Multiomics assessment of dietary protein titration reveals altered hepatic glucose utilization

Dietary protein restriction (PR) has rapid effects on metabolism including improved glucose and lipid homeostasis, via multiple mechanisms. Here, we investigate responses of fecal microbiome, hepatic transcriptome, and hepatic metabolome to six diets with protein from 18% to 0% of energy in mice. PR alters fecal microbial composition, but metabolic effects are not transferable via fecal transplantation. Hepatic transcriptome and metabolome are significantly altered in diets with lower than 10% energy from protein. Changes upon PR correlate with calorie restriction but with a larger magnitude and specific changes in amino acid (AA) metabolism. PR increases steady-state aspartate, serine, and glutamate and decreases glucose and gluconeogenic intermediates. 13C6 glucose and glycerol tracing reveal increased fractional enrichment in aspartate, serine, and glutamate. Changes remain intact in hepatic ATF4 knockout mice. Together, this demonstrates an ATF4-independent shift in gluconeogenic substrate utilization toward specific AAs, with compensation from glycerol to promote a protein-sparing response. [Display omitted] •Physiologic and molecular responses to protein restriction (PR) are dose responsive•PR below 10% of energy produces the strongest responses•Glucose is used for serine, aspartate, and glutamate synthesis upon PR•Metabolic and molecular changes upon PR are independent of hepatic ATF4 MacArthur et al. use multiple unbiased methods to investigate metabolic and molecular responses across six levels of dietary protein restriction in mice. The authors show that many key hepatic responses occur below 10% protein energy and promote ATF4-independent rewiring of glucose metabolism to support serine, aspartate, and glutamate synthesis.