Prenatal treatment with preimplantation factor improves early postnatal neurogenesis and cognitive impairments in a mouse model of Down syndrome.

Down syndrome (DS) is a genetic disease characterized by a supernumerary chromosome 21. Intellectual deficiency (ID) is one of the most prominent features of DS. Central nervous system defects lead to learning disabilities, motor and language delays, and memory impairments. At present, a prenatal treatment for the ID in DS is lacking. Subcutaneous administration of synthetic preimplantation factor (sPIF, a peptide with a range of biological functions) in a model of severe brain damage has shown neuroprotective and anti-inflammatory properties by directly targeting neurons and microglia. Here, we evaluated the effect of PIF administration during gestation and until weaning on Dp(16)1Yey mice (a mouse model of DS). Possible effects at the juvenile stage were assessed using behavioral tests and molecular and histological analyses of the brain. To test the influence of perinatal sPIF treatment at the adult stage, hippocampus-dependent memory was evaluated on postnatal day 90. Dp(16)1Yey pups showed significant behavioral impairment, with impaired neurogenesis, microglial cell activation and a low microglial cell count, and the deregulated expression of genes linked to neuroinflammation and cell cycle regulation. Treatment with sPIF restored early postnatal hippocampal neurogenesis, with beneficial effects on astrocytes, microglia, inflammation, and cell cycle markers. Moreover, treatment with sPIF restored the level of DYRK1A, a protein that is involved in cognitive impairments in DS. In line with the beneficial effects on neurogenesis, perinatal treatment with sPIF was associated with an improvement in working memory in adult Dp(16)1Yey mice. Perinatal treatment with sPIF might be an option for mitigating cognitive impairments in people with DS.

Type 2 Diabetes Mellitus and Alzheimer's Disease: Shared Molecular Mechanisms and Potential Common Therapeutic Targets.

The global prevalence of diabetes mellitus and Alzheimer's disease is increasing alarmingly with the aging of the population. Numerous epidemiological data suggest that there is a strong association between type 2 diabetes and an increased risk of dementia. These diseases are both degenerative and progressive and share common risk factors. The amyloid cascade plays a key role in the pathophysiology of Alzheimer's disease. The accumulation of amyloid beta peptides gradually leads to the hyperphosphorylation of tau proteins, which then form neurofibrillary tangles, resulting in neurodegeneration and cerebral atrophy. In Alzheimer's disease, apart from these processes, the alteration of glucose metabolism and insulin signaling in the brain seems to induce early neuronal loss and the impairment of synaptic plasticity, years before the clinical manifestation of the disease. The large amount of evidence on the existence of insulin resistance in the brain during Alzheimer's disease has led to the description of this disease as "type 3 diabetes". Available animal models have been valuable in the understanding of the relationships between type 2 diabetes and Alzheimer's disease, but to date, the mechanistical links are poorly understood. In this non-exhaustive review, we describe the main molecular mechanisms that may link these two diseases, with an emphasis on impaired insulin and IGF-1 signaling. We also focus on GSK3ß and DYRK1A, markers of Alzheimer's disease, which are also closely associated with pancreatic ß-cell dysfunction and type 2 diabetes, and thus may represent common therapeutic targets for both diseases.

DYRK1A and Activity-Dependent Neuroprotective Protein Comparative Diagnosis Interest in Cerebrospinal Fluid and Plasma in the Context of Alzheimer-Related Cognitive Impairment in Down Syndrome Patients.

Down syndrome (DS) is a complex genetic condition due to an additional copy of human chromosome 21, which results in the deregulation of many genes. In addition to the intellectual disability associated with DS, adults with DS also have an ultrahigh risk of developing early onset Alzheimer's disease dementia. DYRK1A, a proline-directed serine/threonine kinase, whose gene is located on chromosome 21, has recently emerged as a promising plasma biomarker in patients with sporadic Alzheimer's disease (AD). The protein DYRK1A is truncated in symptomatic AD, the increased truncated form being associated with a decrease in the level of full-length form. Activity-dependent neuroprotective protein (ADNP), a key protein for the brain development, has been demonstrated to be a useful marker for symptomatic AD and disease progression. In this study, we evaluated DYRK1A and ADNP in CSF and plasma of adults with DS and explored the relationship between these proteins. We used mice models to evaluate the effect of DYRK1A overexpression on ADNP levels and then performed a dual-center cross-sectional human study in adults with DS in Barcelona (Spain) and Paris (France). Both cohorts included adults with DS at different stages of the continuum of AD: asymptomatic AD (aDS), prodromal AD (pDS), and AD dementia (dDS). Non-trisomic controls and patients with sporadic AD dementia were included for comparison. Full-form levels of DYRK1A were decreased in plasma and CSF in adults with DS and symptomatic AD (pDS and dDS) compared to aDS, and in patients with sporadic AD compared to controls. On the contrary, the truncated form of DYRK1A was found to increase both in CSF and plasma in adults with DS and symptomatic AD and in patients with sporadic AD with respect to aDS and controls. ADNP levels showed a more complex structure. ADNP levels increased in aDS groups vs. controls, in agreement with the increase in levels found in the brains of mice overexpressing DYRK1A. However, symptomatic individuals had lower levels than aDS individuals. Our results show that the comparison between full-length and truncated-form levels of DYRK1A coupled with ADNP levels could be used in trials targeting pathophysiological mechanisms of dementia in individuals with DS.

DYRK1A Overexpression in Mice Downregulates the Gonadotropic Axis and Disturbs Early Stages of Spermatogenesis.

Down syndrome (DS) is the most common chromosomal disorder. It is responsible for intellectual disability (ID) and several medical conditions. Although men with DS are thought to be infertile, some spontaneous paternities have been reported. The few studies of the mechanism of infertility in men with DS are now dated. Recent research in zebrafish has indicated that overexpression of DYRK1A (the protein primarily responsible for ID in DS) impairs gonadogenesis at the embryonic stage. To better ascertain DYRK1A's role in infertility in DS, we investigated the effect of DYRK1A overexpression in a transgenic mouse model. We found that overexpression of DYRK1A impairs fertility in transgenic male mice. Interestingly, the mechanism in mice differs slightly from that observed in zebrafish but, with disruption of the early stages of spermatogenesis, is similar to that seen in humans. Unexpectedly, we observed hypogonadotropic hypogonadism in the transgenic mice.

Metabolic Diseases and Down Syndrome: How Are They Linked Together?

Down syndrome is a genetic disorder caused by the presence of a third copy of chromosome 21, associated with intellectual disabilities. Down syndrome is associated with anomalies of both the nervous and endocrine systems. Over the past decades, dramatic advances in Down syndrome research and treatment have helped to extend the life expectancy of these patients. Improved life expectancy is obviously a positive outcome, but it is accompanied with the need to address previously overlooked complications and comorbidities of Down syndrome, including obesity and diabetes, in order to improve the quality of life of Down syndrome patients. In this focused review, we describe the associations between Down syndrome and comorbidities, obesity and diabetes, and we discuss the understanding of proposed mechanisms for the association of Down syndrome with metabolic disorders. Drawing molecular mechanisms through which Type 1 diabetes and Type 2 diabetes could be linked to Down syndrome could allow identification of novel drug targets and provide therapeutic solutions to limit the development of metabolic and cognitive disorders.

Monosodium Glutamate Supplementation Improves Bone Status in Mice Under Moderate Protein Restriction.

Adequate protein intake during development is critical to ensure optimal bone gain and to attain a higher peak bone mass later. Using a mild protein restriction model in Balb/C mice consuming 6% of their total energy intake as soy protein (LP-SOY)-for which we observed a significantly lower femoral cortical thickness, bone volume, trabecular number, and thickness reduction-we evaluated the effects of monosodium glutamate (MSG) supplementation at different concentrations (0.5, 1, 5, 10, and 20 g/kg of diet) on bone characteristics in LP-SOY-fed mice. After 6 and 12 weeks, LP-SOY-fed mice had lower BMD and reduced body weight related to lower lean mass, which was associated with a reduced IGF-1 level. The negative effect of the LP-SOY diet on BMD correlated with impaired bone formation. MSG supplementation, at 5, 10, and 20 g/kg of diet, and PTH injection, used as a positive control, were able to improve BMD and to increase osteoblast activity markers (P1NP and osteocalcin), as well as glutamine plasma concentration. An analysis of bone microarchitecture found that cortical bone was less sensitive to protein restriction than trabecular bone, and that MSG ingestion was able to preserve bone quality through an increase of collagen synthesis, although it did not allow normal bone growth. Our study reinforces the view that glutamate can act as a functional amino acid for bone physiology and support clinical investigation of glutamate supplementation in adults characterized by poor bone status, notably as a result of insufficient protein intake. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

The Arabidopsis TOR Kinase Specifically Regulates the Expression of Nuclear Genes Coding for Plastidic Ribosomal Proteins and the Phosphorylation of the Cytosolic Ribosomal Protein S6.

Protein translation is an energy consuming process that has to be fine-tuned at both the cell and organism levels to match the availability of resources. The target of rapamycin kinase (TOR) is a key regulator of a large range of biological processes in response to environmental cues. In this study, we have investigated the effects of TOR inactivation on the expression and regulation of Arabidopsis ribosomal proteins at different levels of analysis, namely from transcriptomic to phosphoproteomic. TOR inactivation resulted in a coordinated down-regulation of the transcription and translation of nuclear-encoded mRNAs coding for plastidic ribosomal proteins, which could explain the chlorotic phenotype of the TOR silenced plants. We have identified in the 5' untranslated regions (UTRs) of this set of genes a conserved sequence related to the 5' terminal oligopyrimidine motif, which is known to confer translational regulation by the TOR kinase in other eukaryotes. Furthermore, the phosphoproteomic analysis of the ribosomal fraction following TOR inactivation revealed a lower phosphorylation of the conserved Ser240 residue in the C-terminal region of the 40S ribosomal protein S6 (RPS6). These results were confirmed by Western blot analysis using an antibody that specifically recognizes phosphorylated Ser240 in RPS6. Finally, this antibody was used to follow TOR activity in plants. Our results thus uncover a multi-level regulation of plant ribosomal genes and proteins by the TOR kinase.

Sugar metabolism and the plant target of rapamycin kinase: a sweet operaTOR?

In eukaryotes, the ubiquitous TOR (target of rapamycin) kinase complexes have emerged as central regulators of cell growth and metabolism. The plant TOR complex 1 (TORC1), that contains evolutionary conserved protein partners, has been shown to be implicated in various aspects of C metabolism. Indeed Arabidopsis lines affected in the expression of TORC1 components show profound perturbations in the metabolism of several sugars, including sucrose, starch, and raffinose. Metabolite profiling experiments coupled to transcriptomic analyses of lines affected in TORC1 expression also reveal a wider deregulation of primary metabolism. Moreover recent data suggest that the kinase activity of TORC1, which controls biological outputs like mRNA translation or autophagy, is directly regulated by soluble sugars.

The bacterial effector DspA/E is toxic in Arabidopsis thaliana and is required for multiplication and survival of fire blight pathogen.

The type III effector DspA/E is an essential pathogenicity factor of the phytopathogenic bacterium Erwinia amylovora. We showed that DspA/E was required for transient bacterial growth in nonhost Arabidopsis thaliana leaves, as an E. amylovora dspA/E mutant was unable to grow. We expressed DspA/E in A. thaliana transgenic plants under the control of an oestradiol-inducible promoter, and found that DspA/E expressed in planta restored the growth of a dspA/E mutant. DspA/E expression in these transgenic plants led to the modulation by at least two-fold of the expression of 384 genes, mostly induced (324 genes). Both induced and repressed genes contained high proportions of defence genes. DspA/E expression ultimately resulted in plant cell death without requiring a functional salicylic acid signalling pathway. Analysis of A. thaliana transgenic seedlings expressing a green fluorescent protein (GFP):DspA/E fusion indicated that the fusion protein could only be detected in a few cells per seedling, suggesting the degradation or absence of accumulation of DspA/E in plant cells. Consistently, we found that DspA/E repressed plant protein synthesis when injected by E. amylovora or when expressed in transgenic plants. Thus, we conclude that DspA/E is toxic to A. thaliana: it promotes modifications, among which the repression of protein synthesis could be determinant in the facilitation of necrosis and bacterial growth.

Mutations in the Arabidopsis homolog of LST8/GßL, a partner of the target of Rapamycin kinase, impair plant growth, flowering, and metabolic adaptation to long days.

The conserved Target of Rapamycin (TOR) kinase forms high molecular mass complexes and is a major regulator of cellular adaptations to environmental cues. The Lethal with Sec Thirteen 8/G protein ß subunit-like (LST8/GßL) protein is a member of the TOR complexes, and two putative LST8 genes are present in Arabidopsis thaliana, of which only one (LST8-1) is significantly expressed. The Arabidopsis LST8-1 protein is able to complement yeast lst8 mutations and interacts with the TOR kinase. Mutations in the LST8-1 gene resulted in reduced vegetative growth and apical dominance with abnormal development of flowers. Mutant plants were also highly sensitive to long days and accumulated, like TOR RNA interference lines, higher amounts of starch and amino acids, including proline and glutamine, while showing reduced concentrations of inositol and raffinose. Accordingly, transcriptomic and enzymatic analyses revealed a higher expression of genes involved in nitrate assimilation when lst8-1 mutants were shifted to long days. The transcriptome of lst8-1 mutants in long days was found to share similarities with that of a myo-inositol 1 phosphate synthase mutant that is also sensitive to the extension of the light period. It thus appears that the LST8-1 protein has an important role in regulating amino acid accumulation and the synthesis of myo-inositol and raffinose during plant adaptation to long days.

EDS1 contributes to nonhost resistance of Arabidopsis thaliana against Erwinia amylovora.

Erwinia amylovora causes fire blight in rosaceous plants. In nonhost Arabidopsis thaliana, E. amylovora triggers necrotic symptoms associated with transient bacterial multiplication, suggesting either that A. thaliana lacks a susceptibility factor or that it actively restricts E. amylovora growth. Inhibiting plant protein synthesis at the time of infection led to an increase in necrosis and bacterial multiplication and reduced callose deposition, indicating that A. thaliana requires active protein synthesis to restrict E. amylovora growth. Analysis of the callose synthase-deficient pmr4-1 mutant indicated that lack of callose deposition alone did not lead to increased sensitivity to E. amylovora. Transcriptome analysis revealed that approximately 20% of the genes induced following E. amylovora infection are related to defense and signaling. Analysis of mutants affected in NDR1 and EDS1, two main components of the defense-gene activation observed, revealed that E. amylovora multiplied ten times more in the eds1-2 mutant than in the wild type but not in the ndr1-1 mutant. Analysis of mutants affected in three WRKY transcription factors showing EDS1-dependent activation identified WRKY46 and WRKY54 as positive regulators and WRKY70 as a negative regulator of defense against E. amylovora. Altogether, we show that EDS1 is a positive regulator of nonhost resistance against E. amylovora in A. thaliana and hypothesize that it controls the production of several effective defenses against E. amylovora through the action of WRKY46 and WRKY54, while WRKY70 acts as a negative regulator.

Regulation of plant growth and metabolism by the TOR kinase.

The TOR (target of rapamycin) kinase is present in nearly all eukaryotic organisms and regulates a wealth of biological processes collectively contributing to cell growth. The genome of the model plant Arabidopsis contains a single TOR gene and two RAPTOR (regulatory associated protein of TOR)/KOG1 (Kontroller of growth 1) and GßL/LST8 (G-protein ß-subunit-like/lethal with Sec thirteen 8) genes but, in contrast with other organisms, plants appear to be resistant to rapamycin. Disruption of the RAPTOR1 and TOR genes in Arabidopsis results in an early arrest of embryo development. Plants that overexpress the TOR mRNA accumulate more leaf and root biomass, produce more seeds and are more resistant to stress. Conversely, the down-regulation of TOR by constitutive or inducible RNAi (RNA interference) leads to a reduced organ growth, to an early senescence and to severe transcriptomic and metabolic perturbations, including accumulation of sugars and amino acids. It thus seems that plant growth is correlated to the level of TOR expression. We have also investigated the effect of reduced TOR expression on tissue organization and cell division. We suggest that, like in other eukaryotes, the plant TOR kinase could be one of the main contributors to the link between environmental cues and growth processes.

The Arabidopsis TOR kinase links plant growth, yield, stress resistance and mRNA translation.

Plants, unlike animals, have plastic organ growth that is largely dependent on environmental information. However, so far, little is known about how this information is perceived and transduced into coherent growth and developmental decisions. Here, we report that the growth of Arabidopsis is positively correlated with the level of expression of the TARGET OF RAPAMYCIN (TOR) kinase. Diminished or augmented expression of the AtTOR gene results in a dose-dependent decrease or increase, respectively, in organ and cell size, seed production and resistance to osmotic stress. Strong downregulation of AtTOR expression by inducible RNA interference also leads to a post-germinative halt in growth and development, which phenocopies the action of the plant hormone abscisic acid, to an early senescence and to a reduction in the amount of translated messenger RNA. Thus, we propose that the AtTOR kinase is one of the contributors to the link between environmental cues and growth processes in plants.