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Continuous turnover of intracellular components by autophagy is necessary to preserve cellular homeostasis in all tissues. Alterations in macroautophagy, main responsible for bulk autophagic degradation, have been proposed to contribute to pathogenesis in Huntington’s disease (HD), a genetic neurodegenerative disorder caused by an expanded polyglutamine tract in huntingtin protein. However, the precise mechanism behind macroautophagy malfunctioning in HD is poorly understood. In this work, using cellular and mouse models of HD and cells from HD patients, we have identified a primary defect in the ability of autophagic vacuoles to recognize cytosolic cargo in HD cells. Autophagic vacuoles form at normal or even enhanced rates in HD cells and are adequately eliminated by lysosomes, but they fail to efficiently trap cytosolic cargo in their lumen. We propose that inefficient engulfment of cytosolic components by autophagosomes is responsible for their slower turnover, functional decay and accumulation inside HD cells.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson’s disease (PD). In this work, we demonstrate that LRRK2 can be degraded in lysosomes by chaperone-mediated autophagy (CMA), whereas the most common pathogenic mutant form of LRRK2, G2019S, is poorly degraded by this pathway. In contrast to typical CMA substrates, lysosomal binding of both wild-type and several pathogenic mutant LRRK2 proteins is enhanced in the presence of other CMA substrates, which interferes with the organization of the CMA translocation complex, resulting in defective CMA. Cells respond to such LRRK2-mediated CMA compromise by increasing levels of the CMA lysosomal receptor as seen in neuronal cultures and brains of LRRK2 transgenic mice, iPSC-derived dopaminergic neurons, and brains of mutant LRRK2 PD patients. This novel LRRK2 self-perpetuating inhibitory effect on CMA could underlie toxicity in PD by compromising the degradation of alpha-synuclein, another PD-related protein degraded by this pathway.

SUMMARY Macroautophagy is a lysosomal degradative pathway that maintains cellular homeostasis by turning over cellular components. Here, we demonstrate a role for autophagy in hypothalamic agouti-related peptide (AgRP) neurons in the regulation of food intake and energy balance. We show that starvation-induced hypothalamic autophagy mobilizes neuron-intrinsic lipids to generate endogenous free fatty acids, which in turn regulate AgRP levels. The functional consequences of inhibiting autophagy are the failure to upregulate AgRP in response to starvation, and constitutive increases in hypothalamic levels of pro-opiomelanocortin and its cleavage product α-melanocyte stimulating hormone that typically contribute to a lean phenotype. We propose a new conceptual framework for considering how autophagy-regulated lipid metabolism within hypothalamic neurons may modulate neuropeptide levels to have immediate effects on food intake, as well as long-term effects on energy homeostasis. Regulation of hypothalamic autophagy could become an effective intervention in conditions such as obesity and the metabolic syndrome.

SUMMARY Chaperone-mediated autophagy (CMA), a selective form of degradation of cytosolic proteins in lysosomes, contributes to maintenance of proteostasis and to the cellular adaptation to stress. CMA substrates are delivered by a cytosolic chaperone to the lysosomal surface, where upon unfolding, are internalized through a membrane translocation complex. The molecular components that participate in CMA substrate targeting and translocation are well characterized but those involved in CMA regulation remain mostly unknown. In this study, we have identified that CMA is under the positive control of the phosphatase PHLPP1 that associates with the lysosomal membrane and counteracts the inhibitory effect of mTORC2 on CMA. Lysosomal Akt, a target of the mTORC2/PHLPP1 kinase-phosphatase pair, modulates CMA activity by controlling the dynamics of assembly and disassembly of the CMA translocation complex at the lysosomal membrane. The lysosomal mTORC2/PHLPP1/Akt axis could become a target to restore CMA dysfunction in aging and disease.

Chaperone-mediated autophagy is a selective mechanism for degradation of soluble cytosolic proteins in lysosomes that distinguishes itself from other autophagic pathways by the selectivity with which CMA substrates are targeted for degradation. The recent molecular dissection of this autophagic pathway and the development of experimental models with compromised CMA have unveiled the important contribution of this pathway to protein quality control. In fact, CMA activation seems to be a common mechanism of cellular defense against proteotoxicity.

Autophagy degrades cytoplasmic contents to achieve cellular homeostasis. We show that selective loss of autophagy in hypothalamic proopiomelanocortin (POMC) neurons decreases a-melanocyte-stimulating hormone (MSH) levels, promoting adiposity, impairing lipolysis and altering glucose homeostasis. Ageing reduces hypothalamic autophagy and a-MSH levels, and aged-mice phenocopy, the adiposity and lipolytic defect observed in POMC neuron autophagy-null mice. Intraperitoneal isoproterenol restores lipolysis in both models, demonstrating normal adipocyte catecholamine responsiveness. We propose that an unconventional, autophagosome-mediated form of secretion in POMC neurons controls energy balance by regulating a-MSH production. Modulating hypothalamic autophagy might have implications for preventing obesity and metabolic syndrome of ageing.