Long-Lived Mice with Reduced Growth Hormone Signaling Have a Constitutive Upregulation of Hepatic Chaperone-Mediated Autophagy

Chaperone-mediated autophagy (CMA) is a selective, vesicle-independent, lysosomal degradation pathway for intracellular proteins. CMA modulates proteomic organization through selective protein degradation, with targets including metabolic enzymes, regulators of cell growth, and neurodegeneration-related proteins. CMA activity is low in <i>ad libitum</i>-fed rodents but is increased by prolonged fasting (&gt;16 h). AKT negatively regulates CMA activity at the lysosomal membrane by phosphorylating and inhibiting the CMA regulator GFAP. We have previously reported that long-lived <i>Pou1f1/Pit1</i> mutant (Snell) mice and <i>ghr</i> (growth hormone receptor) knockout mice (<i>ghr</i> KO) have lower AKT activity when fed compared to littermate controls, suggesting the hypothesis that these mice have increased baseline CMA activity. Here, we report that liver lysosomes from fed Snell dwarf mice and <i>ghr</i> KO mice have decreased GFAP phosphorylation and increased CMA substrate uptake activity. Liver lysosomes isolated from fed Snell dwarf mice and <i>ghr</i> KO mice injected with the protease inhibitor leupeptin had increased accumulation of endogenous CMA substrates, compared to littermate controls, suggesting an increase in CMA <i>in vivo</i>. Mice with liver-specific ablation of GH (growth hormone) signaling did not have increased liver CMA, suggesting that a signaling effect resulting from a loss of growth hormone in another tissue causes enhanced CMA in Snell dwarf and <i>ghr</i> KO mice. Finally, we find Snell dwarf mice have decreased protein levels (in liver and kidney) of CIP2A, a well-characterized CMA target protein, without an associated change in <i>Cip2a</i> mRNA. Collectively, these data suggest that CMA is enhanced downstream of an endocrine change resulting from whole-body ablation of GH signaling.