Senescent cells perturb intestinal stem cell differentiation through Ptk7 induced noncanonical Wnt and YAP signaling.

Cellular senescence and the senescence-associated secretory phenotype (SASP) are implicated in aging and age-related disease, and SASP-related inflammation is thought to contribute to tissue dysfunction in aging and diseased animals. However, whether and how SASP factors influence the regenerative capacity of tissues remains unclear. Here, using intestinal organoids as a model of tissue regeneration, we show that SASP factors released by senescent fibroblasts deregulate stem cell activity and differentiation and ultimately impair crypt formation. We identify the secreted N-terminal domain of Ptk7 as a key component of the SASP that activates non-canonical Wnt / Ca2+ signaling through FZD7 in intestinal stem cells (ISCs). Changes in cytosolic [Ca2+] elicited by Ptk7 promote nuclear translocation of YAP and induce expression of YAP/TEAD target genes, impairing symmetry breaking and stem cell differentiation. Our study discovers secreted Ptk7 as a factor released by senescent cells and provides insight into the mechanism by which cellular senescence contributes to tissue dysfunction in aging and disease.

Identifying polyglutamine protein species in situ that best predict neurodegeneration.

Polyglutamine (polyQ) stretches exceeding a threshold length confer a toxic function to proteins that contain them and cause at least nine neurological disorders. The basis for this toxicity threshold is unclear. Although polyQ expansions render proteins prone to aggregate into inclusion bodies, this may be a neuronal coping response to more toxic forms of polyQ. The exact structure of these more toxic forms is unknown. Here we show that the monoclonal antibody 3B5H10 recognizes a species of polyQ protein in situ that strongly predicts neuronal death. The epitope selectively appears among some of the many low-molecular-weight conformational states assumed by expanded polyQ and disappears in higher-molecular-weight aggregated forms, such as inclusion bodies. These results suggest that protein monomers and possibly small oligomers containing expanded polyQ stretches can adopt a conformation that is recognized by 3B5H10 and is toxic or closely related to a toxic species.

Structural and functional alterations in amyloid-ß precursor protein induced by amyloid-ß peptides.

Alzheimer's disease-associated amyloid-ß (Aß) peptide is neurotoxic as an oligomer, but not as a monomer, by an unknown mechanism. We showed previously that Aß interacts with the amyloid-ß precursor protein (AßPP), leading to caspase cleavage and cell death induction. To characterize this structure and interaction further, we purified the extracellular domain of AßPP695 (eAßPP) and its complex with Aß oligomers (AßOs) of varying sizes, and then performed small angle X-ray scattering (SAXS). In the absence of any Aß, eAßPP was a compact homodimer with a tight association between the E1 and E2 domains. Dimeric Aß oligomers induced monomerization of eAßPP while larger oligomers also bound eAßPP but preserved the homodimer. Efficient binding of the larger oligomers correlated with the presence of prefibrillar oligomers, suggesting that the eAßPP binding is limited to a conformational subset of Aß oligomers. Both forms of Aß bound to eAßPP at the Aß-cognate region and induced dissociation of the E1 and E2 domains. Our data provide the first structural evidence for Aß-AßPP binding and suggest a mechanism for differential modulation of AßPP processing and cell death signaling by Aß dimers versus conformationally-specific larger oligomers.