Live-cell super-resolution microscopy reveals a primary role for diffusion in polyglutamine-driven aggresome assembly

The mechanisms leading to self-assembly of misfolded proteins into amyloid aggregates have been studied extensively in the test tube under well-controlled conditions. However, to what extent these processes are representative of those in the cellular environment remains unclear. Using super-resolution imaging of live cells, we show here that an amyloidogenic polyglutamine-containing protein first forms small, amorphous aggregate clusters in the cytosol, chiefly by diffusion. Dynamic interactions among these clusters limited their elongation and led to structures with a branched morphology, differing from the predominantly linear fibrils observed in vitro. Some of these clusters then assembled via active transport at the microtubule-organizing center and thereby initiated the formation of perinuclear aggresomes. Although it is widely believed that aggresome formation is entirely governed by active transport along microtubules, here we demonstrate, using a combined approach of advanced imaging and mathematical modeling, that diffusion is the principal mechanism driving aggresome expansion. We found that the increasing surface area of the expanding aggresome increases the rate of accretion caused by diffusion of cytosolic aggregates and that this pathway soon dominates aggresome assembly. Our findings lead to a different view of aggresome formation than that proposed previously. We also show that aggresomes mature over time, becoming more compacted as the structure grows. The presence of large perinuclear aggregates profoundly affects the behavior and health of the cell, and our super-resolution imaging results indicate that aggresome formation and development are governed by highly dynamic processes that could be important for the design of potential therapeutic strategies

Involvement of IL-18 in the Expansion of Unique Hepatic T Cells with Unconventional Cytokine Profiles during Schistosoma mansoni Infection

Infection with schistosomes invokes severe fibrotic granulomatous responses in the liver of the host. Schistosoma mansoni infection induces dramatic fluctuations in Th1 or Th2 cytokine responses systemically; Th1 reactions are provoked in the early phase, whilst Th2 responses become dominant after oviposition begins. In the liver, various unique immune cells distinct from those of conventional immune competent organs or tissues exist, resulting in a unique immunological environment. Recently, we demonstrated that S. mansoni infection induces unique CD4+ T cell populations exhibiting unconventional cytokine profiles in the liver of mice during the period between Th1- and Th2-phases, which we term the transition phase. They produce both IFN-γ and IL-4 or both IFN-γ and IL-13 simultaneously. Moreover, T cells secreting triple cytokines IFN-γ, IL-13 and IL-4 were also induced. We term these cells Multiple Cytokine Producing Hepatic T cells (MCPHT cells). During the transition phase, when MCPHT cells increase, IL-18 secretion was up-regulated in the liver and sera. In S. mansoni-infected IL-18-deficient mice, expansion of MCPHT cells was curtailed. Thus our data suggest that IL-18 produced during S. mansoni infection play a role in the expansion of MCPHT cells

Experimental evidence for sustained carbon sequestration in fire-managed, peat moorlands.

Peat moorlands are important habitats in the boreal region, where they store approximately 30% of the global soil carbon (C). Prescribed burning on peat is a very contentious management strategy, widely linked with loss of carbon. Here, we quantify the effects of prescribed burning for lightly managed boreal moorlands and show that the impacts on peat and C accumulation rates are not as bad as is widely thought. We used stratigraphical techniques within a unique replicated ecological experiment with known burn frequencies to quantify peat and C accumulation rates (0, 1, 3 and 6 managed burns since around 1923). Accumulation rates were typical of moorlands elsewhere, and were reduced significantly only in the 6-burn treatment. However, impacts intensified gradually with burn frequency; each additional burn reduced the accumulation rates by 4.9 g m−2 yr−1 (peat) and 1.9 g C cm−2 yr−1, but did not prevent accumulation. Species diversity and the abundance of peat-forming species also increased with burn frequency. Our data challenge widely held perceptions that a move to 0 burning is essential for peat growth, and show that appropriate prescribed burning can both mitigate wildfire risk in a warmer world and produce relatively fast peat growth and sustained C sequestration