Use of mouse liver mesothelial cells to prevent postoperative adhesion and promote liver regeneration after hepatectomy

Hepatocyte Growth Factor DNA Aptamer for Prevention of Postoperative Peritoneal Adhesion via Enhancement of Fibrinolysis and Inhibition of Mesothelial Mesenchymal Transition

Postoperative peritoneal adhesion (PPA) is a prevalent complication of abdominal surgery, posing a significant hindrance to postsurgical recovery. Although several strategies have been developed to alleviate and prevent adhesions, their efficacy remains unsatisfactory. For the first time, we studied the therapeutic effect and mechanism of our recently developed thermally stable oligonucleotide-based mimetics of hepatocyte growth factor (HGF DNA aptamer) to prevent PPA. The HGF DNA aptamer effectively inhibited canonical TGF-β1 signaling transduction, partially suppressing mesothelial mesenchymal transition. Additionally, the aptamer, respectively, upregulated and downregulated the expression of tissue plasminogen activator and plasminogen activator inhibitor 1, thereby enhancing fibrinolytic activity. As a pleiotropic factor, the HGF DNA aptamer also enhanced the migratory and proliferative capacities of mesothelial cells. Finally, the aptamer demonstrated a higher level of effectiveness in preventing PPAs than the commercially available antiperitoneal adhesion barrier, Seprafilm. Due to its therapeutic benefits, excellent stability, biosafety, cost-effectiveness, and versatility, the HGF DNA aptamer demonstrates promise for preventing PPA in future clinical settings.

LPCAT3/LPLAT12 deficiency in the liver ameliorates acetaminophen-induced acute liver injury

Acetaminophen (APAP) is a double-edged sword, mainly depending on the dosage. A moderate dose of APAP is effective for fever and pain relief; however, an overdose induces acute liver injury. The mechanism underlying APAP-induced acute liver failure is unclear, and its treatment is limited. A recent report has shown that several oxidized phospholipids are associated with APAP-induced acute liver failure. Lysophosphatidylcholine acyltransferase 3 (Lpcat3, Lplat12), which is highly expressed in the liver, preferentially catalyzes the incorporation of arachidonate into lysophospholipids (PLs). In the present study, we investigated the roles of Lpcat3 on APAP-induced acute liver injury using liver-specific Lpcat3-knockout mice. Hepatic Lpcat3 deficiency reduced the degree of APAP-induced necrosis of hepatocytes around Zone 3 and ameliorated the elevation of hepatic injury serum marker levels, and prolonged survival. Lipidomic analysis showed that the accumulation of oxidized and hydroperoxidized phospholipids was suppressed in Lpcat3-knockout mice. The amelioration of APAP-induced acute liver injury was due not only to the reduction in the lipid synthesis of arachidonic acid PLs because of Lpcat3 deficiency, but also to the promotion of the APAP detoxification pathway by facilitating the conjugation of glutathione and N-acetyl-p-benzoquinone imine. Our findings suggest that Lpcat3 is a potential therapeutic target for treating APAP-induced acute liver injury.

Extracellular Vesicles Derived from Adipose Mesenchymal Stem Cells Promote Peritoneal Healing by Activating MAPK-ERK1/2 and PI3K-Akt to Alleviate Postoperative Abdominal Adhesion

Peritoneal regeneration and repair can alleviate postoperative intraperitoneal adhesions, and mesenchymal stem cells (MSCs) have demonstrated the potential for peritoneal repair and regeneration. However, extracellular vesicles (EVs) are the main carriers for the MSC activity. Thus far, the roles of MSC-derived EVs on peritoneal repair are not well understood. To investigate the therapeutic effect of adipose-derived mesenchymal stem cell-derived EVs (ADSC-EVs) in peritoneal injuries, ADSC-EVs were injected in vivo via the tail vein of rats. The antiadhesion effects were evaluated following abdominal surgery. In addition, the levels of the peritoneal fibrinolysis system were determined via enzyme-linked immunosorbent assay. Expression differences in inflammatory and apoptotic markers were detected using immunofluorescence. The expression of extracellular matrix-related indexes and peritoneal healing were observed using immunohistochemistry. In vitro, rat peritoneal mesothelial cell proliferation was assessed via a 5-ethynyl-2-deoxyuridine assay. Cell migration was determined using scratch wound and transwell assays. Related signaling networks were estimated based on sequencing and bioinformatics analyses. The roles of the MAPK–ERK1/2 and PI3K–Akt signaling networks were analyzed using immunoblotting. This is the first report of the effectiveness of ADSC-EVs in the treatment of postoperative adhesions. ADSC-EVs were incorporated in vitro and induced rat peritoneal mesothelial cell proliferation and migration. This was mediated by stimulation of the MAPK–ERK1/2 and PI3K–Akt axes. ADSC-EVs promote the healing of the injured peritoneum, suggesting a promising therapeutic approach for peritoneal adhesions.

TAZ/WWTR1 mediates liver mesothelial-mesenchymal transition induced by stiff extracellular environment, TGF-β1, and lysophosphatidic acid

Mesothelial cells cover the surface of the internal organs and the walls of body cavities, facilitating the movement between organs by secretion of a lubricating fluid. Upon injury, mesothelial cells undergo a mesothelial-mesenchymal transition (MMT) and give rise to myofibroblasts during organ fibrosis, including in the liver. Although transforming growth factor-β1 (TGF-β1) was shown to induce MMT, molecular and cellular mechanisms underlying MMT remain to be clarified. In the present study, we examined how the extracellular environment, soluble factors, and cell density control the phenotype of liver mesothelial cells by culturing them at different cell densities or on hydrogels of different stiffness. We found that TGF-β1 does not fully induce MMT in mesothelial cells cultured at high cell density or in the absence of fetal bovine serum. Extracellular lysophosphatidic acid (LPA) synergistically induced MMT in the presence of TGF-β1 in mesothelial cells. LPA induced nuclear localization of WW domain-containing transcription regulator1 (WWTR1/TAZ) and knockdown of Taz, which suppressed LPA-induced MMT. Mesothelial cells cultured on stiff hydrogels upregulated nuclear localization of TAZ and myofibroblastic differentiation. Knockdown of Taz suppressed MMT of mesothelial cells cultured on stiff hydrogels, but inhibition of TGF-β1 signaling failed to suppress MMT. Our data indicate that TAZ mediates MMT induced by TGF-β1, LPA, and a stiff matrix. The microenvironment of a stiff extracellular matrix is a strong inducer of MMT.

Post-Operative Adhesions: A Comprehensive Review of Mechanisms

Post-surgical adhesions are common in almost all surgical areas and are associated with significant rates of morbidity, mortality, and increased healthcare costs, especially when a patient requires repeat operative interventions. Many groups have studied the mechanisms driving post-surgical adhesion formation. Despite continued advancements, we are yet to identify a prevailing mechanism. It is highly likely that post-operative adhesions have a multifactorial etiology. This complex pathophysiology, coupled with our incomplete understanding of the underlying pathways, has resulted in therapeutic options that have failed to demonstrate safety and efficacy on a consistent basis. The translation of findings from basic and preclinical research into robust clinical trials has also remained elusive. Herein, we present and contextualize the latest findings surrounding mechanisms that have been implicated in post-surgical adhesion formation.

Advancement of Biomaterial-Based Postoperative Adhesion Barriers

Postoperative peritoneal adhesion (PPA) is a prevalent incidence that generally happens during the healing process of traumatized tissues. It causes multiple severe complications such as intestinal obstruction, chronic abdominal pain, and female infertility. To prevent PPA, several antiadhesion materials and drug delivery systems composed of biomaterials are used clinically, and clinical antiadhesive is one of the important applications nowadays. In addition to several commercially available materials, like film, spray, injectable hydrogel, powder, or solution type have been energetically studied based on natural and synthetic biomaterials such as alginate, hyaluronan, cellulose, starch, chondroitin sulfate, polyethylene glycol, polylactic acid, etc. Moreover, many kinds of animal adhesion models, such as cecum abrasion models and unitary horn models, are developed to evaluate new materials' efficacy. A new animal adhesion model based on hepatectomy and conventional animal adhesion models is recently developed and a new adhesion barrier by this new model is also developed. In summary, many kinds of materials and animal models are studied; thus, it is quite important to overview this field's current progress. Here, PPA is reviewed in terms of the species of biomaterials and animal models and several problems to be solved to develop better antiadhesion materials in the future are discussed.

[Liver regeneration: resolved and problem issues]

Liver is an exceptional organ due to unique anatomical and physiological features, as well as advanced regenerative ability. Discovery of molecular mechanisms governing liver regeneration allowed researchers to use them to enhance liver regeneration. However, significant progress in this area was achieved through the introduction of gene therapy. In this manuscript, the authors consider stem cells for cell therapy and tissue engineering, as well as an alternative to liver transplantation.

Evaluation of adhesion barrier types in a rat hepatectomy-induced adhesion model

Background

Adhesion formation after hepatectomy creates problems for repeat hepatectomy. This study aimed to compare the effectiveness of a spray (AdSpray) and sheet adhesion barrier (Seprafilm) in a rat hepatectomy-induced adhesion model.

Methods

Thirty male Sprague-Dawley rats underwent partial resection of the left lateral liver lobe. They were randomly assigned to control (n = 10), AdSpray (n = 10), and Seprafilm groups. Seven days after surgery, the animals were sacrificed, and adhesions at the hepatic resection surface were blindly evaluated.

Results

In the control group, adhesions were formed in all 10 animals (100%), with a 69% adhesion extent (mean). In the AdSpray group, the incidence of adhesions (40%) and the adhesion extent (mean, 10%) were significantly lower than in the control group (incidence; p = 0.0147, adhesion extent; p = 0.0007). In the Seprafilm group, the incidence of adhesions was 70%. The adhesion extent of Seprafilm (mean, 30%) was significantly lower than in the control group (p = 0.0492). No significant differences were observed between the AdSpray and Seprafilm groups. As for histopathological examination, animals in the AdSpray group showed a similar healing profile to that of the control group without delayed healing and regeneration of mesothelial cells. In contrast, the Seprafilm group showed ongoing foreign body reaction to Seprafilm, and regeneration of mesothelial cells was immature at 7 days.

Conclusions

Both the spray-type gel and sheet adhesion barriers significantly reduced adhesion formation after hepatectomy. The spray-type adhesion barrier caused no adverse events and induced favorable healing. These adhesion barriers may be effective in hepatectomy. Further animal studies and clinical trials are required to determine their benefits in clinical use.

[Liver regeneration after resection in clinical and experimental conditions]

The researches devoted to postoperative liver regeneration and influence in this process were analyzed. Liver injury is followed by hypertrophy of residual liver parenchyma. The use of various cytokines is perspective for activation, acceleration and inhibition of liver recovery. Cellular technologies in the treatment of liver diseases can affect its repair. Moreover, these methods could make unnecessary resection and transplantation of liver in certain cases. It is generally accepted that the main effect of multipotent stromal cells (MSC) in liver failure is associated with their differentiation to the cellular elements of this organ. At the same time, recent reports revealed that MSC injection to the liver is followed by their quick death, dissemination to other organs and tissues or even elimination from the organism. Regeneration of non-parenchymal structures (vascular network and bile ducts) should be considered in addition to functional recovery of liver parenchyma after resection. Clarification of indications and contraindications for MSC therapy, as well as prevention of possible complications associated with cellular technologies are required.

Generation of mesothelial progenitor-like cells from mouse-induced pluripotent stem cells

Mesothelial cells, which cover the surface of visceral organs and serous cavities in mammals, play a crucial role in preventing adhesion. We previously reported that primary mesothelial progenitor cells (MPCs) can not only prevent postoperative adhesion but also promote liver regeneration after hepatectomy. Induced pluripotent stem cells (iPSCs) have the potential to be used for regenerative medicine. Here, we have established a differentiation protocol for mouse iPSC-derived MPCs (miMPCs) via the exposure to defined factors, as well as purification using MPC-specific cell surface antigens. Furthermore, the miMPCs had the ability to suppress postoperative adhesion and facilitate liver regeneration. This is the first report highlighting the generation of functional miMPCs, which may offer potential for de novo cell therapy.

Surgical adhesions in mice are derived from mesothelial cells and can be targeted by antibodies against mesothelial markers

Peritoneal adhesions are fibrous tissues that tether organs to one another or to the peritoneal wall and are a major cause of postsurgical and infectious morbidity. The primary molecular chain of events leading to the initiation of adhesions has been elusive, chiefly due to the lack of an identifiable cell of origin. Using clonal analysis and lineage tracing, we have identified injured surface mesothelium expressing podoplanin (PDPN) and mesothelin (MSLN) as a primary instigator of peritoneal adhesions after surgery in mice. We demonstrate that an anti-MSLN antibody diminished adhesion formation in a mouse model where adhesions were induced by surgical ligation to form ischemic buttons and subsequent surgical abrasion of the peritoneum. RNA sequencing and bioinformatics analyses of mouse mesothelial cells from injured mesothelium revealed aspects of the pathological mechanism of adhesion development and yielded several potential regulators of this process. Specifically, we show that PDPN+MSLN+ mesothelium responded to hypoxia by early up-regulation of hypoxia-inducible factor 1 alpha (HIF1α) that preceded adhesion development. Inhibition of HIF1α with small molecules ameliorated the injury program in damaged mesothelium and was sufficient to diminish adhesion severity in a mouse model. Analyses of human adhesion tissue suggested that similar surface markers and signaling pathways may contribute to surgical adhesions in human patients.

Mesothelial to mesenchyme transition as a major developmental and pathological player in trunk organs and their cavities

The internal organs embedded in the cavities are lined by an epithelial monolayer termed the mesothelium. The mesothelium is increasingly implicated in driving various internal organ pathologies, as many of the normal embryonic developmental pathways acting in mesothelial cells, such as those regulating epithelial-to-mesenchymal transition, also drive disease progression in adult life. Here, we summarize observations from different animal models and organ systems that collectively point toward a central role of epithelial-to-mesenchymal transition in driving tissue fibrosis, acute scarring, and cancer metastasis. Thus, drugs targeting pathways of mesothelium’s transition may have broad therapeutic benefits in patients suffering from these diseases.

Tim Koopmans and Yuval Rinkevich review recent findings linking the mesothelium’s embryonic programs that drive epithelial-to-mesenchyme transition with adult pathologies, such as fibrosis, acute scarring, and cancer metastasis. They highlight new avenues for drug development that would target pathways of the mesothelium’s mesenchymal transition.

Mesothelial cells and peritoneal homeostasis

The mesothelium was traditionally thought to be a simple tissue with the sole function of providing a slippery, nonadhesive, and protective surface to allow easy movement of organs within their body cavities. However, our knowledge of mesothelial cell physiology is rapidly expanding, and the mesothelium is now recognized as a dynamic cellular membrane with many other important functions. When injured, mesothelial cells initiate a cascade of processes leading either to complete regeneration of the mesothelium or the development of pathologies such as adhesions. Normal mesothelial healing is unique in that, unlike with other epithelial-like surfaces, healing appears diffusely across the denuded surface, whereas for epithelium healing occurs solely at the wound edges. This is because of a free-floating population of mesothelial cells which attach to the injured serosa. Taking advantage of this phenomenon, intraperitoneal injections of mesothelial cells have been assessed for their ability to prevent adhesion formation. This review discusses some of the functions of mesothelial cells regarding maintenance of serosal integrity and outlines the mechanisms involved in mesothelial healing. In addition, the pathogenesis of adhesion formation is discussed with particular attention to the potential role of mesothelial cells in both preventing and inducing their development.

The Role of Mesothelial Cells in Liver Development, Injury, and Regeneration

Mesothelial cells (MCs) cover the surface of visceral organs and the parietal walls of cavities, and they synthesize lubricating fluids to create a slippery surface that facilitates movement between organs without friction. Recent studies have indicated that MCs play active roles in liver development, fibrosis, and regeneration. During liver development, the mesoderm produces MCs that form a single epithelial layer of the mesothelium. MCs exhibit an intermediate phenotype between epithelial cells and mesenchymal cells. Lineage tracing studies have indicated that during liver development, MCs act as mesenchymal progenitor cells that produce hepatic stellate cells, fibroblasts around blood vessels, and smooth muscle cells. Upon liver injury, MCs migrate inward from the liver surface and produce hepatic stellate cells or myofibroblast depending on the etiology, suggesting that MCs are the source of myofibroblasts in capsular fibrosis. Similar to the activation of hepatic stellate cells, transforming growth factor β induces the conversion of MCs into myofibroblasts. Further elucidation of the biological and molecular changes involved in MC activation and fibrogenesis will contribute to the development of novel approaches for the prevention and therapy of liver fibrosis.

Ductular reactions in the liver regeneration process with local inflammation after physical partial hepatectomy

Partial hepatectomy models in mice have been widely used for liver regeneration studies. A typical procedure removes ~2/3 of the liver by lobular ligation without tissue dissection. However, hepatectomy in humans involves physical damage (ie, physical partial hepatectomy, PPHx). Therefore, the liver regeneration process after PPHx should involve reactions to acute local injury followed by systematic remodeling. To clarify the liver regeneration process after PPHx, we used a murine liver injury model that mimics the actual human surgical procedure. A 20-30% PPHx was performed by transection of the left lobe of the liver using an ultrasonically activated scalpel in mice. Gene expression and morphological characteristics were analyzed during the liver regeneration process. Liver weight continuously increased by hypertrophic reaction of hepatocytes, whereas Ki67 staining showed hepatocyte proliferation. At the transected border, emergence of ductular reactions, a representative process of hepatic tissue remodeling that contain liver stem/progenitor cells, were observed. Gene expression of the transected border and non-damaged lobes revealed that inflammatory cytokine- and extracellular matrix-associated genes were significantly upregulated at the transected border. Our PPHx model triggered local extracellular matrix remodeling that resulted in ductular reactions. These processes occurred during the tissue repair process in local inflammatory responses as well as compensatory hepatocyte hypertrophy of the entire liver. These findings may provide insight for elucidating the mechanism of tissue repair and regeneration of the liver after PPHx.

Extracellular-signal regulated kinase (Erk1/2), mitogen-activated protein kinase-activated protein kinase 2 (MK2) and tristetraprolin (TTP) comprehensively regulate injury-induced immediate early gene (IEG) response in in vitro liver organ culture

Differentiated hepatocytes are long-lived and normally do not undergo cell division, however they have the unique capacity to autonomously decide their replication fate after liver injury. In this context, the key players of liver regeneration immediately after injury have not been adequately studied. Using an in vitro liver culture system, we show that after liver injury, p38 mitogen-activated protein kinase (p38MAPK), mitogen-activated protein kinase-activated protein kinase 2 (MK2) and extracellular-signal regulated kinase (Erk)1/2 were activated within 15 min and continued to be phosphorylated for more than 2h. Both p38MAPK and Erk1/2 were activated at the edge of the cut as well as on the liver surface where the mesothelial cell sheet expresses several cytokines. Notably, in human liver Erk1/2 was also activated under the mesothelial cell sheet shortly after liver resections. Furthermore, in in vitro liver slice culture immediate early genes (IEGs) were upregulated within 1-2 h and the S phase marker proliferation-cell-nuclear-antigen (PCNA) appeared 24 h after injury. Although Erk1/2 was activated after injury, in MK2 depleted liver a set of IEGs, such as Dusp1, Cox2, or c-Myc and proliferation marker gene Ki67 were not induced. In addition, in immortalized hepatocyte cells, THLE-2, the same subset of genes was upregulated upon stimulation with lipopolysaccharide (LPS), but not in the presence of MK2 inhibitor. The protein level of tristetraprolin (TTP), a substrate for MK2 that plays a role in mRNA degradation, was increased in the presence of MK2 inhibitor. In this context, the depletion of TTP gene rescued Dusp1, Cox2, or c-Myc upregulation in the presence of MK2 inhibitor. These data imply that MK2 pathway is positively involved in Erk1/2 induced IEG response after liver injury. These data also suggest that in vitro liver culture may be a useful tool for measuring the proliferation potential of hepatocytes in individual liver.

Use of Mesothelial Cells and Biological Matrices for Tissue Engineering of Simple Epithelium Surrogates

Tissue-engineering technologies have progressed rapidly through last decades resulting in the manufacture of quite complex bioartificial tissues with potential use for human organ and tissue regeneration. The manufacture of avascular monolayered tissues such as simple squamous epithelia was initiated a few decades ago and is attracting increasing interest. Their relative morphostructural simplicity makes of their biomimetization a goal, which is currently accessible. The mesothelium is a simple squamous epithelium in nature and is the monolayered tissue lining the walls of large celomic cavities (peritoneal, pericardial, and pleural) and internal organs housed inside. Interestingly, mesothelial cells can be harvested in clinically relevant numbers from several anatomical sources and not less important, they also display high transdifferentiation capacities and are low immunogenic characteristics, which endow these cells with therapeutic interest. Their combination with a suitable scaffold (biocompatible, degradable, and non-immunogenic) may allow the manufacture of tailored serosal membranes biomimetics with potential spanning a wide range of therapeutic applications, principally for the regeneration of simple squamous-like epithelia such as the visceral and parietal mesothelium vascular endothelium and corneal endothelium among others. Herein, we review recent research progresses in mesothelial cells biology and their clinical sources. We make a particular emphasis on reviewing the different types of biological scaffolds suitable for the manufacture of serosal mesothelial membranes biomimetics. Finally, we also review progresses made in mesothelial cells-based therapeutic applications and propose some possible future directions.

All-trans retinoic Acid reduces joint adhesion formation: an experimental study in rats

Background

Intra-articular adhesion is a common complication in post-surgical knees. The formation of post-surgical joint adhesion could lead to serious conditions. All-trans retinoic acid (ATRA) is a physiological metabolite of vitamin A that has a wide range of biological activities. The aim of the study was to verify the effects of (ATRA) in preventing adhesions in the post-operative rat knee.

Material/Methods

Eighty healthy adult male Wistar rats underwent femoral condyle-exposing surgery. After surgery, cotton pads soaked with the vehicle or various concentrations of ATRA (0.1%, 0.05%, 0.025%) were applied to the surgery site for 5 min. The post-surgical knee joints were fixed with micro-Kirschner wires in a flexed position for 4 weeks. The rats were killed 4 weeks after surgery. The effect of ATRA on the prevention of intra-articular adhesion was evaluated using histological analyses, hydroxyproline content, visual score, and inflammatory factor activity evaluation.

Results

No obvious postoperative complications or signs of infection in the rats were observed. None of the rats died before the scheduled time. The rats in the 0.1% ATRA group showed better outcomes, as suggested by the visual scores, hydroxyproline contents, and inflammatory factors expressional levels, than the other 2 groups. The local application of 0.1% ATRA was able to suppress adhesions, collagen expression, and inflammatory activity in the post-surgical rat knees.

Conclusions

In the rat knee surgery model, the application of intra-articular ATRA was able to decrease intra-articular scar adhesion formation, collagen expression, and inflammatory activities. ATRA was found to work in a dose-dependent manner, with 0.1% being possible optimal concentration.