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Lrtm1 - A Novel Sensor of Insulin Signaling and Regulator of Metabolism and Activity

ABSTRACT: Insulin regulates glucose uptake and metabolism in muscle via the insulin receptor. Here we show that Lrtm1 (Leucine Rich Repeats and Transmembrane Domains 1), a protein of unknown function enriched in insulin-responsive metabolic tissues, senses changes in insulin signaling in muscle and serves as a regulator of metabolic response. Thus, whole-body Lrtm1 deficient mice exhibit reduced fat mass, increased lean mass, and enhanced glucose tolerance and insulin sensitivity compared to control mice, under both chow and high fat diet conditions. Lrtm1 whole-body deficiency also affects dopamine signaling in the brain leading to hyperactivity. The improvements in glucose and insulin tolerance, but not the behavioral or body composition changes, are also observed in skeletal muscle-specific Lrtm1 knockout mice. The effects are independent of the classical insulin receptor-Akt signaling. Thus, Lrtm1 senses changes in insulin receptor signaling and serves as a novel post-receptor regulator of metabolic and behavioral activity.

ORGANISM(S): Mus musculus

PROVIDER: GSE281831 | GEO | 2025/04/30

REPOSITORIES: GEO

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Project description:Identification and validation of the pathways and functions regulated by the orphan nuclear receptor, ROR alpha1, in skeletal muscle The retinoic acid receptor-related orphan receptor (ROR) alpha has been demonstrated to regulate lipid metabolism. We were interested in the physiologically relevant roles, and pathways regulated by RORalpha1 action in skeletal muscle. This major mass organ accounts for ~40% of the total body mass, and significant levels of lipid catabolism, glucose disposal and energy expenditure. We utilized the strategy of targeted muscle specific expression of a truncated (dominant negative) RORalphaâDE in transgenic mice, to investigate RORalpha1 signalling (and function) in this peripheral tissue. Expression profiling and pathway analysis indicated that RORalpha regulated genes involved in: (i) lipid and carbohydrate metabolism, cardiovascular and metabolic disease; and (ii) the LXR nuclear receptor signaling pathway and, (iii) the Akt and AMPK signaling cascades. This analysis was extensively validated by rigorous qPCR analysis using TaqMan Low Density Arrays, coupled to rigorous statistical analysis (with Empirical Bayes, and Benjamini-Hochberg). Moreover, westerns and metabolic profiling were utilized to validate the genes, proteins and pathways (lipogenic, Akt, AMPK and fatty acid oxidation) involved in the regulation of metabolism by RORalph1. The identified genes and pathways were in concordance with the demonstration of hyperglycemia, glucose intolerance, attenuated insulin stimulated phosphorylation of Akt, and impaired glucose uptake in the transgenic heterozygous Tg-RORalphaâDE animals. In conclusion, we propose that RORalpha1 is involved in regulating the Akt2-AMPK signalling pathways in the context of lipid homeostasis in skeletal muscle. Total RNA was compared from quadriceps femoris of both transgenic and wild type mice. Transgenic mice contained a truncated version of human RORalpha1 (RORalpha1delDE) where the entire E region and part of the hinge/D region have been removed. This transgene is driven by a skeletal muscle specific human skeletal alpha-actin (HSA) promoter.

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Lrtm1 - A Novel Sensor of Insulin Signaling and Regulator of Metabolism and Activity

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