In this reporting period of the project, we have 1) developed and characterized new cell and animal models of class 3 PI3K activation and inhibition; 2) progressed on detailing the molecular mechanisms of the non-canonical functions of class 3 PI3K and functionally interrogated their input in the cellular metabolic activities both in acute fasting and during physiological feeding cycles and 3) obtained first evidence on specific metabolic rearrangements in human rare liver diseases.
In first objective, we discovered that class 3 PI3K is important for metabolic adaptation to fasting. We found that its acute inactivation in liver, results in massive defects in gene transcription in response to fasting. We reported that this response is partially linked to activity of key transcription factor activated in fasting, a Glucocorticoid Receptor (Y. Shibayama et al., Acta Physiologica, 2022; highlighted in the editorial). We expanded these analyses by performing bulk transcriptomic, proteomics, and metabolomics analyses in liver of mice that were challenged by fasting. These analyses were fructuous and provided several candidates. We are now performing molecular validation studies in order to dissect how class 3 PI3K controls specific cellular metabolic activities in fasting in different ages of young and old male and female animals. Moreover, from cell to the organism scale, the metabolic demands fluctuate rhythmically relying on coordination between the circadian clock and nutrient sensing signaling pathways. Thus, in second objective, we progressed in understanding how class 3 PI3K expression and activity is changing around the clock. We also demonstrated its requirement for metabolic rhythmicity in liver. We are now investigating in details the molecular mechanisms of its potential crosstalk with the clock in different organs. We also apply our expertise of basic science in the field of nutrient sensing signaling and metabolism to investigate novel metabolic signatures on rare pediatric diseases with manifestations in liver such as biliary atresia (BA). BA is an uncurable disease that manifests as obliteration of the extrahepatic bile ducts and alteration of the intrahepatic biliary tree in neonates. Left untreated, it quickly progresses to cirrhosis and liver failure leading to death in the first 2 years of life. While rare (a worldwide incidence of ~1:20,000 live births), BA remains the most frequent cause of liver transplantation in children. In this funding period, we have established the biobank of patient derived material, generated patient derived cell models and animal models of BA that were instrumental in performing molecular analyses. Our findings in this direction have indicated potential therapeutic targets that we are in process of validation.
