Cryopreservation of hepatic stellate cells

Cordycepin alleviates metabolic dysfunction-associated liver disease by restoring mitochondrial homeostasis and reducing oxidative stress via Parkin-mediated mitophagy

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) keeps rising with only a few drugs available. The present study aims to investigate the effects and mechanisms of cordycepin on MASLD. Male C57BL/6 mice were induced with a 90-day high-fat diet (HFD) and intraperitoneal administration with streptozotocin to establish MASLD murine model. Then they were randomly divided into the HFD and cordycepin groups (15, 30, 45 mg/kg). Cordycepin was orally given for 30 days. Serum total cholesterol (TC), triacylglyceride (TG), and aspartate aminotransferase (AST) levels were measured. L02 cells were induced by oleate acid (OA) or lipopolysaccharides (LPS), and treated with cordycepin or combined with inhibitors including chloroquine, 3-Methyladenine, and compound C. Atg7 and Parkin were knocked down in L02 cells using siRNA. Oil Red O and Nile Red staining for measuring lipid deposition. Mitochondria were visualized by transfection with mCherry-TOMM20-N10. Quantitative real-time PCR, Western blotting, and immunofluorescence staining were used to determine expressions of key molecules in inflammation, lipid metabolism, mitochondria homeostasis, and oxidative stress. Cordycepin significantly mitigated lipid deposition and ballooning in the livers of MASLD mice. Serum TC, TG, and AST levels were decreased by cordycepin. Cordycepin alleviated OA-induced lipid deposition and LPS-induced inflammation in L02 cells, attenuated oxidative stress, promoted autophagy, and maintained the autophagic flux by activating AMP-activated protein kinase (AMPK). Cordycepin reduced the accumulation of impaired mitochondria by enhancing Parkin-dependent mitophagy and promoting mitochondrial biogenesis. Cordycepin alleviates MASLD by restoring mitochondrial homeostasis and reducing oxidative stress via activating the Parkin-mediated mitophagy.

Vitamin A: too good to be bad?

Vitamin A is a micronutrient important for vision, cell growth, reproduction and immunity. Both deficiency and excess consuming of vitamin A cause severe health consequences. Although discovered as the first lipophilic vitamin already more than a century ago and the definition of precise biological roles of vitamin A in the setting of health and disease, there are still many unresolved issues related to that vitamin. Prototypically, the liver that plays a key role in the storage, metabolism and homeostasis of vitamin A critically responds to the vitamin A status. Acute and chronic excess vitamin A is associated with liver damage and fibrosis, while also hypovitaminosis A is associated with alterations in liver morphology and function. Hepatic stellate cells are the main storage site of vitamin A. These cells have multiple physiological roles from balancing retinol content of the body to mediating inflammatory responses in the liver. Strikingly, different animal disease models also respond to vitamin A statuses differently or even opposing. In this review, we discuss some of these controversial issues in understanding vitamin A biology. More studies of the interactions of vitamin A with animal genomes and epigenetic settings are anticipated in the future.

Isolation, Purification, and Culture of Primary Murine Hepatic Stellate Cells: An Update

In the healthy liver, quiescent hepatic stellate cells (HSCs) are found in the perisinusoidal space (i.e., the space of Dissé) in close proximity to endothelial cells and hepatocytes. HSCs represent 5-8% of the total number of liver cells and are characterized by numerous fat vacuoles that store vitamin A in the form of retinyl esters. Upon liver injury caused by different etiologies, HSCs become activated and acquire a myofibroblast (MFB) phenotype in a process called transdifferentiation. In contrast to quiescent HSC, MFB become highly proliferative and are characterized by an imbalance in extracellular matrix (ECM) homeostasis, by producing an excess of collagen and blocking its turnover by synthesis of protease inhibitors. This leads to a net accumulation of ECM during fibrosis. In addition to HSC, there are fibroblasts in the portal fields (pF), which also have the potency to acquire a myofibroblastic phenotype (pMF). The contributions of these two fibrogenic cell types (i.e., MFB and pMF) vary based on the etiology of liver damage (parenchymal vs. cholestatic). Based on their importance to hepatic fibrosis, the isolation and purification protocols of these primary cells are in great demand. Moreover, established cell lines may offer only limited information about the in vivo behavior of HSC/MFB and pF/pMF.Here we describe a method for high-purity isolation of HSC from mice. In the first step, the liver is digested with pronase and collagenase, and the cells are dissociated from the tissue. In the second step, HSCs are enriched by density gradient centrifugation of the crude cell suspension using a Nycodenz gradient. The resulting cell fraction can be further optionally purified by flow cytometric enrichment to generate ultrapure HSC.

Isolation and Culture of Primary Murine Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are found in the perisinusoidal space of the liver (i.e., the space of Dissé). They represent 5-8% of the total number of liver cells. In normal liver, these cells have a quiescent phenotype and are characterized by numerous fat vacuoles that store vitamin A in a form of retinyl ester. In injured liver, these cells transdifferentiate into a myofibroblast phenotype, become highly proliferative and are responsible for excess collagen synthesis and deposition during fibrosis. Due to their exceptional pathophysiological relevance, several isolation and purification protocols of primary HSCs have been established that provide the basis for studying HSC biology in vitro. We here describe a method for high-purity isolation of HSCs from mice. This protocol includes the enzymatic digestion of the liver tissue by pronase and collagenase, cellular enrichment by centrifugation of the crude cell suspension through a Nycodenz density gradient, and a final (optional) flow cytometric enrichment that allows generating ultrapure HSC fractions.

Cell sources for in vitro human liver cell culture models

In vitro liver cell culture models are gaining increasing importance in pharmacological and toxicological research. The source of cells used is critical for the relevance and the predictive value of such models. Primary human hepatocytes (PHH) are currently considered to be the gold standard for hepatic in vitro culture models, since they directly reflect the specific metabolism and functionality of the human liver; however, the scarcity and difficult logistics of PHH have driven researchers to explore alternative cell sources, including liver cell lines and pluripotent stem cells. Liver cell lines generated from hepatomas or by genetic manipulation are widely used due to their good availability, but they are generally altered in certain metabolic functions. For the past few years, adult and pluripotent stem cells have been attracting increasing attention, due their ability to proliferate and to differentiate into hepatocyte-like cells in vitro However, controlling the differentiation of these cells is still a challenge. This review gives an overview of the major human cell sources under investigation for in vitro liver cell culture models, including primary human liver cells, liver cell lines, and stem cells. The promises and challenges of different cell types are discussed with a focus on the complex 2D and 3D culture approaches under investigation for improving liver cell functionality in vitro Finally, the specific application options of individual cell sources in pharmacological research or disease modeling are described.

Lipocalin-2 (LCN2) regulates PLIN5 expression and intracellular lipid droplet formation in the liver

Lipocalin-2 (LCN2) belongs to the superfamily of lipocalins and plays critical roles in the control of cellular homeostasis during inflammation and in responses to cellular stress or injury. In the liver, LCN2 triggers protective effects following acute or chronic injury, and its expression is a reliable indicator of liver damage. However, little is known about LCN2's functions in the homeostasis and metabolism of hepatic lipids or in the development of steatosis. In this study, we fed wild type (WT) and LCN2-deficient (Lcn2(-/-)) mice a methionine- and choline-deficient (MCD) diet as a nutritional model of non-alcoholic steatohepatitis, and compared intrahepatic lipid accumulation, lipid droplet formation, mitochondrial content, and expression of the Perilipin proteins that regulate cellular lipid metabolism. We found that Lcn2(-/-) mice fed an MCD diet accumulated more lipids in the liver than WT controls, and that the basal expression of the lipid droplet coat protein Perilipin 5 (PLIN5, also known as OXPAT) was significantly reduced in these animals. Similarly, the overexpression of LCN2 and PLIN5 were also found in animals that were fed with a high fat diet. Furthermore, the loss of LCN2 and/or PLIN5 in hepatocytes prevented normal intracellular lipid droplet formation both in vitro and in vivo. Restoration of LCN2 in Lcn2(-/-) primary hepatocytes by either transfection or adenoviral vector infection induced PLIN5 expression and restored proper lipid droplet formation. Our data indicate that LCN2 is a key modulator of hepatic lipid homeostasis that controls the formation of intracellular lipid droplets by regulating PLIN5 expression. LCN2 may therefore represent a novel therapeutic drug target for the treatment of liver diseases associated with elevated fat accumulation and steatosis.

Hyaluronan-supplemented buffers preserve adhesion mechanisms facilitating cryopreservation of human hepatic stem/progenitor cells

The supply of human hepatic stem cells (hHpSCs) and other hepatic progenitors has been constrained by the limited availability of liver tissues from surgical resections, the rejected organs from organ donation programs, and the need to use cells immediately. To facilitate accessibility to these precious tissue resources, we have established an effective method for serum-free cryopreservation of the cells, allowing them to be stockpiled and stored for use as an off-the-shelf product for experimental or clinical programs. The method involves use of buffers, some serum-free, designed for cryopreservation and further supplemented with hyaluronans (HA) that preserve adhesion mechanisms facilitating postthaw culturing of the cells and preservation of functions. Multiple cryopreservation buffers were found to yield high viabilities (80-90%) of cells on thawing of the progenitor cells. Serum-free CS10 supplemented with 0.05% hyaluronan proved the most effective, both in terms of viabilities of cells on thawing and in yielding cell attachment and formation of expanding colonies of cells that stably maintain the stem/progenitor cell phenotype. Buffers to which 0.05 or 0.1% HAs were added showed cells postthaw to be phenotypically stable as stem/progenitors, as well as having a high efficiency of attachment and expansion in culture. Success correlated with improved expression of adhesion molecules, particularly CD44, the hyaluronan receptor, E-cadherin, β4 integrin in hHpSCs, and β1 integrins in hepatoblasts. The improved methods in cryopreservation offer more efficient strategies for stem cell banking in both research and potential therapy applications.

Human primary cultured hepatic stellate cells can be cryopreserved

We compared the morphological and functional characteristics of cultured unfrozen hepatic stellate cells (HSCs) and cryopreserved HSCs obtained from human livers. We used liver tissues obtained by surgical resection from patients with metastatic liver cancer or with hepatocellular carcinoma. HSCs were isolated and allowed to spread in culture. Comparison of morphological and functional features between the unfrozen HSCs and cryopreserved HSCs was performed at each passage using the following techniques: light microscopy, immunohistochemistry, cell growth curve, metallothionein (MTT) assay, and PI staining, Western blot, real-time polymerase chain reaction (PCR), and gene expression analysis using microarrays. The purity of HSCs was more than 90% in all passages. alpha-Smooth muscle actin (SMA-)positive HSCs gradually increased in successive passages, and the positive cell rate and rate of increase in cell number were similar in both groups. Expression of platelet-derived growth factor (PDGF) receptor, transforming growth factor (TGF)-beta receptor, and alpha-SMA mRNAs and protein was similar during each passage in the two groups. Gene expression was nearly identical at each passage in unfrozen and frozen/thawed samples obtained from the same patient. In conclusion, an adequate protocol for the cryopreservation of human primary cultured HSCs could be established.

Hypothermic storage of hepatocytes used for bioartificial liver support system: current status and recent advances

The problem that high-quality hepatocytes are difficult to obtain restricts the use of bioartificial liver support system (BLASS) in clinical practice. Finding an effective way to preserve hepatocytes and constructing a "ready-to-use" hepatocyte bank would efficiently promote the development of the BLASS. Nowadays, the methods for hypothermic storage of hepatocytes could be classified into two types: conventional hypothermic storage at 4 °C or subzero nonfreezing storage, and cryopreservation at -80 °C or -196 °C. Each type of hypothermic storage method has its advantages and disadvantages. Many factors may affect the effect of hypothermic storage (cryopreservation), such as storage solution and cryoprotective agent. Although the precise mechanism underlying the death of hepatocytes during hypothermic storage is not well understood, numerous studies have indicated that apoptosis plays an important role in hypothermic storage injury.

Activation of hepatic stellate cells is associated with cytokine expression in thioacetamide-induced hepatic fibrosis in mice

The pathophysiological mechanisms of thioacetamide (TAA)-induced hepatic fibrogenesis are not yet fully understood. In particular, the role of hepatic stellate cells (HSCs) remains unclear. We therefore examined proliferation and transdifferentiation of HSC as well as the underlying molecular mechanisms in TAA-induced fibrosis. Hepatic fibrogenesis was induced in mice by addition of TAA to drinking water. Liver damage was determined by assessment of alanine aminotransferase and aspartate aminotransferase levels, and measurement of collagen deposition. Additionally, expression patterns of alpha-smooth muscle actin, glial fibrillary acidic protein (GFAP, specific hepatic biomarker for HSC), cysteine- and glycine-rich protein 2 (CRP2, specific marker of HSC transdifferentiation), tissue inhibitor of metalloproteinases-1, matrix metalloproteinase-9 (MMP-9), interleukins (IL-1beta, IL-6), platelet-derived growth factors (PDGF-B, PDGF-D) , tumor necrosis factor (TNF)-alpha, and (transforming growth factor (TGF)-beta1 were assessed by real-time PCR. Transcription of GFAP and CRP2 were transiently upregulated during TAA-induced fibrogenesis (punctum maxima (p.m.) week 10 for GFAP and week 14 for CRP2). Similar transient expression patterns were demonstrated for IL-1beta, IL-6, TGF-beta1, and PDGF-B (p.m. week 12) whereas TNF-alpha and PDGF-D continuously increased with ongoing liver injury. In particular, not only neutrophil granulocytes, but also macrophages and leukocytes served as a major source for MMP-9 expression. GFAP and CRP2 expression patterns demonstrated transiently increased HSC-activation during TAA-induced hepatic fibrogenesis. The rate of increase of transcription of GFAP correlated best with PDGF-B, whereas CRP2 levels correlated with PDGF-B, PDGF-D, and IL-1beta expression. This study demonstrates for the first time that transiently increased activation patterns of HSC are observed in toxically induced hepatic fibrosis. Thus, TAA in drinking water is an effective and elegant model to induce reproducible states of liver fibrosis without parenchymal damage in mice.

Targeted disruption of the mouse Csrp2 gene encoding the cysteine- and glycine-rich LIM domain protein CRP2 result in subtle alteration of cardiac ultrastructure

BACKGROUND

The cysteine and glycine rich protein 2 (CRP2) encoded by the Csrp2 gene is a LIM domain protein expressed in the vascular system, particularly in smooth muscle cells. It exhibits a bimodal subcellular distribution, accumulating at actin-based filaments in the cytosol and in the nucleus. In order to analyze the function of CRP2 in vivo, we disrupted the Csrp2 gene in mice and analysed the resulting phenotype.

RESULTS

A approximately 17.3 kbp fragment of the murine Csrp2 gene containing exon 3 through 6 was isolated. Using this construct we confirmed the recently determined chromosomal localization (Chromosome 10, best fit location between markers D10Mit203 proximal and D10Mit150 central). A gene disruption cassette was cloned into exon 4 and a mouse strain lacking functional Csrp2 was generated. Mice lacking CRP2 are viable and fertile and have no obvious deficits in reproduction and survival. However, detailed histological and electron microscopic studies reveal that CRP2-deficient mice have subtle alterations in their cardiac ultrastructure. In these mice, the cardiomyocytes display a slight increase in their thickness, indicating moderate hypertrophy at the cellular level. Although the expression of several intercalated disc-associated proteins such as beta-catenin, N-RAP and connexin-43 were not affected in these mice, the distribution of respective proteins was changed within heart tissue.

CONCLUSION

We conclude that the lack of CRP2 is associated with alterations in cardiomyocyte thickness and hypertrophy.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

The expression of CSRP2 encoding the LIM domain protein CRP2 is mediated by TGF-β in smooth muscle and hepatic stellate cells

Transforming growth factor-beta (TGF-beta) is a cytokine implicated in differentiation of smooth muscle cells and other mesenchymal-derived cells. During hepatic fibrogenesis, TGF-beta has a pivotal role in the initiation, promotion, and progression of transdifferentiation of hepatic stellate cells into myofibroblasts that play a central role in the synthesis of extracellular matrix components. Both, smooth muscle and activated hepatic stellate cells, express smooth muscle alpha-actin, the calponin-related protein SM22alpha, and CSRP2 encoding the cysteine- and glycine-rich LIM domain protein 2 (CRP2). The aim of the present study was to determine whether the expression of CSRP2 is influenced by TGF-beta. Stimulation as well as sequestering experiments demonstrated that TGF-beta markedly influences CSRP2 gene activity. Inhibition experiments using the ALK5 inhibitor SB-431542 further reveal that the transcriptional stimulation of the CSRP2 gene is mediated via the ALK5/Smad2/Smad3 signalling pathway. By use of bisulfite genomic analysis of CpG islands within the 5' regulatory regions we could exclude methylation-associated silencing, previously found to be responsible for the transcriptional inactivity of CSRP2 in a variety of human cancer cells and in a multistage carcinogenesis model, as a cause for CSRP2 inactivity in hepatocytes or fully transdifferentiated myofibroblasts.