Targeting whole body metabolism and mitochondrial bioenergetics in the drug development for Alzheimer's disease

Aging is by far the most prominent risk factor for Alzheimer's disease (AD), and both aging and AD are associated with apparent metabolic alterations. As developing effective therapeutic interventions to treat AD is clearly in urgent need, the impact of modulating whole-body and intracellular metabolism in preclinical models and in human patients, on disease pathogenesis, have been explored. There is also an increasing awareness of differential risk and potential targeting strategies related to biological sex, microbiome, and circadian regulation. As a major part of intracellular metabolism, mitochondrial bioenergetics, mitochondrial quality-control mechanisms, and mitochondria-linked inflammatory responses have been considered for AD therapeutic interventions. This review summarizes and highlights these efforts.

Tobacco hairy root's peroxidases are rhythmically controlled by phenol exposure

Plants like almost all living organisms, have developed a biological clock or circadian clock (CC) capable of synchronizing and adjusting various metabolic and physiological processes at certain times of the day and in a period of 24 h. This endogenous timekeeping is able to predict the environmental changes providing adaptive advantages against stressful conditions. Therefore, the aim of this work was to analyze the possible link between metabolism of xenobiotic compounds (MXC) and the CC. Synchronized Nicotiana tabacum hairy roots (HRs) were used as a validated plant model system, and peroxidases (PODs), key enzymes of the phase I in the MCX, were evaluated after phenol treatment. Two POD genes were selected and their temporal expression profiles as well as the total POD activity were analyzed in order to find circadian oscillations either under control conditions or phenol treatment. It was demonstrated that these PODs genes showed oscillatory profiles with an ultradian period (period length shorter than the circadian period), and preserving the same phases and expression peaks still under phenol treatment. The total PODs activity showed also a marked oscillatory behavior mainly in phenol-treated HRs with the highest levels at ZT23. Untreated HRs showed decrease and increase in the intensity of some basic isoforms at light and dark phase, respectively, while in phenol- treated HRs, an increase in the intensity of almost all isoforms was observed, mainly during the dark phase, being coincident with the high PODs activity detected at ZT23. The periodic analysis determined an ultradian period either in total POD activity or in the POD activity of isoform VI, being 18.7 and 15.3 h, respectively. Curiously, in phenol treated HRs, the period length of total POD activity was longer than in untreated HRs, suggesting that phenol could induce a marked oscillatory behavior in the POD activity with better performance during the dark phase, which explain the higher phenol removal efficiencies at ZT23. These findings showed novel information about the performance of PODs, which would be rhythmically controlled at biochemical level, by phenol exposure.

Impact of phenol on the glycerophospholipid turnover and potential role of circadian clock in the plant response against this pollutant in tobacco hairy roots

Glycerophospholipids (GPLs) from cell membranes (CM) are a proper source for the synthesis of lipid messengers able to activate signal pathways that will define the plant survival under changing and stressful environmental conditions. Little is known about how GPLs metabolism (GPLsM) is regulated and the effects of phenol treatment on GPLs composition. In this work, we studied the effects of phenol both on GPLs turnover and on the expression of GPLsM-related genes potentially regulated by the circadian clock, using tobacco hairy root cultures (HRC). Phenol decreased the total PC levels and increased PE, PG and CL levels in the dark phase. Different molecular species of PC and PE showed the same trend than the total PC and PE upon phenol treatment. Besides, significant differences in the expression of all studied genes related to GPLsM were found. NtCCT2 expression was affected at all analyzed times while NtPECT1 and NtAAPT1 showed similar expression patterns. NtCDS1, NtPGPS2 and NtCLS genes showed significant and differential expression profiles both in untreated and treated HRC. PECT1 and NtPGPS2 genes seem to conserve a circadian expression profile mainly in untreated HRC. However, phenol was able to modify the GPLs composition and the expression of genes related to GPLs synthesis. The GPLs modification could be explained by the up-regulation of NtPECT1, NtAAPT1 and NtCLS genes during the dark phase, suggesting for being a crucial moment for HRC to trigger an adaptive response against this organic pollutant.

GABA in the suprachiasmatic nucleus refines circadian output rhythms in mice

In mammals, the circadian rhythms are regulated by the central clock located in the hypothalamic suprachiasmatic nucleus (SCN), which is composed of heterogeneous neurons with various neurotransmitters. Among them an inhibitory neurotransmitter, γ-Amino-Butyric-Acid (GABA), is expressed in almost all SCN neurons, however, its role in the circadian physiology is still unclear. Here, we show that the SCN of fetal mice lacking vesicular GABA transporter (VGAT-/-) or GABA synthesizing enzyme, glutamate decarboxylase (GAD65-/-/67-/-), shows burst firings associated with large Ca2+ spikes throughout 24 hours, which spread over the entire SCN slice in synchrony. By contrast, circadian PER2 rhythms in VGAT-/- and GAD65-/-/67-/- SCN remain intact. SCN-specific VGAT deletion in adult mice dampens circadian behavior rhythm. These findings indicate that GABA in the fetal SCN is necessary for refinement of the circadian firing rhythm and, possibly, for stabilizing the output signals, but not for circadian integration of multiple cellular oscillations.

Overview and Evaluation of Recent Methods for Statistical Inference of Gene Regulatory Networks from Time Series Data

A challenging problem in systems biology is the reconstruction of gene regulatory networks from postgenomic data. A variety of reverse engineering methods from machine learning and computational statistics have been proposed in the literature. However, deciding on the best method to adopt for a particular application or data set might be a confusing task. The present chapter provides a broad overview of state-of-the-art methods with an emphasis on conceptual understanding rather than a deluge of mathematical details, and the pros and cons of the various approaches are discussed. Guidance on practical applications with pointers to publicly available software implementations are included. The chapter concludes with a comprehensive comparative benchmark study on simulated data and a real-work application taken from the current plant systems biology.

Kidney volume, kidney function, and ambulatory blood pressure in children born extremely preterm with and without nephrocalcinosis

BACKGROUND

Reduced kidney volume (KV) following prematurity is a proxy for reduced nephron number and is associated with the development of hypertension and end-stage renal disease in adults. We investigated whether extreme prematurity affects KV, function, and blood pressure in school-aged children and if nephrocalcinosis (NC) developed during the neonatal period had additional effects.

METHODS

We investigated 60 children at a mean age of 7.7 years: 20 born extremely preterm (EPT < 28 weeks gestational age with NC (NC+)), 20 born EPT without NC (NC-), and 19 born as full-term infants (control). We measured KV by ultrasound, collected blood and urine samples to evaluate renal function, and measured office and 24-h ambulatory blood pressure (ABPM).

RESULTS

Children born EPT had significantly smaller kidneys (EPT (NC+ NC-) vs control (estimated difference, 11.8 (CI - 21.51 to - 2.09 ml), p = 0.018) and lower but normal cystatin C-based glomerular filtration rate compared with control (estimated difference, - 10.11 (CI - 0.69 to - 19.5), p = 0.035). KV and function were not different between NC+ and NC- groups. Change in KV in relation to BSA (KV/BSA) from the neonatal period to school age showed significantly more EPT children with neonatal NC having a negative evolution of KV (p = 0.01). Blood pressure was normal and not different between the 3 groups. Fifty percent of EPT had a less than 10% day-to-night decline in ABPM.

CONCLUSIONS

Kidney growth and volume is affected by EPT birth with NC being a potential aggravating factor. Circadian blood pressure regulation seems abnormal in EPT-born children.

Dissection of glucocorticoid receptor-mediated inhibition of the hypothalamic-pituitary-adrenal axis by gene targeting in mice

Negative feedback regulation of glucocorticoid (GC) synthesis and secretion occurs through the function of glucocorticoid receptor (GR) at sites in the hypothalamic-pituitary-adrenal (HPA) axis, as well as in brain regions such as the hippocampus, prefrontal cortex, and sympathetic nervous system. This function of GRs in negative feedback coordinates basal glucocorticoid secretion and stress-induced increases in secretion that integrate GC production with the magnitude and duration of the stressor. This review describes the effects of GR loss along major sites of negative feedback including the entire brain, the paraventricular nucleus of the hypothalamus (PVN), and the pituitary. In genetic mouse models, we evaluate circadian regulation of the HPA axis, stress-stimulated neuroendocrine response and behavioral activity, as well as the integrated response of organism metabolism. Our analysis provides information on contributions of region-specific GR-mediated negative feedback to provide insight in understanding HPA axis dysregulation and the pathogenesis of psychiatric and metabolic disorders.

Aquaporins and leaf hydraulics: poplar sheds new light

To help understand leaf hydraulic conductance (Kleaf) modulation under high irradiance, well-watered poplars (Populus trichocarpa Torr. & Gray ex Hook and Populus nigra L.) were studied diurnally at molecular and ecophysiological scales. Transcriptional and translational modulations of plasma membrane intrinsic protein (PIP) aquaporins were evaluated in leaf samples during diurnal time courses. Among the 15 poplar PIP genes, a subset of two PIP1s and seven PIP2s are precociously induced within the first hour of the photoperiod concomitantly with a Kleaf increase. Since expression patterns were cyclic and reproducible over several days, we hypothesized that endogenous signals could be involved in PIP transcriptional regulation. To address this question, plants were submitted to forced darkness during their subjective photoperiod and compared with their control counterparts, which showed that some PIP1s and PIP2s have circadian regulation while others did not. Promoter analysis revealed that a large number of hormone, light, stress response and circadian elements are present. Finally, involvement of aquaporins is supported by the reduction of Kleaf by HgCl2 treatment.