**Abstract**

This chapter provides novel information about the survival features of hepatic resident stem/progenitor cells (NG2+ HSPs) during liver fibrosis/cirrhotic development. A well-defined diethylnitrosamine (DEN)-induced liver fibrosis/cirrhotic/ cancer mouse model was developed to evaluate the fate of the HSPs and its clinical implications. This model possess three time-zones during the disease development: fibrosis (3–5 weeks post-DEN), cirrhosis (6–10 weeks post-DEN), and cancers (up to 10 weeks post-DEN). During this process, the model represents histological patterns similar to those described in humans and shows better survival of the HSPs in the fibrotic zone, which was correlated with inflammatory signals, as compared to the cirrhotic zone. It has also been discovered that immune CD8+ T cells in the fibrotic zone are beneficial in liver fibrosis resolution, suggesting that the fibrotic time zone is important for mobilizing endogenous HSPs and cell-based therapy. As such, we hypothesize that clinical strategies in fibrotic/cirrhotic liver treatment are necessary either in time at the fibrotic phase or to adopt an approach of regulating HSP viability when the disease develops into the cirrhotic phase.

**Keywords:** apoptosis, diethylnitrosamine, hepatic stem/progenitor cells, inflammation, liver fibrosis/cirrhosis, proliferation

### **1. Introduction**

The healthy liver performs over 500 different functions to maintain its homeostasis [1, 2], and any assault could not only impact the architecture of hepatic cells [3] but also injure niche cells, like inflammatory and immune cells such as CD8-positive cytotoxic T lymphocyte subset (CD8+ T cells) which have been recently highlighted [4]. Liver cirrhosis is an end-stage liver disease (ESLD) and a major cause of morbidity and mortality globally [5]. It is often caused by acute liver injury or the progressive development of liver fibrosis or other chronic liver disease such as virus infection, etc. In China, the total number of patients with various types of chronic liver disease exceeds

300 million, and more than 1 million people die each year from ESLD [6]. According to the Centers for Disease Control (CDC), ESLD is the twelfth leading cause of death in the United States, with approximately 44,000 deaths per year [7]. For example, chronic hepatitis B virus (HBV) infection-mediated ESLD and inflammatory disease are global public health issues. It was estimated in 2017 that 257 million people live with chronic HBV infection, a prevalence of 3.5% [8], and there are 93 million people infected with HBV living in China [9]. Approximately 15–40% of patients with chronic HBV will develop liver cirrhosis, and 4–5% of patients may progress toward decompensated liver cirrhosis (DLC) [9], denoted in the chemical reagent diethylnitrosamine (DEN)-induced liver fibrosis/cirrhosis animal model at 6–10 weeks post-DEN in this chapter [9]. The 5-year mortality in patients with compensated liver cirrhosis (CLC), denoted as fibrotic phase (6–10 weeks post-DEN) in this chapter, is 14–20% and with DLC as high as 70–86% [5, 8, 9] which imposes a substantial health burden on many countries. It has been studied in animals that continuous activation of hepatic stellate cells (HSCs) leading to accumulation and over-deposition of the extracellular matrix (ECM) in the parenchymal liver compartment [10, 11] is a key mechanism for the liver from homeostasis to fibrosis (3–5 weeks post-DEN) to cirrhosis (6–10 weeks post-DEN) and eventually the outcomes of liver cancer like hepatocyte cellular carcinoma (HCC, >10 weeks post-DEN), which is the most common liver cancer (**Figure 1A**). In humans, there are generally four categories from healthy liver to HCC, including homeostasis, compensation liver cirrhosis phase (CLC), decompensation liver cirrhosis phase (DLC), and liver cancer (HCC) (**Figure 1A**). Of note, there are currently none of available treatments to specifically target other than liver transplantation. Unfortunately, there are simply not enough donated livers to meet the demands; therefore, research on nonsurgical strategies to prevent the development of chronic liver disease is urgently needed. Stem cell therapy is one of the options for treating liver fibrosis/cirrhosis [12] and can partially recover liver function [13, 14]. However, the problem is that clinical trials using stem cells to treat liver fibrosis/cirrhosis, especially for DLC treatment, seem not to be so successful [12, 15–17] because of the short-term survival of cells in DLC microenvironment [18].

#### **Figure 1.**

*Application of DEN produces a relatively sharp line in different phases during the model disease development. (A) Evolution of ESLD during disease development. (B) Masson trichrome staining identified pathogenesis (blue, boxes) in hepatic sections at different phases of DEN-induced liver fibrosis-cirrhosis-cancers (HCC, an arrow) in a mouse model. Scale bar = 100 μm.*

*Survival Fate of Hepatic Stem/Progenitor and Immune Cells in a Liver Fibrosis/Cirrhosis… DOI: http://dx.doi.org/10.5772/intechopen.106220*

Therefore, if animal models with liver fibrosis/cirrhosis laboratory scores capture patients with the same disease, pathological features would be very meaningful for future clinical stem cell-based therapeutic strategies. As such, we have for the first time successfully set up a liver fibrosis/cirrhosis/cancer animal model in C57BL/6 mice in 2015, demonstrating histological patterns similar to those described in humans during the disease process [19]. Interestingly, this model shows that during the disease process, the resident HSPs (denoted as NG2+ HSPs) [18] respond to DENmediated inflammatory signals differently, resulting in different fates during liver fibrosis/cirrhosis development. More interestingly, immune CD8+ T cells have also been found recently to involve in improving liver fibrotic load [20]. In this chapter, we have provided novel information on the correlation of hepatic inflammatory activity with microenvironment resident HSPs (NG2<sup>+</sup> HSPs) and how HSP survival fate are also related to the hepatic resident CD8+ T cells during the disease development on this model.
