Ana Belén Plata-Gómez, María Crespo, Celia de la Calle Arregui, Lucía de Prado-Rivas, Guadalupe Sabio, Alejo Efeyan.
We present a protocol for measuring the activity of the mechanistic target of rapamycin (mTOR) pathway in ex vivo isolated mouse primary hepatocytes. It can be used as a tool for genetic, pharmacological, metabolomic, and signal transduction procedures.
We discuss critical aspects for improving yield, viability, and modulation of the mTOR pathway. This protocol can be adapted to other signaling cascades and is compatible with multiple readouts.
Celia de la Calle Arregui, Ana Belén Plata-Gómez, Nerea Deleyto-Seldas, Fernando García, Ana Ortega-Molina, Julio Abril-Garrido, Elena Rodriguez, Ivan Nemazanyy, Laura Tribouillard, Alba de Martino, Eduardo Caleiras, Ramón Campos-Olivas, Francisca Mulero, Mathieu Laplante, Javier Muñoz, Mario Pende, Guadalupe Sabio, David M. Sabatini & Alejo Efeyan.
The mechanistic target of rapamycin complex 1 (mTORC1) integrates cellular nutrient signaling and hormonal cues to control metabolism. We have previously shown that constitutive nutrient signaling to mTORC1 by means of genetic activation of RagA (expression of GTP-locked RagA, or RagAGTP) in mice resulted in a fatal energetic crisis at birth.
Herein, we rescue neonatal lethality in RagAGTP mice and find morphometric and metabolic alterations that span glucose, lipid, ketone, bile acid and amino acid homeostasis in adults, and a median lifespan of nine months. Proteomic and metabolomic analyses of livers from RagAGTP mice reveal a failed metabolic adaptation to fasting due to a global impairment in PPARα transcriptional program. These metabolic defects are partially recapitulated by restricting activation of RagA to hepatocytes, and revert by pharmacological inhibition of mTORC1. Constitutive hepatic nutrient signaling does not cause hepatocellular damage and carcinomas, unlike genetic activation of growth factor signaling upstream of mTORC1.
In summary, RagA signaling dictates dynamic responses to feeding-fasting cycles to tune metabolism so as to match the nutritional state.
CD69 regulates lymphocyte egress from the thymus and lymph nodes through cis-interactions and the downregulation of surface sphingosine-1-phosphate (S1P) receptor-1 (S1P1). However, its role in the regulation of cell egress from bone marrow has not been extensively studied.
mTOR pathway activation in bone marrow (Image: Magdalena Leiva).
We show here that CD69 targeting induced rapid and massive mobilization of BM leukocytes, which was inhibited by desensitization to S1P with FTY720. This mobilization was reproduced with anti-human CD69 mAb treatment of mice expressing human CD69. In this strain, the mobilization occurred to the same extent as that induced by AMD3100. The anti-human CD69 treatment highly increased LSK and CLP cell proliferation and numbers, both in the periphery and in the BM, and also augmented S1P1 and CXCR4 expression. Additionally, increased mTOR, p70S6K, S6, and 4E-BP1 phosphorylation was detected after in vivo anti-CD69 treatment in the bone marrow. Importantly, mTOR inhibition with rapamycin inhibited anti-huCD69-induced mobilization of hematopoietic stem and progenitor cells (HSPCs).
Together, our results indicated that CD69 targeting induces not only mobilization but also high proliferation of HSPCs, and thus is crucial for precursor cell replenishment over time. These results suggest that anti-CD69 mAbs are putative novel candidates for mobilization strategies.