Hypoxia-inducible factor-1α (HIF-1α) potentiates ß-cell survival after islet transplantation of human and mouse islets.

A high proportion of ß-cells die within days of islet transplantation. Reports suggest that induction of hypoxia-inducible factor-1α (HIF-1α) predicts adverse transplant outcomes. We hypothesized that this was a compensatory response and that HIF-1α protects ß-cells during transplantation. Transplants were performed using human islets or murine ß-cell-specific HIF-1α-null (ß-HIF-1α-null) islets with or without treatment with deferoxamine (DFO) to increase HIF-1α. ß-HIF-1α-null transplants had poor outcomes, demonstrating that lack of HIF-1α impaired transplant efficiency. Increasing HIF-1α improved outcomes for mouse and human islets. No effect was seen in ß-HIF-1α-null islets. The mechanism was decreased apoptosis, resulting in increased ß-cell mass posttransplantation. These findings show that HIF-1α is a protective factor and is required for successful islet transplant outcomes. Iron chelation with DFO markedly improved transplant success in a HIF-1α-dependent manner, thus demonstrating the mechanism of action. DFO, approved for human use, may have a therapeutic role in the setting of human islet transplantation.

Islet transplantation: factors in short-term islet survival.

Islet transplantation has the potential to cure type 1 diabetes. In recent years, the proportion of patients achieving initial insulin independence has improved, but longer term outcomes remain poor compared to those for whole pancreas transplants. This review article will discuss factors affecting islet yield and viability leading up to transplantation and in the immediate post-transplant period.

Substrate-specific reduction of PP2A activity exaggerates tau pathology.

Phosphorylation of the microtubule-associated protein tau is regulated by the balanced interplay of kinases and phosphatases. Disturbance of this balance causes hyperphosphorylation of tau and neurofibrillary tangle formation in Alzheimer's disease brain. Here, we crossed Dom5 mice that express a substrate-specific dominant negative mutant form, L309A Calpha, of protein phosphatase 2A (PP2A) with neurofibrillary-tangle-forming P301L mutant tau transgenic pR5 mice. This exacerbated the tau pathology of pR5 mice significantly. Double-transgenic Dom5/pR5 mice showed 7-fold increased numbers of hippocampal neurons that specifically phosphorylated the pathological S422 epitope of tau. They showed 8-fold increased numbers of tangles compared to pR5 mice, in agreement with our previous finding that tangle formation is correlated with and preceded by phosphorylation of tau at the S422 epitope. This suggests that, in addition to kinases, PP2A and its regulatory subunits may be a therapeutic target for Alzheimer's disease.

Divergent phosphorylation pattern of tau in P301L tau transgenic mice.

Aggregates of hyperphosphorylated tau are prominent in brains of patients with Alzheimer's disease or frontotemporal dementia (FTD). They have been reproduced in animal models following the identification of tau mutations in familial cases of FTD. This includes our previously generated transgenic model, pR5, which expresses FTD (P301L) mutant tau in neurons. The mice are characterized by tau aggregation including tangle (NFT) formation, memory impairment and mitochondrial dysfunction. In 8-month-old mice, S422 phosphorylation of tau is linked to NFT formation, however, a detailed analysis of tau solubility, phosphorylation and aggregation has not been done nor have the mice been monitored until a high age. Here, we undertook an analysis by immunohistochemistry, Gallyas impregnation and Western blotting of brains from 3 month- up to 20 month-old mice. NFTs first appeared at 6 months in the amygdala, followed by the CA1 region of the hippocampus. As the mice get older, the solubility of tau is decreased as determined by sequential extractions. Histological analysis revealed increased phosphorylation at the AT180, AT270 and 12E8 epitopes with ageing. The numbers of AT8-positive neurons increased from 3 to 6 months old. However, whereas S422 appeared only late and concomitantly with NFT formation, the only neurons left with AT8-reactivity at 20 months were those that had undergone NFT formation. As hyperphosphorylated tau continued to accumulate, the lack of AT8-reactivity suggests regulatory mechanisms in specifically dephosphorylating the AT8 epitope in the remaining neurons. Thus, differential regulation of phosphorylation is important for NFT formation in neurodegenerative diseases with tau pathology.

Functional genomics dissects pathomechanisms in tauopathies: mitosis failure and unfolded protein response.

BACKGROUND: Alzheimer's disease (AD) is characterized by beta-amyloid (Abeta) peptide-containing plaques and tau-containing neurofibrillary tangles. By intracerebral injection of Abeta(42), both pathologies have been combined in P301L tau mutant mice. Furthermore, in cell culture, Abeta(42) induces tau aggregation. While both Abeta(42) and mutant tau cause neuronal dysfunction, their modes of action are only vaguely understood. METHODS: To determine which processes are disrupted by Abeta(42) and/or P301L mutant tau, we used transcriptomic and proteomic techniques followed by functional validation and analysis of human AD tissue. RESULTS: Our transcriptomic study in the SH-SY5Y cell culture system revealed that Abeta(42) and P301L tau expression independently affect genes controlling the cell cycle and cell proliferation. Proteomics applied to Abeta(42)-treated P301L tau-expressing SH-SY5Y cells and the amygdala of Abeta(42)-injected P301L transgenic mice revealed that a significant fraction of proteins altered in both systems belonged to the same functional categories, i.e. stress response and metabolism. Among the proteins identified was valosin-containing protein (VCP), a component of the quality control system during endoplasmic reticulum stress. Mutations in VCP have recently been linked to frontotemporal dementia. CONCLUSION: Our data support the mitosis failure hypothesis that claims that aberrant cell cycle reentry of postmitotic neurons induces apoptosis. Furthermore, our data underline a role of Abeta(42) in the stress response associated with protein folding.

A decade of tau transgenic animal models and beyond.

The first tau transgenic mouse model was established more than a decade ago. Since then, much has been learned about the role of tau in Alzheimer's disease and related disorders. Animal models, both in vertebrates and invertebrates, were significantly improved and refined as a result of the identification of pathogenic mutations in Tau in human cases of frontotemporal dementia. They have been instrumental for dissecting the cross-talk between tau and the second hallmark lesion of Alzheimer's disease, the Abeta peptide-containing amyloid plaque. We discuss how the tau models have been used to unravel the pathophysiology of Alzheimer's disease, to search for disease modifiers and to develop novel treatment strategies. While tau has received less attention than Abeta, it is rapidly acquiring a more prominent position and the emerging view is one of a synergistic action of Abeta and tau in Alzheimer's disease. Moreover, the existence of a number of neurodegenerative diseases with tau pathology in the absence of extracellular deposits underscores the relevance of research on tau.

Inhibitors of glutamate transport modulate distinct patterns in brain metabolism.

High affinity uptake of glutamate plays a major role in the termination of excitatory neurotransmission. Identification of the ramifications of transporter function is essential to understand the diseases in which defective excitatory amino acid transporters (EAAT) have been implicated. In this work we incubated Guinea pig cortical tissue slices with [3-(13)C]pyruvate and major currently available glutamate uptake inhibitors and studied the resultant metabolic sequelae by (13)C and (1)H NMR spectroscopy using a multivariate statistical approach. Perturbation of glutamate uptake produced significant effects on metabolic flux through the Krebs cycle, and on glutamate/glutamine cycling rates, with this effect accounting for 76% of the variation in the total data set. The effects of all inhibitors were separable from each other along three major principal components. The competitive inhibitor L-CCG III ((2S,1'S,2'R)-2-carboxycyclopropyl)glycine) differed most from the other inhibitors, showing negative weightings on both the first and second principal components, whereas the EAAT2-specific inhibitor dihydrokainate (DHK) showed metabolic patterns similar to that of anti-endo-3,4-methanopyrolidine dicarboxylate but separate from those of DL-threo-beta-benzyloxyaspartate (TBOA) and L-trans-pyrrolidine-2,4-dicarboxylate (L-tPDC). This indicates that different inhibition mechanisms or different colocalisation of the separate transporter subtypes with glutamate receptors can produce significantly different metabolic and functional outcomes for the brain.