Redundant and Antagonistic Roles of XTP3B and OS9 in Decoding Glycan and Non-glycan Degrons in ER-Associated Degradation.

Glycoproteins engaged in unproductive folding in the ER are marked for degradation by a signal generated by progressive demannosylation of substrate N-glycans that is decoded by ER lectins, but how the two lectins, OS9 and XTP3B, contribute to non-glycosylated protein triage is unknown. We generated cell lines with homozygous deletions of both lectins individually and in combination. We found that OS9 and XTP3B redundantly promote glycoprotein degradation and stabilize the SEL1L/HRD1 dislocon complex, that XTP3B profoundly inhibits the degradation of non-glycosylated proteins, and that OS9 antagonizes this inhibition.

Tryptophan metabolism: entering the field of aging and age-related pathologies.

Aging is an important risk factor for many debilitating diseases, including cancer and neurodegeneration. In model organisms, interfering with metabolic signaling pathways, including the insulin/insulin-like growth factor (IGF) 1 (IIS) and TOR pathways, can protect against age-related pathologies and increase lifespan. Recent studies in multiple organisms have implicated tryptophan metabolism as a powerful regulator of age-related diseases and lifespan.

Delaying aging and the aging-associated decline in protein homeostasis by inhibition of tryptophan degradation.

Toxicity of aggregation-prone proteins is thought to play an important role in aging and age-related neurological diseases like Parkinson and Alzheimer's diseases. Here, we identify tryptophan 2,3-dioxygenase (tdo-2), the first enzyme in the kynurenine pathway of tryptophan degradation, as a metabolic regulator of age-related α-synuclein toxicity in a Caenorhabditis elegans model. Depletion of tdo-2 also suppresses toxicity of other heterologous aggregation-prone proteins, including amyloid-β and polyglutamine proteins, and endogenous metastable proteins that are sensors of normal protein homeostasis.

A FRET sensor for non-invasive imaging of amyloid formation in vivo.

Misfolding and aggregation of amyloidogenic polypeptides lie at the root of many neurodegenerative diseases. Whilst protein aggregation can be readily studied in vitro by established biophysical techniques, direct observation of the nature and kinetics of aggregation processes taking place in vivo is much more challenging. We describe here, however, a Förster resonance energy transfer sensor that permits the aggregation kinetics of amyloidogenic proteins to be quantified in living systems by exploiting our observation that amyloid assemblies can act as energy acceptors for variants of fluorescent proteins.

Identification of MOAG-4/SERF as a regulator of age-related proteotoxicity.

Fibrillar protein aggregates are the major pathological hallmark of several incurable, age-related, neurodegenerative disorders. These aggregates typically contain aggregation-prone pathogenic proteins, such as amyloid-beta in Alzheimer's disease and alpha-synuclein in Parkinson's disease. It is, however, poorly understood how these aggregates are formed during cellular aging.

Chaperone proteostasis in Parkinson's disease: stabilization of the Hsp70/alpha-synuclein complex by Hip.

The ATP-dependent protein chaperone heat-shock protein 70 (Hsp70) displays broad anti-aggregation functions and has a critical function in preventing protein misfolding pathologies. According to in vitro and in vivo models of Parkinson's disease (PD), loss of Hsp70 activity is associated with neurodegeneration and the formation of amyloid deposits of alpha-synuclein (alphaSyn), which constitute the intraneuronal inclusions in PD patients known as Lewy bodies. Here, we show that Hsp70 depletion can be a direct result of the presence of aggregation-prone polypeptides.