Each organ is thought to primarily comprise of 4 main cell types that form a minimal tissue module: parenchymal cells, endothelial cells, fibroblasts and macrophages. The liver is mainly constituted of hepatocytes (~60%), liver sinusoidal endothelial cells (LSECs) (~15%), liver-resident fibroblasts called stellate cells (~15%) and liver-resident macrophages called Kupffer cells (KCs) (~15%).Macrophages (Macs) are found in all tissues and perform unique functions that are essential to maintain homeostasis in their respective organ, such as synaptic pruning in the brain, recycling of surfactant in the lung or electrical conduction in the heart. Transcriptomic profiling has revealed that each tissue-resident Mac expresses a relatively unique gene expression profile controlled by a restricted set of transcription factors. Little is known, however, about the precise cell-cell circuits that underlie the tissue-specific imprinting of Macs. In the case of KCs, previous studies indicate that this identity and functionality is imprinted by the other cells that constitute the liver module (hepatocytes, LSECs and stellate cells) that together form the Kupffer cell niche.
The host lab has previously shown that the transcription factor LXRa controls 30% of liver-specific KC identity and is essential for KC development and survival. ID3, is a transcription factor that is highly expressed in KCs and conserved across species (human, mouse, pig, zebrafish,etc). We hypothesize that the cell-cell circuits within the sinusoidal liver module not only form the blueprint of liver homeostasis, but that perturbations in these cell-cell interactions will lead to the development of liver diseases. The Liver ID3ntity project sought to identify the molecular cues driving ID3 expression, a key transcription factor in KCs, and identify whether mice lacking these signals would display aberrant liver responses.
The overall objectives of this project were to: Design an in vivo CRISPR pipeline to screen and identify key genes driving ID3 expression, identify the cell-cell interactions and define the pathophysiological implications of these cell-cell interactions.
The effect of KCs on the steady-state identity of the other module cells remains almost completely unknown. Deciphering the reciprocal cell-cell interactions by which these cells imprint the liver sinusoidal identity on one another in vivo is not only key to understand liver biology, it also paves the way to the development of in vitro liver organoids that will more closely resemble the in vivo liver.
