The Effect of Fat Intake with Increased Omega-6-to-Omega-3 Polyunsaturated Fatty Acid Ratio in Animal Models of Early and Late Alzheimer's Disease-like Pathogenesis.

This work aims to clarify the effect of dietary polyunsaturated fatty acid (PUFA) intake on the adult brain affected by amyloid pathology. McGill-R-Thy1-APP transgenic (Tg) rat and 5xFAD Tg mouse models that represent earlier or later disease stages were employed. The animals were exposed to a control diet (CD) or an HFD based on corn oil, from young (rats) or adult (mice) ages for 24 or 10 weeks, respectively. In rats and mice, the HFD impaired reference memory in wild-type (WT) animals but did not worsen it in Tg, did not cause obesity, and did not increase triglycerides or glucose levels. Conversely, the HFD promoted stronger microglial activation in Tg vs. WT rats but had no effect on cerebral amyloid deposition. IFN-γ, IL-1ß, and IL-6 plasma levels were increased in Tg rats, regardless of diet, while CXCL1 chemokine levels were increased in HFD-fed mice, regardless of genotype. Hippocampal 3-nitrotyrosine levels tended to increase in HFD-fed Tg rats but not in mice. Overall, an HFD with an elevated omega-6-to-omega-3 ratio as compared to the CD (25:1 vs. 8.4:1) did not aggravate the outcome of AD regardless of the stage of amyloid pathology, suggesting that many neurobiological processes relevant to AD are not directly dependent on PUFA intake.

Perturbed mitochondria-ER contacts in live neurons that model the amyloid pathology of Alzheimer's disease.

The use of fixed fibroblasts from familial and sporadic Alzheimer's disease patients has previously indicated an upregulation of mitochondria-ER contacts (MERCs) as a hallmark of Alzheimer's disease. Despite its potential significance, the relevance of these results is limited because they were not extended to live neurons. Here we performed a dynamic in vivo analysis of MERCs in hippocampal neurons from McGill-R-Thy1-APP transgenic rats, a model of Alzheimer's disease-like amyloid pathology. Live FRET imaging of neurons from transgenic rats revealed perturbed 'lipid-MERCs' (gap width <10 nm), while 'Ca2+-MERCs' (10-20 nm gap width) were unchanged. In situ TEM showed no significant differences in the lipid-MERCs:total MERCs or lipid-MERCs:mitochondria ratios; however, the average length of lipid-MERCs was significantly decreased in neurons from transgenic rats as compared to controls. In accordance with FRET results, untargeted lipidomics showed significant decreases in levels of 12 lipids and bioenergetic analysis revealed respiratory dysfunction of mitochondria from transgenic rats. Thus, our results reveal changes in MERC structures coupled with impaired mitochondrial functions in Alzheimer's disease-related neurons.This article has an associated First Person interview with the first author of the paper.

Effect of antioxidant supplements on lipid peroxidation levels in primary cortical neuron cultures.

Oxidative stress, specifically lipid peroxidation, is a major driving force in neurodegenerative processes. However, the exact role of lipid peroxidation remains elusive as reliable real-time detection and quantification of lipid peroxyl radicals proves to be challenging in vitro and in vivo. Motivated by this methodological limitation, we have optimized conditions for real-time imaging and quantification of lipid peroxyl radical generation in primary neuron cultures using the lipophilic fluorogenic antioxidant H4BPMHC (8-((6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)-methyl)-1,5-di(3-chloropropyl)-pyrromethene fluoroborate), an α-tocopherol analog probe. By subjecting neurons to different antioxidant conditions in the presence and absence of lipid peroxidation inducing stressors (Haber-Weiss reagents), we maximized H4BPMHC sensitivity and confirmed its potential to temporally resolve subtle and marked differences in lipid peroxidation levels in real-time. Herein we report imaging and quantification of homeostatic and induced lipid peroxidation in primary neuron cultures, supporting the use of this probe for investigating healthy and diseased states. Overall these results provide the necessary foundation and impetus towards using H4BPMHC for elucidating and mapping lipid peroxyl radical contributions to ROS-associated pathological processes in neurons.

Synaptosomal bioenergetic defects are associated with cognitive impairment in a transgenic rat model of early Alzheimer's disease.

Synaptic bioenergetic deficiencies may be associated with early Alzheimer's disease (AD). To explore this concept, we assessed pre-synaptic mitochondrial function in hemizygous (+/-)TgMcGill-R-Thy1-APP rats. The low burden of Aß and the wide array of behavioral and cognitive impairments described in 6-month-old hemizygous TgMcGill-R-Thy1-APP rats (Tg(+/-)) support their use to investigate synaptic bioenergetics deficiencies described in subjects with early Alzheimer's disease (AD). In this report, we show that pre-synaptic mitochondria from Tg(+/-) rats evidence a decreased respiratory control ratio and spare respiratory capacity associated with deficits in complex I enzymatic activity. Cognitive impairments were prevented and bioenergetic deficits partially reversed when Tg(+/-) rats were fed a nutritionally complete diet from weaning to 6-month-old supplemented with pyrroloquinoline quinone, a mitochondrial biogenesis stimulator with antioxidant and neuroprotective effects. These results provide evidence that, as described in AD brain and not proven in Tg mice models with AD-like phenotype, the mitochondrial bioenergetic capacity of synaptosomes is not conserved in the Tg(+/-) rats. This animal model may be suitable for understanding the basic biochemical mechanisms involved in early AD.

Therapeutic benefits of the methyl donor S-adenosylmethionine on nerve injury-induced mechanical hypersensitivity and cognitive impairment in mice.

Despite considerable advances in understanding mechanisms involved in chronic pain, effective treatment remains elusive. Comorbid conditions including anxiety, depression, and cognitive impairment further impact quality of life. Chronic pain is associated with reversible changes in brain anatomy and function and with long-term changes in gene expression. Epigenetic mechanisms, including DNA methylation, contribute to wide-spread and long-lasting reprogramming of gene expression. We previously reported decreases in global DNA methylation in the mouse frontal cortex 6 months after induction of neuropathic pain using the spared nerve injury (SNI) model. Here, we examined the therapeutic effect of increasing DNA methylation using the methyl donor S-adenosylmethionine (SAM). S-adenosylmethionine is marketed as a nutritional supplement for a range of conditions including liver disease, depression, osteoarthritis, fibromyalgia, and dementia. Three months after SNI or sham surgery, animals were treated with SAM (20 mg/kg, 3×/week) or saline orally for 4 months, and the impact on sensory, motor, motivational, and cognitive indices was measured. S-adenosylmethionine attenuated SNI-induced mechanical hypersensitivity and reduced active avoidance of mechanical stimuli but had no effect on cold sensitivity or motor capacity. S-adenosylmethionine completely blocked nerve injury-induced cognitive impairment and attenuated SNI-induced decreases in global DNA methylation in the frontal cortex. In summary, chronic oral administration of the methyl donor, SAM, attenuated sensory and cognitive symptoms associated with nerve injury in mice. These effects may be mediated, in part, through modulation of DNA methylation in the central nervous system by systemic administration of the methyl donor SAM.

Intracellular Aß pathology and early cognitive impairments in a transgenic rat overexpressing human amyloid precursor protein: a multidimensional study.

Numerous studies have implicated the abnormal accumulation of intraneuronal amyloid-ß (Aß) as an important contributor to Alzheimer's disease (AD) pathology, capable of triggering neuroinflammation, tau hyperphosphorylation and cognitive deficits. However, the occurrence and pathological relevance of intracellular Aß remain a matter of controversial debate. In this study, we have used a multidimensional approach including high-magnification and super-resolution microscopy, cerebro-spinal fluid (CSF) mass spectrometry analysis and ELISA to investigate the Aß pathology and its associated cognitive impairments, in a novel transgenic rat model overexpressing human APP. Our microscopy studies with quantitative co-localization analysis revealed the presence of intraneuronal Aß in transgenic rats, with an immunological signal that was clearly distinguished from that of the amyloid precursor protein (APP) and its C-terminal fragments (CTFs). The early intraneuronal pathology was accompanied by a significant elevation of soluble Aß42 peptides that paralleled the presence and progression of early cognitive deficits, several months prior to amyloid plaque deposition. Aß38, Aß39, Aß40 and Aß42 peptides were detected in the rat CSF by MALDI-MS analysis even at the plaque-free stages; suggesting that a combination of intracellular and soluble extracellular Aß may be responsible for impairing cognition at early time points. Taken together, our results demonstrate that the intraneuronal development of AD-like amyloid pathology includes a mixture of molecular species (Aß, APP and CTFs) of which a considerable component is Aß; and that the early presence of these species within neurons has deleterious effects in the CNS, even before the development of full-blown AD-like pathology.