Chaperone-mediated autophagy

About: Chaperone-mediated autophagy is a research topic. Over the lifetime, 434 publications have been published within this topic receiving 55025 citations. The topic is also known as: CMA.

Chaperone-Mediated Autophagy Markers in Parkinson Disease Brains

Abstract: Objective: To investigate chaperone-mediated autophagy in the pathogenesis of Parkinson disease (PD).Design: Postmortem observational study.Setting: University Department of Clinical Neuroscience, Institute of Neurology, University College London.Subjects: Postmortem samples from 7 PD, 6 Alzheimer disease (AD), and 8 control brains.Main Outcome Measure: Lysosomal-associated membrane protein 2A (LAMP2A) and heat shock cognate 70 (hsc70) protein levels were compared in the substantia nigra pars compacta and amygdala of PD, AD, and control brain samples. To provide insight into the turnover of alpha-synuclein, degradation pathways for this protein were studied in a dopaminergic cell line.Results: The expression levels of the chaperone-mediated autophagy proteins LAMP2A and hsc70 were significantly reduced in the substantia nigra pars compacta and amygdala of PD brains compared with age-matched AD and control brain samples. Lewy bodies in these regions contained autophagy-related proteins. We demonstrated that decreased LAMP2A levels in dopaminergic cell lines reduced chaperone-mediated autophagy activity and increased the half-life of alpha-synuclein.Conclusions: These findings suggest that there is reduced chaperone-mediated autophagy activity in the PD brain, provide evidence for the role of autophagy in PD pathogenesis and Lewy body formation, and suggest that this pathway may be a suitable therapeutic target in PD.

Glucocerebrosidase deficiency in substantia nigra of parkinson disease brains

Abstract: The lysosomal storage disorder Gaucher disease (GD) is caused by autosomal recessive mutations in the glucocerebrosidase (GBA) gene. GBA encodes a lysosomal enzyme (GCase) that catalyses the metabolism of the sphingolipid glucosylceramide to ceramide and glucose. Deficiency of GCase activity results in accumulation of substrate in the lysosomes of several tissues, including brain. Mutations in GBA result in 3 clinical manifestations. Type 1 GD occurs in both children and adults and predominantly impacts on the non-neuronal organs, whereas types 2 and 3 have an onset in childhood and adolescence, respectively, and exhibit neurological deficits.1 Parkinson disease (PD) is primarily characterized by the motor symptoms of resting tremor, bradykinesia, rigidity, and postural instability. Pathological hallmarks include loss of dopaminergic neurons from the substantia nigra (SN) and the presence of cytoplasmic inclusions known as Lewy bodies in the surviving cells of affected brain regions.2 Typical parkinsonism is among the neurological complications of GD (including type 1).3, 4 The neuropathology of GD brains includes the typical hallmarks of PD, such as cortical and brainstem Lewy bodies.5 Heterozygote carriers of GBA mutations also have an increased frequency of PD, and these mutations are the most common genetic risk factor for developing the disease.6–8 Although the pathogenesis of PD is still unknown, the accumulation of α-synuclein and other ubiquitinated proteins in Lewy bodies has implicated protein mishandling as a putative cause. The proteasome and lysosomes are the 2 principal mechanisms for degrading cellular constituents. Autophagy utilizes lysosomes to degrade long-lived proteins, misfolded/aggregated proteins, and organelles such as mitochondria.9 Defective autophagy and/or lysosomal depletion have been implicated in PD.10–13 Cellular or animal models of GCase deficiency have caused α-synuclein accumulation.14–18 GCase has also been suggested to bind directly with α-synuclein in lysosomes19 and the GCase substrate glucosylceramide stabilizes soluble oligomeric α-synuclein species.18 These observations have led to the notion that GCase deficiency might contribute to the α-synuclein aggregation characteristic of PD pathology. Despite the recognized association between GBA mutations and PD, it is unknown how heterozygous GBA mutations affect GCase activity in PD brains. In this paper, we provide the first report of the activity of GCase in several regions of PD brains from GBA mutation carriers and sporadic PD brains. GCase deficiency was greatest in the SN of PD brains with GBA mutations. This loss of activity was in part mediated by a decrease in GCase protein levels. GCase activity was also significantly decreased in the SN of sporadic PD brains.

Restoration of chaperone-mediated autophagy in aging liver improves cellular maintenance and hepatic function

Abstract: Chaperone-mediated autophagy (CMA), a mechanism for the lysosomal degradation of proteins, declines in aging cells. Using transgenic mice in which such a decline does not occur in the liver, the authors found that preserving CMA leads to reduced accumulation of damaged proteins and improved organ function in aged mice ( pages 909–910 ). Chaperone-mediated autophagy (CMA), a selective mechanism for degradation of cytosolic proteins in lysosomes, contributes to the removal of altered proteins as part of the cellular quality-control systems1,2. We have previously found that CMA activity declines in aged organisms and have proposed that this failure in cellular clearance could contribute to the accumulation of altered proteins, the abnormal cellular homeostasis and, eventually, the functional loss characteristic of aged organisms. To determine whether these negative features of aging can be prevented by maintaining efficient autophagic activity until late in life, in this work we have corrected the CMA defect in aged rodents. We have generated a double transgenic mouse model in which the amount of the lysosomal receptor for CMA, previously shown to decrease in abundance with age3, can be modulated. We have analyzed in this model the consequences of preventing the age-dependent decrease in receptor abundance in aged rodents at the cellular and organ levels. We show here that CMA activity is maintained until advanced ages if the decrease in the receptor abundance is prevented and that preservation of autophagic activity is associated with lower intracellular accumulation of damaged proteins, better ability to handle protein damage and improved organ function.

Degradation of lipid droplet-associated proteins by chaperone-mediated autophagy facilitates lipolysis

Abstract: Chaperone-mediated autophagy (CMA) selectively degrades a subset of cytosolic proteins in lysosomes. A potent physiological activator of CMA is nutrient deprivation, a condition in which intracellular triglyceride stores or lipid droplets (LDs) also undergo hydrolysis (lipolysis) to generate free fatty acids for energetic purposes. Here we report that the LD-associated proteins perilipin 2 (PLIN2) and perilipin 3 (PLIN3) are CMA substrates and their degradation through CMA precedes lipolysis. In vivo studies revealed that CMA degradation of PLIN2 and PLIN3 was enhanced during starvation, concurrent with elevated levels of cytosolic adipose triglyceride lipase (ATGL) and macroautophagy proteins on LDs. CMA blockage both in cultured cells and mouse liver or expression of CMA-resistant PLINs leads to reduced association of ATGL and macrolipophagy-related proteins with LDs and the subsequent decrease in lipid oxidation and accumulation of LDs. We propose a role for CMA in LD biology and in the maintenance of lipid homeostasis.

The chaperone-mediated autophagy receptor organizes in dynamic protein complexes at the lysosomal membrane.

Abstract: Chaperone-mediated autophagy (CMA) is a selective type of autophagy by which specific cytosolic proteins are sent to lysosomes for degradation. Substrate proteins bind to the lysosomal membrane through the lysosome-associated membrane protein type 2A (LAMP-2A), one of the three splice variants of the lamp2 gene, and this binding is limiting for their degradation via CMA. However, the mechanisms of substrate binding and uptake remain unknown. We report here that LAMP-2A organizes at the lysosomal membrane into protein complexes of different sizes. The assembly and disassembly of these complexes are a very dynamic process directly related to CMA activity. Substrate proteins only bind to monomeric LAMP-2A, while the efficient translocation of substrates requires the formation of a particular high-molecular-weight LAMP-2A complex. The two major chaperones related to CMA, hsc70 and hsp90, play critical roles in the functional dynamics of the LAMP-2A complexes at the lysosomal membrane. Thus, we have identified a novel function for hsc70 in the disassembly of LAMP-2A from these complexes, whereas the presence of lysosome-associated hsp90 is essential to preserve the stability of LAMP-2A at the lysosomal membrane.