Molecular hysteresis: residual effects of hormones and glucose on genes during aging

Novel small molecules inhibit proteotoxicity and inflammation: Mechanistic and therapeutic implications for Alzheimer's Disease, healthspan and lifespan- Aging as a consequence of glycolysis

Inflammation drives many age-related, especially neurological, diseases, and likely mediates age-related proteotoxicity. For example, dementia due to Alzheimer's Disease (AD), cerebral vascular disease, many other neurodegenerative conditions is increasingly among the most devastating burdens on the American (and world) health system and threatens to bankrupt the American health system as the population ages unless effective treatments are developed. Dementia due to either AD or cerebral vascular disease, and plausibly many other neurodegenerative and even psychiatric conditions, is driven by increased age-related inflammation, which in turn appears to mediate Abeta and related proteotoxic processes. The functional significance of inflammation during aging is also supported by the fact that Humira, which is simply an antibody to the pro-inflammatory cytokine TNF-a, is the best-selling drug in the world by revenue. These observations led us to develop parallel high-throughput screens to discover small molecules which inhibit age-related Abeta proteotoxicity in a C. elegans model of AD AND LPS-induced microglial TNF-a. In the initial screen of 2560 compounds (Microsource Spectrum library) to delay Abeta proteotoxicity, the most protective compounds were, in order, phenylbutyrate, methicillin, and quetiapine, which belong to drug classes (HDAC inhibitors, beta lactam antibiotics, and tricyclic antipsychotics, respectably) already robustly implicated as promising to protect in neurodegenerative diseases, especially AD. RNAi and chemical screens indicated that the protective effects of HDAC inhibitors to reduce Abeta proteotoxicity are mediated by inhibition of HDAC2, also implicated in human AD, dependent on the HAT Creb binding protein (Cbp), which is also required for the protective effects of both dietary restriction and the daf-2 mutation (inactivation of IGF-1 signaling) during aging. In addition to methicillin, several other beta lactam antibiotics also delayed Abeta proteotoxicity and reduced microglial TNF-a. In addition to quetiapine, several other tricyclic antipsychotic drugs also delayed age-related Abeta proteotoxicity and increased microglial TNF-a, leading to the synthesis of a novel congener, GM310, which delays Abeta as well as Huntingtin proteotoxicity, inhibits LPS-induced mouse and human microglial and monocyte TNF-a, is highly concentrated in brain after oral delivery with no apparent toxicity, increases lifespan, and produces molecular responses highly similar to those produced by dietary restriction, including induction of Cbp inhibition of inhibitors of Cbp, and genes promoting a shift away from glycolysis and toward metabolism of alternate (e.g., lipid) substrates. GM310, as well as FDA-approved tricyclic congeners, prevented functional impairments and associated increase in TNF-a in a mouse model of stroke. Robust reduction of glycolysis by GM310 was functionally corroborated by flux analysis, and the glycolytic inhibitor 2-DG inhibited microglial TNF-a and other markers of inflammation, delayed Abeta proteotoxicity, and increased lifespan. These results support the value of phenotypic screens to discover drugs to treat age-related, especially neurological and even psychiatric diseases, including AD and stroke, and to clarify novel mechanisms driving neurodegeneration (e.g., increased microglial glycolysis drives neuroinflammation and subsequent neurotoxicity) suggesting novel treatments (selective inhibitors of microglial glycolysis).

Biological age and environmental risk factors for dementia and stroke: Molecular mechanisms

Since the development of antibiotics and vaccination, as well as major improvements in public hygiene, the main risk factors for morbidity and mortality are age and chronic exposure to environmental factors, both of which can interact with genetic predispositions. As the average age of the population increases, the prevalence and costs of chronic diseases, especially neurological conditions, are rapidly increasing. The deleterious effects of age and environmental risk factors, develop chronically over relatively long periods of time, in contrast to the relatively rapid deleterious effects of infectious diseases or accidents. Of particular interest is the hypothesis that the deleterious effects of environmental factors may be mediated by acceleration of biological age. This hypothesis is supported by evidence that dietary restriction, which universally delays age-related diseases, also ameliorates deleterious effects of environmental factors. Conversely, both age and environmental risk factors are associated with the accumulation of somatic mutations in mitotic cells and epigenetic modifications that are a measure of "biological age", a better predictor of age-related morbidity and mortality than chronological age. Here we review evidence that environmental risk factors such as smoking and air pollution may also drive neurological conditions, including Alzheimer's Disease, by the acceleration of biological age, mediated by cumulative and persistent epigenetic effects as well as somatic mutations. Elucidation of such mechanisms could plausibly allow the development of interventions which delay deleterious effects of both aging and environmental risk factors.

Glucose-Induced Transcriptional Hysteresis: Role in Obesity, Metabolic Memory, Diabetes, and Aging

During differentiation transient, inducers produce permanent changes in gene expression. A similar phenomenon, transcriptional hysteresis, produced by transient or prolonged exposure to glucose, leads to cumulative, persistent, and largely irreversible effects on glucose-regulated gene expression, and may drive key aspects of metabolic memory, obesity, diabetes, and aging, and explain the protective effects of dietary restriction during aging. The most relevant effects of glucose-induced transcriptional hysteresis are the persistent effects of elevated glucose on genes that control glucose metabolism itself. A key observation is that, as with the lac operon, glucose induces genes that promote glycolysis and inhibits gene expression of alternative metabolic pathways including the pentose pathway, beta oxidation, and the TCA cycle. A similar pattern of metabolic gene expression is observed during aging, suggesting that cumulative exposure to glucose during aging produces this metabolic shift. Conversely, dietary restriction, which increases lifespan and delays age-related impairments, produces the opposite metabolic profile, leading to a shift away from glycolysis and toward the use of alternative substrates, including lipid and ketone metabolisms. The effect of glucose on gene expression leads to a positive feedback loop that leads to metastable persistent expression of genes that promote glycolysis and inhibit alternative pathways, a phenomenon first observed in the regulation of the lac operon. On the other hand, this pattern of gene expression can also be inhibited by activation of peroxisome proliferator activating receptor transcription factors that promote beta oxidation and inhibit metabolism of glucose-derived carbon bonds in the TCA cycle. Several pathological consequences may arise from glucose-induced transcriptional hysteresis. First, elevated glucose induces glycolytic genes in pancreatic beta cells, which induces a semi-stable persistent increase in insulin secretion, which could drive obesity and insulin resistance, and also due to glucose toxicity could eventually lead to beta-cell decompensation and diabetes. Diabetic complications persist even after complete normalization of glucose, a phenomenon known as metabolic memory. This too can be explained by persistent bistable expression of glucose-induced glycolytic genes.

Testing the critical window of estradiol replacement on gene expression of vasopressin, oxytocin, and their receptors, in the hypothalamus of aging female rats

The current study tested the "critical window" hypothesis of menopause that postulates that the timing and duration of hormone treatment determine their potential outcomes. Our focus was genes in the rat hypothalamus involved in social and affiliative behaviors that change with aging and/or estradiol (E2): Avp, Avpr1a, Oxt, Oxtr, and Esr2 in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Rats were reproductively mature or aging adults, ovariectomized, given E2 or vehicle treatment of different durations, with or without a post-ovariectomy delay. Our hypothesis was that age-related changes in gene expression are mitigated by E2 treatments. Contrary to this, PVN Oxtr increased with E2, and Avpr1a increased with age. In the SON, Avpr1a increased with age, Oxtr with age and timing, and Avp was altered by duration. Thus, chronological age and E2 have independent actions on gene expression, with the "critical window" hypothesis supported by the observed timing and duration effects.

Secrets of the lac operon. Glucose hysteresis as a mechanism in dietary restriction, aging and disease

Elevated blood glucose associated with diabetes produces progressive and apparently irreversible damage to many cell types. Conversely, reduction of glucose extends life span in yeast, and dietary restriction reduces blood glucose. Therefore it has been hypothesized that cumulative toxic effects of glucose drive at least some aspects of the aging process and, conversely, that protective effects of dietary restriction are mediated by a reduction in exposure to glucose. The mechanisms mediating cumulative toxic effects of glucose are suggested by two general principles of metabolic processes, illustrated by the lac operon but also observed with glucose-induced gene expression. First, metabolites induce the machinery of their own metabolism. Second, induction of gene expression by metabolites can entail a form of molecular memory called hysteresis. When applied to glucose-regulated gene expression, these two principles suggest a mechanism whereby repetitive exposure to postprandial excursions of glucose leads to an age-related increase in glycolytic capacity (and reduction in beta-oxidation of free fatty acids), which in turn leads to an increased generation of oxidative damage and a decreased capacity to respond to oxidative damage, independent of metabolic rate. According to this mechanism, dietary restriction increases life span and reduces pathology by reducing exposure to glucose and therefore delaying the development of glucose-induced glycolytic capacity.

Changes in estrogenic regulation of estrogen receptor alpha mRNA and progesterone receptor mRNA in the female rat hypothalamus during aging: an in situ hybridization study

We examined two molecular responses to estrogen, reduction in estrogen receptor alpha (ER alpha) mRNA and increase in progesterone receptor (PR) mRNA, in the hypothalamus of 3- (young) and 10-month-old (middle-aged) cycling, and 15-month-old (old) acyclic, Fischer 344 female rats. The rats were ovariectomized and then given silastic capsules containing 5% 17beta-estradiol. or empty implants, and killed 4 days after implantation. By means of in situ hybridization, we found that, in young rats, estrogen reduced ER alpha mRNA in both the ventromedial hypothalamus (VMH) and arcuate nucleus (ARC) but not in the preoptic area (POA). In contrast, the effect of estrogen on ER alpha mRNA in the VMH and ARC of middle-aged and old rats was not statistically significant. On the other hand in all regions the induction of PR mRNA by estrogen was at least as strong in middle-aged and old as in young rats. The present study revealed that the induction of PR mRNA by estrogen in the hypothalamus was not impaired with age but ER alpha mRNA in the VMH and ARC was significantly impaired with age, but not in the POA.

Estrogen increases arginine-vasopressin V1a receptor mRNA in the preoptic area of young but not of middle-aged female rats

We determined whether estrogen regulates the expression of arginine-vasopressin (AVP) receptor mRNA in the preoptic area (POA) of female rats. By reverse transcription-polymerase chain reaction (PCR), we found that all three types of the AVP receptor mRNA, V1a, V1b and V2, were expressed in the POA, though the amount of PCR products was apparently different among them. In situ hybridization indicated that AVP V1a receptor mRNA was densely expressed in the POA, especially in the anteroventral periventricular nucleus of the POA; in contrast, AVP V1b and V2 receptor mRNAs were not abundant in this area. Finally, we demonstrated by Northern blot that estrogen significantly increased the expression of AVP V1a receptor mRNA in the POA of young ovariectomized rats. However, this regulation by estrogen was lost in middle-aged rats, indicating an age-related impairment in the regulation of AVP V1a receptor mRNA by estrogen in the POA.

Effects of quinidine, verapamil, nifedipine and ouabain on hysteresis in atrial refractoriness in the conscious dog: an approach to ionic mechanisms

1. This work determines the effects of quinidine, verapamil, nifedipine and ouabain on the hysteresis of the atrial effective refractory period (AERP) in the conscious dog. 2. AERP was always longer in the increasing phase than in the decreasing phase of the extrastimulus method, thus demonstrating the existence of AERP hysteresis. Calculated as the difference between the two values, hysteresis was between 8+/-0.8 and 11+/-1.0 msec. 3. Quinidine increased hysteresis from 9+/-0.7 to 13+/-0.7 msec, whereas verapamil decreased it from 10+/-0.9 to 5+/-0.5 msec and nifedipine did not affect it. Ouabain also lengthened hysteresis from 8+/-0.8 to 11+/-1.2 msec. 4. Thus, these results confirm the existence of a hysteresis phenomenon in the AERP in the conscious dog and are evidence that the fast sodium and slow calcium specific membrane currents participate in this phenomenon.

Changes in neurotensin mRNA by estrogen in the female rat preoptic area during aging: an in situ hybridization histochemistry study

The present study examined changes in the response of neurotensin mRNA to estrogen during aging at the single cell level. Ten days after ovariectomy, 3-, 10-, and 15-month-old female rats were implanted with estrogen or cholesterol and sacrificed 4 days later. An in situ hybridization study revealed that estrogen significantly increased the number of cells expressing neurotensin mRNA in the preoptic area of all age groups. Furthermore, frequency analysis indicated that estrogen significantly increased the proportion of heavily labeled cells in older rats but not in younger rats. Distributions of the grains/cells between cholesterol- and estrogen-treated rats suggested that older rats were at least as responsive to estrogen as young rats and possibly even more responsive. The result suggests that, at least as reflected by neurotensin mRNA, reproductive senescence in rats is not due to a general decrease in sensitivity to estrogen. Indeed, there is evidence of an increased responsiveness to estrogen with age.

Hysteresis in atrial refractoriness in the conscious dog: influence of stimulation parameters and control by the autonomic nervous system

This work (a) provides evidence for hysteresis in the atrial effective refractory period (AERP) in the conscious dog; (b) studies the main stimulation parameters that may affect this phenomenon; and (c) evaluates the influence of the autonomic nervous system. AERP was measured by the extrastimulus method in the conscious dog with chronic atrioventricular block (n = 6) during the increasing and decreasing phases of an S1S2 fixed protocol. AERP was longer during the increasing phase than during the decreasing phase, thus demonstrating hysteresis, calculated as the difference between the two values. Hysteresis was greater with an S1S1 basic cycle length of 300 ms than with a basic cycle length of 400 ms, 9 +/- 0.9, and 7 +/- 0.9 ms, respectively. It was also greater with trains of six basic cycles before each extrastimulus S2 than with trains of 12 basic cycles, 9 +/- 0.9 and 7 +/- 1.0 ms, respectively. Suppression of vagal tone with atropine reduced hysteresis from 8 +/- 0.6 to 4 +/- 0.6 ms, whereas suppression of cardioaccelerator tone with propranolol increased it from 9 +/- 0.9 to 14 +/- 1.2 ms. These data were confirmed by the neostigmine-induced increase in hysteresis from 8 +/- 0.8 to 11 +/- 0.8 ms and the isoproterenol-induced decrease in hysteresis from 9 +/- 0.6 to 4 +/- 0.4 ms. Overall, these results provide evidence for a hysteresis effect in the AERP in the conscious dog that is stimulation frequency-dependent and modulated by the autonomic nervous system with permanent increase by vagal tone and decrease by cardioaccelerator tone.