Dietary energy tissue specifically regulates endoplasmic reticulum chaperone gene expression in the liver of mice

A number of putative molecular chaperones seem to play essential roles in the correct folding, assembly and glycosylation of membrane and secreted proteins in the endoplasmic reticulum. We have shown that life span-extending dietary energy restriction significantly and specifically reduces GRP78 mRNA and protein by 50-75% in mice. Here, 5-mo-old female C3B10RF(1) mice were given free access to food after being fed 50% less dietary energy since weaning. Hepatic GRP78 mRNA increased linearly, reaching the same level after 2 wk as was found in the liver of 20-mo-old mice with free access to food. This increase took place with no change in body weight. The mRNA levels of endoplasmic reticulum, cytosolic and mitochondrial chaperones were determined in young (7-mo-old) and old (21- or 28-mo-old) female C3B10RF(1) mice. Each age group was either 50% energy restricted or was fed approximately 10% less energy than consumed by mice given free access to food. In young and old energy-restricted mice, hepatic expression of the endoplasmic reticulum chaperones ERp57 (37%), GRP170 (51%), ERp72 (43%), calreticulin (54%) and calnexin (23%) was significantly and specifically reduced. The GRP78, GRP94, GRP170, ERp57 and calnexin mRNA response to diet occurred reproducibly only in liver, and not in adipose, brain, heart, kidney, lung, muscle or small intestine. The mRNA for GRP75, a mitochondrial chaperone, HSC70, a cytoplasmic chaperone, protein disulfide isomerase, an endoplasmic reticulum chaperone, and C/EBP alpha, a transcription factor, was not regulated. Hepatic C/EBP beta was 15% higher in old energy-restricted mice. Thus the expression of nearly all endoplasmic reticulum chaperones responded rapidly and specifically to dietary energy in mice.