Increased number and function of endothelial progenitor cells stimulate angiogenesis by resident liver sinusoidal endothelial cells (SECs) in cirrhosis through paracrine factors

Liver Fibrosis: From Basic Science towards Clinical Progress, Focusing on the Central Role of Hepatic Stellate Cells

The burden of chronic liver disease is globally increasing at an alarming rate. Chronic liver injury leads to liver inflammation and fibrosis (LF) as critical determinants of long-term outcomes such as cirrhosis, liver cancer, and mortality. LF is a wound-healing process characterized by excessive deposition of extracellular matrix (ECM) proteins due to the activation of hepatic stellate cells (HSCs). In the healthy liver, quiescent HSCs metabolize and store retinoids. Upon fibrogenic activation, quiescent HSCs transdifferentiate into myofibroblasts; lose their vitamin A; upregulate α-smooth muscle actin; and produce proinflammatory soluble mediators, collagens, and inhibitors of ECM degradation. Activated HSCs are the main effector cells during hepatic fibrogenesis. In addition, the accumulation and activation of profibrogenic macrophages in response to hepatocyte death play a critical role in the initiation of HSC activation and survival. The main source of myofibroblasts is resident HSCs. Activated HSCs migrate to the site of active fibrogenesis to initiate the formation of a fibrous scar. Single-cell technologies revealed that quiescent HSCs are highly homogenous, while activated HSCs/myofibroblasts are much more heterogeneous. The complex process of inflammation results from the response of various hepatic cells to hepatocellular death and inflammatory signals related to intrahepatic injury pathways or extrahepatic mediators. Inflammatory processes modulate fibrogenesis by activating HSCs and, in turn, drive immune mechanisms via cytokines and chemokines. Increasing evidence also suggests that cellular stress responses contribute to fibrogenesis. Recent data demonstrated that LF can revert even at advanced stages of cirrhosis if the underlying cause is eliminated, which inhibits the inflammatory and profibrogenic cells. However, despite numerous clinical studies on plausible drug candidates, an approved antifibrotic therapy still remains elusive. This state-of-the-art review presents cellular and molecular mechanisms involved in hepatic fibrogenesis and its resolution, as well as comprehensively discusses the drivers linking liver injury to chronic liver inflammation and LF.

GDF11 promotes wound healing in diabetic mice via stimulating HIF-1ɑ-VEGF/SDF-1ɑ-mediated endothelial progenitor cell mobilization and neovascularization

Non-healing diabetic wounds (DW) are a serious clinical problem that remained poorly understood. We recently found that topical application of growth differentiation factor 11 (GDF11) accelerated skin wound healing in both Type 1 DM (T1DM) and genetically engineered Type 2 diabetic db/db (T2DM) mice. In the present study, we elucidated the cellular and molecular mechanisms underlying the action of GDF11 on healing of small skin wound. Single round-shape full-thickness wound of 5-mm diameter with muscle and bone exposed was made on mouse dorsum using a sterile punch biopsy 7 days following the onset of DM. Recombinant human GDF11 (rGDF11, 50 ng/mL, 10 μL) was topically applied onto the wound area twice a day until epidermal closure (maximum 14 days). Digital images of wound were obtained once a day from D0 to D14 post-wounding. We showed that topical application of GDF11 accelerated the healing of full-thickness skin wounds in both type 1 and type 2 diabetic mice, even after GDF8 (a muscle growth factor) had been silenced. At the cellular level, GDF11 significantly facilitated neovascularization to enhance regeneration of skin tissues by stimulating mobilization, migration and homing of endothelial progenitor cells (EPCs) to the wounded area. At the molecular level, GDF11 greatly increased HIF-1ɑ expression to enhance the activities of VEGF and SDF-1ɑ, thereby neovascularization. We found that endogenous GDF11 level was robustly decreased in skin tissue of diabetic wounds. The specific antibody against GDF11 or silence of GDF11 by siRNA in healthy mice mimicked the non-healing property of diabetic wound. Thus, we demonstrate that GDF11 promotes diabetic wound healing via stimulating endothelial progenitor cells mobilization and neovascularization mediated by HIF-1ɑ-VEGF/SDF-1ɑ pathway. Our results support the potential of GDF11 as a therapeutic agent for non-healing DW.

Dimethyloxalylglycine Attenuates Steroid-Associated Endothelial Progenitor Cell Impairment and Osteonecrosis of the Femoral Head by Regulating the HIF-1α Signaling Pathway

Endothelial impairment and dysfunction are closely related to the pathogenesis of steroid-associated osteonecrosis of the femoral head (SONFH). Recent studies have showed that hypoxia inducible factor-1α (HIF-1α) plays a crucial role in endothelial homeostasis maintenance. Dimethyloxalylglycine (DMOG) could suppress HIF-1 degradation and result in nucleus stabilization by repressing prolyl hydroxylase domain (PHD) enzymatic activity. Our results showed that methylprednisolone (MPS) remarkably undermined biological function of endothelial progenitor cells (EPC) by inhibiting colony formation, migration, angiogenesis, and stimulating senescence of EPCs, while DMOG treatment alleviated these effects by promoting HIF-1α signaling pathway, as evidenced by senescence-associated β-galactosidase (SA-β-Gal) staining, colony-forming unit, matrigel tube formation, and transwell assays. The levels of proteins related to angiogenesis were determined by ELISA and Western blotting. In addition, active HIF-1α bolstered the targeting and homing of endogenous EPCs to the injured endothelium in the femoral head. Histopathologically, our in vivo study showed that DMOG not only alleviated glucocorticoid-induced osteonecrosis but also promoted angiogenesis and osteogenesis in the femoral head as detected by microcomputed tomography (Micro-CT) analysis and histological staining of OCN, TRAP, and Factor Ⅷ. However, all of these effects were impaired by an HIF-1α inhibitor. These findings demonstrate that targeting HIF-1α in EPCs may constitute a novel therapeutic approach for the treatment of SONFH.

Endothelial Cell Dysfunction and Nonalcoholic Fatty Liver Disease (NAFLD): A Concise Review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. It is strongly associated with obesity, type 2 diabetes (T2DM), and other metabolic syndrome features. Reflecting the underlying pathogenesis and the cardiometabolic disorders associated with NAFLD, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has recently been proposed. Indeed, over the past few years, growing evidence supports a strong correlation between NAFLD and increased cardiovascular disease (CVD) risk, independent of the presence of diabetes, hypertension, and obesity. This implies that NAFLD may also be directly involved in the pathogenesis of CVD. Notably, liver sinusoidal endothelial cell (LSEC) dysfunction appears to be implicated in the progression of NAFLD via numerous mechanisms, including the regulation of the inflammatory process, hepatic stellate activation, augmented vascular resistance, and the distortion of microcirculation, resulting in the progression of NAFLD. Vice versa, the liver secretes inflammatory molecules that are considered pro-atherogenic and may contribute to vascular endothelial dysfunction, resulting in atherosclerosis and CVD. In this review, we provide current evidence supporting the role of endothelial cell dysfunction in the pathogenesis of NAFLD and NAFLD-associated atherosclerosis. Endothelial cells could thus represent a "golden target" for the development of new treatment strategies for NAFLD and its comorbid CVD.

Liver Regeneration by Hematopoietic Stem Cells: Have We Reached the End of the Road?

The liver is the organ with the highest regenerative capacity in the human body. However, various insults, including viral infections, alcohol or drug abuse, and metabolic overload, may cause chronic inflammation and fibrosis, leading to irreversible liver dysfunction. Despite advances in surgery and pharmacological treatments, liver diseases remain a leading cause of death worldwide. To address the shortage of donor liver organs for orthotopic liver transplantation, cell therapy in liver disease has emerged as a promising regenerative treatment. Sources include primary hepatocytes or functional hepatocytes generated from the reprogramming of induced pluripotent stem cells (iPSC). Different types of stem cells have also been employed for transplantation to trigger regeneration, including hematopoietic stem cells (HSCs), mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs) as well as adult and fetal liver progenitor cells. HSCs, usually defined by the expression of CD34 and CD133, and MSCs, defined by the expression of CD105, CD73, and CD90, are attractive sources due to their autologous nature, ease of isolation and cryopreservation. The present review focuses on the use of bone marrow HSCs for liver regeneration, presenting evidence for an ongoing crosstalk between the hematopoietic and the hepatic system. This relationship commences during embryogenesis when the fetal liver emerges as the crossroads between the two systems converging the presence of different origins of cells (mesoderm and endoderm) in the same organ. Ample evidence indicates that the fetal liver supports the maturation and expansion of HSCs during development but also later on in life. Moreover, the fact that the adult liver remains one of the few sites for extramedullary hematopoiesis—albeit pathological—suggests that this relationship between the two systems is ongoing. Can, however, the hematopoietic system offer similar support to the liver? The majority of clinical studies using hematopoietic cell transplantation in patients with liver disease report favourable observations. The underlying mechanism—whether paracrine, fusion or transdifferentiation or a combination of the three—remains to be confirmed.

Recombinant DTβ4-inspired porous 3D vascular graft enhanced antithrombogenicity and recruited circulating CD93+/CD34+ cells for endothelialization

Matching material degradation with host remodeling, including endothelialization and muscular remodeling, is important to vascular regeneration. We fabricated 3D PGS-PCL vascular grafts, which presented tunable polymer components, porosity, mechanical strength, and degrading rate. Furthermore, highly porous structures enabled 3D patterning of conjugated heparin-binding peptide, dimeric thymosin β4 (DTβ4), which played key roles in antiplatelets, fibrinogenesis inhibition, and recruiting circulating progenitor cells, thereafter contributed to high patency rate, and unprecedentedly acquired carotid arterial regeneration in rabbit model. Through single-cell RNA sequencing analysis and cell tracing studies, a subset of endothelial progenitor cells, myeloid-derived CD93⁺/CD34⁺ cells, was identified as the main contributor to final endothelium regeneration. To conclude, DTβ4-inspired porous 3DVGs present adjustable physical properties, superior anticoagulating, and re-endothelializing potentials, which leads to the regeneration of small-caliber artery, thus offering a promising tool for vessel replacement in clinical applications.

Dynamics of endothelial progenitor cells in patients with advanced hepatocellular carcinoma

BACKGROUND AND AIMS

Circulating endothelial progenitor cells (EPC) predict tumor vascularization and disease progression, but limited information is available on their dynamics in hepatocellular carcinoma (HCC) undergoing systemic treatment.

METHODS

We prospectively analyzed different populations of EPC in 16 patients with advanced HCC receiving sorafenib. Patients were studied before therapy (T0, n = 16) and after two (T2, n = 12) and eight weeks (T8, n = 8), using high-performance flow-cytometry. The tumor response at T8 was categorized as progressive disease (PD) or clinical benefit (CB, all other responses).

RESULTS

At T0, higher levels of CD34⁺CD133⁺KDR⁺ and CD34⁺KDR⁺ were observed in patients with alpha-fetoprotein ≥400 ng/ml or non-viral liver disease, whereas CD34⁺CD133⁺KDR⁺ cells were virtually absent in patients with vascular invasion. CD34⁺KDR⁺ and CD34⁺CD133⁺KDR⁺ were directly correlated with platelet count. Frequencies of all populations of EPC declined in patients receiving sorafenib. Levels of CD34⁺CD133⁺ were higher at T0 in patients with CB compared to patients with PD. In patients belonging to the CB group CD34⁺KDR⁺ cells at T0 were directly correlated to platelet count.

CONCLUSION

In patients with advanced HCC, EPC are directly correlated with platelet count, suggesting a common activation of selected bone marrow pathways. Levels of a CD34⁺KDR⁺ are higher at baseline in patients responding to sorafenib.

Oxidative Stress and Redox Signaling in the Pathophysiology of Liver Diseases

The increased production of derivatives of molecular oxygen and nitrogen in the form of reactive oxygen species (ROS) and reactive nitrogen species (RNS) lead to molecular damage called oxidative stress. Under normal physiological conditions, the ROS generation is tightly regulated in different cells and cellular compartments. Any disturbance in the balance between the cellular generation of ROS and antioxidant balance leads to oxidative stress. In this article, we discuss the sources of ROS (endogenous and exogenous) and antioxidant mechanisms. We also focus on the pathophysiological significance of oxidative stress in various cell types of the liver. Oxidative stress is implicated in the development and progression of various liver diseases. We narrate the master regulators of ROS-mediated signaling and their contribution to liver diseases. Nonalcoholic fatty liver diseases (NAFLD) are influenced by a "multiple parallel-hit model" in which oxidative stress plays a central role. We highlight the recent findings on the role of oxidative stress in the spectrum of NAFLD, including fibrosis and liver cancer. Finally, we provide a brief overview of oxidative stress biomarkers and their therapeutic applications in various liver-related disorders. Overall, the article sheds light on the significance of oxidative stress in the pathophysiology of the liver. © 2022 American Physiological Society. Compr Physiol 12:3167-3192, 2022.

Hepatic Regeneration in Cirrhosis

End-stage liver disease is characterized by massive hepatocyte death resulting in clinical decompensation and organ failures. Clinical consequences in cirrhosis are the results of the loss of functional hepatocytes and excessive scarring. The only curative therapy in advanced cirrhosis is orthotropic liver transplantation, but the clinical demand outweighs the availability of acceptable donor organs. Moreover, this also necessitates lifelong immunosuppression and carries associated risks. The liver has a huge capability for regeneration. Self-replication of quiescent differentiated hepatocytes and cholangiocytes occurs in patients with acute liver injury. Due to limited hepatocyte self-renewal capacity in advanced cirrhosis, great interest has therefore been shown in characterizing the possible role of hepatic progenitor cells and bone marrow-derived stem cells to therapeutically aid this process. Transplantation of cells from various sources that can be properly differentiated into functional liver cells or use of growth factors for ex-vivo expansion of progenitor cells is needed at utmost priority. Multiple researches over the last two decades have aided researchers in refining proliferation, differentiation, and storage techniques and understand the functionality of these cells for use in clinical practice. However, these cell-based therapies are still experimental and have to be used in trial settings.

Immunonano-Lipocarrier-Mediated Liver Sinusoidal Endothelial Cell-Specific RUNX1 Inhibition Impedes Immune Cell Infiltration and Hepatic Inflammation in Murine Model of NASH

Background: Runt-related transcription factor (RUNX1) regulates inflammation in non-alcoholic steatohepatitis (NASH). Methods: We performed in vivo targeted silencing of the RUNX1 gene in liver sinusoidal endothelial cells (LSECs) by using vegfr3 antibody tagged immunonano-lipocarriers encapsulated RUNX1 siRNA (RUNX1 siRNA) in murine models of methionine choline deficient (MCD) diet-induced NASH. MCD mice given nanolipocarriers-encapsulated negative siRNA were vehicle, and mice with standard diet were controls. Results: Liver RUNX1 expression was increased in the LSECs of MCD mice in comparison to controls. RUNX1 protein expression was decreased by 40% in CD31-positive LSECs of RUNX1 siRNA mice in comparison to vehicle, resulting in the downregulation of adhesion molecules, ICAM1 expression, and VCAM1 expression in LSECs. There was a marked decrease in infiltrated T cells and myeloid cells along with reduced inflammatory cytokines in the liver of RUNX1 siRNA mice as compared to that observed in the vehicle. Conclusions: In vivo LSEC-specific silencing of RUNX1 using immunonano-lipocarriers encapsulated siRNA effectively reduces its expression of adhesion molecules, infiltrate on of immune cells in liver, and inflammation in NASH.

Liver sinusoidal endothelial cells are implicated in multiple fibrotic mechanisms

Chronic liver diseases are attributed to liver injury. Development of fibrosis from chronic liver diseases is a dynamic process that involves multiple molecular and cellular processes. As the first to be impacted by injury, liver sinusoidal endothelial cells (LSECs) are involved in the pathogenesis of liver diseases caused by a variety of etiologies. Moreover, capillarization of LSECs has been recognized as an important event in the development of chronic liver diseases and fibrosis. Studies have reported that various cytokines (such as vascular endothelial growth factor, transforming growth factor-β), and pathways (such as hedgehog, and Notch), as well as epigenetic and metabolic factors are involved in the development of LSEC-mediated liver fibrosis. This review describes the complexity and plasticity of LSECs in fibrotic liver diseases from several perspectives, including the cross-talk between LSECs and other intra-hepatic cells. Moreover, it summarizes the mechanisms of several kinds of LSECs-targeting anti-fibrosis chemicals, and provides a theoretical basis for future studies.

Stem cell therapy and tissue engineering strategies using cell aggregates and decellularized scaffolds for the rescue of liver failure

Liver failure is a lethal condition with hepatocellular dysfunction, and liver transplantation is presently the only effective treatment. However, due to the limited availability of donors and the potential immune rejection, novel therapeutic strategies are actively sought to restore the normal hepatic architectures and functions, especially for livers with inherited metabolic dysfunctions or chronic diseases. Although the conventional cell therapy has shown promising results, the direct infusion of hepatocytes is hampered by limited hepatocyte sources, poor cell viability, and engraftment. Hence, this review mainly highlights the role of stem cells and progenitors as the alternative cell source and summarizes the potential approaches based on tissue engineering to improve the delivery efficiency of cells. Particularly, the underlying mechanisms for cell therapy using stem cells and progenitors are discussed in two main aspects: paracrine effect and cell differentiation. Moreover, tissue-engineering approaches using cell aggregates and decellularized liver scaffolds for bioengineering of functional hepatic constructs are discussed and compared in terms of the potential to replicate liver physiological structures. In the end, a potentially effective strategy combining the premium advantages of stem cell aggregates and decellularized liver scaffolds is proposed as the future direction of liver tissue engineering and regeneration.

Sinusoidal Endothelial Cell Progenitor Cells Promote Tumour Progression in Patients with Hepatocellular Carcinoma

Objective

As sinusoidal endothelial cell progenitor cells (SEPCs) play a significant role in liver regeneration, it is necessary to elucidate whether SEPCs participate in tumour progression of hepatocellular carcinoma (HCC).

Methods

A total of 45 patients with primary HCC who underwent liver resection were included in this study. The liver tumours were removed from the patients, and partial tissues were prepared to identify SEPCs through double staining of CD133/CD45 and CD133/CD31 at the same location. Blood samples were collected to examine liver function parameters and tumour markers. The demographics and clinicopathological characteristics of the patients were collected for correlation analysis with SEPCs.

Results

SEPCs were observed in several blood vessels within the HCC nodules of all 45 patients, but no SEPCs were detected in the tumour-adjacent tissues. The number of SEPCs was correlated with the expression levels of HCC tumour markers α-fetoprotein (AFP) and CA199. There was a positive correlation between the expression of SEPC markers and diameter of HCC tumours in differently differentiated specimens (P < 0.01). The expression levels of SEPC markers were significantly higher in patients with poorly differentiated HCC than in patients with moderately and highly differentiated HCC (P < 0.05).

Conclusions

SEPCs are closely associated with HCC progression; therefore, SEPCs may be considered potential prognostic and metastatic biomarkers and therapeutic candidates for HCC.

Cirrhotic Endothelial Progenitor Cells Enhance Liver Angiogenesis and Fibrosis and Aggravate Portal Hypertension in Bile Duct-Ligated Cirrhotic Rats

Background

Circulating cirrhotic endothelial progenitor cells (EPC) interact with both liver sinusoidal endothelial cells (LSEC) and hepatic stellate cells (HSC) and promote angiogenesis in vitro. This study evaluated the effect of cirrhotic and control EPCs on hepatic angiogenesis, microcirculation, and fibrosis in vivo in rat models of cirrhosis.

Methodology

Animal models of cirrhosis were prepared by bile duct ligation (BDL). Circulating EPCs isolated from healthy human and cirrhotic blood were characterized by flow cytometry, cultured and administered through the tail vein in BDL rats after 2 weeks of ligation. The cells were given thrice a week for 2 weeks. The untreated group of BDL rats received only saline. Fibrosis was evaluated by Masson’s trichrome staining. Dedifferentiated LSECs were identified by the expression of CD31, and activated HSCs were marked as alpha-SMA-positive cells and were studied by immunohistochemistry and western blotting in saline-, healthy EPC-, and cirrhotic EPC-treated rats. In vivo, hepatic and systemic hemodynamic parameters were evaluated. Liver functions were evaluated.

Results

In comparison to controls, BDL rats revealed an increase of fibrosis and angiogenesis. Among the treated rats, cirrhotic EPC-treated rats had increased fibrosis grade as compared to healthy EPC-treated and saline-treated rats. There was an increase of both fibrosis and angiogenesis markers, alpha-SMA and CD31 in cirrhotic EPC-treated rats as compared to healthy EPC-treated and saline-treated rats in immunohistochemistry and western blot studies. Cirrhotic EPC-treated BDL rats had high portal pressure and portal blood flow with significantly elevated hepatic vascular resistance in comparison with healthy EPC- and saline-treated BDL animals, without significant differences in mean arterial pressure. Cirrhotic EPC-treated BDL rats also showed a substantial increase in the hepatic expression of angiogenic receptors, VEGFR2 and CXCR4 in comparison with saline-treated rats.

Conclusion

The study suggests that transplantation of cirrhotic EPCs enhances LSEC differentiation and angiogenesis, activates HSCs and worsens fibrosis, thus resulting in hepatic hemodynamic derangements in BDL-induced cirrhosis.

Angiogenesis-Related Genes in Endothelial Progenitor Cells May Be Involved in Sickle Cell Stroke

Background The clinical aspects of sickle cell anemia (SCA) are heterogeneous, and different patients may present significantly different clinical evolutions. Almost all organs can be affected, particularly the central nervous system. Transient ischemic events, infarcts, and cerebral hemorrhage can be observed and affect ≈25% of the patients with SCA. Differences in the expression of molecules produced by endothelial cells may be associated with the clinical heterogeneity of patients affected by vascular diseases. In this study, we investigated the differential expression of genes involved in endothelial cell biology in SCA patients with and without stroke. Methods and Results Endothelial progenitor cells from 4 SCA patients with stroke and 6 SCA patients without stroke were evaluated through the polymerase chain reaction array technique. The analysis of gene expression profiling identified 29 differentially expressed genes. Eleven of these genes were upregulated, and most were associated with angiogenesis (55%), inflammatory response (18%), and coagulation (18%) pathways. Downregulated expression was observed in 18 genes, with the majority associated with angiogenesis (28%), apoptosis (28%), and cell adhesion (22%) pathways. Remarkable overexpression of the MMP1 (matrix metalloproteinase 1) gene in the endothelial progenitor cells of all SCA patients with stroke (fold change: 204.64; P=0.0004) was observed. Conclusions Our results strongly suggest that angiogenesis is an important process in sickle cell stroke, and differences in the gene expression profile of endothelial cell biology, especially MMP1, may be related to stroke in SCA patients.

Clinical significance of endothelial progenitor cells in patients with liver cirrhosis with or without hepatocellular carcinoma

BACKGROUND AND OBJECTIVE

The role of endothelial progenitor cells in patients with cirrhosis has seldom been investigated. This study was conducted to assess the clinical significance of circulating endothelial progenitor cells in patients with liver cirrhosis with or without hepatocellular carcinoma.

METHODS

A blood sample was collected once from patients with cirrhosis alone (n = 34) or cirrhosis and hepatocellular carcinoma (n = 46) and healthy controls (n = 27) for assessing levels of endothelial progenitor cells and vascular endothelial growth factor. Blood cells staining positive for CD34/CD133/KDR using flow cytometry were characterized as endothelial progenitor cells. Plasma vascular endothelial growth factor was quantified by ELISA.

RESULTS

The levels of CD34/KDR-positive endothelial progenitor cells, CD133/KDR-positive endothelial progenitor cells, and vascular endothelial growth factor were higher in patients with cirrhosis ± hepatocellular carcinoma than in healthy controls (P = 0.017, P < 0.001 and P < 0.001, respectively). The levels of endothelial progenitor cells and vascular endothelial growth factor did not show statistical difference according to Child-Turcotte-Pugh class. There was a moderately significant correlation between vascular endothelial growth factor levels and hepatocellular carcinoma stage (ρ = 0.464, P = 0.001). Smoking, ascites, and portal vein thrombosis were independently related to lower levels of circulating CD34/KDR-positive endothelial progenitor cells, higher levels of CD133/KDR-positive endothelial progenitor cells, and higher levels of vascular endothelial growth factor, respectively (P = 0.041, P = 0.023, and P < 0.001, respectively).

CONCLUSION

Circulating endothelial progenitor cells and plasma vascular endothelial growth factor levels were higher in patients with liver cirrhosis ± hepatocellular carcinoma compared to healthy controls. The increase in endothelial progenitor cells and vascular endothelial growth factor may have a possible role in the development of complications, especially ascites and portal vein thrombosis, or in progression of hepatocellular carcinoma.

Natural Killer Cells Contribute to Pathogenesis of Severe Alcoholic Hepatitis by Inducing Lysis of Endothelial Progenitor Cells

BACKGROUND

Endothelial progenitor cells (EPCs) help in neovascularization and endothelial repair during injury. Patients with cirrhosis show increased number and function of EPCs in circulation.

METHODS

Since natural killer (NK) cells regulate EPCs, we investigated the relationship between the 2 in alcoholic cirrhosis (AC, n = 50) and severe alcoholic hepatitis (SAH, n = 18) patients and compared with nonalcoholic cirrhosis (n = 15) and healthy controls (HC, n = 30). Levels of systemic inflammatory cytokines were measured, and coculture assays were performed between EPCs and NK cells in contact-dependent and contact-independent manner. NK cell-mediated killing of EPCs was evaluated, and expression of receptors including fractalkine (FKN) on EPCs and its cognate receptor CX3CR1 on NK cells was studied by RT-PCR assays.

RESULTS

Patients with SAH had higher regulated on activation, normal T cell expressed and secreted (RANTES) (p = 0.01), vascular endothelial growth factor (VEGF) (p = 0.04), IL-1β (p = 0.04), and IL-6 (p = 0.00) growth factors and proinflammatory cytokines as compared to AC and HC. Distinct populations of CD31+ CD34+ EPCs with low and high expression of CD45 were significantly lower in SAH than HC (CD45^low , p = 0.03; CD45^hi , p = 0.04) and AC (CD45^low , p = 0.05; CD45^hi , p = 0.02). SAH patients, however, showed increased functional capacity of EPCs including colony formation and LDL uptake. NK cells were reduced in SAH compared with AC (p = 0.002), however with higher granzyme ability (p < 0.001 and p = 0.04, respectively). In SAH, EPC-NK cell interaction assays showed that NK cells lysed the EPCs in both contact-dependent and contact-independent assays. Expression of interaction receptor CX3CR1 was significantly higher on NK cells (p = 0.0005), while its cognate receptor, FKN, was increased on EPCs in SAH patients as compared to HC (p = 0.0055).

CONCLUSION

We conclude that in SAH, NK cells induce killing of EPCs via CX3CR1/FKN axis that may be one of the key events contributing to disease severity and proinflammatory responses in SAH.

Mechanisms Underlying Cell Therapy in Liver Fibrosis: An Overview

Fibrosis is a common feature in most pathogenetic processes in the liver, and usually results from a chronic insult that depletes the regenerative capacity of hepatocytes and activates multiple inflammatory pathways, recruiting resident and circulating immune cells, endothelial cells, non-parenchymal hepatic stellate cells, and fibroblasts, which become activated and lead to excessive extracellular matrix accumulation. The ongoing development of liver fibrosis results in a clinically silent and progressive loss of hepatocyte function, demanding the constant need for liver transplantation in clinical practice, and motivating the search for other treatments as the chances of obtaining compatible viable livers become scarcer. Although initially cell therapy has emerged as a plausible alternative to organ transplantation, many factors still challenge the establishment of this technique as a main or even additional therapeutic tool. Herein, the authors discuss the most recent advances and point out the corners and some controversies over several protocols and models that have shown promising results as potential candidates for cell therapy for liver fibrosis, presenting the respective mechanisms proposed for liver regeneration in each case.

Circulating Endothelial Progenitor Cells Present an Inflammatory Phenotype and Function in Patients With Alcoholic Liver Cirrhosis

Background and Aim: Endothelial progenitor cells (EPCs) have been implicated in liver injury and repair. However, the phenotype and potential of these heterogenous EPCs remain elusive. In particular, their involvement in the pathogenesis of alcoholic liver cirrhosis (ALC) remains unclear. The current study extensively characterized the phenotype and functions of EPCs to understand their role in ALC pathogenesis. Methods: Circulating EPCs were identified as CD34+CD133+CD31+ cells by flow cytometer in ALC patients (n = 7) and healthy controls (HC, n = 7). A comprehensive characterization of circulating EPCs using more than 30 phenotype markers was performed by mass cytometer time of flight (CyTOF) in an independent cohort of age and gender matched ALC patients (n = 4) and controls (n = 5). Ex vivo cultures of circulating EPCs from ALC patients (n = 20) and controls (n = 18) were also tested for their functions, including colony formation, LDL uptake, lectin binding and cytokine secretion (ELISA). Results: Three distinct populations of circulating EPCs (CD34+CD133+CD31+) were identified, classified on their CD45 expression (negative: CD45-; intermediate: CD45int; high: CD45hi). CD45int and CD45hi EPCs significantly increased in ALC patients compared to controls (p-val = 0.006). CyTOF data showed that CD45hi EPCs were distinct from CD45- and CD45int EPCs, with higher expression of T cell and myeloid markers, including CD3, CD4, HLA-DR, and chemokine receptors, CCR2, CCR5, CCR7, and CX3CR1. Similar to circulating EPCs, percentage of CD45hiCD34+CD31+ EPCs in ex-vivo cultures from patients, were significantly higher compared to controls (p < 0.05). Cultured EPCs from patients also showed increased LDL uptake, lectin binding and release of TNF-alpha, RANTES, FGF-2, and VEGF. Conclusions: We report the first extensive characterization of circulating human EPCs with distinct EPC subtypes. Increase in CD45hi EPC subtype in ALC patients with enhanced functions, inflammatory cytokines and angiogenic mediators in patients suggests an inflammatory role for these cells in ALC.

Pathological process of liver sinusoidal endothelial cells in liver diseases

Cirrhosis develops from liver fibrosis and is the severe pathological stage of all chronic liver injury. Cirrhosis caused by hepatitis B virus and hepatitis C virus infection is especially common. Liver fibrosis and cirrhosis involve excess production of extracellular matrix, which is closely related to liver sinusoidal endothelial cells (LSECs). Damaged LSECs can synthesize transforming growth factor-beta and platelet-derived growth factor, which activate hepatic stellate cells and facilitate the synthesis of extracellular matrix. Herein, we highlight the angiogenic cytokines of LSECs related to liver fibrosis and cirrhosis at different stages and focus on the formation and development of liver fibrosis and cirrhosis. Inhibition of LSEC angiogenesis and antiangiogenic therapy are described in detail. Targeting LSECs has high therapeutic potential for liver diseases. Further understanding of the mechanism of action will provide stronger evidence for the development of anti-LSEC drugs and new directions for diagnosis and treatment of liver diseases.

Phase 1-2 pilot clinical trial in patients with decompensated liver cirrhosis treated with bone marrow-derived endothelial progenitor cells

The aim of this nonrandomized, open label, phase 1 clinical trial was to evaluate the safety and the feasibility of the treatment with autologous bone marrow-derived endothelial progenitor cells (EPC) in decompensated liver cirrhosis. In addition, the changes in liver function and hepatic venous pressure gradient (HVPG) and their relation with the characteristics of the cellular product were analyzed. Twelve patients with Child-Pugh ≥8 liver cirrhosis underwent bone marrow harvest for ex vivo differentiation of EPC. The final product was administered through the hepatic artery in a single administration. Patients underwent clinical and radiologic follow-up for 12 months. The phenotype and the ability to produce cytokines and growth factors of the final cellular suspension were analyzed. Eleven patients were treated (feasibility 91%). No treatment-related severe adverse events were observed as consequence of any study procedure or treatment. Model for end-stage liver disease score improved significantly (P 0.042) in the first 90 days after cells administration and 5 of the 9 patients alive at 90 days showed a decreased of HVPG. There was a direct correlation between the expression of acetylated-low density lipoprotein and von Willebrand factor in the cellular product and the improvement in liver function and HVPG. The treatment with EPCs in patients with decompensated liver cirrhosis is safe and feasible and might have therapeutic potential. Patients receiving a higher amount of functionally active EPC showed an improvement of liver function and portal hypertension suggesting that the potential usefulness of these cells for the treatment of liver cirrhosis deserves further evaluation.

Bone marrow endothelial progenitor cells activate hepatic stellate cells and aggravate carbon tetrachloride induced liver fibrosis in mice via paracrine factors

OBJECTIVES

Bone marrow derived endothelial progenitor cells (BM-EPCs) are increased in chronic liver disease (CLD). Their role in hepatic fibrosis and regeneration remains an area of intense studies. We investigated the migration and secretory functions of BM-EPCs in fibrotic mice liver.

MATERIALS AND METHODS

Bone marrow cells from C57BL6-GFP mice were transplanted into the femur of irradiated C57BL6 mice, followed by CCl₄ doses for 8 weeks, to develop hepatic fibrosis (n = 36). Transplanted C57BL6 mice without CCl₄ treatment were used as controls. EPCs were analyzed in BM, blood and liver by flow cytometry and immunofluorescence. VEGF and TGF-β were analysed in the hepatic stellate cells (HSCs) and BM-EPCs co-cultures using ELISAs.

RESULTS

There was a significant migration of EPCs from BM to blood and to the liver (P ≤ 0.01). Percentage of GFP⁺ CD31⁺ EPCs and collagen proportionate area was substantially increased in the liver at 4th week of CCl₄ dosage compared to the controls (19.8% vs 1.9%, P ≤ 0.05). Levels of VEGF (533.6 pg/ml) and TGF-β (327.44 pg/ml) also increased significantly, when HSCs were treated with the EPC conditioned medium, as compared to controls (25.66 pg/ml and 5.87 pg/ml, respectively; P ≤ 0.001).

CONCLUSIONS

Present findings suggest that BM-EPCs migrate to the liver during CCl4-induced liver injury and contribute to fibrosis.

Number and function of circulating endothelial progenitor cells in patients with primary Budd-Chiari syndrome

BACKGROUND AND AIM

Primary Budd-Chiari syndrome (BCS) is associated with vascular endothelial injury. Circulating endothelial progenitor cells (EPCs) provide an endogenous mechanism to repair endothelial injury. This study investigated the levels and functionality of EPCs in patients with primary BCS.

METHODS

EPCs (CD34⁺/CD133⁺/KDR⁺) were quantified in 82 patients with primary BCS (inferior vena cava type: n=19; hepatic vein type: n=22; and mixed type: n=41), 10 cirrhosis controls (CC group) and 10 age-matched healthy controls (HC group), using flow cytometry. EPCs proliferation was detected by MTT assay, adhesion by adhesion activity assay, and migration capacity by Transwell assay.

RESULTS

EPCs levels were significantly lower in the BCS group (0.020±0.005%) than in the CC and HC groups (0.260±0.201%, 0.038±0.007%; P<0.001 for each). EPCs cultured in vitro from BCS and CC groups had, respectively, lower proliferation activity (0.20±0.04, 0.23±0.06 vs 0.58±0.07, each P<0.001), adhesion activity (15.8±1.7, 18.2±4.3 vs 35.0±2.5 cells/random microscopic field (RMF), each P<0.001) and migration activity (16.1±1.5, 16.7±3.0 vs 23.9±2.0 cells/RMF, each P<0.001) than in the HC group. EPCs functionality did not significantly differ between the BCS and CC groups. The numbers and functions of EPCs did not significantly differ among patients with inferior vena cava type, hepatic vein type and mixed type of BCS.

CONCLUSION

Patients with primary BCS had lower EPCs levels, with less proliferation, adhesion and migration activities. These findings suggest that lower levels of less functional EPCs may be associated with venous occlusion in primary BCS patients.

Liver sinusoidal endothelial cells: Physiology and role in liver diseases

Liver sinusoidal endothelial cells (LSECs) are highly specialized endothelial cells representing the interface between blood cells on the one side and hepatocytes and hepatic stellate cells on the other side. LSECs represent a permeable barrier. Indeed, the association of 'fenestrae', absence of diaphragm and lack of basement membrane make them the most permeable endothelial cells of the mammalian body. They also have the highest endocytosis capacity of human cells. In physiological conditions, LSECs regulate hepatic vascular tone contributing to the maintenance of a low portal pressure despite the major changes in hepatic blood flow occurring during digestion. LSECs maintain hepatic stellate cell quiescence, thus inhibiting intrahepatic vasoconstriction and fibrosis development. In pathological conditions, LSECs play a key role in the initiation and progression of chronic liver diseases. Indeed, they become capillarized and lose their protective properties, and they promote angiogenesis and vasoconstriction. LSECs are implicated in liver regeneration following acute liver injury or partial hepatectomy since they renew from LSECs and/or LSEC progenitors, they sense changes in shear stress resulting from surgery, and they interact with platelets and inflammatory cells. LSECs also play a role in hepatocellular carcinoma development and progression, in ageing, and in liver lesions related to inflammation and infection. This review also presents a detailed analysis of the technical aspects relevant for LSEC analysis including the markers these cells express, the available cell lines and the transgenic mouse models. Finally, this review provides an overview of the strategies available for a specific targeting of LSECs.

Mechanisms of adaptation of the hepatic vasculature to the deteriorating conditions of blood circulation in liver cirrhosis

PubMed, EMBASE, Orphanet, MIDLINE, Google Scholar and Cochrane Library were searched for articles published between 1983 and 2015. Relevant articles were selected by using the following terms: “Liver cirrhosis”, “Endothelial dysfunction”, “Sinusoidal remodeling”, “Intrahepatic angiogenesis” and “Pathogenesis of portal hypertension”. Then the reference lists of identified articles were searched for other relevant publications as well. Besides gross hepatic structural disorders related to diffuse fibrosis and formation of regenerative nodules, the complex morphofunctional rearrangement of the hepatic microvascular bed and intrahepatic angiogenesis also play important roles in hemodynamic disturbances in liver cirrhosis. It is characterized by endothelial dysfunction and impaired paracrine interaction between activated stellate hepatocytes and sinusoidal endotheliocytes, sinusoidal remodeling and capillarization, as well as development of the collateral microcirculation. In spite of the fact that complex morphofunctional rearrangement of the hepatic microvascular bed and intrahepatic angiogenesis in liver cirrhosis are the compensatory-adaptive reaction to the deteriorating conditions of blood circulation, they contribute to progression of disease and development of serious complications, in particular, related to portal hypertension.

Acute-on-chronic liver failure: terminology, mechanisms and management

Acute-on-chronic liver failure (ACLF) is a distinct clinical entity and differs from acute liver failure and decompensated cirrhosis in timing, presence of acute precipitant, course of disease and potential for unaided recovery. The definition involves outlining the acute and chronic insults to include a homogenous patient group with liver failure and an expected outcome in a specific timeframe. The pathophysiology of ACLF relates to persistent inflammation, immune dysregulation with initial wide-spread immune activation, a state of systematic inflammatory response syndrome and subsequent sepsis due to immune paresis. The disease severity and outcome can be predicted by both hepatic and extrahepatic organ failure(s). Clinical recovery is expected with the use of nucleoside analogues for hepatitis B, and steroids for severe alcoholic hepatitis and, possibly, severe autoimmune hepatitis. Artificial liver support systems help remove toxins and metabolites and serve as a bridge therapy before liver transplantation. Hepatic regeneration during ongoing liver failure, although challenging, is possible through the use of growth factors. Liver transplantation remains the definitive treatment with a good outcome. Pre-emptive antiviral agents for hepatitis B before chemotherapy to prevent viral reactivation and caution in using potentially hepatotoxic drugs can prevent the development of ACLF.

Particle Radiation-Induced Nontargeted Effects in Bone-Marrow-Derived Endothelial Progenitor Cells

Bone-marrow- (BM-) derived endothelial progenitor cells (EPCs) are critical for endothelial cell maintenance and repair. During future space exploration missions astronauts will be exposed to space irradiation (IR) composed of a spectrum of low-fluence protons ((1)H) and high charge and energy (HZE) nuclei (e.g., iron-(56)Fe) for extended time. How the space-type IR affects BM-EPCs is limited. In media transfer experiments in vitro we studied nontargeted effects induced by (1)H- and (56)Fe-IR conditioned medium (CM), which showed significant increase in the number of p-H2AX foci in nonirradiated EPCs between 2 and 24 h. A 2-15-fold increase in the levels of various cytokines and chemokines was observed in both types of IR-CM at 24 h. Ex vivo analysis of BM-EPCs from single, low-dose, full-body (1)H- and (56)Fe-IR mice demonstrated a cyclical (early 5-24 h and delayed 28 days) increase in apoptosis. This early increase in BM-EPC apoptosis may be the effect of direct IR exposure, whereas late increase in apoptosis could be a result of nontargeted effects (NTE) in the cells that were not traversed by IR directly. Identifying the role of specific cytokines responsible for IR-induced NTE and inhibiting such NTE may prevent long-term and cyclical loss of stem and progenitors cells in the BM milieu.

Soluble CD146, a novel endothelial marker, is related to the severity of liver disease

OBJECTIVES

Angiogenesis and inflammation have been involved in the progression of fibrosis in patients with chronic liver disease (CLD). Soluble CD146 (sCD146), a biomarker that was recently characterized as a novel component of the endothelial junction is implicated in endothelial proliferation. Our study evaluates the performance of sCD146 in assessing liver fibrosis and cirrhosis, and determines if its levels are related to the severity of liver disease in patients with cirrhosis.

MATERIAL AND METHODS

sCD146 levels were determined by a commercially available immunoenzymatic technique in 62 consecutive patients with cirrhosis, 43 patients with CLD and 27 healthy controls.

RESULTS

Patients with cirrhosis compared to non-cirrhotics with CLD had a higher median sCD146 concentration (639 vs. 317 ng/ml). In receiver operating characteristic (ROC) curve analysis, the cut-off of 412 ng/ml showed a sensitivity of 78% and a specificity of 75% for diagnosis of cirrhosis, offering good diagnostic accuracy (area under the ROC curve [AUROC: 0.838]). Patients with compensated compared to those with decompensated cirrhosis had a lower median sCD146 concentration (399 vs. 848 ng/ml, respectively). A cut-off of 534 ng/ml offered a sensitivity of 83% and a specificity of 78% for differentiating compensated from decompensated cirrhosis (AUROC: 0.866). Furthermore, in cirrhotics, sCD146 correlated positively with AST, bilirubin levels and most importantly with international normalized ratio and model for end-stage liver disease (r = 0.648, p < 0.001 and r = 0.567, p < 0.001, respectively).

CONCLUSION

sCD146 can be used as a surrogate, inexpensive biomarker for the diagnosis of cirrhosis. It is also well correlated with severity of liver disease in cirrhotic patients. Further studies are needed to define its role in clinical practice.

To study the effect of curcumin on the growth properties of circulating endothelial progenitor cells

Curcumin has been shown to regulate the expression of genes implicated in tumor cell proliferation, metastasis, chemotherapy resistance, and angiogenesis. Endothelial progenitor cells (EPCs) have been recently described in the peripheral blood as cells contributing to both physiological and pathological angiogenesis. In the current study, we evaluated the effect of curcumin on these angiogenic cells. EPCs were isolated, expanded, and characterized ex vivo. These cells were then treated with different concentrations of curcumin. The formation of EPC colonies in culture and their proliferation was analyzed by 5'-bromo-2'-deoxyuridine assays in absence and presence of curcumin. Further, the expression of two important cell cycle inhibitory proteins, p21 and p53, in the curcumin- and culture medium-treated cells without curcumin was evaluated by intracellular flow cytometry. The results showed that there was a significant decrease in the formation of EPC colonies in culture. EPC proliferation was significantly inhibited by curcumin in a dose-dependent manner. Flow cytometry analysis showed a twofold increase in the expression of both p21 and p53 in curcumin-treated cells as compared to the medium-treated cells, suggesting that curcumin inhibits EPC growth by mainly inhibiting the G1 to S phase transition in the cell cycle. It would be further worthwhile to study the effect of curcumin on EPC-mediated angiogenic activity.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

Angiogenesis in liver regeneration and fibrosis: "a double-edged sword"

Angiogenesis, defined as the formation of new microvasculature from preexisting blood vessels and mature endothelial cells, plays a major role in wound healing and scar formation, and it is associated with inflammatory responses. Angiogenesis can occur in physiological conditions, such as during liver regeneration, and in pathological situations, such as during the progression of fibrosis to cirrhosis and also during tumor angiogenesis. Cellular cross-talk among liver sinusoidal endothelial cells (LSECs), hepatic stellate cells and hepatocytes is believed to play an important role in the angiogenesis process during both liver regeneration and development of cirrhosis. In addition to mature endothelial cells, bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs) have been recently identified for their contribution to post-natal vasculogenesis/angiogenesis. In vivo, EPCs are mobilized into the peripheral blood in response to tissue ischemia or traumatic injury, migrate to the sites of injured endothelium and differentiate into mature endothelial cells. In our recent studies, we have explored the role of EPC-mediated angiogenesis in liver regeneration and/or cirrhosis. Results have demonstrated significantly increased endogenous levels of circulating EPCs in cirrhotic patients in comparison to the controls. Also, EPCs from cirrhotic patients have been observed to stimulate substantial angiogenesis by resident LSECs in vitro via paracrine factors such as vascular endothelial growth factor and platelet-derived growth factor. This review gives an overview of the angiogenesis process in liver regeneration and disease and discusses a new mechanism for intrahepatic angiogenesis mediated by BM-derived EPCs.

Relationship between vascular endothelial growth factors and liver diseases

Vascular endothelial growth factors play an important role in the processes of cell differentiation and maturation. As a kind of multi-functional factor, they are closely related to the occurrence and progression of liver diseases. They can not only promote postoperative liver regeneration but also repress the propagation of chronic hepatitis B and liver cirrhosis. In addition, they have a role in cancer diagnosis and treatment and graft rejection in liver transplantation. In this paper, we will give a brief introduction of vascular growth factors and their role in liver regeneration, cirrhosis, liver cancer and liver transplantation.

Bone marrow contributions to fibrosis

Bone marrow transplant experiments in mice using labelled donor bone marrow have indicated that following injury bone marrow derived cells can circulate and home to the injured organs. In particular fibrocytes and myofibroblasts are capable of contributing to the wound healing response, including collagen deposition. In chronic injury this can lead to a pathological degree of fibrosis. Experiments have shown that this can be a relatively insignificant contribution to the scar forming population in certain organs and that the majority of the scar forming cells are intrinsic to the organ. Conversely, in certain circumstances, the circulating cells become major players in the organs fibrotic response. Whilst cell tracking experiments are relatively simple to perform, to actually determine a functional contribution to a fibrotic response more sophisticated approaches are required. This can include the use of bone marrow transplantation from recipients with collagen reporter systems which gives a read out of bone marrow derived cells that are transcriptional active for collagen production in a damaged organ. Another technique is to use bone marrow transplants from donors that have a mutation in the collagen to demonstrate a functional difference in fibrosis when bone marrow transplants performed. Recent reports have identified factors mediating recruitment of circulating fibrocytes to injured organs, such as CXCL12 and CXCL16 and shown that blocking these factors reduced fibrocyte recruitment and subsequent fibrosis. The identification of such factors may enable the development of novel therapies to block further fibrocyte engraftment and fibrosis in situations of pathological scarring. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.