Study the mechanism whereby factors produced by liver macrophages regulate insulin sensitivity.

We have recently discovered that mice fed a high fat diet (HFD) become rapidly obese and insulin resistant independently of liver inflammation, which was thought to be an important driver in obesity-induced insulin resistance. On the other hand, depletion studies have shown that removing liver macrophages (LMs) prevents insulin resistance induced by obesity, suggesting an important role of LMs in the regulation of insulin sensitivity. Using RNAseq, we identified genes specifically expressed by liver macrophages, whose expression significantly increases with obesity and insulin resistance. We then took advantage of a powerful and unique tool, called glucan encapsulated RNAi particles (GeRP), that deliver siRNA and silence genes specifically in macrophages in vivo.

This technology is based on small interfering RNA (siRNA) encapsulated within glucan particles derived from baker’s yeast. By using intraperitoneal injections, we showed that GeRPs delivered siRNA and silenced genes specifically in macrophages in the adipose tissue of obese mice. However, by using intravenous administration, we showed that GeRPs delivered siRNA and silenced genes in LMs but not in hepatocytes or macrophages within other tissues.

Image: Scanning electron microscopy image of primary mouse macrophages (pink) phagocytozing glucan particles (green). Myriam Aouadi et al. developed a siRNA delivery technology to silence gene expression specifically in macrophages in vivo.

Using this unique method, we found that silencing genes of interest specifically in LMs improves insulin sensitivity in obese mice. This project has so far confirmed that liver macrophages can play a role in the regulation of insulin sensitivity independantly of inflammation. This opened a new avenue towards the discovery of the multiple roles of immune cells other than only the inflammatory response.

Identify distinct phenotypes and functions of macrophages in liver and adipose tissue.

Macrophages are able to modulate their properties upon contact with different cell types as well as extracellular matrix. Their intrinsic heterogeneity during differentiation is compounded by reciprocal interactions with neighbouring cells, including other macrophages. In many different tissues, macrophages can occupy different anatomical niches and perform specialized functions even within the same organ. Emerging data suggest that macrophages acquire specialized functions, which are tailored for assisting local homeostasis, within each particular organ.

We use scRNAseq, metabolomics, flow cytometry, CytOF and in situ transcriptomic to study the heterogeneity of resident macrophage in liver and adipose tissue in health and metabolic disease.

Decoding the phenotype of macrophages through the study of non-coding RNA

We aim at identifying dysregulated genes but also non-coding RNAs such as microRNAs, enhancer RNAs, and long non-coding RNAs which have recently emerged as important regulators of gene expression, and which expression have been associated with several diseases.

Using the Global Run-On sequencing (GRO-seq) to directly measure rates of nascent transcription genome-wide, we propose to identify all transcript, genes and non-coding RNAs dysregulated in LMs in obesity that could be involved in the development of insulin resistance.

We are especially interested in enhancers, which are regions of DNA important for the regulation of genes transcription, and can be transcribed as non-coding RNAs called enhancer-derived RNAs (eRNAs).

The eRNAs can regulate the expression of the nearby gene, and have also been shown to be superior markers for active enhancers because of their small size and high dynamic ranges.

The mining of the GRO-seq data for eRNAs transcription to map functional enhancers, combined with genome-wide de novo motif analysis performed at sites of eRNAs dysregulation in LMs from obese and insulin resistant mice compared to lean mice, will allow us to identify the transcription factor(s) that could be involved in gene dysregulation in LMs in obesity.

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