The Hepatic Central Vein: Structure, Fibrosis, and Role in Liver Biology

Hepatic stellate cells in zone 1 engage in capillarization rather than myofibroblast formation in murine liver fibrosis

The combination of lineage tracing and immunohistochemistry has helped to identify subpopulations and fate of hepatic stellate cells (HSC) in murine liver. HSC are sinusoidal pericytes that act as myofibroblast precursors after liver injury. Single cell RNA sequencing approaches have recently helped to differentiate central and portal HSC. A specific Cre line to lineage trace portal HSC has not yet been described. We used three Cre lines (Lrat-Cre, PDGFRβ-CreERT2 and SMMHC-CreERT2) known to label mesenchymal cells including HSC in combination with a tdTomato-expressing reporter. All three Cre lines labeled populations of HSC as well as smooth muscle cells (SMC). Using the SMMHC-CreERT2, we identified a subtype of HSC in the periportal area of the hepatic lobule (termed zone 1-HSC). We lineage traced tdTomato-expressing zone 1-HSC over 1 year, described fibrotic behavior in two fibrosis models and investigated their possible role during fibrosis. This HSC subtype resides in zone 1 under healthy conditions; however, zonation is disrupted in preclinical models of liver fibrosis (CCl4 and MASH). Zone 1-HSC do not transform into αSMA-expressing myofibroblasts. Rather, they participate in sinusoidal capillarization. We describe a novel subtype of HSC restricted to zone 1 under physiological conditions and its possible function after liver injury. In contrast to the accepted notion, this HSC subtype does not transform into αSMA-positive myofibroblasts; rather, zone 1-HSC adopt properties of capillary pericytes, thereby participating in sinusoidal capillarization.

Evaluation of the Superficial Collecting Lymph Vessels' Vasa Vasorum in Lymphoedematous Limbs Using Video Capillaroscopy

OBJECTIVE

The pre-collecting and collecting lymph vessels have smooth muscle cells, and sufficient perfusion is vital to maintain their function. Although the vasa vasorum of the collecting lymph vessels (VVCL) have been histologically investigated, little is known about their physiology. This study aimed to investigate the relationship between morphology and blood flow of the VVCL in lymphoedematous limbs.

METHODS

Medical records of lower extremity lymphoedema patients who underwent video capillaroscopy observation during supermicrosurgical lymphaticovenous anastomosis (LVA) surgery were reviewed. The collecting lymph vessels, dissected for LVA, were examined under video capillaroscopy (GOKO Bscan-ZD, GOKO Imaging Devices Co., Japan) with a magnification of 175x and 620x. Blood flow velocity of the VVCL was calculated by measuring the red blood cell movement using software (GOKO-VIP ver. 1.0.0.4, GOKO Imaging Devices Co., Japan). Based on the video capillaroscopy findings, the VVCL were grouped according to their morphology; the VVCL morphology types and blood flow velocity were then compared according to the lymphosclerosis severity grade.

RESULTS

Sixty-seven lymph vessels in 20 lower extremity lymphoedema patients were evaluated, including s0 in 19 (28.4%), s1 in 34 (50.7%), s2 in 10 (14.9%), and s3 in four (6.0%) lymph vessels. The VVCLs were grouped into four types: type 1 (n = 4), type 2 (n = 37), type 3 (n = 19), and type 4 (n = 7). Blood flow velocity of the VVCL ranged 0 - 189.3 μm/sec (average 26.40 μm/sec). There were statistically significant differences in VVCL morphology (p < .001) and blood flow velocity (p < .001) according to lymphosclerotic severity.

CONCLUSION

Vasa vasorum of the collecting lymph vessels could be grouped into four types with different characteristics. Morphological and physiological changes of the VVCL were related to sclerotic changes of the collecting lymph vessels.

In vivo liver function reserve assessments in alcoholic liver disease by scalable photoacoustic imaging

We present a rapid and high-resolution photoacoustic imaging method for evaluating the liver function reserve (LFR). To validate its accuracy, we establish alcoholic liver disease (ALD) models and employ dual-wavelength spectral unmixing to assess oxygen metabolism. An empirical mathematical model fits the photoacoustic signals, obtaining liver metabolism curve and LFR parameters. Liver oxygen metabolism significantly drops in ALD with the emergence of abnormal hepatic lobular structure. ICG half-life remarkably extends from 241 to 568 s in ALD. A significant decline in LFR occurs in terminal region compared to central region, indicated by a 106.9 s delay in ICG half-life, likely due to hepatic artery and vein damage causing hypoxia and inadequate nutrition. Reduced glutathione repairs LFR with a 43% improvement by reducing alcohol-induced oxidative damage. Scalable photoacoustic imaging shows immense potential for assessing LFR in alcoholic-related diseases, providing assistance to early detection and management of liver disease.

Wnt-β-catenin in hepatobiliary homeostasis, injury, and repair

Wnt-β-catenin signaling has emerged as an important regulatory pathway in the liver, playing key roles in zonation and mediating contextual hepatobiliary repair after injuries. In this review, we will address the major advances in understanding the role of Wnt signaling in hepatic zonation, regeneration, and cholestasis-induced injury. We will also touch on some important unanswered questions and discuss the relevance of modulating the pathway to provide therapies for complex liver pathologies that remain a continued unmet clinical need.

Manifestations of Liver Impairment and the Effects of MH-76, a Non-Quinazoline α1-Adrenoceptor Antagonist, and Prazosin on Liver Tissue in Fructose-Induced Metabolic Syndrome

Excessive fructose consumption may lead to metabolic syndrome, metabolic dysfunction-associated fatty liver disease (MAFLD) and hypertension. α1-adrenoceptors antagonists are antihypertensive agents that exert mild beneficial effects on the metabolic profile in hypertensive patients. However, they are no longer used as a first-line therapy for hypertension based on Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) outcomes. Later studies have shown that quinazoline-based α1-adrenolytics (prazosin, doxazosin) induce apoptosis; however, this effect was independent of α1-adrenoceptor blockade and was associated with the presence of quinazoline moiety. Recent studies showed that α1-adrenoceptors antagonists may reduce mortality in COVID-19 patients due to anti-inflammatory properties. MH-76 (1-[3-(2,6-dimethylphenoxy)propyl]-4-(2-methoxyphenyl)piperazine hydrochloride)) is a non-quinazoline α1-adrenoceptor antagonist which, in fructose-fed rats, exerted anti-inflammatory, antihypertensive properties and reduced insulin resistance and visceral adiposity. In this study, we aimed to evaluate the effect of fructose consumption and treatment with α1-adrenoceptor antagonists of different classes (MH-76 and prazosin) on liver tissue of fructose-fed rats. Livers were collected from four groups (Control, Fructose, Fructose + MH-76 and Fructose + Prazosin) and subjected to biochemical and histopathological studies. Both α1-adrenolytics reduced macrovesicular steatosis and triglycerides content of liver tissue and improved its antioxidant capacity. Treatment with MH-76, contrary to prazosin, reduced leucocytes infiltration as well as decreased elevated IL-6 and leptin concentrations. Moreover, the MH-76 hepatotoxicity in hepatoma HepG2 cells was less than that of prazosin. The use of α1-adrenolytics with anti-inflammatory properties may be an interesting option for treatment of hypertension with metabolic complications.

Probabilistic embedding, clustering, and alignment for integrating spatial transcriptomics data with PRECAST

Spatially resolved transcriptomics involves a set of emerging technologies that enable the transcriptomic profiling of tissues with the physical location of expressions. Although a variety of methods have been developed for data integration, most of them are for single-cell RNA-seq datasets without consideration of spatial information. Thus, methods that can integrate spatial transcriptomics data from multiple tissue slides, possibly from multiple individuals, are needed. Here, we present PRECAST, a data integration method for multiple spatial transcriptomics datasets with complex batch effects and/or biological effects between slides. PRECAST unifies spatial factor analysis simultaneously with spatial clustering and embedding alignment, while requiring only partially shared cell/domain clusters across datasets. Using both simulated and four real datasets, we show improved cell/domain detection with outstanding visualization, and the estimated aligned embeddings and cell/domain labels facilitate many downstream analyses. We demonstrate that PRECAST is computationally scalable and applicable to spatial transcriptomics datasets from different platforms.

Bisphenol A enhances apoptosis, fibrosis, and biochemical fluctuations in the liver of adult male rats with possible regression after recovery

Bisphenol A (BPA) is an environmental contaminant that might be harmful. Human exposure to BPA can occur during the fetal and postnatal periods and extends throughout life. This study aimed to estimate the effects of oral administration of BPA on rat liver and assess the possibility of recovery after cessation. Adult male albino rats were orally administered with BPA (50 mg/kg body weight) for 8 weeks, and then one group was left to recover for 4 weeks. Histological, immunohistochemical, biochemical, and quantitative real-time polymerase chain reaction assessments were performed. Loss of hepatic architecture, vascular dilatation congestion, and exudation, as well as cellular vacuolation, fat accumulation, and pyknotic nuclei were detected. Furthermore, inflammatory infiltration, localized metaplasia, and excessive collagen deposition in the portal triad were observed. Expression of Bcl-2-associated X protein and transforming growth factor beta 1 was prominent, denoting apoptosis and fibrosis. After the administration of BPA, serum levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, cholesterol, triglycerides, and low-density lipoproteins were enhanced. Additionally, total protein, albumin, and high-density lipoproteins decreased. After a recovery for 4 weeks, hepatic cellular and vascular pathologies returned to normal, except for some inflammatory infiltration. Regarding biochemical affection, most of the parameters were directed toward normal during recovery. However, most of them were still significantly different from controls. This explored BPA hepatotoxicity from structural and functional aspects, and the possible spontaneous reversibility was confirmed. However, the precise mechanisms underlying hepatotoxicity or recovery need more in-depth investigations.

T1 mapping of the myocardium and liver in the single ventricle population

BACKGROUND

Fontan associated liver disease (FALD) is an increasingly recognized complication of the single ventricle circulation characterized by hepatic venous congestion leading to hepatic fibrosis. Within the Fontan myocardium, fibrotic myocardial remodeling may occur and lead to ventricular dysfunction. Magnetic resonance imaging (MRI) T1 mapping can characterize both myocardial and liver properties.

OBJECTIVE

The aim of this study was to compare myocardial and liver T1 between single ventricle patients with and without a Fontan and biventricular controls.

MATERIALS AND METHODS

A retrospective study of 3 groups of patients: 16 single ventricle patients before Fontan (SV_pre 2 newborns, 9 pre-Glenn, 5 pre-Fontan, 31% single right ventricle [SRV]), 16 Fontans (56% SRV) and 10 repaired d-transposition of the great arteries (TGA). Native modified Look-Locker inversion T1 times were measured in the myocardium and liver. Cardiac MRI parameters, myocardial and liver T1 values were compared in the three groups. Correlations were assessed between liver T1 and cardiac parameters.

RESULTS

Myocardial T1 was higher in SV_pre (1,056 ± 48 ms) and Fontans (1,047 ± 41 ms) compared to TGA (1,012 ± 48 ms, P < 0.05). Increased liver T1 was found in both SV_pre (683 ± 82 ms) and Fontan (727 ± 49 ms) patients compared to TGA patients (587 ± 58 ms, P < 0.001). There was no difference between single left ventricle (SLV) versus SRV myocardial or liver T1. Liver T1 showed moderate correlations with myocardial T1 (r = 0.48, confidence interval [CI] 0.26-0.72) and ejection fraction (r = -0.36, CI -0.66-0.95) but not with other volumetric parameters.

CONCLUSION

Increased liver T1 at both pre- and post-Fontan stages suggests there are intrinsic liver abnormalities early in the course of single ventricle palliation. Increased myocardial T1 and its relationship to liver T1 suggest a combination of edema from passive venous congestion and/or myocardial fibrosis occurring in this population. Liver T1 may provide an earlier marker of liver disease warranting further study.

A review of hepatic fibrosis-associated histopathology in aged cadavers

This article reviews hepatic fibrosis-associated histopathology of aged cadavers (mean age 82 years). A study of 68 livers identified steatosis in 35.5%, central vein fibrosis in 49.2%, perisinusoidal fibrosis in 63.2%, portal tract fibrosis in 47.7%, septa formation in 44.1%, bridging fibrosis in 30.8%, and cirrhosis in 4.4% of the samples as well as one hepatocellular carcinoma and six metastatic tumors. Other studies have revealed that collagens I, III, IV, V, and VI and fibronectin constitute the matrices of fibrous central veins, perisinusoidal space, portal tracts, and septa. Elastin is rich in portal tracts and fibrous septa but absent from the perisinusoidal space. Hepatic stellate cells are ubiquitous in the liver parenchyma while myofibroblasts localize in fibrotic foci. Factor VIII-related antigen expression signals sinusoidal to systemic vascular endothelium transformation while collagen IV and laminin codistribution indicates formation of perisinusoidal membranes. Their coincidence reflects focalized capillarization of sinusoids in the aged liver. In response to fibrogenesis, hepatic progenitor cells residing in the canal of Hering in the periportal parenchyma undergo expansion and migration deep into the lobule. Concomitantly, intermediate hepatocyte-like cells increase in advanced fibrosis stages, which is possibly related to hepatic regeneration. Metabolic zonation of glutamine synthetase expands from the perivenous to non-perivenous parenchyma in fibrosis progression but its expression is lost in cirrhosis, while cytochrome P-4502E1 expression is maintained in centrilobular and midlobular zones in fibrosis progression and expressed in cirrhosis. Hence, cadaveric livers provide a platform for further investigation of hepatic histopathologies associated with the aging liver.

Liver Endothelial Heg Regulates Vascular/Biliary Network Patterning and Metabolic Zonation Via Wnt Signaling

BACKGROUND & AIMS

The liver has complex interconnecting blood vessel and biliary networks; however, how the vascular and biliary network form and regulate each other and liver function are not well-understood. We aimed to examine the role of Heg in mammalian liver development and functional maintenance.

METHODS

Global (Heg^-/-) or liver endothelial cell (EC)-specific deletion of Heg (Lyve1-Cre;Heg^fl/fl ) mice were used to study the in vivo function of Heg in the liver. Carbon-ink anterograde and retrograde injection were used to visualize the 3-dimensional patterning of liver portal and biliary networks, respectively. RNA sequencing, histology, and molecular and biochemical assays were used to assess liver gene expression, protein distribution, liver injury response, and function.

RESULTS

Heg deficiency in liver ECs led to a sparse liver vascular and biliary network. This network paucity does not compromise liver function under baseline conditions but did alter liver zonation. Molecular analysis revealed that endothelial Heg deficiency decreased expression of Wnt ligands/agonists including Wnt2, Wnt9b, and Rspo3 in ECs, which limits Axin2 mediated canonical Wnt signaling and the expression of cytochrome P450 enzymes in hepatocytes. Under chemical-induced stressed conditions, Heg-deficiency in liver ECs protected mice from drug-induced liver injuries.

CONCLUSION

Our study found that endothelial Heg is essential for the 3-D patterning of the liver vascular and indirectly regulates biliary networks and proper liver zonation via its regulation of Wnt ligand production in liver endothelial cells. The endothelial Heg-initiated changes of the liver metabolic zonation and metabolic enzyme expression in hepatocytes was functionally relevant to xenobiotic metabolism and drug induced liver toxicity.

Hepatic pseudolesions caused by alterations in intrahepatic hemodynamics

Hepatic pseudolesion may occur in contrast-enhanced computed tomography and magnetic resonance imaging due to the unique haemodynamic characteristics of the liver. The concept of hepatic arterial buffer response (HABR) has become mainstream for the understanding of the mechanism of the reciprocal effect between hepatic arterial and portal venous flow. And HABR is thought to be significantly related to the occurrence of the abnormal imaging findings on arterial phase of contrast enhanced images, such as hepatic arterial-portal vein shunt and transient hepatic attenuation difference, which mimic hypervascular tumor and may cause clinical problems. Third inflow to the liver also cause hepatic pseudolesion, and some of the cases may show histopathologic change such as focal hyperplasia, focal fatty liver, and focal sparing of fatty liver, and called pseudotumor. To understand these phenomena might be valuable for interpreting the liver imaging findings.

Hepatic sinusoids versus central veins: Structures, markers, angiocrines, and roles in liver regeneration and homeostasis

The blood circulates through the hepatic sinusoids delivering nutrients and oxygen to the liver parenchyma and drains into the hepatic central vein, yet the structures and phenotypes of these vessels are distinctively different. Sinusoidal endothelial cells are uniquely fenestrated, lack basal lamina and possess organelles involved in endocytosis, pinocytosis, degradation, synthesis and secretion. Hepatic central veins are nonfenestrated but are also active in synthesis and secretion. Endothelial cells of sinusoids and central veins secrete angiocrines that play respective roles in hepatic regeneration and metabolic homeostasis. The list of markers for identifying sinusoidal endothelial cells is long and their terminologies are complex. Further, their uses vary in different investigations and, in some instances, could be confusing. Central vein markers are fewer but more distinctive. Here we analyze and categorize the molecular pathways/modules associated with the sinusoid-mediated liver regeneration in response to partial hepatectomy and chemical-induced acute or chronic injury. Similarly, we highlight the findings that central vein-derived angiocrines interact with Wnt/β-catenin in perivenous hepatocytes to direct gene expression and maintain pericentral metabolic zonation. The proposal that perivenous hepatocytes behave as stem/progenitor cells to provoke hepatic homeostatic cell renewal is reevaluated and newer concepts of broad zonal distribution of hepatocyte proliferation in liver homeostasis and regeneration are updated. Thus, this review integrates the structures, biology and physiology of liver sinusoids and central veins in mediating hepatic regeneration and metabolic homeostasis.