Ultrastructure of liver progenitor/oval cells in children with nonalcoholic steatohepatitis

The Ultrastructure of Hepatic Stellate Cell-Macrophage Intercellular Crosstalk as a New Morphological Insight into Phenomenon of Fibrogenesis in Pediatric Autoimmune Hepatitis

The aim of the study was the pioneering retrospective ultrastructural evaluation of respective forms of hepatic stellate cells (HSCs) and analysis of their crosstalk with other adjacent nonparenchymal cells (NPCs), especially Kupffer cells/macrophages (KCs/MPs), in pediatric autoimmune hepatitis (AIH).

METHODS

Ultrastructural assessment of the HSC population and NPCs was performed in transmission electron microscopy (TEM) using pretreatment liver biopsies from 25 children (8 boys and 17 girls) aged 4-17 with clinic-pathologically diagnosed untreated AIH.

RESULTS

Submicroscopic evaluation allowed easy identification of numerous HSCs in the form of transitory cells, i.e., T-HSCs, accompanied by signs of fibrosis. T-HSCs included cells with features of activation initiation (iHSCs) and activation perpetuation (pHSCs), indicating high HSC activation plasticity. The pHSCs were markedly elongated and mainly showed a distinct loss of lipid cytoplasmic material, expanded and dilated channels of granular endoplasmic reticulum, and linear bundles of microfilaments beneath the cell membrane. They were surrounded by usually mature collagen fibers. Frequently activated KCs/MPs adhered directly to T-HSCs. Between them, tight intercellular junctions were formed by means of point desmosomes.

CONCLUSIONS

Our qualitative TEM observations indicate a key role of T-HSCs in liver fibrogenesis in pediatric AIH, with the essential involvement of activated KCs/MPs that directly adhere to them. Tight intercellular junctions, being the ultrastructural exponent of the specific cellular mechanisms of the crosstalk between NPCs, can play a vital role in hepatic collagen fibroplasia. A better understanding of HSC population morphology at the ultrastructural level in AIH seems important not only to improve the disease morphological diagnostics but to also provide new insights into therapeutic interventions for the phenomenon of liver fibrogenesis.

Ultrastructural Profile Combined with Immunohistochemistry of a Hepatic Progenitor Cell Line in Pediatric Autoimmune Hepatitis: New Insights into the Morphological Pattern of the Disease

Considering that the heterogenic population of a hepatic progenitor cell line (HPCL) can play a vital role in autoimmune hepatitis (AIH), we decided to conduct pioneering retrospective evaluation of these cells in pediatric AIH by means of transmission electron microscopy (TEM). The aim of the study was to assess the ultrastructure of the HPCL in children with untreated AIH. Ultrastructural analysis of the HPCL population, preceded by immunohistochemical staining for cytokeratin 7 (CK7), was performed using pretreatment liver biopsies from 23 children with clinicopathologically diagnosed AIH. Immunohistochemical assessment for CK7 allowed detection of proliferating immature epithelial cells differentiating towards periportal and intralobular intermediate hepatocytes without marked formation of ductular reactions in AIH children. Using TEM, we distinguished three morphological types of HPCs: I—the most undifferentiated progenitor cells; III—intermediate hepatocyte-like cells; II—intermediate bile duct cells. Most frequent were the cells differentiating towards hepatocytes, most rare—those differentiating towards cholangiocytes. The results indicate that an HPCL may be an important source of hepatocyte regeneration. Ultrastructural analyses of the HPCL population, combined with immunohistochemistry for CK7, might be a useful tool to evaluate liver cell regeneration, including fibrogenesis, and may help better understand the morphological pattern of the disease, in pediatric AIH. Frequent appearance of an HPCL in the vicinity of fibrotic foci, often accompanied by hyperactive Kupffer cells and transitional hepatic stellate cells, may indicate their significant involvement in liver fibrogenesis.

Ultrastructural characteristics of the respective forms of hepatic stellate cells in chronic hepatitis B as an example of high fibroblastic cell plasticity. The first assessment in children

PURPOSE

Activation of hepatic stellate cells (HSCs), mainly responsible for extracellular matrix synthesis, is assumed to be central event in the process of liver fibrogenesis. The major objective of the research was to analyze the ultrastructural profile of activated HSCs in children with chronic hepatitis B (chB), with respect to fibrosis intensity.

MATERIALS/METHODS

Ultrastructural investigations of HSCs were conducted on liver bioptates from 70 children with clinicopathologically diagnosed chB before antiviral treatment. Biopsy material, fixed in paraformaldehyde and glutaraldehyde solution, was routinely processed for electron-microscopic analysis.

RESULTS

In children with intensive liver fibrosis (S-2 and S-3), the ultrastructural picture showed almost total replacement of quiescent HSCs (Q-HSCs) by activated, i.e. transitional HSCs (T-HSCs). Among T-HSCs, two types of cells were distinguished: cells exhibiting initiation of HSC activation (Ti-HSCs), never before described in chB, that were frequently accompanied by activated Kupffer cells, and cells with features of perpetuation of activation (Tp-HSCs). Tp-HSCs were elongated and characterized by substantial loss of cytoplasmic lipid material; they contained an increased number of cytoskeletal components, extremely dilated channels of granular endoplasmic reticulum and activated Golgi apparatus, which indicated their marked involvement in intensive synthesis of extracellular matrix proteins. Many collagen fibers were found to adhere directly to Tp-HSCs.

CONCLUSIONS

The current study showed T-HSCs to be an important link between Q-HSCs and myofibroblastic HSCs (Mf-HSCs). Transformation of HSCs into new morphological variations (Ti-HSCs; Tp-HSCs and Mf-HSCs), observed along with growing fibrosis, indicates their high plasticity and a key role in fibrogenesis in pediatric chB.

Activation of pluripotent genes in hepatic progenitor cells in the transition of nonalcoholic steatohepatitis to pre-malignant lesions

Nonalcoholic steatohepatitis is considered as a precancerous condition. However, hepatic carcinogenesis from NASH is poorly understood. This study aims to investigate the activation of pluripotent genes (c-Myc, Oct-4, KLF-4, and Nanog) and morphogenic gene (Gli-1) in hepatic progenitor cells from patient specimens and in an animal model to determine the possibility of normal stem/progenitor cells becoming the origin of NASH-HCC. In this study, expression of pluripotent and morphogenic genes in human NASH-HCC tissues was significantly upregulated compared to adjacent non-tumor liver tissues. After feeding high-fat/calorie diet plus high fructose/glucose in drinking water (HFC diet plus HF/G) for up to 12 months, mice developed obesity, insulin resistance, and steatohepatitis with significant necroptotic inflammation and fibrotic progression, as well as occurrence of hyperplastic nodules with dysplasia; and this model represents pathohistologically as a transition from NASH to NASH-HCC in a pre-carcinomatous stage. High expression of pluripotent and morphogenic genes was immunohistochemically visualized in the dysplasia areas of mouse liver, where there were many OV-6-positive cells, indicating proliferation of HOCs in NASH with fibrotic progression. Moreover, oncogenic transcription factors (c-Myc, KLF-4, and Nanog) were co-localized in these hepatic progenitor cells. In conclusion, pluripotent and morphogenic genes may contribute to the reprogramming of hepatic progenitor cells in driving these cells to be the origin of NASH-HCC in a steatotic and inflamed microenvironment.

Glassy droplet inclusions within the cytoplasm of Kupffer cells: A novel ultrastructural feature for the diagnosis of pediatric autoimmune hepatitis

Since Kupffer cells/macrophages (KCs/MPs) may be involved in the pathogenesis of autoimmune hepatitis (AIH), this pioneer study was undertaken to evaluate KCs/MPs in pediatric AIH in transmission-electron microscope.

METHODS

Ultrastructural analyses were performed using liver biopsies from 14 children with clinicopathologically diagnosed AIH.

RESULTS

In all AIH children, ultrastructural findings revealed changes in the cells lining sinusoidal vessels, especially KCs/MPs and endothelial cells. KCs/MPs showed increased phagocytic activity and damaged mitochondria, frequently with accompanying intense fibrosis. In 10/14 AIH patients, the cytoplasm of sinusoidal KCs/MPs contained characteristic glassy droplet inclusions. They were round, sharply circumscribed, and contained homogeneous material and distinct translucent fields. Their ultrastructure was identical with the Russel bodies of plasma cells, which were also found in liver biopsies in the same patients.

CONCLUSION

Ultrastructural identification of characteristic cytoplasmic droplets with glassy appearance in KCs/MPs, never before described in AIH, provides a useful novel morphological feature in the diagnosis of this disease.

Ultrastructural Characteristics of Rat Hepatic Oval Cells and Their Intercellular Contacts in the Model of Biliary Fibrosis: New Insights into Experimental Liver Fibrogenesis

PURPOSE

Recently, it has been emphasized that hepatic progenitor/oval cells (HPCs) are significantly involved in liver fibrogenesis. We evaluated the multipotential population of HPCs by transmission electron microscope (TEM), including relations with adherent hepatic nonparenchymal cells (NPCs) in rats with biliary fibrosis induced by bile duct ligation (BDL).

METHODS

The study used 6-week-old Wistar Crl: WI(Han) rats after BDL for 1, 6, and 8 weeks.

RESULTS

Current ultrastructural analysis showed considerable proliferation of HPCs in experimental intensive biliary fibrosis. HPCs formed proliferating bile ductules and were scattered in periportal connective tissue. We distinguished 4 main types of HPCs: 0, I, II (bile duct-like cells; most common), and III (hepatocyte-like cells). We observed, very seldom presented in literature, cellular interactions between HPCs and adjacent NPCs, especially commonly found transitional hepatic stellate cells (T-HSCs) and Kupffer cells/macrophages. We showed the phenomenon of penetration of the basement membrane of proliferating bile ductules by cytoplasmic processes sent by T-HSCs and the formation of direct cell-cell contact with ductular epithelial cells related to HPCs.

CONCLUSIONS

HPC proliferation induced by BDL evidently promotes portal fibrogenesis. Better understanding of the complex cellular interactions between HPCs and adjacent NPCs, especially T-HSCs, may help develop antifibrotic therapies in the future.

Pediatric non-alcoholic steatohepatitis: The first report on the ultrastructure of hepatocyte mitochondria

AIM: To investigate the ultrastructure of abnormal hepatocyte mitochondria, including their cellular and hepatic zonal distribution, in bioptates in pediatric non-alcoholic steatohepatitis (NASH).

METHODS: Ultrastructural investigations were conducted on biopsy liver specimens obtained from 10 children (6 boys and 4 girls) aged 2-14 years with previously clinicopathologically diagnosed NASH. The disease was diagnosed if liver biopsy revealed steatosis, inflammation, ballooned hepatocytes, Mallory hyaline, or focal necrosis, varying degrees of fibrosis in the absence of clinical, serological, or histological findings of infectious liver diseases, autoimmune hepatitis, metabolic liver diseases, or celiac disease. For ultrastructural analysis, fresh small liver blocks (1 mm³ volume) were fixed in a solution containing 2% paraformaldehyde and 2.5% glutaraldehyde in 0.1 mol/L cacodylate buffer. The specimens were postfixed in osmium tetroxide, subsequently dehydrated through a graded series of ethanols and propylene oxide, and embedded in Epon 812. The material was sectioned on a Reichert ultramicrotome to obtain semithin sections, which were stained with methylene blue in sodium borate. Ultrathin sections were contrasted with uranyl acetate and lead citrate, and examined using an Opton EM 900 transmission electron microscope.

RESULTS: Ultrastructural analysis of bioptates obtained from children with non-alcoholic steatohepatitis revealed characteristic repetitive mitochondrial abnormalities within hepatocytes; mainly mitochondrial polymorphisms such as megamitochondria, loss of mitochondrial cristae, and the presence of linear crystalline inclusions within the mitochondrial matrix of an increased electron density. The crystalline inclusions were particularly evident within megamitochondria (MMC), which seemed to be distributed randomly both within the hepatic parenchymal cell and the zones of hepatic lobule, without special variations in abundance. The inclusions appeared as bundles viewed longitudinally, or as an evenly spaced matrix in cross section, and frequently caused mitochondrial deformation. The average diameter of these linear structures was 10 nm and the average space between them 20 nm. Sometimes enlarged intramitochondrial granules were seen in their vicinity. Foamy cytoplasm of hepatocytes was found, resulting from the proliferation of smooth endoplasmic reticulum and glycogen accumulation. The perivascular space of Disse was frequently dilated, and contained transitional hepatic stellate cells, as well as mature and/or newly forming collagen fiber bundles.

CONCLUSION: Marked ultrastructural abnormalities observed in hepatocyte mitochondria, especially their polymorphism in the form of MMC and loss of mitochondrial cristae, accompanied by foamy cytoplasm, clearly indicate a major role of these organelles in the morphogenesis of pediatric NASH. Our findings seem to prove the high effectiveness of electron microscopy in the diagnosis of the disease.

The role of Kupffer cells in the morphogenesis of nonalcoholic steatohepatitis - ultrastructural findings. The first report in pediatric patients

OBJECTIVE

Until now studies concerning the involvement of hepatic nonparenchymal cells (NPCs), particularly Kupffer cells/macrophages (KCs/MPs), in the pathogenesis of human nonalcoholic steatohepatitis (NASH) have been limited to adult patients; there are no similar reports referring to children. This study aimed to explore, based on ultrastructural analysis, the role of KCs/MPs in the morphogenesis of nonalcoholic steatohepatitis (NASH) in children.

MATERIAL AND METHODS

Ultrastructural investigations of KCs were conducted on liver bioptates obtained from 10 children, aged 2-14 years, with clinicopathologically diagnosed NASH. Bioptatic material was fixed in solution of paraformaldehyde and glutaraldehyde in cacodylate buffer, routinely processed for transmission-electron microscopic analysis and examined using an Opton EM microscope.

RESULTS

The current ultrastructural study revealed within the hepatic sinusoids the presence of numerous enlarged KCs with increased phagocytic activity, which reduced or blocked vascular lumen. Interestingly, the activated KCs not only contained primary and secondary lysosomes, altered mitochondria, and well-developed Golgi apparatus, but also absorbed fragments of erythrocytes. Such macrophages were frequently seen very close to the transformed hepatic stellate cells (T-HSCs) and progenitor/oval cells. Intensive fibrosis was observed in the vicinity of activated KCs/MPs. Bundles of collagen fibers were seen directly adhering to these cells and to other NPCs, especially T-HSCs.

CONCLUSIONS

KCs are involved in the morphogenesis and development of pediatric NASH. Engulfment of erythrocytes by hepatic macrophages may lead to the accumulation of iron derived from hemoglobin in liver and play a role in triggering the generation of oxidative stress in the disease course.