Space of Disse: a stem cell niche in the liver

Role of T cells in liver metastasis

The liver is a major metastatic site (organ) for gastrointestinal cancers (such as colorectal, gastric, and pancreatic cancers) as well as non-gastrointestinal cancers (such as lung, breast, and melanoma cancers). Due to the innate anatomical position of the liver, the apoptosis of T cells in the liver, the unique metabolic regulation of hepatocytes and other potential mechanisms, the liver tends to form an immunosuppressive microenvironment and subsequently form a pre-metastatic niche (PMN), which can promote metastasis and colonization by various tumor cells(TCs). As a result, the critical role of immunoresponse in liver based metastasis has become increasingly appreciated. T cells, a centrally important member of adaptive immune response, play a significant role in liver based metastases and clarifying the different roles of the various T cells subsets is important to guide future clinical treatment. In this review, we first introduce the predisposing factors and related mechanisms of liver metastasis (LM) before introducing the PMN and its transition to LM. Finally, we detail the role of different subsets of T cells in LM and advances in the management of LM in order to identify potential therapeutic targets for patients with LM.

Neutrophil extracellular traps promote MASH fibrosis by metabolic reprogramming of HSC

BACKGROUND AND AIMS

Metabolic dysfunction-associated steatohepatitis (MASH) fibrosis is a reversible stage of liver disease accompanied by inflammatory cell infiltration. Neutrophils extrude a meshwork of chromatin fibers to establish neutrophil extracellular traps (NETs), which play important roles in inflammatory response regulation. Our previous work demonstrated that NETs promote HCC in MASH. However, it is still unknown if NETs play a role in the molecular mechanisms of liver fibrosis.

APPROACH AND RESULTS

Following 12 weeks of Western diet/carbon tetrachloride, MASH fibrosis was identified in C57BL/6 mice with increased NET formation. However, NET depletion using DNase I treatment or mice knocked out for peptidyl arginine deaminase type IV significantly attenuated the development of MASH fibrosis. NETs were demonstrated to induce HSCs activation, proliferation, and migration through augmented mitochondrial and aerobic glycolysis to provide additional bioenergetic and biosynthetic supplies. Metabolomic analysis revealed markedly an altered metabolic profile upon NET stimulation of HSCs that were dependent on arachidonic acid metabolism. Mechanistically, NET stimulation of toll-like receptor 3 induced cyclooxygenase-2 activation and prostaglandin E2 production with subsequent HSC activation and liver fibrosis. Inhibiting cyclooxygenase-2 with celecoxib reduced fibrosis in our MASH model.

CONCLUSIONS

Our findings implicate NETs playing a critical role in the development of MASH hepatic fibrosis by inducing metabolic reprogramming of HSCs through the toll-like receptor 3/cyclooxygenase-2/cyclooxygenase-2 pathway. Therefore, NET inhibition may represent an attractive treatment target for MASH liver fibrosis.

Molecular and cellular basis of the dose-rate-dependent adverse effects of radiation exposure in animal models. Part II: Hematopoietic system, lung and liver

While epidemiological data have greatly contributed to the estimation of the dose and dose-rate effectiveness factor (DDREF) for human populations, studies using animal models have made significant contributions to provide quantitative data with mechanistic insights. The current article aims at compiling the animal studies, specific to rodents, with reference to the dose-rate effects of cancer development. This review focuses specifically on the results that explain the biological mechanisms underlying dose-rate effects and their potential involvement in radiation-induced carcinogenic processes. Since the adverse outcome pathway (AOP) concept together with the key events holds promise for improving the estimation of radiation risk at low doses and low dose-rates, the review intends to scrutinize dose-rate dependency of the key events in animal models and to consider novel key events involved in the dose-rate effects, which enables identification of important underlying mechanisms for linking animal experimental and human epidemiological studies in a unified manner.

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

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

Role of extracellular vesicles in cancer-specific interactions between tumour cells and the vasculature

Cancer progression impacts and exploits the vascular system in several highly consequential ways. Among different types of vascular cells, blood cells and mediators that are engaged in these processes, endothelial cells are at the centre of the underlying circuitry, as crucial constituents of angiogenesis, angiocrine stimulation, non-angiogenic vascular growth, interactions with the coagulation system and other responses. Tumour-vascular interactions involve soluble factors, extracellular matrix molecules, cell-cell contacts, as well as extracellular vesicles (EVs) carrying assemblies of molecular effectors. Oncogenic mutations and transforming changes in the cancer cell genome, epigenome and signalling circuitry exert important and often cancer-specific influences upon pathways of tumour-vascular interactions, including the biogenesis, content, and biological activity of EVs and responses of cancer cells to them. Notably, EVs may carry and transfer bioactive, oncogenic macromolecules (oncoproteins, RNA, DNA) between tumour and vascular cells and thereby elicit unique functional changes and forms of vascular growth and remodeling. Cancer EVs influence the state of the vasculature both locally and systemically, as exemplified by cancer-associated thrombosis. EV-mediated communication pathways represent attractive targets for therapies aiming at modulation of the tumour-vascular interface (beyond angiogenesis) and could also be exploited for diagnostic purposes in cancer.

Stem cells for treatment of liver fibrosis/cirrhosis: clinical progress and therapeutic potential

Cost-effective treatment strategies for liver fibrosis or cirrhosis are limited. Many clinical trials of stem cells for liver disease shown that stem cells might be a potential therapeutic approach. This review will summarize the published clinical trials of stem cells for the treatment of liver fibrosis/cirrhosis and provide the latest overview of various cell sources, cell doses, and delivery methods. We also describe the limitations and strengths of various stem cells in clinical applications. Furthermore, to clarify how stem cells play a therapeutic role in liver fibrosis, we discuss the molecular mechanisms of stem cells for treatment of liver fibrosis, including liver regeneration, immunoregulation, resistance to injury, myofibroblast repression, and extracellular matrix degradation. We provide a perspective for the prospects of future clinical implementation of stem cells.

An Updated Review and Meta Analysis of Lipoprotein Glomerulopathy

More than 200 cases of lipoprotein glomerulopathy (LPG) have been reported since it was first discovered 30 years ago. Although relatively rare, LPG is clinically an important cause of nephrotic syndrome and end-stage renal disease. Mutations in the APOE gene are the leading cause of LPG. APOE mutations are an important determinant of lipid profiles and cardiovascular health in the population and can precipitate dysbetalipoproteinemia and glomerulopathy. Apolipoprotein E-related glomerular disorders include APOE2 homozygote glomerulopathy and LPG with heterozygous APOE mutations. In recent years, there has been a rapid increase in the number of LPG case reports and some progress in research into the mechanism and animal models of LPG. We consequently need to update recent epidemiological studies and the molecular mechanisms of LPG. This endeavor may help us not only to diagnose and treat LPG in a more personized manner but also to better understand the potential relationship between lipids and the kidney.

Vessel co-option and angiotropic extravascular migratory metastasis: a continuum of tumour growth and spread?

Two fields of cancer research have emerged dealing with the biology of tumour cells localised to the abluminal vascular surface: vessel co-option (VCo), a non-angiogenic mode of tumour growth and angiotropic extravascular migratory metastasis (EVMM), a non-hematogenous mode of tumour migration and metastasis. VCo is a mechanism by which tumour cells gain access to a blood supply by spreading along existing blood vessels in order to grow locally. Angiotropic EVMM involves "pericytic mimicry" (PM), which is characterised by tumour cells continuously migrating in the place of pericytes distantly along abluminal vascular surfaces. When cancer cells are engaged in PM and EVMM, they migrate along blood vessels beyond the advancing front of the tumour to secondary sites with the formation of regional and distant metastases. In the present perspective, the authors review the current scientific literature, emphasising the analogies between embryogenesis and cancer progression, the re-activation of embryonic signals by "cancer stem cells", and the important role of laminins and epithelial-mesenchymal-transition. This perspective maintains that VCo and angiotropic EVMM constitute complementary processes and represent a continuum of cancer progression from the primary tumour to metastases and of tumour growth to EVMM, analogous to the embryonic development program.

Carving the senescent phenotype by the chemical reactivity of catecholamines: An integrative review

Macromolecules damaged by covalent modifications produced by chemically reactive metabolites accumulate in the slowly renewable components of living bodies and compromise their functions. Among such metabolites, catecholamines (CA) are unique, compared with the ubiquitous oxygen, ROS, glucose and methylglyoxal, in that their high chemical reactivity is confined to a limited set of cell types, including the dopaminergic and noradrenergic neurons and their direct targets, which suffer from CA propensities for autoxidation yielding toxic quinones, and for Pictet-Spengler reactions with carbonyl-containing compounds, which yield mitochondrial toxins. The functions progressively compromised because of that include motor performance, cognition, reward-driven behaviors, emotional tuning, and the neuroendocrine control of reproduction. The phenotypic manifestations of the resulting disorders culminate in such conditions as Parkinson's and Alzheimer's diseases, hypertension, sarcopenia, and menopause. The reasons to suspect that CA play some special role in aging accumulated since early 1970-ies. Published reviews address the role of CA hazardousness in the development of specific aging-associated diseases. The present integrative review explores how the bizarre discrepancy between CA hazardousness and biological importance could have emerged in evolution, how much does the chemical reactivity of CA contribute to the senescent phenotype in mammals, and what can be done with it.

The extracellular matrix of hematopoietic stem cell niches

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Comprehensive overview of different classes of ECM molecules in the HSC niche.

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Overview of current knowledge on role of biophysics of the HSC niche.

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Description of approaches to create artificial stem cell niches for several application.

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Importance of considering ECM in drug development and testing.

Hematopoietic stem cells (HSCs) are the life-long source of all types of blood cells. Their function is controlled by their direct microenvironment, the HSC niche in the bone marrow. Although the importance of the extracellular matrix (ECM) in the niche by orchestrating niche architecture and cellular function is widely acknowledged, it is still underexplored. In this review, we provide a comprehensive overview of the ECM in HSC niches. For this purpose, we first briefly outline HSC niche biology and then review the role of the different classes of ECM molecules in the niche one by one and how they are perceived by cells. Matrix remodeling and the emerging importance of biophysics in HSC niche function are discussed. Finally, the application of the current knowledge of ECM in the niche in form of artificial HSC niches for HSC expansion or targeted differentiation as well as drug testing is reviewed.

Bioprinting of Complex Multicellular Organs with Advanced Functionality-Recent Progress and Challenges Ahead

Bioprinting has emerged as one of the most promising strategies for fabrication of functional organs in the lab as an alternative to transplant organs. While progress in the field has mostly been restricted to a few miniaturized tissues with minimal biological functionality until a few years ago, recent progress has advanced the concept of building three-dimensional multicellular organ complexity remarkably. This review discusses a series of milestones that have paved the way for bioprinting of tissue constructs that have advanced levels of biological and architectural functionality. Critical materials, engineering and biological challenges that are key to addressing the desirable function of engineered organs are presented. These are discussed in light of the many difficulties to replicate the heterotypic organization of multicellular solid organs, the nanoscale precision of the extracellular microenvironment in hierarchical tissues, as well as the advantages and limitations of existing bioprinting methods to adequately overcome these barriers. In summary, the advances of the field toward realistic manufacturing of functional organs have never been so extensive, and this manuscript serves as a road map for some of the recent progress and the challenges ahead.

Regulatory T-Cell Therapy in Liver Transplantation and Chronic Liver Disease

The constant exposure of the liver to gut derived foreign antigens has resulted in this organ attaining unique immunological characteristics, however it remains susceptible to immune mediated injury. Our understanding of this type of injury, in both the native and transplanted liver, has improved significantly in recent decades. This includes a greater awareness of the tolerance inducing CD4+ CD25+ CD127low T-cell lineage with the transcription factor FoxP3, known as regulatory T-Cells (Tregs). These cells comprise 5-10% of CD4+ T cells and are known to function as an immunological "braking" mechanism, thereby preventing immune mediated tissue damage. Therapies that aim to increase Treg frequency and function have proved beneficial in the setting of both autoimmune diseases and solid organ transplantations. The safety and efficacy of Treg therapy in liver disease is an area of intense research at present and has huge potential. Due to these cells possessing significant plasticity, and the potential for conversion towards a T-helper 1 (Th1) and 17 (Th17) subsets in the hepatic microenvironment, it is pre-requisite to modify the microenvironment to a Treg favourable atmosphere to maintain these cells' function. In addition, implementation of therapies that effectively increase Treg functional activity in the liver may result in the suppression of immune responses and will hinder those that destroy tumour cells. Thus, fine adjustment is crucial to achieve this immunological balance. This review will describe the hepatic microenvironment with relevance to Treg function, and the role these cells have in both native diseased and transplanted livers.

Role of vasodilation in liver regeneration and health

Recently, we have shown that an enhanced blood flow through the liver triggers hepatocyte proliferation and thereby liver growth. In this review, we first explain the literature on hepatic blood flow and its changes after partial hepatectomy (PHx), before we present the different steps of liver regeneration that take place right after the initial hemodynamic changes induced by PHx. Those parts of the molecular mechanisms governing liver regeneration, which are directly associated with the hepatic vascular system, are subsequently reviewed. These include β1 integrin-dependent mechanotransduction in liver sinusoidal endothelial cells (LSECs), triggering mechanically-induced activation of the vascular endothelial growth factor receptor-3 (VEGFR3) and matrix metalloproteinase-9 (MMP9) as well as release of growth-promoting angiocrine signals. Finally, we speculate how advanced age and obesity negatively affect the hepatic vasculature and thus liver regeneration and health, and we conclude our review with some recent technical progress in the clinic that employs liver perfusion. In sum, the mechano-elastic properties and alterations of the hepatic vasculature are key to better understand and influence liver health, regeneration, and disease.

The Provocative Roles of Platelets in Liver Disease and Cancer

Both platelets and the liver play important roles in the processes of coagulation and innate immunity. Platelet responses at the site of an injury are rapid; their immediate activation and structural changes minimize the loss of blood. The majority of coagulation proteins are produced by the liver—a multifunctional organ that also plays a critical role in many processes: removal of toxins and metabolism of fats, proteins, carbohydrates, and drugs. Chronic inflammation, trauma, or other causes of irreversible damage to the liver can dysregulate these pathways leading to organ and systemic abnormalities. In some cases, platelet-to-lymphocyte ratios can also be a predictor of disease outcome. An example is cirrhosis, which increases the risk of bleeding and prothrombotic events followed by activation of platelets. Along with a triggered coagulation cascade, the platelets increase the risk of pro-thrombotic events and contribute to cancer progression and metastasis. This progression and the resulting tissue destruction is physiologically comparable to a persistent, chronic wound. Various cancers, including colorectal cancer, have been associated with increased thrombocytosis, platelet activation, platelet-storage granule release, and thrombosis; anti-platelet agents can reduce cancer risk and progression. However, in cancer patients with pre-existing liver disease who are undergoing chemotherapy, the risk of thrombotic events becomes challenging to manage due to their inherent risk for bleeding. Chemotherapy, also known to induce damage to the liver, further increases the frequency of thrombotic events. Depending on individual patient risks, these factors acting together can disrupt the fragile balance between pro- and anti-coagulant processes, heightening liver thrombogenesis, and possibly providing a niche for circulating tumor cells to adhere to—thus promoting both liver metastasis and cancer-cell survival following treatment (that is, with minimal residual disease in the liver).

Improved Recovery from Liver Fibrosis by Crenolanib

Chronic liver diseases are associated with excessive deposition of extracellular matrix proteins. This so-called fibrosis can progress to cirrhosis and impair vital functions of the liver. We examined whether the receptor tyrosine kinase (RTK) class III inhibitor Crenolanib affects the behavior of hepatic stellate cells (HSC) involved in fibrogenesis. Rats were treated with thioacetamide (TAA) for 18 weeks to trigger fibrosis. After TAA treatment, the animals received Crenolanib for two weeks, which significantly improved recovery from liver fibrosis. Because Crenolanib predominantly inhibits the RTK platelet-derived growth factor receptor-β, impaired HSC proliferation might be responsible for this beneficial effect. Interestingly, blocking of RTK signaling by Crenolanib not only hindered HSC proliferation but also triggered their specification into hepatic endoderm. Endodermal specification was mediated by p38 mitogen-activated kinase (p38 MAPK) and c-Jun-activated kinase (JNK) signaling; however, this process remained incomplete, and the HSC accumulated lipids. JNK activation was induced by stress response-associated inositol-requiring enzyme-1α (IRE1α) in response to Crenolanib treatment, whereas β-catenin-dependent WNT signaling was able to counteract this process. In conclusion, the Crenolanib-mediated inhibition of RTK impeded HSC proliferation and triggered stress responses, initiating developmental processes in HSC that might have contributed to improved recovery from liver fibrosis in TAA-treated rats.

The Space of Disse: The Liver Hub in Health and Disease

Since it was first described by the German anatomist and histologist, Joseph Hugo Vincenz Disse, the structure and functions of the space of Disse, a thin perisinusoidal area between the endothelial cells and hepatocytes filled with blood plasma, have acquired great importance in liver disease. The space of Disse is home for the hepatic stellate cells (HSCs), the major fibrogenic players in the liver. Quiescent HSCs (qHSCs) store vitamin A, and upon activation they lose their retinol reservoir and become activated. Activated HSCs (aHSCs) are responsible for secretion of extracellular matrix (ECM) into the space of Disse. This early event in hepatic injury is accompanied by loss of the pores—known as fenestrations—of the endothelial cells, triggering loss of balance between the blood flow and the hepatocyte, and underlies the link between fibrosis and organ dysfunction. If the imbalance persists, the expansion of the fibrotic scar followed by the vascularized septae leads to cirrhosis and/or end-stage hepatocellular carcinoma (HCC). Thus, researchers have been focused on finding therapeutic targets that reduce fibrosis. The space of Disse provides the perfect microenvironment for the stem cells niche in the liver and the interchange of nutrients between cells. In the present review article, we focused on the space of Disse, its components and its leading role in liver disease development.

Sensory nerves in the spotlight of the stem cell niche

Niches are specialized tissue microenvironments that control stem cells functioning. The bone marrow mesenchymal stem cell niche defines a location within the marrow in which mesenchymal stem cells are retained and produce new cells throughout life. Deciphering the signaling mechanisms by which the niche regulates stem cell fate will facilitate the use of these cells for therapy. Recent studies, by using state-of-the-art methodologies, including sophisticated in vivo inducible genetic techniques, such as lineage-tracing Cre/loxP mediated systems, in combination with pharmacological inhibition, provide evidence that sensory neuron is an important component of the bone marrow mesenchymal stem cell niche. Strikingly, knockout of a specific receptor in sensory neurons blocked stem cell function in the bone marrow. The knowledge arising from these discoveries will be crucial for stem cell manipulation in the future. Here, we review recent progress in our understanding of sensory nerves biology in the stem cell niche.

Are Liver Pericytes Just Precursors of Myofibroblasts in Hepatic Diseases? Insights from the Crosstalk between Perivascular and Inflammatory Cells in Liver Injury and Repair

Cirrhosis, a late form of liver disease, is characterized by extensive scarring due to exacerbated secretion of extracellular matrix proteins by myofibroblasts that develop during this process. These myofibroblasts arise mainly from hepatic stellate cells (HSCs), liver-specific pericytes that become activated at the onset of liver injury. Consequently, HSCs tend to be viewed mainly as myofibroblast precursors in a fibrotic process driven by inflammation. Here, the molecular interactions between liver pericytes and inflammatory cells such as macrophages and neutrophils at the first moments after injury and during the healing process are brought into focus. Data on HSCs and pericytes from other tissues indicate that these cells are able to sense pathogen- and damage-associated molecular patterns and have an important proinflammatory role in the initial stages of liver injury. On the other hand, further data suggest that as the healing process evolves, activated HSCs play a role in skewing the initial proinflammatory (M1) macrophage polarization by contributing to the emergence of alternatively activated, pro-regenerative (M2-like) macrophages. Finally, data suggesting that some HSCs activated during liver injury could behave as hepatic progenitor or stem cells will be discussed.