Characterization of isolated liver sinusoidal endothelial cells for liver bioengineering

LiverMap pipeline for 3D imaging of human liver reveals volumetric spatial dysregulation of cirrhotic vasculobiliary architecture

The liver contains an intricate microstructure that is critical for liver function. Architectural disruption of this spatial structure is pathologic. Unfortunately, 2D histopathology - the gold standard for pathological understanding of many liver diseases - can misrepresent or leave gaps in our understanding of complex 3D structural features. Here, we utilized immunostaining, tissue clearing, microscopy, and computational software to create 3D multilobular reconstructions of both non-fibrotic and cirrhotic human liver tissue. We found that spatial architecture in human cirrhotic liver samples with varying etiologies had sinusoid zonation dysregulation, reduction in glutamine synthetase-expressing pericentral hepatocytes, regression of central vein networks, disruption of hepatic arterial networks, and fragmentation of biliary networks, which together suggest a pro-portalization/decentralization phenotype in cirrhotic tissue. Further implementation of 3D pathological analyses may provide a deeper understanding of cirrhotic pathobiology and inspire novel treatments for liver disease.

New advances of NG2-expressing cell subset in marrow mesenchymal stem cells as novel therapeutic tools for liver fibrosis/cirrhosis

BACKGROUND

Bone marrow-derived mesenchymal stem cell (BMMSC)-based therapy has become a major focus for treating liver fibrosis/cirrhosis. However, although these cell therapies promote the treatment of this disease, the heterogeneity of BMMSCs, which causes insufficient efficacy during clinical trials, has not been addressed. In this study, we describe a novel Percoll-Plate-Wait procedure (PPWP) for the isolation of an active cell subset from BMMSC cultures that was characterized by the expression of neuroglial antigen 2 (NG2/BMMSCs).

METHODS

By using the key method of PPWP and other classical biological techniques we compared NG2/BMMSCs with parental BMMSCs in biological and functional characteristics within a well-defined diethylnitrosamine (DEN)-induced liver fibrosis/cirrhosis injury male C57BL/6 mouse model also in a culture system. Of note, the pathological alterations in the model is quite similar to humans'.

RESULTS

The NG2/BMMSCs revealed more advantages compared to parentalBMMSCs. They exhibited greater proliferation potential than parental BMMSCs, as indicated by Ki-67 immunofluorescence (IF) staining. Moreover, higher expression of SSEA-3 (a marker specific for embryonic stem cells) was detected in NG2/BMMSCs than in parental BMMSCs, which suggested that the "stemness" of NG2/BMMSCs was greater than that of parental BMMSCs. In vivo studies revealed that an injection of NG2/BMMSCs into mice with ongoing DEN-induced liver fibrotic/cirrhotic injury enhanced repair and functional recovery to a greater extent than in mice treated with parental BMMSCs. These effects were associated with the ability of NG2/BMMSCs to differentiate into bile duct cells (BDCs). In particular, we discovered for the first time that NG2/BMMSCs exhibit unique characteristics that differ from those of parental BMMSCs in terms of producing liver sinusoidal endothelial cells (LSECs) to reconstruct injured blood vessels and sinusoidal structures in the diseased livers, which are important for initiating hepatocyte regeneration. This unique potential may also suggest that NG2/BMMSCs could be an novel off-liver progenitor of LSECs. Ex vivo studies revealed that the NG2/BMMSCs exhibited a similar trend to that of their in vivo in terms of functional differentiation responding to the DEN-diseased injured liver cues. Additionally, the obvious core role of NG2/BMMSCs in supporting the functions of BMMSCs in bile duct repair and BDC-mediated hepatocyte regeneration might also be a novel finding.

CONCLUSIONS

Overall, the PPWP-isolated NG2/BMMSCs could be a novel effective cell subset with increased purity to serve as a new therapeutic tool for enhancing treatment efficacy of BMMSCs and special seed cell source (BDCs, LSECs) also for bioliver engineering.

Liver specification of human iPSC-derived endothelial cells transplanted into mouse liver

Background & Aims

Liver sinusoidal endothelial cells (LSECs) are important in liver development, regeneration, and pathophysiology, but the differentiation process underlying their tissue-specific phenotype is poorly understood and difficult to study because primary human cells are scarce. The aim of this study was to use human induced pluripotent stem cell (hiPSC)-derived LSEC-like cells to investigate the differentiation process of LSECs.

Methods

hiPSC-derived endothelial cells (iECs) were transplanted into the livers of Fah-/-/Rag2-/-/Il2rg-/- mice and assessed over a 12-week period. Lineage tracing, immunofluorescence, flow cytometry, plasma human factor VIII measurement, and bulk and single cell transcriptomic analysis were used to assess the molecular and functional changes that occurred following transplantation.

Results

Progressive and long-term repopulation of the liver vasculature occurred as iECs expanded along the sinusoids between hepatocytes and increasingly produced human factor VIII, indicating differentiation into LSEC-like cells. To chart the developmental profile associated with LSEC specification, the bulk transcriptomes of transplanted cells between 1 and 12 weeks after transplantation were compared against primary human adult LSECs. This demonstrated a chronological increase in LSEC markers, LSEC differentiation pathways, and zonation. Bulk transcriptome analysis suggested that the transcription factors NOTCH1, GATA4, and FOS have a central role in LSEC specification, interacting with a network of 27 transcription factors. Novel markers associated with this process included EMCN and CLEC14A. Additionally, single cell transcriptomic analysis demonstrated that transplanted iECs at 4 weeks contained zonal subpopulations with a region-specific phenotype.

Conclusions

Collectively, this study confirms that hiPSCs can adopt LSEC-like features and provides insight into LSEC specification. This humanised xenograft system can be applied to further interrogate LSEC developmental biology and pathophysiology, bypassing current logistical obstacles associated with primary human LSECs.

Impact and implications

Liver sinusoidal endothelial cells (LSECs) are important cells for liver biology, but better model systems are required to study them. We present a pluripotent stem cell xenografting model that produces human LSEC-like cells. A detailed and longitudinal transcriptomic analysis of the development of LSEC-like cells is included, which will guide future studies to interrogate LSEC biology and produce LSEC-like cells that could be used for regenerative medicine.

Immune tolerance promotion by LSEC-specific lentiviral vector-mediated expression of the transgene regulated by the stabilin-2 promoter

Liver sinusoidal endothelial cells (LSECs) are specialized endocytic cells that clear the body from blood-borne pathogens and waste macromolecules through scavenger receptors (SRs). Among the various SRs expressed by LSECs is stabilin-2 (STAB2), a class H SR that binds to several ligands, among which endogenous coagulation products. Given the well-established tolerogenic function of LSECs, we asked whether the STAB2 promoter (STAB2p) would enable us to achieve LSEC-specific lentiviral vector (LV)-mediated transgene expression, and whether the expression of this transgene would be maintained over the long term due to tolerance induction. Here, we show that STAB2p ensures LSEC-specific green fluorescent protein (GFP) expression by LV in the absence of a specific cytotoxic CD8+ T cell immune response, even in the presence of GFP-specific CD8+ T cells, confirming the robust tolerogenic function of LSECs. Finally, we show that our delivery system can partially and permanently restore FVIII activity in a mouse model of severe hemophilia A without the formation of anti-FVIII antibodies. Overall, our findings establish the suitability of STAB2p for long-term LSEC-restricted expression of therapeutic proteins, such as FVIII, or to achieve antigen-specific immune tolerance in auto-immune diseases.

Technology for the formation of engineered microvascular network models and their biomedical applications

Tissue engineering and regenerative medicine have made great progress in recent decades, as the fields of bioengineering, materials science, and stem cell biology have converged, allowing tissue engineers to replicate the structure and function of various levels of the vascular tree. Nonetheless, the lack of a fully functional vascular system to efficiently supply oxygen and nutrients has hindered the clinical application of bioengineered tissues for transplantation. To investigate vascular biology, drug transport, disease progression, and vascularization of engineered tissues for regenerative medicine, we have analyzed different approaches for designing microvascular networks to create models. This review discusses recent advances in the field of microvascular tissue engineering, explores potential future challenges, and offers methodological recommendations.

The roles of liver sinusoidal endothelial cells in liver ischemia/reperfusion injury

Liver ischemia/reperfusion injury (IRI) is a major complication after partial hepatectomy and liver transplantation and during hypovolemic shock and hypoxia-related diseases. Liver IRI is a current research hotspot. The early stage of liver IRI is characterized by injury and dysfunction of liver sinusoidal endothelial cells (LSECs), which, along with hepatocytes, are the major cells involved in liver injury. In this review, we elaborate on the roles played by LSECs in liver IRI, including the pathological features of LSECs, LSECs exacerbation of the sterile inflammatory response, LSECs interactions with platelets and the promotion of liver regeneration, and the activation of LSECs autophagy. In addition, we discuss the study of LSECs as therapeutic targets for the treatment of liver IRI and the existing problems when applying LSECs in liver IRI research.

Generation of functional liver sinusoidal endothelial-like cells from human bone marrow-derived mesenchymal stem cells

Introduction

Liver sinusoidal endothelial cells (LSECs) are specialized vascular endothelial cells that play an important role in the maintenance of biological homeostasis. However, the lack of versatile human LSECs has hindered research on LSECs and development of medical technologies for liver diseases including hemophilia A. In this study, we developed a technique to induce LSEC differentiation from human bone marrow-derived mesenchymal stem cells (BM-MSCs).

Methods

To induce LSECs from human BM-MSCs, cytokines and chemical compounds associated with signaling implicated in LSEC differentiation and liver development were screened. Then LSEC-related genes and proteins expression in the differentiated cells were analyzed by qPCR and flow cytometry analysis, respectively. LSEC-related functions of the differentiated cells were also examined.

Results

We found that the gene expression of LSEC markers, such as LYVE1, was considerably increased by culturing human BM-MSCs with bone morphogenetic protein 4, fibroblast growth factor 8b, transforming growth factor-β signal inhibitor, and cyclic AMP. Furthermore, the differentiated cells expressed LSEC marker proteins and clearly demonstrated LSEC-specific functions, such as the uptake of hyaluronic acid.

Conclusions

Our result indicate that the functional LSEC-like cells were successfully generated from human BM-MSCs using our established protocol.

A method to generate perfusable physiologic-like vascular channels within a liver-on-chip model

The human vasculature is essential in organs and tissues for the transport of nutrients, metabolic waste products, and the maintenance of homeostasis. The integration of vessels in in vitro organs-on-chip may, therefore, improve the similarity to the native organ microenvironment, ensuring proper physiological functions and reducing the gap between experimental research and clinical outcomes. This gap is particularly evident in drug testing and the use of vascularized models may provide more realistic insights into human responses to drugs in the pre-clinical phases of the drug development pipeline. In this context, different vascularized liver models have been developed to recapitulate the architecture of the hepatic sinusoid, exploiting either porous membranes or bioprinting techniques. In this work, we developed a method to generate perfusable vascular channels with a circular cross section within organs-on-chip without any interposing material between the parenchyma and the surrounding environment. Through this technique, vascularized liver sinusoid-on-chip systems with and without the inclusion of the space of Disse were designed and developed. The recapitulation of the Disse layer, therefore, a gap between hepatocytes and endothelial cells physiologically present in the native liver milieu, seems to enhance hepatic functionality (e.g., albumin production) compared to when hepatocytes are in close contact with endothelial cells. These findings pave the way to numerous further uses of microfluidic technologies coupled with vascularized tissue models (e.g., immune system perfusion) as well as the integration within multiorgan-on-chip settings.

Oit3, a promising hallmark gene for targeting liver sinusoidal endothelial cells

Liver sinusoidal endothelial cells (LSECs) play a pivotal role in maintaining liver homeostasis and influencing the pathological processes of various liver diseases. However, neither LSEC-specific hallmark genes nor a LSEC promoter-driven Cre mouse line has been introduced before, which largely restricts the study of liver diseases with vascular disorders. To explore LSEC-specific hallmark genes, we compared the top 50 marker genes between liver endothelial cells (ECs) and liver capillary ECs and identified 18 overlapping genes. After excluding globally expressed genes and those with low expression percentages, we narrowed our focus to two final candidates: Oit3 and Dnase1l3. Through single-cell RNA sequencing (scRNA-seq) and analysis of the NCBI database, we confirmed the extrahepatic expression of Dnase1l3. The paired-cell sequencing data further demonstrated that Oit3 was predominantly expressed in the midlobular liver ECs. Subsequently, we constructed inducible Oit3-CreERT2 transgenic mice, which were further crossed with ROSA26-tdTomato mice. Microscopy validated that the established Oit3-CreERT2-tdTomato mice exhibited significant fluorescence in the liver rather than in other organs. The staining analysis confirmed the colocalization of tdTomato and EC markers. Ex-vivo experiments further confirmed that isolated tdTomato+ cells exhibited well-differentiated fenestrae and highly expressed EC markers, confirming their identity as LSECs. Overall, Oit3 is a promising hallmark gene for tracing LSECs. The establishment of Oit3-CreERT2-tdTomato mice provides a valuable model for studying the complexities of LSECs in liver diseases.

3D organoid modeling of extramedullary hematopoiesis

Background:

Under certain clinical and experimental conditions hematopoiesis occurs in other site than bone marrow (BM), such as the liver. Here, we develop a 3D organoid that mimics several components of the hematopoietic niche present during liver extramedullary hematopoiesis.

Aim:

To evaluate the capacity of a 3D hematopoietic organoid (3D-HO) to function as a hematopoietic like-niche allowing for blood cell production outside of the BM

Methods:

The 3D-HO is constituted by liver sinusoidal endothelial cells (LSEC) as the stromal component, BM isolated from 5-FU treated mice (FU-BMCs), collagen microspheres and plasma clot as scaffolds. The ability of the 3D-HO to support the survival and functionality of FU-BMCs was investigated by using confocal microscopy, histology analysis, flow cytometry, and clonogenic assays.

Results:

After 15 and 30 days, post-ectopic implantation, histological studies of the 3D-HO showed the presence of cells with myeloid and lymphoid lineage morphology. Flow cytometry analysis of these cells showed the presence of cells expressing hematopoietic stem progenitor cells (HSPC) (Sca-1+/c-Kit+), myeloid (Gr-1+) and lymphoid (B220+ and CD19+) markers. Clonogenic assays showed that cells from the 3D-HO formed hematopoietic colonies. Expression of the Sry gene by cells from the 3D-HO, implanted for 30 days in female mice, indicated that male donor cells persist in this model of extramedullary hematopoiesis.

Conclusions:

The 3D-HO constitutes an extramedullary hematopoietic-like niche which supports the survival and functionality of FU-BMCs. It may constitute an efficient model for investigating, in vitro and in vivo, those factors that control hematopoiesis outside BM.

A Cytological Atlas of the Human Liver Proteome from PROTEOMESKY-LIVERHu 2.0, a Publicly Available Database

The liver plays a unique role as a metabolic center of the body, and also performs other important functions such as detoxification and immune response. Here, we establish a cell type-resolved healthy human liver proteome including hepatocytes (HCs), hepatic stellate cells (HSCs), Kupffer cells (KCs), and liver sinusoidal endothelial cells (LSECs) by high-resolution mass spectrometry. Overall, we quantify total 8354 proteins for four cell types and over 6000 proteins for each cell type. Analysis of this data set and regulatory pathway reveals the cellular labor division in the human liver follows the pattern that parenchymal cells make the main components of pathways, but nonparenchymal cells trigger these pathways. Human liver cells show some novel molecular features: HCs maintain KCs and LSECs homeostasis by producing cholesterol and ketone bodies; HSCs participate in xenobiotics metabolism as an agent deliverer; KCs and LSECs mediate immune response through MHC class II-TLRs and MHC class I-TGFβ cascade, respectively; and KCs play a central role in diurnal rhythms regulation through sensing diurnal IGF and temperature flux. Together, this work expands our understandings of liver physiology and provides a useful resource for future analyses of normal and diseased livers.

The Immunomodulatory Properties of Mesenchymal Stem Cells Play a Critical Role in Inducing Immune Tolerance after Liver Transplantation

Although liver transplantation is considered to be the best choice for patients with end-stage liver diseases, postoperative immune rejection still cannot be overlooked. Patients with liver transplantation have to take immunosuppressive drugs for a long time or even their entire lives, in which heavy economic burden and side effects caused by the drugs have become the major impediment for liver transplantation. There is a growing body of evidences indicating that mesenchymal stem cell (MSC) transplantation, a promising tool in regenerative medicine, can be used as an effective way to induce immune tolerance after liver transplantation based on their huge expansion potential and unique immunomodulatory properties. MSCs have been reported to inhibit innate immunity and adaptive immunity to induce a tolerogenic microenvironment. In in vitro studies, transplanted MSCs show plasticity in immune regulation by altering their viability, migration, differentiation, and secretion in the interactions with the surrounding host microenvironment. In this review, we aim to provide an overview of the current understanding of immunomodulatory properties of MSCs in liver transplantation, to elucidate the potential mechanisms behind MSCs regulating immune response, especially in vivo and the influence of the microenvironment, and ultimately to discuss the feasible strategies to improve the clinical prognosis of liver transplantation. Only after exhaustive understanding of potential mechanisms of the MSC immunomodulation can we improve the safety and effectiveness of MSC treatment and achieve better therapeutic effects.

Prevascularized Micro-/Nano-Sized Spheroid/Bead Aggregates for Vascular Tissue Engineering

Efficient strategies to promote microvascularization in vascular tissue engineering, a central priority in regenerative medicine, are still scarce; nano- and micro-sized aggregates and spheres or beads harboring primitive microvascular beds are promising methods in vascular tissue engineering. Capillaries are the smallest type and in numerous blood vessels, which are distributed densely in cardiovascular system. To mimic this microvascular network, specific cell components and proangiogenic factors are required. Herein, advanced biofabrication methods in microvascular engineering, including extrusion-based and droplet-based bioprinting, Kenzan, and biogripper approaches, are deliberated with emphasis on the newest works in prevascular nano- and micro-sized aggregates and microspheres/microbeads.

Critical Role of LSEC in Post-Hepatectomy Liver Regeneration and Failure

Liver sinusoids are lined by liver sinusoidal endothelial cells (LSEC), which represent approximately 15 to 20% of the liver cells, but only 3% of the total liver volume. LSEC have unique functions, such as fluid filtration, blood vessel tone modulation, blood clotting, inflammatory cell recruitment, and metabolite and hormone trafficking. Different subtypes of liver endothelial cells are also known to control liver zonation and hepatocyte function. Here, we have reviewed the origin of LSEC, the different subtypes identified in the liver, as well as their renewal during homeostasis. The liver has the exceptional ability to regenerate from small remnants. The past decades have seen increasing awareness in the role of non-parenchymal cells in liver regeneration despite not being the most represented population. While a lot of knowledge has emerged, clarification is needed regarding the role of LSEC in sensing shear stress and on their participation in the inductive phase of regeneration by priming the hepatocytes and delivering mitogenic factors. It is also unclear if bone marrow-derived LSEC participate in the proliferative phase of liver regeneration. Similarly, data are scarce as to LSEC having a role in the termination phase of the regeneration process. Here, we review what is known about the interaction between LSEC and other liver cells during the different phases of liver regeneration. We next explain extended hepatectomy and small liver transplantation, which lead to "small for size syndrome" (SFSS), a lethal liver failure. SFSS is linked to endothelial denudation, necrosis, and lobular disturbance. Using the knowledge learned from partial hepatectomy studies on LSEC, we expose several techniques that are, or could be, used to avoid the "small for size syndrome" after extended hepatectomy or small liver transplantation.

From arteries to capillaries: approaches to engineering human vasculature

From micro-scaled capillaries to millimeter-sized arteries and veins, human vasculature spans multiple scales and cell types. The convergence of bioengineering, materials science, and stem cell biology has enabled tissue engineers to recreate the structure and function of different hierarchical levels of the vascular tree. Engineering large-scale vessels has been pursued over the past thirty years to replace or bypass damaged arteries, arterioles, and venules, and their routine application in the clinic may become a reality in the near future. Strategies to engineer meso- and microvasculature have been extensively explored to generate models to study vascular biology, drug transport, and disease progression, as well as for vascularizing engineered tissues for regenerative medicine. However, bioengineering of large-scale tissues and whole organs for transplantation, have failed to result in clinical translation due to the lack of proper integrated vasculature for effective oxygen and nutrient delivery. The development of strategies to generate multi-scale vascular networks and their direct anastomosis to host vasculature would greatly benefit this formidable goal. In this review, we discuss design considerations and technologies for engineering millimeter-, meso-, and micro-scale vessels. We further provide examples of recent state-of-the-art strategies to engineer multi-scale vasculature. Finally, we identify key challenges limiting the translation of vascularized tissues and offer our perspective on future directions for exploration.

Role of Liver-Mediated Tolerance in Nanoparticle-Based Tumor Therapy

In the last decades, the use of nanocarriers for immunotherapeutic purposes has gained a lot of attention, especially in the field of tumor therapy. However, most types of nanocarriers accumulate strongly in the liver after systemic application. Due to the default tolerance-promoting role of liver non-parenchymal cells (NPCs), Kupffer cells (KCs), liver sinusoidal endothelial cells (LSECs), and hepatic stellate cells (HSCs), their potential role on the immunological outcome of systemic nano-vaccination approaches for therapy of tumors in the liver and in other organs needs to be considered. Concerning immunological functions, KCs have been the focus until now, but recent studies have elucidated an important role of LSECs and HSCs as well. Therefore, this review aims to summarize current knowledge on the employment of nanocarriers for immunotherapeutic therapy of liver diseases and the overall role of liver NPCs in the context of nano-vaccination approaches. With regard to the latter, we discuss strategies on how to address liver NPCs, aiming to exploit and modulate their immunological properties, and alternatively how to avoid unwanted engagement of nano-vaccines by liver NPCs for tumor therapy.

Liver sinusoidal endothelial cells promote the differentiation and survival of mouse vascularised hepatobiliary organoids

The structural and physiological complexity of currently available liver organoids is limited, thereby reducing their relevance for drug studies, disease modelling, and regenerative therapy. In this study we combined mouse liver progenitor cells (LPCs) with mouse liver sinusoidal endothelial cells (LSECs) to generate hepatobiliary organoids with liver-specific vasculature. Organoids consisting of 5x10³ cells were created from either LPCs, or a 1:1 combination of LPC/LSECs. LPC organoids demonstrated mild hepatobiliary differentiation in vitro with minimal morphological change; in contrast LPC/LSEC organoids developed clusters of polygonal hepatocyte-like cells and biliary ducts over a 7 day period. Hepatic (albumin, CPS1, CYP3A11) and biliary (GGT1) genes were significantly upregulated in LPC/LSEC organoids compared to LPC organoids over 7 days, as was albumin secretion. LPC/LSEC organoids also had significantly higher in vitro viability compared to LPC organoids. LPC and LPC/LSEC organoids were transplanted into vascularised chambers created in Fah^-/-/Rag2^-/-/Il2rg^-/- mice (50 LPC organoids, containing 2.5x10⁵ LPCs, and 100 LPC/LSEC organoids, containing 2.5x10⁵ LPCs). At 2 weeks, minimal LPCs survived in chambers with LPC organoids, but robust hepatobiliary ductular tissue was present in LPC/LSEC organoids. Morphometric analysis demonstrated a 115-fold increase in HNF4α+ cells in LPC/LSEC organoid chambers (17.26 ± 4.34 cells/mm² vs 0.15 ± 0.15 cells/mm², p = 0.018), and 42-fold increase in Sox9+ cells in LPC/LSEC organoid chambers (28.29 ± 6.05 cells/mm² vs 0.67 ± 0.67 cells/mm², p = 0.011). This study presents a novel method to develop vascularised hepatobiliary organoids, with both in vitro and in vivo results confirming that incorporating LSECs with LPCs into organoids significantly increases the differentiation of hepatobiliary tissue within organoids and their survival post-transplantation.

Spliced X-box binding protein 1 induces liver cancer cell death via activating the Mst1-JNK-mROS signalling pathway

Previous studies have found that the primary pathogenesis of liver cancer progression is linked to excessive cancer cell proliferation and rapid metastasis. Although therapeutic advances have been made for the treatment of liver cancer, the mechanism underlying the liver cancer progression has not been fully addressed. In the present study, we explored the role of spliced X-box binding protein 1 (XBP1) in regulating the viability and death of liver cancer cells in vitro. Our study demonstrated that XBP1 was upregulated in liver cancer cells when compared to the primary hepatocytes. Interestingly, the deletion of XBP1 could reduce the viability of liver cancer cells in vitro via inducing apoptotic response. Further, we found that XBP1 downregulation was also linked to proliferation arrest and migration inhibition. At the molecular levels, XBP1 inhibition is followed by activation of the Mst1 pathway which promoted the phosphorylation of c-Jun N-terminal kinase (JNK). Then, the active Mst1-JNK pathway mediated mitochondrial reactive oxygen species (mROS) overproduction and then excessive ROS induced cancer cell death. Therefore, our study demonstrated a novel role played by XBP1 in modulating the viability of liver cancer cells via the Mst1-JNK-mROS pathways.

Exendin-4 attenuates inflammation-mediated endothelial cell apoptosis in varicose veins through inhibiting the MAPK-JNK signaling pathway

Context: Inflammation response has been found to be associated with endothelial cell death in the progression of varicose veins. Exendin-4 is able to reduce inflammation and thus attenuate cell apoptosis.Aim: The aim of our study is to explore the influence of Exendin-4 on LPS-treated endothelial cells.Methods: Cells were treated with LPS. Exendin-4 was added into the medium of cells. Western blots, qPCR, and ELISA were used to analyze the role of Exendin-4 in LPS-mediated cell death.Results: We found that LPS treatment caused significantly cell death. Whereas this trend could be attenuated by Exendin-4. After treatment with Exendin-4, inflammation factors upregulation and oxidative stress activation were significantly repressed, an effect that was followed by a drop in the levels of glucose production and lactic acid generation. At the molecular levels, Exendin-4 treatment inhibited the activity of MAPK-JNK signaling pathway in the presence of LPS treatment.Conclusions: LPS causes cell apoptosis through inducing inflammation response, oxidative stress and energy stress. Exendin-4 treatment enhances cell survival, reduces inflammation, and improves energy stress through inhibiting the MAPK-JNK signaling pathway.

Melatonin improves mitochondrial biogenesis through the AMPK/PGC1α pathway to attenuate ischemia/reperfusion-induced myocardial damage

Cardiac ischemia/reperfusion injury is associated with reduced mitochondrial turnover and regeneration. There is currently no effective approach to stimulate mitochondrial biogenesis in the reperfused myocardium. In this study, we investigated whether melatonin could increase mitochondrial biogenesis and thus promote mitochondrial homeostasis in cardiomyocytes. Cardiomyocytes were subjected to hypoxia/reoxygenation (H/R) injury with or without melatonin treatment, and various mitochondrial functions were measured. H/R injury repressed mitochondrial biogenesis in cardiomyocytes, whereas melatonin treatment restored mitochondrial biogenesis through the 5’ adenosine monophosphate-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) pathway. Melatonin enhanced mitochondrial metabolism, inhibited mitochondrial oxidative stress, induced mitochondrial fusion and prevented mitochondrial apoptosis in cardiomyocytes subjected to H/R injury. The melatonin-induced improvement in mitochondrial biogenesis was associated with increased cardiomyocyte survival during H/R injury. On the other hand, silencing of PGC1α attenuated the protective effects of melatonin on cardiomyocyte viability, thereby impairing mitochondrial bioenergetics, disrupting the mitochondrial morphology, and activating mitochondrial apoptosis. Thus, H/R injury suppressed mitochondrial biogenesis, while melatonin activated the AMPK/PGC1α pathway and restored mitochondrial biogenesis, ultimately protecting the reperfused heart.

Macrophage stimulating 1-induced inflammation response promotes aortic aneurysm formation through triggering endothelial cells death and activating the NF-κB signaling pathway

Aortic aneurysm formation is associated with endothelial cells dysfunction through an undefined mechanism. Macrophage stimulating 1 (Mst1) and NF-κB signaling pathway have been found to be related to inflammation response in endothelial cell damage. The goal of our study is to explore the role of Mst1 in regulating endothelial cell viability with a focus on NF-κB signaling pathway and inflammation response. Endothelial cell viability and death were determined via immunofluorescence and ELISA. Agonist of NF-κB signaling pathway and siRNA against Mst1 were used. The results in our study demonstrated that Mst1 transcription and expression were significantly elevated after exposure to oxidative stress in endothelial cells. Once loss of Mst1 through transfection of siRNA (si-Mst1), endothelial cell viability and survival rate were rapidly increased in response to oxidative stress. In addition, we also found that Mst1 controlled inflammation response and mitochondrial function in endothelial cells. Re-activation of NF-κB signaling pathway was followed by an activation of inflammation response and mitochondrial dysfunction, as evidenced by increased expression of inflammation factors and decreased ATP synthesis. Altogether, our results identify Mst1 as the primary factors responsible for endothelial cells dysfunction in aneurysms formation through inducing inflammation response, endothelial apoptosis, and NF-κB signaling pathway activation.

MST1-Hippo pathway regulates inflammation response following myocardial infarction through inhibiting HO-1 signaling pathway

Context: Mammalian STE20-like protein kinases 1 (MST1) has been found to be associated with cardiomyocyte damage following acute myocardial infarction.Aim: The aim of our study is to explore the influence of MST1 in inflammation response following myocardial infarction.Methods: Cardiomyocyte cell line was used in vitro with hypoxia treatment to establish myocardial infarction model. ELISA, qPCR, Western blots, and siRNA technology were used to analyze the role of MST1 in inflammation response following myocardial infarction.Results: The transcription and expression of MST1 was significantly elevated following myocardial infarction. Loss of MST1 attenuated the levels of inflammation response and thus contributed to the survival of cardiomyocyte in vitro. Mechanistically, MST1 deletion reversed the activity of heme oxygenase-1 (HO-1) and thus reduced hypoxia-mediated cardiomyocyte death.Conclusions: Altogether, in this study, we found that MST1-Hippo pathway is activated in myocardial infarction and contributes to the inflammation response in cardiomyocytes through inhibiting the HO-1 signaling pathway. This finding would provide a potential target to reverse cardiomyocyte viability and reduce inflammation response in myocardial infarction.

Emerging Roles for Lymphatics in Chronic Liver Disease

Chronic liver disease (CLD) is a global health epidemic causing ∼2 million deaths annually worldwide. As the incidence of CLD is expected to rise over the next decade, understanding the cellular and molecular mediators of CLD is critical for developing novel therapeutics. Common characteristics of CLD include steatosis, inflammation, and cholesterol accumulation in the liver. While the lymphatic system in the liver has largely been overlooked, the liver lymphatics, as in other organs, are thought to play a critical role in maintaining normal hepatic function by assisting in the removal of protein, cholesterol, and immune infiltrate. Lymphatic growth, permeability, and/or hyperplasia in non-liver organs has been demonstrated to be caused by obesity or hypercholesterolemia in humans and animal models. While it is still unclear if changes in permeability occur in liver lymphatics, the lymphatics do expand in number and size in all disease etiologies tested. This is consistent with the lymphatic endothelial cells (LEC) upregulating proliferation specific genes, however, other transcriptional changes occur in liver LECs that are dependent on the inflammatory mediators that are specific to the disease etiology. Whether these changes induce lymphatic dysfunction or if they impact liver function has yet to be directly addressed. Here, we will review what is known about liver lymphatics in health and disease, what can be learned from recent work on the influence of obesity and hypercholesterolemia on the lymphatics in other organs, changes that occur in LECs in the liver during disease and outstanding questions in the field.

Resveratrol attenuates cerebral ischaemia reperfusion injury via modulating mitochondrial dynamics homeostasis and activating AMPK-Mfn1 pathway

The pathogenesis of cerebral ischaemia reperfusion injury (IRI) has not been fully described. Accordingly, there is little effective drug available for the treatment of cerebral IRI. The aim of our study was to explore the exact role played by Mfn1-mediated mitochondrial protection in cerebral IRI and evaluate the beneficial action of resveratrol on reperfused brain. Our study demonstrated that hypoxia-reoxygenation (HR) injury caused N2a cell apoptosis and this process was highly affected by mitochondrial dysfunction. Decreased mitochondrial membrane potential, increased mitochondrial oxidative stress, and an activated mitochondrial apoptosis pathway were noted in HR-treated N2a cells. Interestingly, resveratrol treatment could attenuate N2a cell apoptosis via sustaining mitochondrial homeostasis. Further, we found that resveratrol modulated mitochondrial performance via activating the Mfn1-related mitochondrial protective system. Knockdown of Mfn1 could abolish the beneficial effects of resveratrol on HR-treated N2a cells. Besides, we also report that resveratrol regulated Mfn1 expression via the AMPK pathway; inhibition of AMPK pathway also neutralized the anti-apoptotic effect of resveratrol on N2a cells in the setting of cerebral IRI. Taken together our results show that mitochondrial damage is closely associated with the progression of cerebral IRI. In addition we also demonstrate the protective action played by resveratrol on reperfused brain and show that this effect is achieved via activating the AMPK-Mfn1 pathway.

Vascular endothelial growth factor enhances tendon-bone healing by activating Yes-associated protein for angiogenesis induction and rotator cuff reconstruction in rats

Local angiogenesis following rotator cuff reconstruction is crucial for tendon-bone healing. The current research on the mechanism underlying angiogenesis that promotes tendon-bone healing is scarce. This study investigates the mechanism underlying vascular endothelial growth factor (VEGF)-Hippo signaling pathway's involvement in tendon-bone healing following rotator cuff reconstruction. Verteporfin, the inhibitor of the Yes-associated protein (YAP), was used to mechanically test and analyze two groups of tensile-failure loads following rotator cuff reconstruction and to detect collagen and angiogenesis-related marker expressions in the tendon. The interaction mechanism of the VEGF-Hippo signaling pathway was assessed using human umbilical vein endothelial cells (HUVECs). The diameter of the supraspinatus tendon reduced following verteporfin treatment. Mechanical tests revealed that verteporfin significantly reduces the tensile-failure load of the supraspinatus tendon. Verteporfin significantly reduces collagen 1 (Col 1), Col 3, Angiopoietin 2, CD31, Von Willebrand factor, CTGF, and CYR61 expressions. In HUVECs, VEGF activates VEGF receptors and inhibits LATS and YAP phosphorylation. YAP is then transferred to the nucleus to further activate downstream pathways. Therefore, verteporfin can inhibit VEGF-induced YAP pathway activation by inhibiting YAP activity. Angiogenesis in tendon-bone healing following rotator cuff reconstruction requires VEGF-Hippo signaling pathway synergy.

Therapeutic effects of bone mesenchymal stem cells on oral and maxillofacial defects: a novel signaling pathway involving miR-31/CXCR4/Akt axis

Context: Although bone mesenchymal stem cells (BMSCs) have been used for the treatment of oral and maxillofacial defects, the survival rate and limited proliferation reduces the therapeutic efficiency of BMSC.Objective: The aim of our study is to explore the role of miR-31 in regulating survival, proliferation, and migration of BMSC in vitro.Materials and methods: LPS was used in vitro to induce BMSC damage and then miR-31 was used to incubate with BMSC. Subsequently, BMSC proliferation, survival, and migration were determined via ELISA, qPCR, western blots, and immunofluorescence.Results: The expression of miR-31 was downregulated in response to LPS stress. Interestingly, supplementation of miR-31 could reverse the survival, proliferation and migration of BMSC under LPS. Mechanically, miR-31 treatment inhibited the activation of caspase, and thus promoted BMSC survival. Besides, miR-31 upregulated the genes related to cell proliferation, an effect that was followed by an increase in the levels of migratory factors. Further, we found that miR-31 treatment activated the CXCR4/Akt pathway and blockade of CXCR4/Akt could abolish the beneficial effects of miR-31 on BMSC proliferation, survival, and migration.Conclusions: miR-31 could increase the therapeutic efficiency of BMSC via the CXCR4/Akt pathway.

Pretreatment of bone mesenchymal stem cells with miR181-c facilitates craniofacial defect reconstruction via activating AMPK-Mfn1 signaling pathways

Context: Bone mesenchymal stem cells (BMSC)-based regenerative therapy is critical for the craniofacial defect reconstruction. However, oxidative stress micro-environment after transplantation limits the therapeutic efficiency of BMSC. The miR-181c has been found to be associated with cell survival and proliferation. Objective: Herein, we investigated whether prior miR-181c treatment promoted BMSC proliferation and survival under oxidative stress injury. Materials and methods: Cells were treated with hydrogen peroxide (H₂O₂) and then cell viability was determined via MTT assay, TUNEL staining and ELISA. Western blotting and immunofluorescence assay were used to detect those alterations of mitochondrial function. Results: H₂O₂ treatment reduced BMSC viability and this effect could be reversed via additional supplementation of miR181-c. Mechanistically, oxidative stress increased cell apoptosis, augmented caspase-3 activity, promoted reactive oxygen species (ROS) synthesis, impaired mitochondrial potential, and induced mitochondrial dynamics imbalance. However, miR-181c pretreatment reversed these effects of oxidative stress on BMSC. Moreover, miR-181c treatment improved BMSC proliferation, migration and paracrine, which are very important for craniofacial reconstruction. In addition, we identified that AMPK-Mfn1 axis was the direct targets of miR-181c in BMSC. Mfn1 silencing impaired the protective effects miR-181c on BMSC viability and proliferation under oxidative stress environment. Conclusions: Collectively, our results indicate that miR-181c participates in oxidative stress-mediated BMSC damage by modulating the AMPK-Mfn1 signaling pathway, suggesting miR-181c-AMPK-Mfn1 axis may serves as novel therapeutic targets to facilitate craniofacial defect reconstruction.

Cyp1b1 expression impacts the angiogenic and inflammatory properties of liver sinusoidal endothelial cells

Cytochrome P450 1B1 (CYP1B1) is a member of the cytochrome p450 family of enzymes that catalyze mono-oxygenase reactions. Although constitutive Cyp1b1 expression is limited in hepatocytes, its expression and function in liver sinusoidal endothelial cells (LSEC) remains unknown. Here we determined the impact of Cyp1b1 expression on LSEC properties prepared from Cyp1b1+/+ and Cyp1b1-/- mice. LSEC expressed PECAM-1, VE-cadherin, and B4 lectin similar to EC from other mouse tissues. Cyp1b1 +/+ LSEC constitutively expressed significant levels of Cyp1b1, while Cyp1b1-/- LSEC lacked Cyp1b1 expression. LSEC also expressed VEGFR3, PROX-1, and LYVE-1, VEGFR1 and VEGFR2, as well as other cell adhesion molecules including ICAM-1, ICAM-2, VCAM-1, and thrombospondin-1 (TSP1) receptors, CD36 and CD47. However, the expression of PV-1 and stabilin (fenestration markers), and endoglin were limited in these cells. The Cyp1b1-/- LSEC showed limited fenestration, and decreased levels of VEGF and BMP6. Cyp1b1-/- LSEC also showed a decrease in the levels of VE-cadherin and ZO-1 impacting adherens and gap junction formation. Cyp1b1-/- LSEC were significantly more apoptotic, proliferated at a faster rate, and were less adherent and more migratory. These changes were attributed, in part, to decreased amounts of TSP1 and increased AKT and ERK activation. The expressions of integrins were also altered by the lack of Cyp1b1, but the ability of these cells to undergo capillary morphogenesis was minimally affected. Furthermore, Cyp1b1-/- LSEC expressed lower levels of inflammatory mediators MCP-1 and TNF-α. Thus, Cyp1b1 expression has a significant impact on LSEC angiogenic and inflammatory functions.