From form to function – how liver cells mature

A new study by the Meissner and Hnisz labs, published in Developmental Cell, reveals in new detail the genetic programs that guide liver cells as they develop into fully functional hepatocytes. The findings could have implications for biotechnology and regenerative medicine.

From breakfast to after-work drinks and even while you sleep, your liver works around the clock to metabolize nutrients, break down fats, detoxify your body, and store energy to keep you going. Hepatocytes make up most of the liver’s mass and carry out its primary functions. Liver diseases are rising globally, and loss of hepatocyte function is life-threatening. Although hepatocytes can be grown in the lab with stem-cell-based approaches, their practical application remains limited. 

“We lack a comprehensive understanding of the regulators and signals that induce the maturation of embryonic hepatocytes into functional adult hepatocytes,” explains Atsuhiro Taguchi, one of the study’s first authors and a former postdoc in the Meissner lab. “Consequently, stem-cell-derived hepatocytes more closely resemble an embryonic state and lack the expression of key metabolic genes required for hepatocyte function.” 

In their current study, the team first identified developmentally late-onset transcriptional regulators by analyzing the global gene expression profiles of hepatocytes from embryonic to adult stages, gaining deeper insight into how hepatocytes mature into fully functional cells. They then used a Cas9-based gene-activation screen in cultured mouse embryonic hepatocytes  and integrated single-cell RNA sequencing with multiple bioinformatic approaches to functionally test the identified candidates.

“In essence, we identified the gene Nr1i3 as an activator of metabolic gene elements, and Nfix as a key regulator that helps suppress the embryonic genetic program,” explains Alexandre Magalhães, another first author and a postdoc in the Hnisz lab. 

The scientists also considered a phenomenon called zonation. The mature liver has a distinct functional architecture in which different regions perform different metabolic activities. This spatial organization is crucial for the liver to carry out its diverse functions efficiently. The team reasoned that fully inducing zonation-specific functions would require an activation strategy tailored to the distinct microenvironments within the zone.

“We boosted late-onset transcriptional regulators that are activated in specific regions of the liver, along with local signaling factors. This combination triggered an unprecedented activation of the metabolic gene network,” says Taguchi. “Our findings show that maturation is not just a whole-body process — it also depends on the local microenvironment, even within a single organ.” 

Although the findings were generated in mouse models, they hold promise for human applications. Recent studies have shown that Nfix is also expressed in human adult hepatocytes but is notably underrepresented in stem-cell-derived hepatocytes. Therefore, forced activation of the identified regulators may help enhance the functional maturation of lab-generated hepatocytes.  Such improved  hepatocytes could advance biotechnology, regenerative medicine, and organoid systems for basic research. “Overall, our study is an important step toward creating truly mature hepatocytes in vitro,” concludes Taguchi.