The transcriptional regulator p53 has an essential role in tumor suppression. Almost 50% of human cancers are associated with the loss of p53 functions, where p53 often accumulates in the nucleus as well as in cytoplasm. Although it has been previously suggested that amyloid formation could be a cause of p53 loss-of-function in subset of tumors, the characterization of these amyloids and its structure-function relationship is not yet established. In the current study, we provide several evidences for the presence of p53 amyloid formation (in human and animal cancer tissues); along with its isolation from human cancer tissues and the biophysical characterization of these tissue-derived fibrils. Using amyloid seed of p53 fragment (P8, p53(250-257)), we show that p53 amyloid formation in cells not only leads to its functional inactivation but also transforms it into an oncoprotein. The in vitro studies further show that cancer-associated mutation destabilizes the fold of p53 core domain and also accelerates the aggregation and amyloid formation by this protein. Furthermore, we also show evidence of prion-like cell-to-cell transmission of different p53 amyloid species including full-length p53, which is induced by internalized P8 fibrils. The present study suggests that p53 amyloid formation could be one of the possible cause of p53 loss of function and therefore, inhibiting p53 amyloidogenesis could restore p53 tumor suppressor functions.

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Extracellular matrices (ECM) play an enormous role in any living system, controlling various factors and eventually fates of cells. ECM regulates cell fate by providing constant exogenous signals altering intracellular signal transduction for diverse pathways including proliferation, migration, differentiation, and apoptosis. Biomaterial scaffolds are designed to mimic the natural extracellular matrix such that the cells could recapitulate natural events alike their natural niche. Therefore, the success of tissue engineering is largely dependent on how one can engineer the natural matrix properties at nanoscale precision. In this aspect, several recent studies have suggested that, as long as amyloid fibrils are not toxic, they can be utilized for cell adhesion and tissue engineering applications due to its ECM mimetic surface topography and ability to mediate active cell adhesion via focal adhesions. Although historically associated with human diseases, amyloids have presently emerged as one of the excellent biomaterials evolved in nature. In this review, we focus on the recent advances of amyloid-based biomaterials for cell adhesion and tissue engineering applications.

We report a new class of amyloid-inspired peptide hydrogels that was designed and based on α-synuclein protein for which hydrogel formation is triggered by various stimuli, such as heating/cooling or changes in pH. The peptides resemble a cross-β-sheet-rich amyloid, and they assemble into a nanofibrous meshwork that mimics the natural extracellular matrix. Our design principle allows easy manipulation of the gelator sequence to exploit the desirable properties of amyloids for use in cell replacement therapies for neurodegenerative diseases. The amyloid hydrogels facilitate the attachment and neuronal differentiation of mesenchymal stem cells (MSCs) and assist in the delivery and engraftment of MSCs in the substantia nigra and caudate putamen of a Parkinsonian mouse model.

Background: Peptide/protein hormones are stored as amyloids within endocrine secretory granules. Results: Disulfide bond cleavage enhances conformational dynamics and aggregation kinetics in somatostatin-14, resulting in amyloid fibrils with increased resistance to denaturing conditions and decreased reversibility. Conclusion: Disulfide bond could be a key modulating factor in somatostatin-14 amyloid formation associated with secretory granule biogenesis. Significance: Defective disulfide bonding might cause dysregulation of hormone storage/secretion.

Amyloids are cross-β-sheet fibrillar aggregates, associated with various human diseases and native functions such as protein/peptide hormone storage inside secretory granules of neuroendocrine cells. In the current study, using amyloid detecting agents, we show that growth hormone (GH) could be stored as amyloid in the pituitary of rat. Moreover, to demonstrate the formation of GH amyloid in vitro, we studied various conditions (solvents, glycosaminoglycans, salts and metal ions) and found that in presence of zinc metal ions (Zn(II)), GH formed short curvy fibrils. The amyloidogenic nature of these fibrils was examined by Thioflavin T binding, Congo Red binding, transmission electron microscopy and X-ray diffraction. Our biophysical studies also suggest that Zn(II) initiates the early oligomerization of GH that eventually facilitates the fibrillation process. Furthermore, using immunofluorescence study of pituitary tissue, we show that GH in pituitary significantly co-localizes with Zn(II), suggesting the probable role of zinc in GH aggregation within secretory granules. We also found that GH amyloid formed in vitro is capable of releasing monomers. The study will help to understand the possible mechanism of GH storage, its regulation and monomer release from the somatotrophs of anterior pituitary.

Alpha-synuclein (α-Syn) aggregation into oligomers and fibrils is associated with dopaminergic neuron loss occurring in Parkinson’s disease (PD) pathogenesis. Compounds that modulate α-Syn aggregation and interact with preformed fibrils/oligomers and convert them to less toxic species could have promising applications in the drug development efforts against PD. Curcumin is one of the Asian food ingredient which showed promising role as therapeutic agent against many neurological disorders including PD. However, the instability and low solubility makes it less attractive for the drug development. In this work, we selected various curcumin analogs and studied their toxicity, stability and efficacy to interact with different α-Syn species and modulation of their toxicity. We found a subset of curcumin analogs with higher stability and showed that curcumin and its various analogs interact with preformed fibrils and oligomers and accelerate α-Syn aggregation to produce morphologically different amyloid fibrils in vitro. Furthermore, these curcumin analogs showed differential binding with the preformed α-Syn aggregates. The present data suggest the potential role of curcumin analogs in modulating α-Syn aggregation.

Parkinson's disease is mainly a sporadic disorder in which both environmental and cellular factors play a major role in the initiation of this disease. Glycosaminoglycans (GAG) are integral components of the extracellular matrix and are known to influence amyloid aggregation of several proteins, including α-synuclein (α-Syn). However, the mechanism by which different GAGs and related biological polymers influence protein aggregation and the structure and intercellular spread of these aggregates remains elusive. In this study, we used three different GAGs and related charged polymers to establish their role in α-Syn aggregation and associated biological activities of these aggregates. Heparin, a representative GAG, affected α-Syn aggregation in a concentration-dependent manner, whereas biphasic α-Syn aggregation kinetics was observed in the presence of chondroitin sulfate B. Of note, as indicated by 2D NMR analysis, different GAGs uniquely modulated α-Syn aggregation because of the diversity of their interactions with soluble α-Syn. Moreover, subtle differences in the GAG backbone structure and charge density significantly altered the properties of the resulting amyloid fibrils. Each GAG/polymer facilitated the formation of morphologically and structurally distinct α-Syn amyloids, which not only displayed variable levels of cytotoxicity but also exhibited an altered ability to internalize into cells. Our study supports the role of GAGs as key modulators in α-Syn amyloid formation, and their distinct activities may regulate amyloidogenesis depending on the type of GAG being up- or down-regulated .