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Dalle Pezze P.,Vitality
Science signaling | Year: 2012

The kinase mammalian target of rapamycin (mTOR) exists in two multiprotein complexes (mTORC1 and mTORC2) and is a central regulator of growth and metabolism. Insulin activation of mTORC1, mediated by phosphoinositide 3-kinase (PI3K), Akt, and the inhibitory tuberous sclerosis complex 1/2 (TSC1-TSC2), initiates a negative feedback loop that ultimately inhibits PI3K. We present a data-driven dynamic insulin-mTOR network model that integrates the entire core network and used this model to investigate the less well understood mechanisms by which insulin regulates mTORC2. By analyzing the effects of perturbations targeting several levels within the network in silico and experimentally, we found that, in contrast to current hypotheses, the TSC1-TSC2 complex was not a direct or indirect (acting through the negative feedback loop) regulator of mTORC2. Although mTORC2 activation required active PI3K, this was not affected by the negative feedback loop. Therefore, we propose an mTORC2 activation pathway through a PI3K variant that is insensitive to the negative feedback loop that regulates mTORC1. This putative pathway predicts that mTORC2 would be refractory to Akt, which inhibits TSC1-TSC2, and, indeed, we found that mTORC2 was insensitive to constitutive Akt activation in several cell types. Our results suggest that a previously unknown network structure connects mTORC2 to its upstream cues and clarifies which molecular connectors contribute to mTORC2 activation. Source

Vascular dementia (VaD) is recognised as a neurocognitive disorder, which is explained by numerous vascular causes in the general absence of other pathologies. The heterogeneity of cerebrovascular disease makes it challenging to elucidate the neuropathological substrates and mechanisms of VaD as well as vascular cognitive impairment (VCI). Consensus and accurate diagnosis of VaD relies on wide-ranging clinical, neuropsychometric and neuroimaging measures with subsequent pathological confirmation. Pathological diagnosis of suspected clinical VaD requires adequate postmortem brain sampling and rigorous assessment methods to identify important substrates. Factors that define the subtypes of VaD include the nature and extent of vascular pathologies, degree of involvement of extra and intracranial vessels and the anatomical location of tissue changes. Atherosclerotic and cardioembolic diseases appear the most common substrates of vascular brain injury or infarction. Small vessel disease characterised by arteriolosclerosis and lacunar infarcts also causes cortical and subcortical microinfarcts, which appear to be the most robust substrates of cognitive impairment. Diffuse WM changes with loss of myelin and axonal abnormalities are common to almost all subtypes of VaD. Medial temporal lobe and hippocampal atrophy accompanied by variable hippocampal sclerosis are also features of VaD as they are of Alzheimer’s disease. Recent observations suggest that there is a vascular basis for neuronal atrophy in both the temporal and frontal lobes in VaD that is entirely independent of any Alzheimer pathology. Further knowledge on specific neuronal and dendro-synaptic changes in key regions resulting in executive dysfunction and other cognitive deficits, which define VCI and VaD, needs to be gathered. Hereditary arteriopathies such as cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy or CADASIL have provided insights into the mechanisms of dementia associated with cerebral small vessel disease. Greater understanding of the neurochemical and molecular investigations is needed to better define microvascular disease and vascular substrates of dementia. The investigation of relevant animal models would be valuable in exploring the pathogenesis as well as prevention of the vascular causes of cognitive impairment. © 2016, The Author(s). Source

The integrity of the vascular system is essential for the efficient functioning of the brain. Aging-related structural and functional disturbances in the macro- or microcirculation of the brain make it vulnerable to cognitive dysfunction, leading to brain degeneration and dementing illness. Several faltering controls, including impairment in autoregulation, neurovascular coupling, blood-brain barrier leakage, decreased cerebrospinal fluid, and reduced vascular tone, appear to be responsible for varying degrees of neurodegeneration in old age. There is ample evidence to indicate vascular risk factors are also linked to neurodegenerative processes preceding cognitive decline and dementia. The strongest risk factor for brain degeneration, whether it results from vascular or neurodegenerative mechanisms or both, is age. However, several modifiable risks such as cardiovascular disease, hypertension, dyslipidemia, diabetes, and obesity enhance the rate of cognitive decline and increase the risk of Alzheimer's disease in particular. The ultimate accumulation of brain pathological lesions may be modified by genetic influences, such as the apolipoprotein E ε4 allele and the environment. Lifestyle measures that maintain or improve cardiovascular health, including consumption of healthy diets, moderate use of alcohol, and implementation of regular physical exercise are important factors for brain protection. © 2010 International Life Sciences Institute. Source

Attems J.,Vitality | Jellinger K.A.,Medical University of Vienna
BMC Medicine | Year: 2014

Recent epidemiological and clinico-pathological data indicate considerable overlap between cerebrovascular disease (CVD) and Alzheimer's disease (AD) and suggest additive or synergistic effects of both pathologies on cognitive decline. The most frequent vascular pathologies in the aging brain and in AD are cerebral amyloid angiopathy and small vessel disease. Up to 84% of aged subjects show morphological substrates of CVD in addition to AD pathology. AD brains with minor CVD, similar to pure vascular dementia, show subcortical vascular lesions in about two-thirds, while in mixed type dementia (AD plus vascular dementia), multiple larger infarcts are more frequent. Small infarcts in patients with full-blown AD have no impact on cognitive decline but are overwhelmed by the severity of Alzheimer pathology, while in early stages of AD, cerebrovascular lesions may influence and promote cognitive impairment, lowering the threshold for clinically overt dementia. Further studies are warranted to elucidate the many hitherto unanswered questions regarding the overlap between CVD and AD as well as the impact of both CVD and AD pathologies on the development and progression of dementia. © 2014 Attems and Jellinger. Source

Previous reports suggest that brain white matter changes, a surrogate for small vessel disease, are related to cerebral amyloid angiopathy (CAA). However, this relationship has not been explored in population-based studies or in the oldest old (>85 years of age). We studied the relationships between white matter hyperintensities (WMH) determined by post-mortem magnetic resonance imaging (MRI) and neuropathologically assessed CAA in demented and nondemented subjects enrolled in the prospective community-based Finnish Vantaa 85+ Study. In this analysis, we evaluated scans and brain samples from 123 subjects (86% women) with a mean age of 90.6 years. We found CAA to be present in 63 % of the 123 subjects, whereas WMH was present in 74%, and dementia in 59 %. The presence of WMH of any severity did not relate to the presence or the degree of CAA severity, irrespective of the dementia status of the subjects. Furthermore, multivariate regression analysis showed a clear association between CAA and dementia but WMH was not related to dementia in this very old sample. We conclude that severe WMH may not be determined by CAA in this very elderly population. Source

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