding liver regeneration in pigs to promote experimental methodological standardization. The Pubmed, Medline, Scopus, and Cochrane Library databases were searched. Studies evaluating liver regeneration through surgical experiments performed on pigs were included. A total of 139 titles were screened, and 41 articles were included in the study, with 689 pigs in total. A total of 29 studies (71% of all) had a survival design, with an average study duration of 13 days. Overall, 36 studies (88%) considered partial hepatectomy, of which four were an associating liver partition and portal vein ligation for staged hepatectomy (ALPPS). Remnant liver volume ranged from 10% to 60%. Only 2 studies considered a hepatotoxic pre-treatment, while 25 studies evaluated additional liver procedures, such as stem cell application, ischemia/reperfusion injury, portal vein modulation, liver scaffold application, bio-artificial, and pharmacological liver treatment. Only nine authors analysed how cytokines and growth factors changed in response to liver resection. The most used imaging system to evaluate liver volume was CT-scan volumetry, even if performed only by nine authors. The pig represents one of the best animal models for the study of liver regeneration. However, it remains a mostly unexplored field due to the lack of experiments reproducing the chronic pathological aspects of the liver and the heterogeneity of existing studies.

The expression of liver TNF-α gene, liver and small intestine histology of thermal stressed growing rabbits affected by allicin and lycopene

OBJECTIVES

Thermal stress negatively affects the productive performance and immunity responses of rabbits. In this study, we examined the effects of two allicin (AL) and lycopene (LP) levels on performance index, a liver tumor necrosis factor (TNF-α) gene expression, histological parameters of liver, and small intestine of V-line growing rabbits exposed to thermal stress.

METHODS

In nine replications of three rabbits per pen under thermal stress, 135 male rabbits (5 weeks old, average weight 772.02 ± 6.41 g) were randomly allocated to five dietary treatments in nine replications of three rabbits per pen under thermal stress (temperature-humidity index average 31.2). The 1st group served as the control, receiving no supplements; The 2nd and 3rd groups received 100 and 200 mg AL/kg of diet supplements; and the 4th and 5th groups were supplemented with 100 and 200 mg LP/kg diet, respectively.

RESULTS

show that AL and LP rabbits had the best final body weight, body gain, and feed conversion ratio compared with the control. compared with control, rabbit liver TNF- α levels significantly decreased in diets containing AL and LP In contrast, AL rabbits were slightly more effective in downregulating the expression of the TNF-α gene than LP groups. Furthermore, dietary supplementation of AL and LP significantly improved antibody titers against sheep red blood titers. Compared with other treatments, AL100 treatment significantly improved immune responses to phytohemagglutinin. In all treatments, histological analysis revealed a significant reduction in binuclear hepatocytes. The diameter of the hepatic lobules, villi height, crypt depth, and absorption surface of heat-stressed rabbits were all positively affected by both doses of LP (100-200 mg/kg diet).

CONCLUSION

rabbit dietary supplementation with AL or LP could positively affect performance, TNF-α, immunity, and histological parameters of growing rabbits under thermal stress.

Extensive accumulation of misfolded protein aggregates during natural aging and senescence

Accumulation of misfolded protein aggregates is a hallmark event in many age-related protein misfolding disorders, including some of the most prevalent and insidious neurodegenerative diseases. Misfolded protein aggregates produce progressive cell damage, organ dysfunction, and clinical changes, which are common also in natural aging. Thus, we hypothesized that aging is associated to the widespread and progressive misfolding and aggregation of many proteins in various tissues. In this study, we analyzed whether proteins misfold, aggregate, and accumulate during normal aging in three different biological systems, namely senescent cells, Caenorhabditis elegans, and mouse tissues collected at different times from youth to old age. Our results show a significant accumulation of misfolded protein aggregates in aged samples as compared to young materials. Indeed, aged samples have between 1.3 and 2.5-fold (depending on the biological system) higher amount of insoluble proteins than young samples. These insoluble proteins exhibit the typical characteristics of disease-associated aggregates, including insolubility in detergents, protease resistance, and staining with amyloid-binding dye as well as accumulation in aggresomes. We identified the main proteins accumulating in the aging brain using proteomic studies. These results show that the aged brain contain large amounts of misfolded and likely non-functional species of many proteins, whose soluble versions participate in cellular pathways that play fundamental roles in preserving basic functions, such as protein quality control, synapsis, and metabolism. Our findings reveal a putative role for protein misfolding and aggregation in aging.

Assessment of Liver Regeneration in Patients Who Have Undergone Living Donor Hepatectomy for Living Donor Liver Transplantation

BACKGROUND

Inflammation and the associated immune pathways are among the most important factors in liver regeneration after living donor hepatectomy. Various biomarkers, especially liver function tests, are used to show liver regeneration. The aim of this study was to evaluate the course of liver regeneration following donor hepatectomy (LDH) by routine and regeneration-related biomarkers.

METHOD

Data from 63 living liver donors (LLDs) who underwent LDH in Inonu University Liver Transplant Institute were prospectively analyzed. Serum samples were obtained on the preoperative day and postoperative days (POD) 1, 3, 5, 10, and 21. Regenerative markers including alfa-fetoprotein (AFP), des carboxy prothrombin (DCP), ornithine decarboxylase (ODC), retinol-binding protein 4 (RBP4), and angiotensin-converting enzyme isotype II (ACEII) and liver function tests including alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP) and total bilirubin levels were all analyzed.

RESULTS

The median age of the LLDs was 29.7 years and 28 LLDs were female. Eight LLDs developed postoperative complications requiring relaparotomy. The routine laboratory parameters including AST (<0.001), ALT (<0.001), ALP (<0.001), and total bilirubin (<0.001) showed a significant increase over time until postoperative day (POD) 3. For the regeneration-related parameters, except for the RBP4, all parameters including ACEII (p = 0.006), AFP (p = 0.002), DCP (p = 0.007), and ODC (p = 0.002) showed a significant increase in POD3. The regeneration parameters showed a different pattern of change. In right-lobe liver grafts, ACEII (p = 0.002), AFP (p = 0.035), and ODC (p = 0.001) showed a significant increase over time. DCP (p = 0.129) and RBP4 (p = 0.335) showed no significant changes in right-lobe liver grafts.

CONCLUSIONS

Regenerative markers are increased in a sustained fashion following LDH. This is more prominent following right-lobe grafts which are indicative of progenitor-associated liver regeneration.

Intravital electrochemical nanosensor as a tool for the measurement of reactive oxygen/nitrogen species in liver diseases

Reactive oxygen/nitrogen species (ROS/RNS) are formed during normal cellular metabolism and contribute to its regulation, while many pathological processes are associated with ROS/RNS imbalances. Modern methods for measuring ROS/RNS are mainly based on the use of inducible fluorescent dyes and protein-based sensors, which have several disadvantages for in vivo use. Intravital electrochemical nanosensors can be used to quantify ROS/RNS with high sensitivity without exogenous tracers and allow dynamic ROS/RNS measurements in vivo. Here, we developed a method for quantifying total ROS/RNS levels in the liver and evaluated our setup in live mice using three common models of liver disease associated with ROS activation: acute liver injury with CCl4, partial hepatectomy (HE), and induced hepatocellular carcinoma (HCC). We have demonstrated using intravital electrochemical detection that any exposure to the peritoneum in vivo leads to an increase in total ROS/RNS levels, from a slight increase to an explosion, depending on the procedure. Analysis of the total ROS/RNS level in a partial hepatectomy model revealed oxidative stress, both in mice 24 h after HE and in sham-operated mice. We quantified dose-dependent ROS/RNS production in CCl4-induced injury with underlying neutrophil infiltration and cell death. We expect that in vivo electrochemical measurements of reactive oxygen/nitrogen species in the liver may become a routine approach that provides valuable data in research and preclinical studies.

The Influence of Interdisciplinary Work towards Advancing Knowledge on Human Liver Physiology

The knowledge accumulated throughout the years about liver regeneration has allowed a better understanding of normal liver physiology, by reconstructing the sequence of steps that this organ follows when it must rebuild itself after being injured. The scientific community has used several interdisciplinary approaches searching to improve liver regeneration and, therefore, human health. Here, we provide a brief history of the milestones that have advanced liver surgery, and review some of the new insights offered by the interdisciplinary work using animals, in vitro models, tissue engineering, or mathematical models to help advance the knowledge on liver regeneration. We also present several of the main approaches currently available aiming at providing liver support and overcoming organ shortage and we conclude with some of the challenges found in clinical practice and the ethical issues that have concomitantly emerged with the use of those approaches.

Influence of constant lightning on liver health: an experimental study

Light pollution has become a serious problem in many urbanized areas of the world. The impact of prolonged exposure to light and consequent disruption of natural circadian rhythms has significant health implications. The current study was undertaken to evaluate the effect of prolonged exposure to light, simulating urban light pollution, on liver health. In order to evaluate the effect of prolonged exposure to light, we examined the morphofunctional state, immunohistochemical and micromorphometric parameters of rat liver in normal conditions and following prolonged lighting exposure. Our results show that nocturnal light disruption triggers a cell death in the liver within 3 weeks (necrosis and apoptosis of hepatocytes) and stimulates a change in normal cellular karyometric parameters. At the same time, intracellular regeneration takes place within the organ, which manifests through hepatocyte hypertrophy. Under the influence of constant illumination, the circadian rhythms (CRs) of the size of hepatocytes and their nuclei are restructured, and the rhythm of the nuclear-cytoplasmic ratio is destroyed. The destruction of the CR of expression of p53 and Ki-67 also occurs against the background of the rearrangement of the daily rhythmicity of Per2 and Bmal1. The revealed changes in the morphofunctional state of the liver under the influence of light pollution indicate that a violation of normal illumination regimes is a potent factor leading to significant structural changes in the liver.

Aberrant regulation of autophagy disturbs fibrotic liver regeneration after partial hepatectomy

Reports indicate that autophagy is essential for maintaining hepatocyte proliferative capacity during liver regeneration. However, the role of autophagy in fibrotic liver regeneration is incompletely elucidated. We investigated the deregulation of autophagic activities in liver regeneration after partial hepatectomy using a CCl4-induced fibrosis mouse model. The baseline autophagic activity was significantly increased in the fibrotic liver. After 50% partial hepatectomy (PHx), liver regeneration was remarkably decreased, accompanied by increased hepatocyte size and binuclearity ratio. Moreover, the expression of autophagy-related proteins was functionally deregulated and resulted in a reduction in the number of autophagosome and autophagosome–lysosome fusions. We further showed upregulation of autophagy activities through verapamil administration, improved hepatocyte proliferation capacity, and restricted cellular hypertrophy and binuclearity ratio. In conclusion, we demonstrated that the impairment of liver regeneration is associated with aberrant autophagy in fibrotic liver and that enhancing autophagy with verapamil may partially restore the impaired liver regeneration following PHx.

Discussing the final size and shape of the reconstructed tissues in tissue engineering

Tissue engineering (TE) has made a revolution in repairing, replacing, or regenerating tissues or organs, but it has still a long way ahead. The mechanical properties along with suitable physicochemical and biological characteristics are the initial criteria for scaffolds in TE that should be fulfilled. This research will provide another point of view toward TE challenges concerning the morphological and geometrical aspects of the reconstructed tissue and which parameters may affect it. Based on our survey, there is a high possibility that the final reconstructed tissue may be different in size and shape compared to the original design scaffold. Thereby, the 3D-printed scaffold might not guarantee an accurate tissue reconstruction. The main justification for this is the unpredicted behavior of cells, specifically in the outer layer of the scaffold. It can also be a concern when the scaffold is implanted while cell migration cannot be controlled through the in vivo signaling pathways, which might cause cancer challenges. To sum up, it is concluded that more studies are necessary to focus on the size and geometry of the final reconstructed tissue.

A natural transdifferentiation event involving mitosis is empowered by integrating signaling inputs with conserved plasticity factors

Transdifferentiation, or direct cell reprogramming, is the conversion of one fully differentiated cell type into another. Whether core mechanisms are shared between natural transdifferentiation events when occurring with or without cell division is unclear. We have previously characterized the Y-to-PDA natural transdifferentiation in Caenorhabditis elegans, which occurs without cell division and requires orthologs of vertebrate reprogramming factors. Here, we identify a rectal-to-GABAergic transdifferentiation and show that cell division is required but not sufficient for conversion. We find shared mechanisms, including erasure of the initial identity, which requires the conserved reprogramming factors SEM-4/SALL, SOX-2, CEH-6/OCT, and EGL-5/HOX. We also find three additional and parallel roles of the Wnt signaling pathway: selection of a specific daughter, removal of the initial identity, and imposition of the precise final subtype identity. Our results support a model in which levels and antagonistic activities of SOX-2 and Wnt signaling provide a timer for the acquisition of final identity.

PARK7 deficiency inhibits fatty acid β-oxidation via PTEN to delay liver regeneration after hepatectomy

Background & aims

Transient regeneration–associated steatosis (TRAS) is a process of temporary hepatic lipid accumulation and is essential for liver regeneration by providing energy generated from fatty acid β‐oxidation, but the regulatory mechanism underlying TRAS remains unknown. Parkinsonism‐associated deglycase (Park7)/Dj1 is an important regulator involved in various liver diseases. In nonalcoholic fatty liver diseased mice, induced by a high‐fat diet, Park7 deficiency improves hepatic steatosis, but its role in liver regeneration remains unknown

Methods

Park7 knockout (Park7^−/−), hepatocyte‐specific Park7 knockout (Park7^△hep) and hepatocyte‐specific Park7‐Pten double knockout mice were subjected to 2/3 partial hepatectomy (PHx)

Results

Increased PARK7 expression was observed in the regenerating liver of mice at 36 and 48 h after PHx. Park7^−/− and Park7^△hep mice showed delayed liver regeneration and enhanced TRAS after PHx. PPARa, a key regulator of β‐oxidation, and carnitine palmitoyltransferase 1a (CPT1a), a rate‐limiting enzyme of β‐oxidation, had substantially decreased expression in the regenerating liver of Park7^△hep mice. Increased phosphatase and tensin homolog (PTEN) expression was observed in the liver of Park7^△hep mice, which might contribute to delayed liver regeneration in these mice because genomic depletion or pharmacological inhibition of PTEN restored the delayed liver regeneration by reversing the downregulation of PPARa and CPT1a and in turn accelerating the utilization of TRAS in the regenerating liver of Park7^△hep mice

Conclusion

Park7/Dj1 is a novel regulator of PTEN‐dependent fatty acid β‐oxidation, and increasing Park7 expression might be a promising strategy to promote liver regeneration.

DNA Damage Repair Classifier Defines Distinct Groups in Hepatocellular Carcinoma

Simple Summary

DNA repair pathways have been implicated in hepatocellular carcinoma outcomes. We found that hepatocellular carcinomas (HCC) could be separated into two groups (high and low) based on the overall expression of genes involved in DNA repair. Among the low repair group, there were three subgroups, one of which shared features of the high repair group. Given the important role of liver in metabolism and detoxification and its regenerative capacity, proliferation and DNA damage responses are critical in subdividing major biological categories of liver tumors. High repair samples showed more proliferative and regenerative signatures and had poorer outcomes versus the low repair that were more associated with the genes involved in normal liver biology. These biological groups suggest that dysregulation in endogenous liver processes promotes a pro-tumorigenic microenvironment that may facilitate tumor progression or identify tumors that require more substantial clinical intervention.

Abstract

DNA repair pathways have been associated with variability in hepatocellular carcinoma (HCC) clinical outcomes, but the mechanism through which DNA repair varies as a function of liver regeneration and other HCC characteristics is poorly understood. We curated a panel of 199 genes representing 15 DNA repair pathways to identify DNA repair expression classes and evaluate their associations with liver features and clinicopathologic variables in The Cancer Genome Atlas (TCGA) HCC study. We identified two groups in HCC, defined by low or high expression across all DNA repair pathways. The low-repair group had lower grade and retained the expression of classical liver markers, whereas the high-repair group had more clinically aggressive features, increased p53 mutant-like gene expression, and high liver regenerative gene expression. These pronounced features overshadowed the variation in the low-repair subset, but when considered separately, the low-repair samples included three subgroups: L1, L2, and L3. L3 had high DNA repair expression with worse progression-free (HR 1.24, 95% CI 0.81–1.91) and overall (HR 1.63, 95% CI 0.98–2.71) survival. High-repair outcomes were also significantly worse compared with the L1 and L2 groups. HCCs vary in DNA repair expression, and a subset of tumors with high regeneration profoundly disrupts liver biology and poor prognosis.

Involvement of Ferroptosis in Diabetes-Induced Liver Pathology

Cell death plays an important role in diabetes-induced liver dysfunction. Ferroptosis is a newly defined regulated cell death caused by iron-dependent lipid peroxidation. Our previous studies have shown that high glucose and streptozotocin (STZ) cause β-cell death through ferroptosis and that ferrostatin-1 (Fer-1), an inhibitor of ferroptosis, improves β-cell viability, islet morphology, and function. This study was aimed to examine in vivo the involvement of ferroptosis in diabetes-related pathological changes in the liver. For this purpose, male C57BL/6 mice, in which diabetes was induced with STZ (40 mg/kg/5 consecutive days), were treated with Fer-1 (1 mg/kg, from day 1–21 day). It was found that in diabetic mice Fer-1 improved serum levels of ALT and triglycerides and decreased liver fibrosis, hepatocytes size, and binucleation. This improvement was due to the Fer-1-induced attenuation of ferroptotic events in the liver of diabetic mice, such as accumulation of pro-oxidative parameters (iron, lipofuscin, 4-HNE), decrease in expression level/activity of antioxidative defense-related molecules (GPX4, Nrf2, xCT, GSH, GCL, HO-1, SOD), and HMGB1 translocation from nucleus into cytosol. We concluded that ferroptosis contributes to diabetes-related pathological changes in the liver and that the targeting of ferroptosis represents a promising approach in the management of diabetes-induced liver injury.

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.

Prenatal glucocorticoid administration accelerates the maturation of fetal rat hepatocytes

BACKGROUND

Prenatal glucocorticoid (GC) is clinically administered to pregnant women who are at risk of preterm birth for the maturation of cardiopulmonary function. Preterm and low-birth-weight infants often experience liver dysfunction after birth because their livers are immature. However, the effects of prenatal GC administration on the liver remain unclear. We aimed to investigate the effects of prenatal GC administration on the maturation of liver hepatocytes in preterm rats.

METHODS AND RESULTS

Dexamethasone (DEX) was administered to pregnant Wistar rats on gestational days 17 and 19 before cesarean section. Real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed to determine the mRNA levels of albumin, hepatocyte nuclear factor-4 alpha (HNF4α), hepatocyte growth factor (HGF), thymus cell antigen 1 (Thy-1), cyclin B, and Cyclin-dependent kinase 1 (CDK1) in the liver samples. Immunohistochemical staining and enzyme-linked immunosorbent assay were performed to examine protein production. The hepatocytes enlarged because of growth and prenatal DEX administration. Albumin, HNF4α, and HGF levels increased secondary to growth and prenatal DEX administration. The levels of the cell cycle markers cyclin B and CDK1 gradually decreased during growth and with DEX administration.

CONCLUSIONS

The results suggest that prenatal GC administration leads to hepatocyte maturation via expression of HNF4α and HGF in preterm fetuses.

Dysfunction of lipid storage droplet-2 suppresses endoreplication and induces JNK pathway-mediated apoptotic cell death in Drosophila salivary glands

The lipid storage droplet-2 (LSD-2) protein of Drosophila is a homolog of mammalian perilipin 2, which is essential for promoting lipid accumulation and lipid droplet formation. The function of LSD-2 as a regulator of lipolysis has also been demonstrated. However, other LSD-2 functions remain unclear. To investigate the role of LSD-2, we performed tissue-specific depletion in the salivary glands of Drosophila using a combination of the Gal4-upstream activating sequence system and RNA interference. LSD-2 depletion inhibited the entry of salivary gland cells into the endoreplication cycle and delayed this process by enhancing CycE expression, disrupting the development of this organ. The deficiency of LSD-2 expression enhanced reactive oxygen species production in the salivary gland and promoted JNK-dependent apoptosis by suppressing dMyc expression. This phenomenon did not result from lipolysis. Therefore, LSD-2 is vital for endoreplication cell cycle and cell death programs.

Ssu72-HNF4α signaling axis classify the transition from steatohepatitis to hepatocellular carcinoma

Growing evidence suggests a mechanistic link between steatohepatitis and hepatocellular carcinoma (HCC). However, the lack of representative animal models hampers efforts to understand pathophysiological mechanisms underlying steatohepatitis-related HCC. We found that liver-specific deletion of Ssu72 phosphatase in mice, leads to a high incidence of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, but not HCC. However, loss of Ssu72 drastically increased the probability of HCC developing, as well as the population of hepatic progenitors, in various chemical and metabolic syndrome-induced HCC models. Importantly, hepatic Ssu72 loss resulted in the induction of mature hepatocyte-to-progenitor cell conversion, by dedifferentiation orchestrated by Ssu72-mediated hypo-phosphorylation of hepatocyte nuclear factor 4α (HNF4α), a master regulator of hepatocyte function. Our findings suggest that Ssu72-mediated HNF4α transcription contributes to the progression of steatohepatitis-associated HCC by regulating the dedifferentiation potential of hepatocytes. Thus, targeting the Ssu72-mediated HNF4α signaling that underlies the pathogenesis of steatohepatitis-associated HCC development could be a novel therapeutic intervention for steatohepatitis-associated HCC.

Durability of transgene expression after rAAV gene therapy

Recombinant adeno-associated virus (rAAV) gene therapy has the potential to transform the lives of patients with certain genetic disorders by increasing or restoring function to affected tissues. Following the initial establishment of transgene expression, it is unknown how long the therapeutic effect will last, although animal and emerging human data show that expression can be maintained for more than 10 years. The durability of therapeutic response is key to long-term treatment success, especially since immune responses to rAAV vectors may prevent re-dosing with the same therapy. This review explores the non-immunological and immunological processes that may limit or improve durability and the strategies that can be used to increase the duration of the therapeutic effect.

Cynara Scolymus (Artichoke) Improves Liver Regeneration after Partial Liver Resection in Rats

Objective: Liver regeneration is necessary to restore hepatic mass and functional capacity after partial hepatectomy (PH). Cynara scolymus (CS) is a pharmacologically important plant that contains phenolic acids and flavonoids, and experimental studies have indicated that it has antioxidant and hepatoprotective effects. The aim of this study was to investigate the role of CS in liver regeneration after PH in rats. Methods: A total of 36 Wistar albino rats weighing 280.5 ± 18.6 g were used. CS leaf extract was administered after partial hepatectomy. The rats were sacrificed at postoperative day 14, and the histological changes were assessed. The mitotic index (MI), nucleus size, hepatocyte size, and binucleation rate (BR) of hepatocytes were assessed using hematoxylin-eosin (H&E) staining. Results: The rats that received CS extract had significant differences in liver regeneration markers, including the hepatocyte size, mitotic index, and Ki-67 proliferation index (p

Prediction of Liver Weight Recovery by an Integrated Metabolomics and Machine Learning Approach After 2/3 Partial Hepatectomy

Liver has an ability to regenerate itself in mammals, whereas the mechanism has not been fully explained. Here we used a GC/MS-based metabolomic method to profile the dynamic endogenous metabolic change in the serum of C57BL/6J mice at different times after 2/3 partial hepatectomy (PHx), and nine machine learning methods including Least Absolute Shrinkage and Selection Operator Regression (LASSO), Partial Least Squares Regression (PLS), Principal Components Regression (PCR), k-Nearest Neighbors (KNN), Support Vector Machines (SVM), Random Forest (RF), eXtreme Gradient Boosting (xgbDART), Neural Network (NNET) and Bayesian Regularized Neural Network (BRNN) were used for regression between the liver index and metabolomic data at different stages of liver regeneration. We found a tree-based random forest method that had the minimum average Mean Absolute Error (MAE), Root Mean Squared Error (RMSE) and the maximum R square (R²) and is time-saving. Furthermore, variable of importance in the project (VIP) analysis of RF method was performed and metabolites with VIP ranked top 20 were selected as the most critical metabolites contributing to the model. Ornithine, phenylalanine, 2-hydroxybutyric acid, lysine, etc. were chosen as the most important metabolites which had strong correlations with the liver index. Further pathway analysis found Arginine biosynthesis, Pantothenate and CoA biosynthesis, Galactose metabolism, Valine, leucine and isoleucine degradation were the most influenced pathways. In summary, several amino acid metabolic pathways and glucose metabolism pathway were dynamically changed during liver regeneration. The RF method showed advantages for predicting the liver index after PHx over other machine learning methods used and a metabolic clock containing four metabolites is established to predict the liver index during liver regeneration.

Transcriptomic entropy benchmarks stem cell-derived cardiomyocyte maturation against endogenous tissue at single cell level

The immaturity of pluripotent stem cell (PSC)-derived tissues has emerged as a universal problem for their biomedical applications. While efforts have been made to generate adult-like cells from PSCs, direct benchmarking of PSC-derived tissues against in vivo development has not been established. Thus, maturation status is often assessed on an ad-hoc basis. Single cell RNA-sequencing (scRNA-seq) offers a promising solution, though cross-study comparison is limited by dataset-specific batch effects. Here, we developed a novel approach to quantify PSC-derived cardiomyocyte (CM) maturation through transcriptomic entropy. Transcriptomic entropy is robust across datasets regardless of differences in isolation protocols, library preparation, and other potential batch effects. With this new model, we analyzed over 45 scRNA-seq datasets and over 52,000 CMs, and established a cross-study, cross-species CM maturation reference. This reference enabled us to directly compare PSC-CMs with the in vivo developmental trajectory and thereby to quantify PSC-CM maturation status. We further found that our entropy-based approach can be used for other cell types, including pancreatic beta cells and hepatocytes. Our study presents a biologically relevant and interpretable metric for quantifying PSC-derived tissue maturation, and is extensible to numerous tissue engineering contexts.

Single-nucleus RNA-seq2 reveals functional crosstalk between liver zonation and ploidy

Single-cell RNA-seq reveals the role of pathogenic cell populations in development and progression of chronic diseases. In order to expand our knowledge on cellular heterogeneity, we have developed a single-nucleus RNA-seq2 method tailored for the comprehensive analysis of the nuclear transcriptome from frozen tissues, allowing the dissection of all cell types present in the liver, regardless of cell size or cellular fragility. We use this approach to characterize the transcriptional profile of individual hepatocytes with different levels of ploidy, and have discovered that ploidy states are associated with different metabolic potential, and gene expression in tetraploid mononucleated hepatocytes is conditioned by their position within the hepatic lobule. Our work reveals a remarkable crosstalk between gene dosage and spatial distribution of hepatocytes.

Echinacea in hepatopathy: A review of its phytochemistry, pharmacology, and safety

BACKGROUND

Echinacea, one of the most popular herbs with double function of immunity and anti-inflammatory activity, has now attracted much interest for a possible alternative for the treatment of hepatopathy. This review is aimed at providing a comprehensive overview of Echinacea regarding its chemical composition, pharmacological action against various hepatopathy, and safety.

METHODS

A comprehensive search of published articles was conducted to focus on original publications related to Echinacea and hepatopathy till the end of 2020 using various literature databases, including China National Knowledge Infrastructure, PubMed, and Web of Science database.

RESULTS

Echinacea exhibited excellent activities in resisting a variety of hepatopathy induced by different causes in preclinical experiments and clinical trials by regulating cell proliferation and apoptosis, antioxidant defense mechanism, voltage-gated sodium channels, lipid metabolism, circadian rhythm, p38 MAPK signaling pathway, JNK signaling pathway, Nrf2/HO-1 signaling pathway, PI3K/AKT signaling pathway, and Akt/GSK3 beta signaling pathways. The high efficacy of Echinacea is related to its immunomodulatory and anti-inflammatory activities. The main ingredients of Echinacea include caffeic acid derivatives, alkylamides, and polysaccharides, which have been well established in preclinical studies of liver diseases. Studies on acute and subacute toxicity show that Echinacea preparations are well-tolerated herbal medicines.

CONCLUSION

Echinacea may offer a novel potential strategy for clinical prevention and treatment of liver diseases and related diseases. Extensive studies are necessary to identify the underlying mechanisms and establish future therapeutic potentials of this herb. Well-designed clinical trials are still warranted to confirm the safety and effectiveness of Echinacea for hepatopathy.

Drosophila MOV10 regulates the termination of midgut regeneration

The molecular mechanisms by which stem cell proliferation is precisely controlled during the course of regeneration are poorly understood. Namely, how a damaged tissue senses when to terminate the regeneration process, inactivates stem cell mitotic activity, and organizes ECM integrity remain fundamental unanswered questions. The Drosophila midgut intestinal stem cell (ISC) offers an excellent model system to study the molecular basis for stem cell inactivation. Here, we show that a novel gene, CG6967 or dMOV10, is induced at the termination stage of midgut regeneration, and shows an inhibitory effect on ISC proliferation. dMOV10 encodes a putative component of the microRNA (miRNA) gene silencing complex (miRISC). Our data, along with previous studies on the mammalian MOV10, suggest that dMOV10 is not a core member of miRISC, but modulates miRISC activity as an additional component. Further analyses identified direct target mRNAs of dMOV10-containing miRISC, including Daughter against Dpp (Dad), a known inhibitor of BMP/TGF-β signaling. We show that RNAi knockdown of Dad significantly impaired ISC division during regeneration. We also identified six miRNAs that are induced at the termination stage and their potential target transcripts. One of these miRNAs, mir-1, is required for proper termination of ISC division at the end of regeneration. We propose that miRNA-mediated gene regulation contributes to the precise control of Drosophila midgut regeneration.

Liver regeneration observed across the different classes of vertebrates from an evolutionary perspective

The liver is a key organ that performs diverse functions such as metabolic processing of nutrients or disposal of dangerous substances (xenobiotics). Accordingly, it seems to be protected by several mechanisms throughout the life of organisms, one of which is compensatory hyperplasia, also known as liver regeneration. This review is a recapitulation of the scientific reports describing the different ways in which the various classes of vertebrates deal with liver injuries, where since mammals have an improved molecular toolkit, exhibit optimized regeneration of the liver compared to lower vertebrates. The main molecules involved in the compensatory process, such as proinflammatory and inhibitory cytokines, are analyzed across vertebrates with an evolutionary perspective. In addition, the possible significance of this mechanism is discussed in the context of the long life span of vertebrates, especially in the case of mammals.

Caspase-3-related apoptosis prevents pathological regeneration in a living liver donor rat model

PURPOSE

The main goal of this study was to determine the relationship of cleaved-caspase-3 (C3)-related apoptosis and hepatic proliferation, during the liver repopulation in a living liver donor rat model.

MATERIAL/METHODS

Thirty-three animals were randomized into eleven groups and evaluated on postoperative from 3 ​h until 384 ​h after 30%-partial hepatectomy (30%-PHx). Liver sections (5 ​μm) were processed by hematoxylin-eosin, and immunostaining for C3, accompanied by hepatic function test. C3 content and the hepatic lobule enlargement were analyzed by optical density, followed by cell counting.

RESULTS

Transient variations of alanine transferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were found. Significant increase in the C3 levels, and cell nuclei number, were detected at 12 ​h and 48 ​h after 30%-PHx, evidencing a correlation of p ​= ​-0.3679.

CONCLUSION

In the 30%-PHx rat model, C3-related apoptosis prevents proliferative pathological conditions during the hepatic lobule re-modeling.

Polyherbal mixture ameliorates hyperglycemia, hyperlipidemia and histopathological changes of pancreas, kidney and liver in a rat model of type 1 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

One of the commonly prescribed 'anti-diabetic' polyherbal mixtures by European herbalists is made of Rubus fruticosus and Vaccinium myrtillus leaves, Potentilla erecta roots, Geum urbanum aerial parts and Phaseolus vulgaris pods.

AIM OF THE STUDY

This study aimed to evaluate the phytochemical composition, antioxidant capacity, potential toxicity, hypoglycemic, hypolipidemic, nephroprotective and hepatoprotective activities of this polyherbal mixture decoction.

MATERIALS AND METHODS

The phytochemical composition was evaluated using HPLC-UV. The antioxidant activity was assessed using the DPPH test. Potential toxicity was evaluated using the acute and sub-chronic oral toxicity method. Diabetes was induced in Wistar female rats with a single intraperitoneal injection of alloxan monohydrate (150 mg/kg). The animals whose blood glucose was >20 mmol/L for 14 consecutive days were considered diabetic. For the next 14 days, D-10 and D-20 groups were treated with the polyherbal mixture (10 and 20 g of dry plant material/kg, respectively). I and M were control groups treated with insulin glargine (13 IU/kg) and metformin (150 mg/kg), respectively. Healthy control (HC) and diabetic control (DC) groups were treated with water. The blood glucose level was measured on days 14, 21 and 28. Lipid profile analysis was done on day 28. Pancreas, kidney and liver histopathology was evaluated using the H&E and Masson's trichrome staining. The liver tissue was additionally tested for PAS-positive cells.

RESULTS

The HPLC-UV analysis revealed the presence of quinic, gallic and caftaric acid, arbutin, rutin, trifolin, astragalin, hyperoside, isoquercetin and quercitrin. The antioxidant activity of the extract was higher than the reference's one (p < 0.01). Treatment with the polyherbal mixture (10 and 20 g/kg) has shown no toxic effects. No major decline in blood sugar was recorded in I and M groups compared to the DC one (22.86 ± 2.58, 28.5 ± 0.42 and 27.82 ± 0.9 mmol/L, respectively). The polyherbal mixture lowered the blood glucose level to the normal value (8.64 ± 4.09, 5.26 ± 1.3 and 6.76 ± 1.54 mmol/L in D-10, D-20 and HC groups, respectively). Furthermore, it decreased the levels of total cholesterol, triglycerides, VLDL, LDL, atherogenic and cardiovascular risk indices (p < 0.001) compared to the DC group. In addition, the extract restored histopathological changes of the pancreas, kidneys and liver to the healthy animal level.

CONCLUSION

Treatment with the polyherbal mixture extract was more effective than the standard drugs (insulin and metformin) in the amelioration of hyperglycemia, hyperlipidemia, and histopathological changes of the pancreas, kidney and liver tissue.

Liver regeneration: biological and pathological mechanisms and implications

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this 'hepatostat' will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, hepatocyte proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote the expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.

A computational model of liver tissue damage and repair

Drug induced liver injury (DILI) and cell death can result from oxidative stress in hepatocytes. An initial pattern of centrilobular damage in the APAP model of DILI is amplified by communication from stressed cells and immune system activation. While hepatocyte proliferation counters cell loss, high doses are still lethal to the tissue. To understand the progression of disease from the initial damage to tissue recovery or death, we computationally model the competing biological processes of hepatocyte proliferation, necrosis and injury propagation. We parametrize timescales of proliferation (α), conversion of healthy to stressed cells (β) and further sensitization of stressed cells towards necrotic pathways (γ) and model them on a Cellular Automaton (CA) based grid of lattice sites. 1D simulations show that a small α/β (fast proliferation), combined with a large γ/β (slow death) have the lowest probabilities of tissue survival. At large α/β, tissue fate can be described by a critical γ/β* ratio alone; this value is dependent on the initial amount of damage and proportional to the tissue size N. Additionally, the 1D model predicts a minimum healthy population size below which damage is irreversible. Finally, we compare 1D and 2D phase spaces and discuss outcomes of bistability where either survival or death is possible, and of coexistence where simulated tissue never completely recovers or dies but persists as a mixture of healthy, stressed and necrotic cells. In conclusion, our model sheds light on the evolution of tissue damage or recovery and predicts potential for divergent fates given different rates of proliferation, necrosis, and injury propagation.

Loss of hepatocyte cell division leads to liver inflammation and fibrosis

The liver possesses a remarkable regenerative capacity based partly on the ability of hepatocytes to re-enter the cell cycle and divide to replace damaged cells. This capability is substantially reduced upon chronic damage, but it is not clear if this is a cause or consequence of liver disease. Here, we investigate whether blocking hepatocyte division using two different mouse models affects physiology as well as clinical liver manifestations like fibrosis and inflammation. We find that in P14 Cdk1Liv-/- mice, where the division of hepatocytes is abolished, polyploidy, DNA damage, and increased p53 signaling are prevalent. Cdk1Liv-/- mice display classical markers of liver damage two weeks after birth, including elevated ALT, ALP, and bilirubin levels, despite the lack of exogenous liver injury. Inflammation was further studied using cytokine arrays, unveiling elevated levels of CCL2, TIMP1, CXCL10, and IL1-Rn in Cdk1Liv-/- liver, which resulted in increased numbers of monocytes. Ablation of CDK2-dependent DNA re-replication and polyploidy in Cdk1Liv-/- mice reversed most of these phenotypes. Overall, our data indicate that blocking hepatocyte division induces biological processes driving the onset of the disease phenotype. It suggests that the decrease in hepatocyte division observed in liver disease may not only be a consequence of fibrosis and inflammation, but also a pathological cue.

Prolonged oxidative stress and delayed tissue repair exacerbate acetaminophen-induced liver injury in aged mice

The liver gradually loses its regenerative capabilities with aging. However, it remains unknown whether aging affects drug-induced liver injury. Here, we used acetaminophen induced acute liver injury model to compare tissue injury and regeneration of aged mice (>80 weeks old) with young ones (8-10 weeks old). The mortality of aged mice after acetaminophen injury was higher than that of young mice. Transient increase of serum GOT and decrease of reduced glutathione (GSH) were not returned to original levels in aged mice even at 48 hours. In addition, Foxm1b and its targets Ccnd1 and Cdk1 were upregulated in young but not in aged mice after 48 hours. Moreover, an apoptosis-related gene, Cidea, was upregulated specifically in aged livers, which was consistent with increased number of TUNEL⁺ hepatocytes. Unexpectedly, damaged hepatocytes were retained in aged liver tissue, which may be caused by impaired recruitment of macrophages to the damaged area, without increases in Ccl2 after acetaminophen injury. Collectively, prolonged oxidative stress due to delayed recovery of GSH and the retention of damaged hepatocytes may suppress tissue repair and hepatocyte proliferation, resulting in exacerbation of acetaminophen injury in aged mice. Thus, aging is a risk factor conferring susceptibility against drug-induced liver injury.

CDK5RAP3 Deficiency Restrains Liver Regeneration after Partial Hepatectomy Triggering Endoplasmic Reticulum Stress

CDK5 regulatory subunit-associated protein 3 (CDK5RAP3) plays a crucial role in mammalian liver development and hepatic function by controlling hepatocyte proliferation and differentiation, glucose and lipid metabolism, UFMylation, and endoplasmic reticulum homeostasis. However, the role of CDK5RAP3 in liver regeneration remains unknown. A liver-specific Cdk5rap3 knockout (CKO) mouse model was used to study the function of CDK5RAP3 during liver regeneration induced by standard two-thirds partial hepatectomy (PHx). Twenty-four hours after PHx, the liver-to-body weight ratio was markedly higher in CKO mice than in wild-type mice. However, this ratio did not increase significantly and gradually over time after PHx in CKO mice. Hepatocyte proliferation was significantly delayed in CKO mice compared with wild-type mice. Meanwhile, CDK5RAP3 deficiency increased lipid accumulation, impaired glycogen synthesis, and lowered blood glucose levels after PHx. Critically, the absence of CDK5RAP3 seemed to promote an inflammatory response and induce apoptosis at a late stage of liver regeneration. In addition, CDK5RAP3 deficiency disrupted UFMylation homeostasis and aggravated endoplasmic reticulum stress in hepatocytes after PHx. Taken together, these data suggest that CDK5RAP3 enhances liver regeneration, at least partially via controlling cell cycle and glucose and lipid metabolism.

Cancer regeneration: Polyploid cells are the key drivers of tumor progression

In spite of significant advancements of therapies for initial eradication of cancers, tumor relapse remains a major challenge. It is for a long time known that polyploid malignant cells are a main source of resistance against chemotherapy and irradiation. However, therapeutic approaches targeting these cells have not been appropriately pursued which could partly be due to the shortage of knowledge on the molecular biology of cell polyploidy. On the other hand, there is a rising trend to appreciate polyploid/ multinucleated cells as key players in tissue regeneration. In this review, we suggest an analogy between the functions of polyploid cells in normal and malignant tissues and discuss the idea that cell polyploidy is an evolutionary conserved source of tissue regeneration also exploited by cancers as a survival factor. In addition, polyploid cells are highlighted as a promising therapeutic target to overcome drug resistance and relapse.

Liver structural transformation after partial hepatectomy and repeated partial hepatectomy in rats: A renewed view on liver regeneration

BACKGROUND

The phenomenon of liver regeneration after partial hepatectomy (PH) is still a subject of considerable interest due to the increasing frequency of half liver transplantation on the one hand, and on the other hand, new surgical approaches which allow removal of massive space-occupying hepatic tumors, which earlier was considered as inoperable. Interestingly, the mechanisms of liver regeneration are extensively studied after PH but less attention is paid to the architectonics of the regenerated organ. Because of this, the question “How does the structure of regenerated liver differ from normal, regular liver?” has not been fully answered yet. Furthermore, almost without any attention is left the liver's structural transformation after repeated hepatectomy (of the re-regenereted liver).

AIM

To compare the architectonics of the lobules and circulatory bed of normal, re-generated and re-regenerated livers.

METHODS

The livers of 40 adult, male, albino Wistar rats were studied. 14 rats were subjected to PH - the 1^st study group (SG1); 10 rats underwent repeated PH – the 2^nd study group (SG2); 16 rats were subjected to sham operation - control group (CG); The livers were studied after 9 months from PH, and after 6 months from repeated PH. Cytological (Schiff reaction for the determination of DNA concen-tration), histological (H&E, Masson trichrome, CK8 Immunohistochemical marker, transparent slides after Indian Ink injection, ), morphometrical (hepatocytes areas, perimeters and ploidy) and Electron Microscopical (Scanning Electron Microscopy of corrosion casts) methods were used.

RESULTS

In the SG1 and SG2, the area of hepatocytes and their perimeter are increased compared to the CG (P < 0.05). However, the areas and perimeters of the hepatocytes of the SG₁ and SG₂ groups reveal a lesser difference. In regenerated (SG₁) and re-regenerated (SG₂) livers, the hepatocytes form the remodeled lobules, which size (300-1200 µm) exceeds the sizes of the lobules from CG (300-600 µm). The remodeled lobules (especially the “mega-lobules” with the sizes 1000-1200 µm) contain the transformed meshworks of the sinusoids, the part of which is dilated asymmetrically. This meshwork might have originated from the several portal venules (interlobular and/or inlet). The boundaries between the adjacent lobules (including mega-lobules) are widened and filled by connective tissue fibers, which gives the liver parenchyma a nodular look. In SG₂ the unevenness of sinusoid diameters, as well as the boundaries between the lobules (including the mega-lobules) are more vividly expressed in comparison with SG₁. The liver tissue of both SG₁ and SG₂ is featured by the slightly expressed ductular reaction.

CONCLUSION

Regenerated and re-regenerated livers in comparison with normal liver contain hypertrophied hepatocytes with increased ploidy which together with transformed sinusoidal and biliary meshworks form the remodeled lobulli.

Large-Scale Profiling of Signaling Pathways Reveals a Distinct Demarcation between Normal and Extended Liver Resection

Despite numerous studies addressing normal liver regeneration, we still lack comprehensive understanding of the biological processes underlying failed liver regeneration. Therefore, we analyzed the activity of 271 intracellular signaling pathways (ISPs) by genome wide profiling of differentially expressed RNAs in murine liver tissue biopsies after normal hepatectomy (nHx; 68% of liver removed) and extended hepatectomy (eHx; 86% of liver removed). Comprehensive, genome-wide transcriptome profiling using RNAseq was performed in liver tissue obtained from mice (sham, nHx, and eHx) harvested 1, 8, 16, 32, and 48 h after operation (n = 3 per group) and the OncoFinder toolkit was used for an unsupervised, unbiased identification of intracellular signaling pathways (ISP) activity. We observed that the normal regenerative process requires a transient activation and silencing of approximately two dozen of ISPs. After nHx, the Akt Pathway represented with 13 branches, the Chromatin Pathway and the DDR Pathways dominated. After eHx, the ATM main pathway and two of its branches (Cell Survival; G2_M Checkpoint Arrest) dominated, as well as the Hypoxia Pathways. Further, 14 ISPs demonstrated a strong inverse regulation, with the Hedgehog and the Brca1 Main Pathways as chief activators after nHx, and the ATM Pathway(G2_M Checkpoint Arrest) as the dominating constraining response after eHx.

Cellular and molecular basis of liver regeneration

Recent advances in genetics and genomics have reinvigorated the field of liver regeneration. It is now possible to combine lineage-tracing with genome-wide studies to genetically mark individual liver cells and their progenies and detect precise changes in their genome, transcriptome, and proteome under normal versus regenerative settings. The recent use of single-cell RNA sequencing methodologies in model organisms has, in some ways, transformed our understanding of the cellular and molecular biology of liver regeneration. Here, we review the latest strides in our knowledge of general principles that coordinate regeneration of the liver and reflect on some conflicting evidence and controversies surrounding this topic. We consider the prominent mechanisms that stimulate homeostasis-related vis-à-vis injury-driven regenerative responses, highlight the likely cellular sources/depots that reconstitute the liver following various injuries and discuss the extrinsic and intrinsic signals that direct liver cells to proliferate, de-differentiate, or trans-differentiate while the tissue recovers from acute or chronic damage.

TLR9 signaling mediates adaptive immunity following systemic AAV gene therapy

An ongoing concern of in vivo gene therapy is adaptive immune responses against the protein product of a transgene, particularly for recessive diseases in which antigens are not presented to lymphocytes during central tolerance induction. Here we show that Toll-like receptor 9 (TLR9) signaling activates T cells against an epitope tagged mitochondria-targeted ornithine transcarbamylase (OTC) following the administration of a systemic adeno-associated virus (AAV) vector. Using a transgenic mouse model system, we demonstrate that TLR9 signaling extrinsic to T cells induces a robust cytotoxic T-cell response against the transgene and results in transgene expression loss. Overall, our results suggest that inflammation mediated by TLR9 signaling and the presence of high affinity transgene-specific T cells is important for the development of adaptive immune responses to transgene products following AAV gene therapy.