Scientists from Kyoto University, Japan, have developed an integrated gut-liver-on-a-chip platform as an in-vitro human model for the study of non-alcoholic fatty liver disease (NAFLD). The authors co-cultured human gut and liver cells and connected them via microfluidics to mimic the human gut-liver axis (GLA). The gut and liver mimicking co-cultured cells exhibit protective effects from apoptosis compared to mono-cultured cells, which exhibit induced apoptosis when treated with free fatty acids (FFAs). The FFAs-treated gut and liver cells exhibit an accumulation of intracellular lipid droplets, as revealed by phenotypic and genomic expression analyses. They also exhibit increased gene expression related to the cellular response to endoplasmic reticulum stress and copper ions. This new Organ-on-chips (OOC) platform will aid in understanding and developing treatments for NAFLD.
Non-Alcoholic Fatty Liver Disease and why we need iGLC
Non-alcoholic fatty liver disease is a life-threatening chronic illness that further leads to hepatic cirrhosis, cancer, and cardiovascular diseases. Due to the involvement of multiple organs in the disease, treatment development has been met with several challenges. As of now, liver transplantation, which is hugely expensive and often difficult to arrange for, is the only cure for patients with severe liver diseases. The disease mechanisms of fatty liver disease remain largely elusive due to the complexity involved in the processes at multiple layers, known as the multiple-hit theory. Processes at the cellular level, like fat accumulation, oxidative stress, endoplasmic reticulum stress, and genetic modifications, are all significant contributors to disease development, as are insulin resistance and inflammatory responses in multiple organs. Developing treatments for fatty liver disease will require intervention at various stages. Thus a thorough and combined understanding of the mechanism can aid in the therapeutics for NAFLD.
The authors chose to concentrate on the gut-liver axis, the GLA, as it is one of the crucial regions for the development and progression of NAFLD. The gut and liver are interlinked, both physiologically as well as pathologically. The gut microbiome and dietary carbohydrates are known to accelerate NAFLD. GLA dysfunction like bacterial overgrowth, intestinal dysbiosis, and others are caused by NAFLD. Thus, these are points of therapeutic targets, but no commercial treatment is available as of now. This is because preclinical animal models do not account well for the multiple hit theory. Thus, the need for the development of a robust yet simplified model system for studying the mechanisms of NAFLD to aid in drug design and the development of therapeutics.
Organs-on-chips, also known as micro-physiological systems (MPSs), are crucial for disease modeling as well as in-vitro preclinical testing. OOCs are based on microfluidics technology that enables precise control of fluids as well as the three-dimensional architecture of flow channels. The spatiotemporal control of the cellular microenvironment is enabled by this technology. Paracrine and endocrine signaling can also be modeled using the circulation of the cell culture medium capabilities. OOCs, in combination with OMICS approaches, can yield a better understanding and quantitative insights into the underlying biological mechanisms of the disease. Previous efforts to recapitulate the crosstalk in the GLA using invitro techniques have limitations in designing. Thus, the authors developed iGLC, an improved and robust OOC platform for the analysis of NAFLD.
Integrated Gut-Liver-Chip platform: iGLC
The simplified in-vitro human model of GLA, iGLC, has the following components:
- The platform has microvalves and a micro pump that enable individual access to cell culture chambers.
- A closed medium circulation flow is maintained to interconnect the gut and liver cells.
The following figure illustrates the design of the platform.
Insights into NAFLD using iGLC
The design of the platform enabled the authors to investigate the crosstalk between the cell cultures of the gut and liver. This generated the following insights into the disease development and progression in NAFLD:
- Co-cultured Hep-G2 ( liver-mimicking cells) and Caco-2(gut-mimicking cells) show a significant difference in gene expression profiles when compared to monoculture cells, thereby highlighting the significance f the crosstalk.
- When treated with FFAs under co-cultured conditions, there was a significant reduction in apoptotic Caco-2 cells and HepG2 cells compared to monoculture conditions.
- The authors performed single-cell profiling analysis, and the mRNA-seq analysis revealed that HepG2 cells co-cultured with Caco-2 cells show increased gene expression related to the cell cycle.
- Under co-culture conditions, FFA-treated HepG2 cells showed a reduction in gene expression associated with cell-cell adhesion.
It is important to note that such changes allude to an imbalance in the cell cycle due to disruptions in metabolic signaling, thereby causing disease. Thus, these findings could be potential targets for drug development and therapeutics for NAFLD.
The development of the iGLC platform is remarkable progress in the field of liver diseases. The authors designed an in-vitro human model of the GLA for recapitulating the physiology and pathology of NAFLD. Future works combining the iGLC platform and OMICS approaches can lead to the development and design of drugs for NAFLD. The platform can be customized to study other gut-related diseases, such as irritable bowel disease (IBD), which have no experimental settings for their study. Needless to say, this OOC platform design involving the crosstalk between different cell lines will open doors to study diseases involving multi-organs and thus contribute to better global health and quality of life.
Article Source: Reference Paper
Banhita is a consulting scientific writing intern at CBIRT. She's a mathematician turned bioinformatician. She has gained valuable experience in this field of bioinformatics while working at esteemed institutions like KTH, Sweden, and NCBS, Bangalore. Banhita holds a Master's degree in Mathematics from the prestigious IIT Madras, as well as the University of Western Ontario in Canada. She's is deeply passionate about scientific writing, making her an invaluable asset to any research team.