Rhenium in the core of porphyrin and rhenium bound to the periphery of porphyrin: synthesis and applications.

An overview of most of the well known rhenium porphyrins (rhenium in the core of porphyrins) is presented here reviewing their synthesis, coordination chemistry, and applications. The important features of oxorhenium(v) porphyrins are discussed elaborately taking into account their application in epoxidation reaction. Moreover, the chemistry of some recently known porphyrin-Re conjugates (rhenium bound to the periphery of porphyrin) is reported considering their applications in the photochemical carbon dioxide reduction process and photodynamic therapy. The number of well characterized rhenium porphyrinoids are limited but they show interesting diverse properties, some of which are also discussed in this review.

Lifelong rapamycin administration ameliorates age-dependent cognitive deficits by reducing IL-1ß and enhancing NMDA signaling.

Understanding the factors that contribute to age-related cognitive decline is imperative, particularly as age is the major risk factor for several neurodegenerative disorders. Levels of several cytokines increase in the brain during aging, including IL-1ß, whose levels positively correlate with cognitive deficits. Previous reports show that reducing the activity of the mammalian target of rapamycin (mTOR) extends lifespan in yeast, nematodes, Drosophila, and mice. It remains to be established, however, whether extending lifespan with rapamycin is accompanied by an improvement in cognitive function. In this study, we show that 18-month-old mice treated with rapamycin starting at 2 months of age perform significantly better on a task measuring spatial learning and memory compared to age-matched mice on the control diet. In contrast, rapamycin does not improve cognition when given to 15-month-old mice with pre-existing, age-dependent learning and memory deficits. We further show that the rapamycin-mediated improvement in learning and memory is associated with a decrease in IL-1ß levels and an increase in NMDA signaling. This is the first evidence to show that a small molecule known to increase lifespan also ameliorates age-dependent learning and memory deficits.

Cognitive decline typical of frontotemporal lobar degeneration in transgenic mice expressing the 25-kDa C-terminal fragment of TDP-43.

Transactive response DNA-binding protein 43 (TDP-43) is the pathological signature protein in several neurodegenerative disorders, including the majority of frontotemporal lobar degeneration cases (FTLD-TDP), motor neuron disease, and amyotrophic lateral sclerosis. Pathological TDP-43 is mislocalized from its nuclear location to the cytoplasm, where it accumulates and is proteolytically cleaved to form C-terminal fragments. Although the 25-kDa C-terminal fragment of TDP-43 (TDP-25) accumulates in affected brain regions, its role in the disease pathogenesis remains elusive. To address this problem, we have generated a novel transgenic mouse that selectively expresses TDP-25 in neurons. We show that transgenic mice expressing TDP-25 develop cognitive deficits associated with the build-up of soluble TDP-25. These cognitive deficits are independent of TDP-43-positive inclusions and occur without overt neurodegeneration. Additionally, we show that the expression of TDP-25 is sufficient to alter the processing of endogenous full-length TDP-43. These studies represent the first in vivo demonstration of a pathological role for TDP-25 and strongly suggest that the onset of cognitive deficits in TDP-43 proteinopathies is independent of TDP-43 inclusions. These data provide a framework for understanding the molecular mechanisms underlying the onset of cognitive deficits in FTLD-TDP and other TDP-43 proteinopathies; thus, the TDP-25 transgenic mice represent a unique tool to reach this goal.

Inducing autophagy by rapamycin before, but not after, the formation of plaques and tangles ameliorates cognitive deficits.

Previous studies have shown that inducing autophagy ameliorates early cognitive deficits associated with the build-up of soluble amyloid-ß (Aß). However, the effects of inducing autophagy on plaques and tangles are yet to be determined. While soluble Aß and tau represent toxic species in Alzheimer's disease (AD) pathogenesis, there is well documented evidence that plaques and tangles also are detrimental to normal brain function. Thus, it is critical to assess the effects of inducing autophagy in an animal model with established plaques and tangles. Here we show that rapamycin, when given prophylactically to 2-month-old 3xTg-AD mice throughout their life, induces autophagy and significantly reduces plaques, tangles and cognitive deficits. In contrast, inducing autophagy in 15-month-old 3xTg-AD mice, which have established plaques and tangles, has no effects on AD-like pathology and cognitive deficits. In conclusion, we show that autophagy induction via rapamycin may represent a valid therapeutic strategy in AD when administered early in the disease progression.

Naturally secreted amyloid-beta increases mammalian target of rapamycin (mTOR) activity via a PRAS40-mediated mechanism.

Reducing the mammalian target of rapamycin (mTOR) activity increases lifespan and health span in a variety of organisms. Alterations in protein homeostasis and mTOR activity and signaling have been reported in several neurodegenerative disorders, including Alzheimer disease (AD); however, the causes of such deregulations remain elusive. Here, we show that mTOR activity and signaling are increased in cell lines stably transfected with mutant amyloid precursor protein (APP) and in brains of 3xTg-AD mice, an animal model of AD. In addition, we show that in the 3xTg-AD mice, mTOR activity can be reduced to wild type levels by genetically preventing Aß accumulation. Similarly, intrahippocampal injections of an anti-Aß antibody reduced Aß levels and normalized mTOR activity, indicating that high Aß levels are necessary for mTOR hyperactivity in 3xTg-AD mice. We also show that the intrahippocampal injection of naturally secreted Aß is sufficient to increase mTOR signaling in the brains of wild type mice. The mechanism behind the Aß-induced mTOR hyperactivity is mediated by the proline-rich Akt substrate 40 (PRAS40) as we show that the activation of PRAS40 plays a key role in the Aß-induced mTOR hyperactivity. Taken together, our data show that Aß accumulation, which has been suggested to be the culprit of AD pathogenesis, causes mTOR hyperactivity by regulating PRAS40 phosphorylation. These data further indicate that the mTOR pathway is one of the pathways by which Aß exerts its toxicity and further support the idea that reducing mTOR signaling in AD may be a valid therapeutic approach.

CBP gene transfer increases BDNF levels and ameliorates learning and memory deficits in a mouse model of Alzheimer's disease.

Cognitive dysfunction and memory loss are common features of Alzheimer's disease (AD). Abnormalities in the expression profile of immediate early genes that play a critical role in memory formation, such as the cAMP-response element binding protein (CREB), have been reported in the brains of AD patients. Here we show that amyloid-ß (Aß) accumulation, which plays a primary role in the cognitive deficits of AD, interferes with CREB activity. We further show that restoring CREB function via brain viral delivery of the CREB-binding protein (CBP) improves learning and memory deficits in an animal model of AD. Notably, such improvements occur without changes in Aß and tau pathology, and instead are linked to an increased level of brain-derived neurotrophic factor. The resulting data suggest that Aß-induced learning and memory deficits are mediated by alterations in CREB function, based on the finding that restoring CREB activity by directly modulating CBP levels in the brains of adult mice is sufficient to ameliorate learning and memory. Therefore, increasing CBP expression in adult brains may be a valid therapeutic approach not only for AD, but also for various brain disorders characterized by alterations in immediate early genes, further supporting the concept that viral vector delivery may be a viable therapeutic approach in neurodegenerative diseases.

Molecular interplay between mammalian target of rapamycin (mTOR), amyloid-beta, and Tau: effects on cognitive impairments.

Accumulation of amyloid-beta (Abeta) and Tau is an invariant feature of Alzheimer disease (AD). The upstream role of Abeta accumulation in the disease pathogenesis is widely accepted, and there is strong evidence showing that Abeta accumulation causes cognitive impairments. However, the molecular mechanisms linking Abeta to cognitive decline remain to be elucidated. Here we show that the buildup of Abeta increases the mammalian target of rapamycin (mTOR) signaling, whereas decreasing mTOR signaling reduces Abeta levels, thereby highlighting an interrelation between mTOR signaling and Abeta. The mTOR pathway plays a central role in controlling protein homeostasis and hence, neuronal functions; indeed mTOR signaling regulates different forms of learning and memory. Using an animal model of AD, we show that pharmacologically restoring mTOR signaling with rapamycin rescues cognitive deficits and ameliorates Abeta and Tau pathology by increasing autophagy. Indeed, we further show that autophagy induction is necessary for the rapamycin-mediated reduction in Abeta levels. The results presented here provide a molecular basis for the Abeta-induced cognitive deficits and, moreover, show that rapamycin, an FDA approved drug, improves learning and memory and reduces Abeta and Tau pathology.

Rapamycin rescues TDP-43 mislocalization and the associated low molecular mass neurofilament instability.

TDP-43 is a nuclear protein involved in exon skipping and alternative splicing. Recently, TDP-43 has been identified as the pathological signature protein in frontotemporal lobar degeneration with ubiquitin-positive inclusions and in amyotrophic lateral sclerosis. In addition, TDP-43-positive inclusions are present in Parkinson disease, dementia with Lewy bodies, and 30% of Alzheimer disease cases. Pathological TDP-43 is redistributed from the nucleus to the cytoplasm, where it accumulates. An approximately 25-kDa C-terminal fragment of TDP-43 accumulates in affected brain regions, suggesting that it may be involved in the disease pathogenesis. Here, we show that overexpression of the 25-kDa C-terminal fragment is sufficient to cause the mislocalization and cytoplasmic accumulation of endogenous full-length TDP-43 in two different cell lines, thus recapitulating a key biochemical characteristic of TDP-43 proteinopathies. We also found that TDP-43 mislocalization is associated with a reduction in the low molecular mass neurofilament mRNA levels. Notably, we show that the autophagic system plays a role in TDP-43 metabolism. Specifically, we found that autophagy inhibition increases the accumulation of the C-terminal fragments of TDP-43, whereas inhibition of mTOR, a key protein kinase involved in autophagy regulation, reduces the 25-kDa C-terminal fragment accumulation and restores TDP-43 localization. Our results suggest that autophagy induction may be a valid therapeutic target for TDP-43 proteinopathies.