Doxycycline inducible overexpression systems: how to induce your gene of interest without inducing misinterpretations

The doxycycline inducible overexpression system is a highly flexible and widely used tool for both in vitro and in vivo studies. However, during the past decade, a handful of reports have explicitly called for caution when using this system. The raised concerns are based on the notion that doxycycline can impair mitochondrial function of mammalian cells and can alter properties such as cell proliferation. As such, experimental outcomes can be confounded with the side effects of doxycycline and valid interpretation can be seriously threatened. Today, no consensus seems to exist about how these problems should be prevented. Moreover, some of the strategies that have been used to cope with these difficulties can actually introduce additional problems that are related to genomic instability and genetic modification of the cells. Here, we elaborate on the above statements and clarify them by some basic examples taken from our personal wet-lab experience. As such, we provide a nuanced overview of the doxycycline inducible overexpression system, some of its limitations and how to deal with them.

A fully defined matrix to support a pluripotent stem cell derived multi-cell-liver steatohepatitis and fibrosis model

Chronic liver injury, as observed in non-alcoholic steatohepatitis (NASH), progressive fibrosis, and cirrhosis, remains poorly treatable. Steatohepatitis causes hepatocyte loss in part by a direct lipotoxic insult, which is amplified by derangements in the non-parenchymal cellular (NPC) interactive network wherein hepatocytes reside, including, hepatic stellate cells, liver sinusoidal endothelial cells and liver macrophages. To create an in vitro culture model encompassing all these cells, that allows studying liver steatosis, inflammation and fibrosis caused by NASH, we here developed a fully defined hydrogel microenvironment, termed hepatocyte maturation (HepMat) gel, that supports maturation and maintenance of pluripotent stem cell (PSC) derived hepatocyte- and NPC-like cells for at least one month. The HepMat-based co-culture system modeled key molecular and functional features of TGFβ-induced liver fibrosis and fatty-acid induced inflammation and fibrosis better than monocultures of its constituent cell populations. The novel co-culture system should open new avenues for studying mechanisms underlying liver steatosis, inflammation and fibrosis as well as for assessing drugs counteracting these effects.

Alternative Cell Sources for Liver Parenchyma Repopulation: Where Do We Stand?

Acute and chronic liver failure is a highly prevalent medical condition with high morbidity and mortality. Currently, the therapy is orthotopic liver transplantation. However, in some instances, chiefly in the setting of metabolic diseases, transplantation of individual cells, specifically functional hepatocytes, can be an acceptable alternative. The gold standard for this therapy is the use of primary human hepatocytes, isolated from livers that are not suitable for whole organ transplantations. Unfortunately, primary human hepatocytes are scarcely available, which has led to the evaluation of alternative sources of functional hepatocytes. In this review, we will compare the ability of most of these candidate alternative cell sources to engraft and repopulate the liver of preclinical animal models with the repopulation ability found with primary human hepatocytes. We will discuss the current shortcomings of the different cell types, and some of the next steps that we believe need to be taken to create alternative hepatocyte progeny capable of regenerating the failing liver.