Project description:The intestine is the critical organ not only for processing and resorbing nutrients from ingested food but also for defending the organism from external stresses such as pathogens. These functions are mainly carried out by the epithelium which is constantly being self-renewed throughout adult life. Intestinal epithelial homeostasis is maintained through well-controlled cell proliferation of the stem cells and transient amplifying cells and the apoptotic degeneration of epithelial cells, mostly at or near the tip of the villi. Many genes and pathways have been found to influence intestinal epithelial cell proliferation. Among them is the mTORC1 signaling pathway, whose activation is known to increase cell proliferation. Here, we report the first intestinal epithelial specific knockout (IEC-KO) of an amino acid transporter capable of activating mTORC1. We show that the transporter, slc7a5, is highly expressed in the intestinal crypt and slc7a5 IEC-KO leads to expected reduction in mTORC1 signal in the crypt or even in intestinal organoids in vitro. Surprisingly, slc7a5 IEC-KO leads to increased proliferation of both transit amplifying cells and crypt base stem cells but a reduction in the secretory cells, particularly mature Paneth cells in the crypt base. Our scRNA-seq and electron microscopic analyses reveals that slc7a5 IEC-KO causes dedifferentiation of the Paneth cells, leading to drastically reduced secretory granules and lysozyme expression without affecting the overall Paneth cell number. We further show that slc7a5 IEC-KO mice are prone to induced colitis due to this loss of Paneth cell differentiation. We propose a model where slc7a5 regulates secretory cell differentiation to affect stem cell niche and/or inflammatory response to regulate cell proliferation in the crypts.
Project description:The effects of loss of the large neutral amino acid transporter Slc7a5 (aka Lat1) on mouse embryonic development were investigated. Slc7a5 fl/fl mice harbouring two copies of the Slc7a5 targeted allele (exon 1 of Slc7a5 flanked with two loxP sites), were crossed with a mouse line ubiquitously expressing cre recombinase under the Bal1 promoter (Bal1-cre) to obtain a global Slc7a5 knockout mouse (Poncet et al. 2014 PLoS One 9: e89547). Heterozygous Slc7a5+/- C57Bl/6 mice were viable and fertile and were bred free of Bal1-cre in subsequent generations. Slc7a5 -/- embryos were obtained by inter-crossing heterozygotes and a phenotype was apparent by E9.5. To identify the first cellular processes affected by Slc7a5 loss RNAseq was carried out to compare transcriptomes of null and wildtype E8.5 embryos.
Project description:Oncogenic KRAS mutations and inactivation of the APC tumour suppressor co-occur in colorectal cancer (CRC). Despite efforts to target mutant KRAS directly, most therapeutic approaches focus upon downstream pathways, albeit with limited efficacy. Moreover, mutant KRAS alters the basal metabolism of cancer cells, rendering them ‘addicted’ to glutamine supporting proliferation. We show that concomitant mutation of Apc and Kras in the mouse intestinal epithelium profoundly rewires metabolism, increasing glutamine consumption. Furthermore, SLC7A5, a glutamine antiporter, is critical for colorectal tumorigenesis in models of both early and late-stage metastatic disease. Mechanistically, SLC7A5 maintains intracellular amino-acid levels following KRAS activation through transcriptional and metabolic reprogramming. This supports the increased demand for bulk protein synthesis that underpins enhanced proliferation of KRAS-mutant cells. Moreover, targeting protein synthesis, via mTORC1 inhibition, cooperates with Slc7a5 deletion to abrogate growth of established KRAS-mutant tumours. Together, these data suggest SLC7A5 as an attractive target for therapy-resistant KRAS-mutant CRC.
Project description:HuR stimulates the activity of intestinal stem cells by enhancing Paneth cell function via activation of mitochondrial metabolism, thus promoting renewal of the intestinal mucosa
Project description:The impact of removal of Mll1 in intestinal Paneth cells expressing an constitutively active form of beta-catenin (beta-cateninGOF) was analysed in 4 pairs of sorted Paneth cells of Lgr5-CreERT2; beta-cateninGOF;Mll1+/- (control) and Lgr5-CreERT2; beta-cateninGOF;Mll1-/- (knockout) mice at 10 days after tamoxifen-induced mutagenesis. Using 75-base-pair reads, around 30 million reads per sample with comparable unique mapped reads (52-93%) were obtained. To analyze differentially expressed genes, we applied DESeq2 analysis to the RNA-seq dataset. Differentially expressed genes in beta-cateninGOF; Mll1-/- versus beta-cateninGOF; Mll1+/- Paneth cells showed both up- and downregulation of genes at a false discovery rate (FDR) of 10%. This included a global increase in the expression of goblet cell-specific genes. Downregulated genes included specific markers of Paneth cells, indicating that ablation of Mll1 in Paneth cells shifted their identity towards a mixed Paneth-goblet cell fate.
Project description:The single cell level Paneth cell transcriptome under gnotobiotic condition has not been resolved. How gut microbiome modulates Paneth cell transcriptome at single cell level in germ-free mice was not known. We used a flow cytometry method to isolate highly pure ileal Paneth cells from germ free (GF) Paneth cell reporter mice (Lyz1-3'UTR-IRES-CreER) and from exGF Paneth cell reporter mice that were transplanted with wild type C57B/l6 mouse gut microbiota (exGF+B6M). These isolated Paneth cells were subjected to single cell RNA sequencing by 10xGenomics.
Project description:Morphological patterns of Paneth cells are a cellular biomarker in western Crohn’s disease (CD) patients. They integrate genetics and environmental factors, and are associated with outcomes. To broaden the applications of Paneth cell phenotype, identification of novel genetic determinants and clinical validation in other ethnic groups is critical.