Aggregated fibrillary microtubule-associated protein tau is the major component of neurofibrillary tangles in Alzheimer's disease. The exact molecular mechanism of tau aggregation is unknown. Microglial cell activation and migration toward amyloid-beta plaques precede the appearance of dysmorphic neurites and formation of neurofibrillary tangles. Here, we analyzed the accumulation of tau at a distance range of expected spontaneous aggregation by fluorescence lifetime-based Förster resonance energy transfer in cultured primary murine neurons cotransfected with the human tau gene tagged to the green fluorescent protein variants Citrine (tau-Citrine) and Cerulean (tau-Cerulean). No spontaneous accumulation of cotransfected tau-Citrine and tau-Cerulean was detected in untreated neurons. Coculture of neurons with activated microglia induced aggregation of tau in neurites. Treatment of neurons with tumor necrosis factor-alpha (TNF-alpha) stimulated reactive oxygen species generation and resulted in the accumulation of tau-Citrine and tau-Cerulean in neurites, which was inhibited by neutralization of TNF and the free radical inhibitor 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox). These data demonstrate that activated microglia and the microglial-derived proinflammatory cytokine TNF can induce accumulation of the aggregation-prone tau molecules in neurites via reactive oxygen species.

In this report, we study the self-assembly of two silk-elastin-like proteins: one is a diblock S(24)E(40) composed of 24 silk-like (S) repeats and 40 elastin-like (E) repeats; the other is a triblock S(12)C(4)E(40), in which the S and E blocks are separated by a random coil block (C(4)). Upon lowering the pH, the acidic silk-like blocks fold and self-assemble into fibrils by a nucleation-and-growth process. While silk-like polymers without elastin-like blocks form fibrils by heterogeneous nucleation, leading to monodisperse populations, the elastin-like blocks allow for homogeneous nucleation, which gives rise to polydisperse length distributions, as well as a concentration-dependent fibril length. Moreover, the elastin-like blocks introduce temperature sensitivity: at high temperature, the fibrils become sticky and tend to bundle and aggregate in an irreversible manner. Concentrated solutions of S(12)C(4)E(40) form weak gels at low pH that irreversibly lose elasticity in temperature cycling; this is also attributed to fibril aggregation.

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Recombinant protein polymers, which can combine different bioinspired self-assembly motifs in a well-defined block sequence, have large potential as building blocks for making complex, hierarchically structured materials. In this paper we demonstrate the stepwise formation of thermosensitive hydrogels by combination of two distinct, orthogonal self-assembly mechanisms. In the first step, fibers are coassembled from two recombinant protein polymers: (a) a symmetric silk-like block copolymer consisting of a central silk-like block flanked by two soluble random coil blocks and (b) an asymmetric silk-collagen-like block copolymer consisting of a central random-coil block flanked on one side by a silk-like block and on the other side a collagen-like block. In the second step, induced by cooling, the collagen-like blocks form triple helices and thereby cross-link the fibers, leading to hydrogels with a thermo-reversibly switchable stiffness. Our work demonstrates how complex self-assembled materials can be formed through careful control of the self-assembly pathway.

Corticotropin releasing factor (CRF) is known to be involved in the stress response and in some degenerative brain disorders. In addition, CRF has a role as a neuromodulator in adult cerebellar circuits. Data from developmental studies suggest a putative role for CRF as a trophic factor during cerebellar development. In this study, we investigated the trophic role for CRF family of peptides by culturing cerebellar neurons in the presence of CRF, urocortin or urocortin II. Primary cell cultures of cerebella from embryonic day 18 mice were established, and cells were treated for either 1, 5 or 9 days with Basal Medium Eagles complete medium alone or complete medium with 1 µM CRF, urocortin, or urocortin II. The number of GABA-positive neurons in each treatment condition was counted at each culture age for monitoring the changes in neuronal survival. Treatment with 1 µM CRF or 1 µM urocortin increased the survival of GABAergic neurons at 6 days in vitro and 10 days in vitro, and this survival promoting effect was abolished by treatment with astressin in the presence of those peptides. Based on these data, we suggest that CRF or urocortin has a trophic role promoting the survival of cerebellar GABAergic neurons in cultures.