Sam Gandy

Formation and maintenance of Alzheimer's disease beta-amyloid plaques in the absence of microglia

In Alzheimers disease, microglia cluster around β-amyloid deposits, suggesting that these cells are important for amyloid plaque formation, maintenance and/or clearance. We crossed two distinct APP transgenic mouse strains with CD11b-HSVTK mice, in which nearly complete ablation of microglia was achieved for up to 4 weeks after ganciclovir application. Neither amyloid plaque formation and maintenance nor amyloid-associated neuritic dystrophy depended on the presence of microglia.

Sorting through the cell biology of Alzheimer's disease: intracellular pathways to pathogenesis.

During the first 100 years of Alzheimers disease research, this devastating and intractable disorder has been characterized at the clinical, histological, and molecular levels. Nevertheless, many key mechanistic questions remain unanswered. Here we will emphasize the importance of the cell biology of Alzheimers disease, reviewing the relevant literature that has expanded our mechanistic understanding, with a particular focus on pathways regulating protein sorting. Accumulated evidence indicates that sorting pathways may be uniquely vulnerable to disease pathogenesis, and recent studies have begun to reveal disease-related defects in the regulation of protein sorting.

Apolipoprotein E, cholesterol metabolism, diabetes, and the convergence of risk factors for Alzheimer's disease and cardiovascular disease

High fat diets and sedentary lifestyles are becoming major concerns for Western countries. They have led to a growing incidence of obesity, dyslipidemia, high blood pressure, and a condition known as the insulin-resistance syndrome or metabolic syndrome. These health conditions are well known to develop along with, or be precursors to atherosclerosis, cardiovascular disease, and diabetes. Recent studies have found that most of these disorders can also be linked to an increased risk of Alzheimers disease (AD). To complicate matters, possession of one or more apolipoprotein E ɛ4 (APOE ɛ4) alleles further increases the risk or severity of many of these conditions, including AD. ApoE has roles in cholesterol metabolism and Aβ clearance, both of which are thought to be significant in AD pathogenesis. The apparent inadequacies of ApoE ɛ4 in these roles may explain the increased risk of AD in subjects carrying one or more APOE ɛ4 alleles. This review describes some of the physiological and biochemical changes that the above conditions cause, and how they are related to the risk of AD. A diversity of topics is covered, including cholesterol metabolism, glucose regulation, diabetes, insulin, ApoE function, amyloid precursor protein metabolism, and in particular their relevance to AD. It can be seen that abnormal lipid, cholesterol and glucose metabolism are consistently indicated as central in the pathophysiology, and possibly the pathogenesis of AD. As diagnosis of mild cognitive impairment and early AD are becoming more reliable, and as evidence is accumulating that health conditions such as diabetes, obesity, and coronary artery disease are risk factors for AD, appropriate changes to diets and lifestyles will likely reduce AD risk, and also improve the prognosis for people already suffering from such conditions.

Ovariectomy and 17β-estradiol modulate the levels of Alzheimer’s amyloid β peptides in brain

Objective: To test whether female gonadal hormone status and estrogen modulate the metabolism of Aβ peptides in vivo. Background: AD is a neurodegenerative disorder characterized by accumulation of aggregated forms of the 40- and 42-amino acid Aβ peptides (Aβ40 and Aβ42). Estrogen replacement therapy in postmenopausal women is associated with decreased risk for AD or delay in disease onset or both. The mechanism by which estrogen exerts this neuroprotective effect is elusive. 17β-estradiol (E2) was shown to reduce the release of Aβ peptides by primary neuronal cultures of murine and human origin. Methods: For this purpose, four experimental sets of guinea pigs were used: intact animals, ovariectomized animals (ovx), and ovariectomized animals that received E2 at two different doses (ovx+low-dose E2 and ovx+high-dose E2). Brain Aβ40 and Aβ42 levels were assessed using Aβ40 and Aβ42-specific ELISA assays. Results: Prolonged ovariectomy resulted in uterine atrophy and decreased serum E2 levels and was associated with a pronounced increase in brain Aβ levels. Total brain Aβ in the ovx animals was increased by 1.5-fold on average as compared to intact controls. E2 treatment of ovariectomized animals led to uterine hypertrophy and a dose-dependent increase in serum E2 levels. In addition, both doses of E2 significantly reversed the ovariectomy-induced increase in brain Aβ levels. The high-dose E2 treatment did not lead to a further decrease in brain Aβ beyond that observed with the low-dose E2 treatment. Conclusions: Our results infer that cessation of ovarian estrogen production in postmenopausal women might facilitate Aβ deposition by increasing the local concentrations of Aβ40 and Aβ42 peptides in brain. In addition, our finding that E2 treatment is associated with diminution of brain Aβ levels suggests that modulation of Aβ metabolism may be one of the ways by which estrogen replacement therapy prevents or delays the onset of AD or both in postmenopausal women.

Expanding the association between the APOE gene and the risk of Alzheimer's disease: possible roles for APOE promoter polymorphisms and alterations in APOE transcription

Alzheimers disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early‐onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the ε4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The ε4 allele of APOE is one of three (ɛ2 ɛ3 and ɛ4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the ɛ4 allele is recognized as the most common identifiable genetic risk factor for late‐onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOEɛ4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the ɛ2/ɛ3/ɛ4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the ɛ2/ɛ3/ɛ4 locus.

Regulated formation of Golgi secretory vesicles containing Alzheimer beta-amyloid precursor protein.

Phorbol esters, activators of protein kinase C (PKC), regulate the relative utilization of alternative processing pathways for the Alzheimer β-amyloid precursor protein (β-APP) in intact cells, increasing the production of nonamyloidogenic soluble β-APP (sβ-APP) and decreasing that of neurotoxic β-amyloid (Aβ) peptide. The molecular and cellular bases of PKC-regulated β-APP cleavage are poorly understood. Here we demonstrate in a reconstituted cell-free system that activation of endogenous PKC increases formation from the trans-Golgi network of secretory vesicles containing β-APP and that this effect can be mimicked by purified PKC. The results demonstrate directly that PKC is involved in regulation of secretory vesicle formation and provide a mechanism by which PKC may reduce the formation of the Aβ peptide characteristic of Alzheimer disease.

Acute and chronic traumatic encephalopathies: pathogenesis and biomarkers.

Over the past decade, public awareness of the long-term pathological consequences of traumatic brain injury (TBI) has increased. Such awareness has been stimulated mainly by reports of progressive neurological dysfunction in athletes exposed to repetitive concussions in high-impact sports such as boxing and American football, and by the rising number of TBIs in war veterans who are now more likely to survive explosive blasts owing to improved treatment. Moreover, the entity of chronic traumatic encephalopathy (CTE)—which is marked by prominent neuropsychiatric features including dementia, parkinsonism, depression, agitation, psychosis, and aggression—has become increasingly recognized as a potential late outcome of repetitive TBI. Annually, about 1% of the population in developed countries experiences a clinically relevant TBI. The goal of this Review is to provide an overview of the latest understanding of CTE pathophysiology, and to delineate the key issues that are challenging clinical and research communities, such as accurate quantification of the risk of CTE, and development of reliable biomarkers for single-incident TBI and CTE.

Generation and Regulation of β‐Amyloid Peptide Variants by Neurons

Abstract: Studies of processing of the Alzheimer β‐amyloid precursor protein (βAPP) have been performed to date mostly in continuous cell lines and indicate the existence of two principal metabolic pathways: the “β‐secretase” pathway, which generates β‐amyloid (Aβ1–40/42; ∼4 kDa), and the “α‐secretase” pathway, which generates a smaller fragment, the “p3” peptide (Aβ17–40/42; ∼3 kDa). To determine whether similar processing events underlie βAPP metabolism in neurons, media were examined following conditioning by primary neuronal cultures derived from embryonic day 17 rats. Immunoprecipitates of conditioned media derived from [35S]methionine pulse‐labeled primary neuronal cultures contained 4‐ and 3‐kDa Aβ‐related species. Radiosequencing analysis revealed that the 4‐kDa band corresponded to conventional Aβ beginning at position Aβ(Asp1), whereas both radio‐sequencing and immunoprecipitation‐mass spectrometry analyses indicated that the 3‐kDa species in these conditioned media began with Aβ(Glu11) at the N terminus, rather than Aβ(Leu17) as does the conventional p3 peptide. Either activation of protein kinase C or inhibition of protein phosphatase 1/2A increased soluble βAPPα release and decreased generation of both the 4‐kDa Aβ and the 3‐kDa N‐truncated Aβ. Unlike results obtained with continuously cultured cells, protein phosphatase 1/2A inhibitors were more potent at reducing Aβ secretion by neurons than were protein kinase C activators. These data indicate that rodent neurons generate abundant Aβ variant peptides and emphasize the role of protein phosphatases in modulating neuronal Aβ generation.

Diabetes-Associated SorCS1 Regulates Alzheimer's Amyloid-β Metabolism: Evidence for Involvement of SorL1 and the Retromer Complex

SorCS1 and SorL1/SorLA/LR11 belong to the sortilin family of vacuolar protein sorting-10 (Vps10) domain-containing proteins. Both are genetically associated with Alzheimers disease (AD), and SORL1 expression is decreased in the brains of patients suffering from AD. SORCS1 is also genetically associated with types 1 and 2 diabetes mellitus (T1DM, T2DM). We have undertaken a study of the possible role(s) for SorCS1 in metabolism of the Alzheimers amyloid-β peptide (Aβ) and the Aβ precursor protein (APP), to test the hypothesis that Sorcs1 deficiency might be a common genetic risk factor underlying the predisposition to AD that is associated with T2DM. Overexpression of SorCS1cβ-myc in cultured cells caused a reduction (p = 0.002) in Aβ generation. Conversely, endogenous murine Aβ40 and Aβ42 levels were increased (Aβ40, p = 0.044; Aβ42, p = 0.007) in the brains of female Sorcs1 hypomorphic mice, possibly paralleling the sexual dimorphism that is characteristic of the genetic associations of SORCS1 with AD and DM. Since SorL1 directly interacts with Vps35 to modulate APP metabolism, we investigated the possibility that SorCS1cβ-myc interacts with APP, SorL1, and/or Vps35. We readily recovered SorCS1:APP, SorCS1:SorL1, and SorCS1:Vps35 complexes from nontransgenic mouse brain. Notably, total Vps35 protein levels were decreased by 49% (p = 0.009) and total SorL1 protein levels were decreased by 29% (p = 0.003) in the brains of female Sorcs1 hypomorphic mice. From these data, we propose that dysfunction of SorCS1 may contribute to both the APP/Aβ disturbance underlying AD and the insulin/glucose disturbance underlying DM.

Perspective: Prevention is better than cure

Attempts to reduce amyloid-β in the brain have yet to show clinical benefits. Starting treatment early is the best hope, says Sam Gandy