BackgroundReduced TOR signaling has been shown to significantly increase lifespan in a variety of organisms [1], [2], [3], [4]. It was recently demonstrated that long-term treatment with rapamycin, an inhibitor of the mTOR pathway[5], or ablation of the mTOR target p70S6K[6] extends lifespan in mice, possibly by delaying aging. Whether inhibition of the mTOR pathway would delay or prevent age-associated disease such as AD remained to be determined.Methodology/Principal FindingsWe used rapamycin administration and behavioral tools in a mouse model of AD as well as standard biochemical and immunohistochemical measures in brain tissue to provide answers for this question. Here we show that long-term inhibition of mTOR by rapamycin prevented AD-like cognitive deficits and lowered levels of Aβ42, a major toxic species in AD[7], in the PDAPP transgenic mouse model. These data indicate that inhibition of the mTOR pathway can reduce Aβ42 levels in vivo and block or delay AD in mice. As expected from the inhibition of mTOR, autophagy was increased in neurons of rapamycin-treated transgenic, but not in non-transgenic, PDAPP mice, suggesting that the reduction in Aβ and the improvement in cognitive function are due in part to increased autophagy, possibly as a response to high levels of Aβ.Conclusions/SignificanceOur data suggest that inhibition of mTOR by rapamycin, an intervention that extends lifespan in mice, can slow or block AD progression in a transgenic mouse model of the disease. Rapamycin, already used in clinical settings, may be a potentially effective therapeutic agent for the treatment of AD.

Aging of the vasculature plays a central role in morbidity and mortality of older people. In order to develop novel treatments for amelioration of unsuccessful vascular aging and prevention of age-related vascular pathologies it is essential to understand the cellular and functional changes that occur in the vasculature during aging. In this review, the pathophysiological roles of fundamental cellular and molecular mechanisms of aging, including oxidative stress, mitochondrial dysfunction, impaired resistance to molecular stressors, chronic low-grade inflammation, genomic instability, cellular senescence, epigenetic alterations, loss of protein homeostasis, deregulated nutrient sensing and stem cell dysfunction in the vascular system are considered in terms of their contribution to the pathogenesis of both micro- and macrovascular diseases associated with old age. The importance of pro-geronic and anti-geronic circulating factors in relation to development of vascular aging phenotypes are discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay age-related vascular pathologies by targeting fundamental cellular and molecular aging processes are presented.

CorrectionsAGRICULTURAL SCIENCES. For the article ''Characterization of capsaicin synthase and identification of its gene (csy1) for pungency factor capsaicin in pepper (Capsicum sp.),'' by B. C. Narasimha

Neurogenesis continues in the adult brain and is increased in certain pathological states. We reported recently that neurogenesis is enhanced in hippocampus of patients with Alzheimer's disease (AD). We now report that the effect of AD on neurogenesis can be reproduced in a transgenic mouse model. PDGF-APPSw,Ind mice, which express the Swedish and Indiana amyloid precursor protein mutations, show increased incorporation of BrdUrd and expression of immature neuronal markers in two neuroproliferative regions: the dentate gyrus and subventricular zone. These changes, consisting of Ϸ2-fold increases in the number of BrdUrdlabeled cells, were observed at age 3 months, when neuronal loss and amyloid deposition are not detected. Because enhanced neurogenesis occurs in both AD and an animal model of AD, it seems to be caused by the disease itself and not by confounding clinical factors. As neurogenesis is increased in PDGF-APPSw,Ind mice in the absence of neuronal loss, it must be triggered by more subtle disease manifestations, such as impaired neurotransmission. Enhanced neurogenesis in AD and animal models of AD suggests that neurogenesis may be a compensatory response and that measures to enhance neurogenesis further could have therapeutic potential. N eurogenesis occurs in the adult brain and can be stimulated further by pathological processes, suggesting that newly generated neurons might be capable of replacing cells that are lost in neurological diseases. Animal models have been useful in identifying and characterizing injury-induced neurogenesis associated with epilepsy (1), ischemic stroke (2), and Parkinson's disease (3). Neurogenesis triggered by ischemia in rodents, for example, is associated with migration of newborn neurons from their sites of origin in the subventricular zone (SVZ) or dentate gyrus subgranular zone (DG-SGZ) into injured areas of the brain (4-6). Neurogenesis also generates functional neurons in adult human brain (7), and increased neurogenesis has been reported in patients with Huntington's disease (8) and Alzheimer's disease (AD) (9). These findings are encouraging with respect to prospects for cell-replacement therapy because the persistent stimulus-responsiveness of neurogenesis in neurodegenerative diseases indicates that additional stimulation and regulation by therapeutic interventions may be possible.Recently, we found that neurogenesis is increased in the DG-SGZ from patients with AD (9). Compared to controls, AD brains showed increased expression of the immature neuronal markers doublecortin (DCX), embryonic nerve cell adhesion molecule, neurogenic differentiation factor Neuro D, and turned-on-after-division͞Ulip-1͞CRMP-4. Expression of DCX and turned-on-after-division͞Ulip-1͞CRMP-4 was associated with neurons in DG-SGZ, the DG granule cell layer, which is the physiological destination of these neurons, and the CA1 region of Ammon's horn, which is the principal site of hippocampal pathology in AD. These findings suggest that neurogenesis is increased in AD hippocampus, where it ...

Vascular pathology is a major feature of Alzheimer's disease (AD) and other dementias. We recently showed that chronic administration of the target-of-rapamycin (TOR) inhibitor rapamycin, which extends lifespan and delays aging, halts the progression of AD-like disease in transgenic human (h)APP mice modeling AD when administered before disease onset. Here we demonstrate that chronic reduction of TOR activity by rapamycin treatment started after disease onset restored cerebral blood flow (CBF) and brain vascular density, reduced cerebral amyloid angiopathy and microhemorrhages, decreased amyloid burden, and improved cognitive function in symptomatic hAPP (AD) mice. Like acetylcholine (ACh), a potent vasodilator, acute rapamycin treatment induced the phosphorylation of endothelial nitric oxide (NO) synthase (eNOS) and NO release in brain endothelium. Administration of the NOS inhibitor L-NG-Nitroarginine methyl ester reversed vasodilation as well as the protective effects of rapamycin on CBF and vasculature integrity, indicating that rapamycin preserves vascular density and CBF in AD mouse brains through NOS activation. Taken together, our data suggest that chronic reduction of TOR activity by rapamycin blocked the progression of AD-like cognitive and histopathological deficits by preserving brain vascular integrity and function. Drugs that inhibit the TOR pathway may have promise as a therapy for AD and possibly for vascular dementias.