Post Doctoral Fellow, University of North Dakota
Brain-Gut communication in Alzheimer's Disease
Due to its dementing characteristic, Alzheimer’s disease (AD) is often characterized by fibrillar amyloid-beta (Aβ) peptide containing plaques and associated reactive microglia in the brain. However, the elderly are also often afflicted with intestinal dysfunction such as constipation or fecal incontinence which could be due to degenerating, proinflammatory changes in the enteric nervous system. Based upon the fact that enteric neurons also express APP we hypothesized that the enteric nervous system may demonstrate Aβ production and deposition along with associated inflammatory changes and behavioral dysfunction during progression of AD that may be temporally unique from changes in the brain. To test this idea, we compared C57BL/6 wild type male and female mice to two models of AD, littermate control APP/PS1 mice and the newly characterized APP (NL-G-F) mice at 3, 6, and 12 months of age. Brain amyloid plaque deposition, microgliosis, astrogliosis, and oligomeric and fibrillar Aβ deposition in APP (NL-G-F) and APP/PS1 mice were increased in an age-dependent manner. The increase in gliosis, oligomeric, and fibrillar Aβ in both male and female APP (NL-G-F) mice preceded that observed in the APP/PS1 mice, observable by 3 months of age. APP (NL-G-F) also demonstrated reduced Aβ 1-40 levels compared to the APP/PS1 mice at 3 months of age correlating with the Iberian mutation to promote a higher Aβ 1-42/1-40 ratio. Interestingly, female but not male APP/PS1 and APP (NL-G-F) mice demonstrated memory dysfunction at 3 months of age. In addition, 3 month old female APP (NL-G-F) mice also presented decreased intestinal motility as compared to the wild type and APP/PS1 mice. However, 3 month old female APP/PS1 mice demonstrated significantly increased intestinal permeability compared to wild type and APP (NL-G-F) mice. These data demonstrate that both AD mouse models have cognitive and intestinal dysfunction by 3 months of age correlating with Aβ production. Interestingly, the unique nature of Aβ production and deposition as well as intestinal changes across the two mouse models suggests that further study is required to better characterize the brain and peripheral disease progression for ultimate comparison to human disease.
Abstract: Alzheimer's disease (AD) brains are characterized by fibrillar amyloid-β (Aβ) peptide containing plaques and associated reactive microglia. The proinflammatory phenotype of the microglia suggests that they may negatively affect disease course and contribute to behavioral decline. This hypothesis predicts that attenuating microglial activation may provide benefit against disease. Prior work from our laboratory and others has characterized a role for the transcription factor, nuclear factor of activated T cells (NFAT), in regulating microglial phenotype in response to different stimuli, including Aβ peptide. We observed that the NFATc2 isoform was the most highly expressed in murine microglia cultures, and inhibition or deletion of NFATc2 was sufficient to attenuate the ability of the microglia to secrete cytokines. In order to determine whether the NFATc2 isoform, in particular, was a valid immunomodulatory target in vivo, we crossed an NFATc2-/- line to a well-known AD mouse model, an AβPP/PS1 mouse line. As expected, the AβPP/PS1 x NFATc2-/- mice had attenuated cytokine levels compared to AβPP/PS1 mice as well as reduced microgliosis and astrogliosis with no effect on plaque load. Although some species differences in relative isoform expression may exist between murine and human microglia, it appears that microglial NFAT activity is a viable target for modulating the proinflammatory changes that occur during AD.
Pub.: 17 May '17, Pinned: 16 Jun '17
Abstract: Reactive microglia have been associated with the histological changes that occur in Parkinson's disease brains and mouse models of the disease. Multiple studies from autopsy brains have verified the presence of microgliosis in several brain regions including substantia nigra, striatum, hippocampus and various cortical areas. MPTP injections in rodents have also shown striato-nigral microgliosis correlating with the loss of dopaminergic neurons. However, consistent data with respect to cytokine and immune cell changes during Parkinson's disease have not been fully defined.In order to improve understanding of the role of neuroinflammation in Parkinson's disease, we employed the MPTP injection model using humanized CD34+ mice along with age-matched C57BL/6 mice. NSG mice engrafted with hu-CD34+ hematopoietic stem cells were injected with MPTP to quantify cytokine changes, neuron loss, gliosis, and behavioral dysfunction. The mice were also treated with or without the calcineurin/NFAT inhibitor, FK506, to determine whether modulating the immune response could attenuate disease. MPTP injections produced impairment of motor performance, increased microgliosis, elevated brain cytokine levels, and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra and striatum of both humanized CD34+ mice and C57BL/6 mice with a strikingly different profile of human versus mouse cytokine elevations observed in each. Interestingly, FK506 injections significantly attenuated the MPTP-induced effects in the humanized CD34+ mice compared the C57BL/6 mice. In addition, analyses of human plasma from Parkinson's disease donors compared to age-matched, healthy controls demonstrated an increase in a number of pro-inflammatory cytokines in female patients similar to that observed in MPTP-injected female CD34+ mice.This study demonstrates for the first time, induction of Parkinson's disease-like symptoms in female humanized CD34+ mice using MPTP. The profile of cytokine changes in the serum and brains of the humanized CD34+ mice following MPTP injection differed significantly from that occurring in the more commonly used C57BL/6 strain of mice. Moreover, several cytokine elevations observed in the MPTP injected humanized CD34+ mice were similarly increased in plasma of PD patients suggesting that these mice offer the more relevant model for the inflammatory aspects of human disease. Consistent with this, the effects of MPTP on loss of tyrosine hydroxylase immunoreactivity, loss of motor strength, and increase in proinflammatory cytokines were attenuated using an immunosuppressant drug, FK506, in the humanized CD34+ but not the C57BL/6 mice. Collectively, these findings suggest that MPTP injected, humanized CD34+ mice represent a more accurate model for assessing inflammatory changes in PD.
Pub.: 16 Feb '17, Pinned: 16 Jun '17
Abstract: Prior work suggests that amyloid precursor protein (APP) can function as a proinflammatory receptor on immune cells, such as monocytes and microglia. Therefore, we hypothesized that APP serves this function in microglia during Alzheimer's disease. Although fibrillar amyloid β (Aβ)-stimulated cytokine secretion from both wild-type and APP knock-out (mAPP(-/-)) microglial cultures, oligomeric Aβ was unable to stimulate increased secretion from mAPP(-/-) cells. This was consistent with an ability of oligomeric Aβ to bind APP. Similarly, intracerebroventricular infusions of oligomeric Aβ produced less microgliosis in mAPP(-/-) mice compared with wild-type mice. The mAPP(-/-) mice crossed to an APP/PS1 transgenic mouse line demonstrated reduced microgliosis and cytokine levels and improved memory compared with wild-type mice despite robust fibrillar Aβ plaque deposition. These data define a novel function for microglial APP in regulating their ability to acquire a proinflammatory phenotype during disease.A hallmark of Alzheimer's disease (AD) brains is the accumulation of amyloid β (Aβ) peptide within plaques robustly invested with reactive microglia. This supports the notion that Aβ stimulation of microglial activation is one source of brain inflammatory changes during disease. Aβ is a cleavage product of the ubiquitously expressed amyloid precursor protein (APP) and is able to self-associate into a wide variety of differently sized and structurally distinct multimers. In this study, we demonstrate both in vitro and in vivo that nonfibrillar, oligomeric forms of Aβ are able to interact with the parent APP protein to stimulate microglial activation. This provides a mechanism by which metabolism of APP results in possible autocrine or paracrine Aβ production to drive the microgliosis associated with AD brains.
Pub.: 12 Aug '16, Pinned: 16 Jun '17
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