Functional Recellularization of Acellular Rat Liver Scaffold by Induced Pluripotent Stem Cells: Molecular Evidence for Wnt/B-Catenin Upregulation

Exploring the roles of non-coding RNAs in liver regeneration

Liver regeneration (LR) is a complex process encompassing three distinct phases: priming, proliferation phase and restoration, all influenced by various regulatory factors. After liver damage or partial resection, the liver tissue demonstrates remarkable restorative capacity, driven by cellular proliferation and repair mechanisms. The essential roles of non-coding RNAs (ncRNAs), predominantly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNA (circRNA), in regulating LR have been vastly studied. Additionally, the impact of ncRNAs on LR and their abnormal expression profiles during this process have been extensively documented. Mechanistic investigations have revealed that ncRNAs interact with genes involved in proliferation to regulate hepatocyte proliferation, apoptosis and differentiation, along with liver progenitor cell proliferation and migration. Given the significant role of ncRNAs in LR, an in-depth exploration of their involvement in the liver's self-repair capacity can reveal promising therapeutic strategies for LR and liver-related diseases. Moreover, understanding the unique regenerative potential of the adult liver and the mechanisms and regulatory factors of ncRNAs in LR are crucial for improving current treatment strategies and exploring new therapeutic approaches for various liver-related diseases. This review provides a brief overview of the LR process and the ncRNA expression profiles during this process. Furthermore, we also elaborate on the specific molecular mechanisms through which multiple key ncRNAs regulate the LR process. Finally, based on the expression characteristics of ncRNAs and their interactions with proliferation-associated genes, we explore their potential clinical application, such as developing predictive indicators reflecting liver regenerative activity and manipulating LR processes for therapeutic purposes.

Strategies for decellularization, re-cellularIzation and crosslinking in liver bioengineering

Liver transplantation is the only definitive treatment for end-stage liver disease and its availability is restricted by organ donor shortages. The development of liver bioengineering provides the probability to create a functional alternative to reduce the gap in organ demand and supply. Decellularized liver scaffolds have been widely applied in bioengineering because they can mimic the native liver microenvironment and retain extracellular matrix (ECM) components. Multiple approaches including chemical, physical and biological methods have been developed for liver decellularization in current studies, but a full set of unified criteria has not yet been established. Each method has its advantages and drawbacks that influence the microstructure and ligand landscape of decellularized liver scaffolds. Optimizing a decellularization method to eliminate cell material while retaining as much of the ECM intact as possible is therefore important for biological scaffold applications. Furthermore, crosslinking strategies can improve the biological performance of scaffolds, including reinforcing biomechanics, delaying degradation in vivo and reducing immune rejection, which can better promote the integration of re-cellularized scaffolds with host tissue and influence the reconstruction process. In this review, we aim to present the different liver decellularization techniques, the crosslinking methods to improve scaffold characteristics with crosslinking and the preparation of soluble ECM.

Recent progresses in neural tissue engineering using topographic scaffolds

Neural tissue engineering as alternatives to recover damaged tissues and organs is getting more and more attention due to the lack of regeneration ability of natural tissue nervous system after injury. Particularly, topographic scaffolds are one of the critical elements to guide nerve orientation and reconnection with characteristics of mimic the natural extracellular matrix. This review focuses on scaffolds preparation technologies, topographical features, scaffolds-based encapsulations delivery strategies for neural tissue regeneration, biological functions on nerve cell guidance and regeneration, and applications of topographic scaffolds in vivo and in vitro. Here, the recent developments in topographic scaffolds for neural tissue engineering by simulating neural cell topographic orientation and differentiation are presented. We also explore the challenges and future perspectives of topographical scaffolds in clinical trials and practical applications.

Advances in Recellularization of Decellularized Liver Grafts with Different Liver (Stem) Cells: Towards Clinical Applications

Liver transplantation is currently the only curative therapy for patients with acute or chronic liver failure. However, a dramatic gap between the number of available liver grafts and the number of patients on the transplantation waiting list emphasizes the need for valid liver substitutes. Whole-organ engineering is an emerging field of tissue engineering and regenerative medicine. It aims to generate transplantable and functional organs to support patients on transplantation waiting lists until a graft becomes available. It comprises two base technologies developed in the last decade; (1) organ decellularization to generate a three-dimensional (3D) extracellular matrix scaffold of an organ, and (2) scaffold recellularization to repopulate both the parenchymal and vascular compartments of a decellularized organ. In this review article, recent advancements in both technologies, in relation to liver whole-organ engineering, are presented. We address the potential sources of hepatocytes and non-parenchymal liver cells for repopulation studies, and the role of stem-cell-derived liver progeny is discussed. In addition, different cell seeding strategies, possible graft modifications, and methods used to evaluate the functionality of recellularized liver grafts are outlined. Based on the knowledge gathered from recent transplantation studies, future directions are summarized.

A Comprehensive Review on Collagen Type I Development of Biomaterials for Tissue Engineering: From Biosynthesis to Bioscaffold

Collagen is the most abundant structural protein found in humans and mammals, particularly in the extracellular matrix (ECM). Its primary function is to hold the body together. The collagen superfamily of proteins includes over 20 types that have been identified. Yet, collagen type I is the major component in many tissues and can be extracted as a natural biomaterial for various medical and biological purposes. Collagen has multiple advantageous characteristics, including varied sources, biocompatibility, sustainability, low immunogenicity, porosity, and biodegradability. As such, collagen-type-I-based bioscaffolds have been widely used in tissue engineering. Biomaterials based on collagen type I can also be modified to improve their functions, such as by crosslinking to strengthen the mechanical property or adding biochemical factors to enhance their biological activity. This review discusses the complexities of collagen type I structure, biosynthesis, sources for collagen derivatives, methods of isolation and purification, physicochemical characteristics, and the current development of collagen-type-I-based scaffolds in tissue engineering applications. The advancement of additional novel tissue engineered bioproducts with refined techniques and continuous biomaterial augmentation is facilitated by understanding the conventional design and application of biomaterials based on collagen type I.

Insights into the use of genetically modified decellularized biomaterials for tissue engineering and regenerative medicine

Various modifications have been performed on biomaterials to improve their applications in tissue engineering and regenerative medicine. However, the challenges of immunogenicity and biocompatibility existed since the application of biomaterials. As a method to solve this problem, the decellularization process removes most living cells from biomaterials to minimize their immunogenicity; and preserves the native structures and compositions that favour cell growth and the subsequent construction of functional tissue. On the other hand, genetic modification of biomaterials aims to achieve specific functions (low immunogenicity, osteogenesis, etc.) or analyse the genetic mechanisms underlying some diseases (cardiac dysfunction, liver fibrosis, etc.). The combination of decellularization and gene modification is highly superior to biomaterials; thus, we must obtain a deeper understanding of these novel biomaterials. In this review, we summarize the fabrication approaches and current applications of genetically modified decellularized biomaterials and then discuss their disadvantages and corresponding future perspectives.

Decellularized Organ-Derived Scaffold Is a Promising Carrier for Human Induced Pluripotent Stem Cells-Derived Hepatocytes

Human induced pluripotent stem cells (hiPSCs) are a promising cell source for elucidating disease pathology and therapy. The mass supply of hiPSC-derived cells is technically feasible. Carriers that can contain a large number of hiPSC-derived cells and evaluate their functions in vivo-like environments will become increasingly important for understanding disease pathogenesis or treating end-stage organ failure. hiPSC-derived hepatocyte-like cells (hiPSC-HLCs; 5 × 10⁸) were seeded into decellularized organ-derived scaffolds under circumfusion culture. The scaffolds were implanted into immunodeficient microminiature pigs to examine their applicability in vivo. The seeded hiPSC-HLCs demonstrated increased albumin secretion and up-regulated cytochrome P450 activities compared with those in standard two-dimensional culture conditions. Moreover, they showed long-term survival accompanied by neovascularization in vivo. The decellularized organ-derived scaffold is a promising carrier for hiPSC-derived cells for ex vivo and in vivo use and is an essential platform for regenerative medicine and research.

Natural Scaffolds Used for Liver Regeneration: A Narrative Update

Annually chronic liver diseases cause two million death worldwide. Although liver transplantation (LT) is still considered the best therapeutic option, the limited number of donated livers and lifelong side effects of LT has led researchers to seek alternative therapies. Tissue engineering (TE) as a promising method is considered for liver repair and regeneration. TE uses natural or synthetic scaffolds, functional somatic cells, multipotent stem cells, and growth factors to develop new organs. Biological scaffolds are notable in TE because of their capacity to mimic extracellular matrices, biodegradability, and biocompatibility. Moreover, natural scaffolds are classified based on their source and function in three separate groups. Hemostat-based scaffolds as the first group were reviewed for their application in coagulation in liver injury or surgery. Furthermore, recent studies showed improvement in the function of biological hydrogels in liver regeneration and vascularity. In addition, different applications of natural scaffolds were discussed and compared with synthetic scaffolds. Finally, we focused on the efforts to improve the performance of decellularized extracellular matrixes for liver implantation.

A new strategy for the decellularization of whole organs by hydrostatic pressure

Tissue engineering has been able to develop novel decellularization-recellularization techniques, which facilitates the research for the generation of functional organs. This is based in the initial obtention of the organ's extracellular matrix (ECM). Therefore, any improvement in the decellularization process would have a positive impact in the results of the recellularization process. Nevertheless, commonly the methods and equipment employed for this process are expensive and thus limit the access of this technique to various research groups globally.

AIM

To develop a decellularization technique with the exclusive use of hydrostatic pressure of detergent solutions, to have an easily accessible and low-cost technique that meets the basic requirements of acellularity and functionality of the ECM.

METHODS

This experimental study was performed in 10 male Wistar rats, obtaining the liver to carry out serial washes, with 1, 2 and 3% Triton X-100 solutions and 0.1% SDS. The washes were performed by using a Gravity Perfusion System (GPS), which assured us a continuous hydrostatic pressure of 7.5 mmHg. The obtained ECM was processed using stains and immunostaining to determine the residual cell content and preservation of its components.

RESULTS

The staining showed a removal of cellular and nuclear components of approximately 97% of the acellular ECM, with an adequate three-dimensional pattern of collagen and proteoglycans. Furthermore, the acellular ECM allowed the viability of a primary hepatocyte culture.

CONCLUSIONS

The use of the GPS decellularization technique allowed us to obtain an acellular and functional ECM, drastically reducing experimentation costs. This article is protected by copyright. All rights reserved.