Is trehalose an autophagic inducer? Unraveling the roles of non-reducing disaccharides on autophagic flux and alpha-synuclein aggregation

Abstract

Autophagy is a pivotal intracellular process by which cellular macromolecules are degraded upon various stimuli. A failure in the degradation of autophagic substrates such as impaired organelles and protein aggregates leads to their accumulations, which are characteristics of many neurodegenerative diseases. Pharmacological activation of autophagy has thus been considered a prospective therapeutic approach for treating neurodegenerative diseases. Among a number of autophagy-inducing agents, trehalose has received attention for its beneficial effects in different disease models of neurodegeneration. However, how trehalose promotes autophagy has not been fully revealed. We investigated the influence of trehalose and other disaccharides upon autophagic flux and aggregation of α-synuclein, a protein linked to Parkinson's disease. In differentiated human neuroblastoma and primary rat cortical neuron culture models, treatment with trehalose and other disaccharides resulted in accumulation of lipidated LC3 (LC3-II), p62, and autophagosomes, whereas it decreased autolysosomes. On the other hand, addition of Bafilomycin A1 to trehalose treatments had relatively marginal effect, an indicative of autophagic flux blockage. In concordance with these results, the cells treated with trehalose exhibited an incremental tendency in α-synuclein aggregation. Secretion of α-synuclein was also elevated in the culture medium upon trehalose treatment, thereby significantly increasing intercellular transmission of this protein. Despite the substantial increase in α-synuclein aggregation, which normally leads to cell death, cell viability was not affected upon treatment with trehalose, suggesting an autophagy-independent protective function of trehalose against protein aggregates. This study demonstrates that, although trehalose has been widely considered an autophagic inducer, it may be actually a potent blocker of the autophagic flux.

Trehalose as a promising therapeutic candidate for the treatment of Parkinson's disease

“…It has been proposed that trehalose can act as an autophagy inducer through an mTOR-independent pathway and enhances the clearance of aggregate-prone proteins like α-synuclein, mutant huntingtin, and prion protein (PrP Sc ; Aguib et al, 2009;Beranger, Crozet, Goldsborough, & Lehmann, 2008;Sarkar, Davies, Huang, Tunnacliffe, & Rubinsztein, 2007). However, as the GLUT8 transporter is tissue-specific and neurons do not contain SLC2A8 (GLUT8) in their plasma membrane, this pathway may not occur in the brain tissue (Yoon et al, 2017). In a recent report, trehalose induced autophagy in hepatocytes through an AMPK-dependent pathway, downstream of GLUT8 .…”

“…In a recent report, trehalose induced autophagy in hepatocytes through an AMPK-dependent pathway, downstream of GLUT8 . However, as the GLUT8 transporter is tissue-specific and neurons do not contain SLC2A8 (GLUT8) in their plasma membrane, this pathway may not occur in the brain tissue (Yoon et al, 2017). Also, trehalose can activate TFEB to enhance ALP by decreasing Akt activity (Palmieri et al, 2017).…”

“…Yoon et al, 2017). Similarly, neuropathological analysis of brains from a mouse model of LB disease by Tanji et al revealed that trehalose increased the accumulation of the autophagic marker LC3-II in the brain with no apparent effect on the abnormal aggregation of α-synuclein, but it decreased the level of insoluble α-synuclein in mice.…”

Uncovering active modulators of native macroautophagy through novel high-content screens

“…Several drugs purported to stimulate autophagy—including trehalose 76, 77 , metformin 78, 79 80, 81 , and carbamezapine 82, 83, 84 —failed to do so in our Dendra2-LC3 cell line. Despite promising results in mouse models of Huntington’s disease 76 , ALS 85 , and Parkinson’s disease 86 , evidence that trehalose induces autophagy is variable, with some studies claiming that the drug actually inhibits flux 87, 88, 69 . Likewise, the ability of carbamazepine to enhance autophagic flux and prevent neurodegeneration was based upon changes in steady-state levels of autophagy intermediates 83, 84 .…”

Potential therapeutics of Alzheimer's diseases: New insights into the neuroprotective role of trehalose‐conjugated beta sheet breaker peptides

“…Recently, the ability of trehalose to induce autophagy and to stimulate lysosomal biogenesis, improving neuronal survival upon exposure to alpha‐synuclein preformed fibrils, has been questioned . Concerns have been raised also towards the hypothesized action of trehalose as an autophagic inducer and controller of alpha‐synuclein aggregation …”