Recently, Prof. Zhang Zhihong from Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology published a research paper entitled Mesoscale visualization of three-dimensional microvascular architecture and immunocyte distribution in intact mouse liver lobes in the journal Theranostics, and this work was selected as a Cover Paper in Volume 12 (Figure 1). The study developed a fast and fluorescence-preserving transparency method for liver clearing, and acquired the three-dimensional (3D) distribution information of blood vessels and immune cells in the intact hepatic lobe via confocal imaging and light sheet imaging.
Figure 1. The cover of Theranostics
The liver is the most important metabolic and detoxification organ in the body. The high incidence of refractory disease in the liver is closely related to the unique anatomical structure, complex vascular network, and immune tolerance status of the liver. The changes in blood vessels and the imbalance of the immune environment in the liver always occur in hepatic diseases, such as hepatitis, hepatic fibrosis, and liver metastasis. The liver has a complex cross-scale vasculature, ranging from liver sinusoids at the micron level to liver vessels at the millimeter level. A detailed analysis of the 3D anatomical structure of the hepatic circulation at different scales is meaningful for understanding liver function, vascular modeling, hemodynamics, and role in various liver pathologies. Meanwhile, the liver is also an immune organ. Dendritic cells (DCs) and macrophages are strategically positioned in the liver and constitute a tight defense network, which plays a unique role in hepatic immune defense and hepatic immune regulation. Imaging the arrangement of DCs/macrophages in an intact liver lobe at single-cell resolution will contribute to uncovering the function and heterogeneity of DCs/macrophages in liver physiology and pathology.
To investigate the morphology of hepatic lobules and the relationship between the arrangement of immune cells and the vascular system, the team developed a fast and fluorescence-preserving transparency method, denoted liver-CUBIC. Based on the liver-CUBIC method, this research quantitatively analyzed the 3D spatial distribution of vasculature and the DCs/macrophages in an intact liver lobe. The team reported that the overall morphology of the hepatic lobules tended to be oblate ellipsoids, particularly in the interior of the liver lobes. In the intact liver lobule, the hepatic sinusoids exhibited heterogeneous arrangement and intricate loop structure, and the hepatic sinusoids preferred a random and decentralized honeycomb network. Hepatic fibrosis induced the change of the lobular feature from a classical lobular feature to a portal lobular feature with increased sinusoidal density, and altered the morphology of the sinusoidal structure with increased sinusoidal branches and loops in the lobule.
The team also reported that CD11c+ DCs in the liver followed a lognormal distribution in the hepatic lobules, skewing toward the lobular boundary in a steady state via simultaneous visualization of immune cells and the vasculature in the intact lobe. CCl4-induced chronic liver injury promoted CD11c+ DC rearrangement at the lobular border before the formation of liver fibrosis, and a large number of CD11c+ cells distributed around the portal lobular border region (or around the CV).
The liver is also highly prone to tumor metastasis. Investigating the tumor-immune cell crosstalk in the intact lobe is helpful to uncover the spatial location characteristics and the molecular mechanism of tumor metastasis in the liver. Through whole-mount imaging of tumor-immune cell-vascular crosstalk in intact lobes based on liver-CUBIC, the researchers demonstrated that the accumulation of CX3CR1+CCR2+F4/80+ macrophages was closely related to the growth of metastatic cells at the early stage of tumor metastasis. Importantly, colorectal cells mobilized CX3CR1+CCR2+F4/80+ macrophage accumulation at liver micrometastases via CCL2 secretion, and the interruption of CCL2-induced macrophage accumulation inhibited early colonization of metastasis in the liver.
In summary, whole-mount imaging of the sinusoidal network and DC/macrophage arrangements through the liver-CUBIC approach provide a powerful platform and new knowledge for understanding hepatic circulatory properties and immune surveillance in the liver.
