Trehalose, a disaccharide present in many non-mammalian species, protects cells against various environmental stresses. Whereas some of the protective effects may be explained by its chemical chaperone properties, its actions are largely unknown. Here we report a novel function of trehalose as an mTOR-independent autophagy activator. Trehalose-induced autophagy enhanced the clearance of autophagy substrates like mutant huntingtin and the A30P and A53T mutants of ␣-synuclein, associated with Huntington disease (HD) and Parkinson disease (PD), respectively. Furthermore, trehalose and mTOR inhibition by rapamycin together exerted an additive effect on the clearance of these aggregate-prone proteins because of increased autophagic activity. By inducing autophagy, we showed that trehalose also protects cells against subsequent pro-apoptotic insults via the mitochondrial pathway. The dual protective properties of trehalose (as an inducer of autophagy and chemical chaperone) and the combinatorial strategy with rapamycin may be relevant to the treatment of HD and related diseases, where the mutant proteins are autophagy substrates.Trehalose is a non-reducing disaccharide found in many organisms, including bacteria, yeast, fungi, insects, invertebrates, and plants. It is the natural hemolymph sugar of invertebrates. It functions to protect the integrity of cells against various environmental stresses like heat, cold, desiccation, dehydration, and oxidation by preventing protein denaturation (1). Many of the stress-protecting properties of trehalose were discovered in yeast (2); however, it also has beneficial effects in mammals where it is not endogenously synthesized. For instance, it may be a valuable tool for cryopreservation of cells (1, 3). It is not clear how trehalose mediates many of its protective effects, but some may be via its ability to act as chemical chaperone and influence protein folding through direct protein-trehalose interactions (4). Trehalose inhibits amyloid formation of insulin in vitro (5) and prevents aggregation of ␤-amyloid associated with Alzheimer disease (6). Recently, trehalose was shown to inhibit polyglutamine (polyQ) 3 -mediated protein aggregation in vitro, reduce mutant huntingtin aggregates and toxicity in cell models and alleviate polyQ-induced pathology in the R6/2 mouse model of Huntington disease (HD) (7). This protective effect was suggested to be caused by trehalose binding to expanded polyQ and stabilizing the partially unfolded mutant protein.HD is an autosomal-dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion, which results in an abnormally long polyQ tract in the N terminus of the huntingtin protein. Asymptomatic individuals have 35 or fewer CAG repeats, whereas HD is caused by 36 or more repeats. HD and related polyQ expansion diseases are associated with the formation of intraneuronal inclusions (also known as aggregates) by the mutant proteins containing the expanded polyQ tracts. The toxicity of mutant huntingtin is thought to be exposed...

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Research into late embryogenesis abundant (LEA) proteins has been ongoing for more than 20 years but, although there is a strong association of LEA proteins with abiotic stress tolerance particularly dehydration and cold stress, for most of that time, their function has been entirely obscure. After their initial discovery in plant seeds, three major groups (numbered 1, 2 and 3) of LEA proteins have been described in a range of different plants and plant tissues. Homologues of groups 1 and 3 proteins have also been found in bacteria and in certain invertebrates. In this review, we present some new data, survey the biochemistry, biophysics and bioinformatics of the LEA proteins and highlight several possible functions. These include roles as antioxidants and as membrane and protein stabilisers during water stress, either by direct interaction or by acting as molecular shields. Along with other hydrophilic proteins and compatible solutes, LEA proteins might also serve as "space fillers" to prevent cellular collapse at low water activities. This multifunctional capacity of the LEA proteins is probably attributable in part to their structural plasticity, as they are largely lacking in secondary structure in the fully hydrated state, but can become more folded during water stress and/or through association with membrane surfaces. The challenge now facing researchers investigating these enigmatic proteins is to make sense of the various in vitro defined functions in the living cell: Are the LEA proteins truly multi-talented, or are they still just misunderstood?

LEA (late embryogenesis abundant) proteins in both plants and animals are associated with tolerance to water stress resulting from desiccation and cold shock. However, although various functions of LEA proteins have been proposed, their precise role has not been defined. Recent bioinformatics studies suggest that LEA proteins might behave as molecular chaperones, and the current study was undertaken to test this hypothesis. Recombinant forms of AavLEA1, a group 3 LEA protein from the anhydrobiotic nematode Aphelenchus avenae, and Em, a group 1 LEA protein from wheat, have been subjected to functional analysis. Heat-stress experiments with citrate synthase, which is susceptible to aggregation at high temperatures, suggest that LEA proteins do not behave as classical molecular chaperones, but they do exhibit a protective, synergistic effect in the presence of the so-called chemical chaperone, trehalose. In contrast, both LEA proteins can independently protect citrate synthase from aggregation due to desiccation and freezing, in keeping with a role in water-stress tolerance; similar results were obtained with lactate dehydrogenase. This is the first evidence of anti-aggregation activity of LEA proteins due to water stress. Again, a synergistic effect of LEA and trehalose was observed, which is significant given that non-reducing disaccharides are known to accumulate during dehydration in plants and nematodes. A model is proposed whereby LEA proteins might act as a novel form of molecular chaperone, or 'molecular shield', to help prevent the formation of damaging protein aggregates during water stress.