Stress responses in down syndrome neurodegeneration: State of the art and therapeutic molecules

Down syndrome (DS) is the most common genomic disorder characterized by the increased incidence of developing early Alzheimer’s disease (AD). In DS, the triplication of genes on chromosome 21 is intimately associated with the increase of AD pathological hallmarks and with the development of brain redox imbalance and aberrant proteostasis. Increasing evidence has re-cently shown that oxidative stress (OS), associated with mitochondrial dysfunction and with the failure of antioxidant responses (e.g., SOD1 and Nrf2), is an early signature of DS, promoting protein oxidation and the formation of toxic protein aggregates. In turn, systems involved in the surveil-lance of protein synthesis/folding/degradation mechanisms, such as the integrated stress response (ISR), the unfolded stress response (UPR), and autophagy, are impaired in DS, thus exacerbating brain damage. A number of pre-clinical and clinical studies have been applied to the context of DS with the aim of rescuing redox balance and proteostasis by boosting the antioxidant response and/or inducing the mechanisms of protein re-folding and clearance, and at final of reducing cognitive decline. So far, such therapeutic approaches demonstrated their efficacy in reverting several aspects of DS phenotype in murine models, however, additional studies aimed to translate these approaches in clinical practice are still needed

Can the size of the contact area body-ground influence the presence of acute pulmonary emphysema in cases of incomplete hanging?

In a recently published study, we showed that acute pulmonary emphysema (APE) was present in cases of death by incomplete hanging and absent in cases of complete hanging. This result suggested a possible role of the hanging position on the respiratory distress of these victims. To further investigate this hypothesis, in the present study, we compared cases of incomplete hanging with a small contact area between body and ground (group A) to cases of incomplete hanging with a large contact area (group B). As positive and negative control group, we investigated cases of freshwater drowning (group C) and acute external bleeding (group D) respectively. Pulmonary samples were histologically examined, and the mean alveolar area (MAA) for each group was measured by digital morphometric analysis. MAA was 23,485 μm <sup>2</sup> for group A and 31,426 μm <sup>2</sup> for group B (p < 0.05). MAA of group B was similar to MAA of positive control group (33,135 μm <sup>2</sup> ) and MAA of group A was similar to MAA of negative control group (21,991 μm <sup>2</sup> ). These results seem to confirm our hypothesis and suggest that the size of the contact area between body and ground influences the presence of APE. Furthermore, the present study showed that APE can be proposed as a vitality sign in incomplete hanging, but only in cases with a large contact area between body and ground

BVR-A deficiency leads to autophagy impairment through the dysregulation of AMPK/mTOR axis in the brain—Implications for neurodegeneration

Biliverdin reductase-A (BVR-A) impairment is associated with increased accumulation of oxidatively-damaged proteins along with the impairment of autophagy in the brain during neurodegenerative disorders. Reduced autophagy inhibits the clearance of misfolded proteins, which then form neurotoxic aggregates promoting neuronal death. The aim of our study was to clarify the role for BVR-A in the regulation of the mTOR/autophagy axis by evaluating age-associated changes (2, 6 and 11 months) in cerebral cortex samples collected from BVR-A knock-out (BVR-A−/−) and wild-type (WT) mice. Our results show that BVR-A deficiency leads to the accumulation of oxidatively-damaged proteins along with mTOR hyper-activation in the cortex. This process starts in juvenile mice and persists with aging. mTOR hyper-activation is associated with the impairment of autophagy as highlighted by reduced levels of Beclin-1, LC3β, LC3II/I ratio, Atg5–Atg12 complex and Atg7 in the cortex of BVR-A−/− mice. Furthermore, we have identified the dysregulation of AMP-activated protein kinase (AMPK) as a critical event driving mTOR hyper-activation in the absence of BVR-A. Overall, our results suggest that BVR-A is a new player in the regulation of autophagy, which may be targeted to arrive at novel therapeutics for diseases involving impaired autophagy

Brain insulin resistance triggers early onset Alzheimer disease in Down syndrome

Dysregulation of insulin signaling pathway with reduced downstream neuronal survival and plasticity mechanisms is a fundamental abnormality observed in Alzheimer's disease (AD) brain. This phenomenon, known as brain insulin resistance, is associated with poor cognitive performance and is driven by the uncoupling of insulin receptor (IR) from its direct substrate (IRS1). Considering that Down syndrome (DS) and AD neuropathology share many common features, we investigated metabolic aspects of neurodegeneration, i.e., brain insulin resistance, in DS and whether it would contribute to early onset AD in DS population. Changes of levels and activation of main brain proteins belonging to the insulin signaling pathway (i.e., IR, IRS1, PTEN, GSK3β, PKCζ, AS160, GLUT4) were evaluated. Furthermore, we analyzed whether changes of these proteins were associated with alterations of: (i) proteins regulating brain energy metabolism; (ii) APP cleavage; and (ii) regulation of synaptic plasticity mechanisms in post-mortem brain samples collected from people with DS before and after the development of AD pathology (DSAD) compared with their age-matched controls. We found that DS cases were characterized by key markers of brain insulin resistance (reduced IR and increased IRS1 inhibition) early in life. Furthermore, downstream from IRS1, an overall uncoupling among the proteins of insulin signaling was observed. Dysregulated brain insulin signaling was associated with reduced hexokinase II (HKII) levels and proteins associated with mitochondrial complexes levels as well as with reduced levels of syntaxin in DS cases. Tellingly, these alterations precede the development of AD neuropathology and clinical presentations in DS. We propose that markers of brain insulin resistance rise earlier with age in DS compared with the general population and may contribute to the cognitive impairment associated with the early development of AD in DS

The dysregulation of OGT/OGA cycle mediates Tau and APP neuropathology in down syndrome

Protein O-GlcNAcylation is a nutrient-related post-translational modification that, since its discovery some 30 years ago, has been associated with the development of neurodegenerative diseases. As reported in Alzheimer’s disease (AD), flaws in the cerebral glucose uptake translate into reduced hexosamine biosynthetic pathway flux and subsequently lead to aberrant protein O-GlcNAcylation. Notably, the reduction of O-GlcNAcylated proteins involves also tau and APP, thus promoting their aberrant phosphorylation in AD brain and the onset of AD pathological markers. Down syndrome (DS) individuals are characterized by the early development of AD by the age of 60 and, although the two conditions present the same pathological hallmarks and share the alteration of many molecular mechanisms driving brain degeneration, no evidence has been sought on the implication of O-GlcNAcylation in DS pathology. Our study aimed to unravel for the first time the role of protein O-GlcNacylation in DS brain alterations positing the attention of potential trisomy-related mechanisms triggering the aberrant regulation of OGT/OGA cycle. We demonstrate the disruption of O-GlcNAcylation homeostasis, as an effect of altered OGT and OGA regulatory mechanism, and confirm the relevance of O-GlcNAcylation in the appearance of AD hallmarks in the brain of a murine model of DS. Furthermore, we provide evidence for the neuroprotective effects of brain-targeted OGA inhibition. Indeed, the rescue of OGA activity was able to restore protein O-GlcNAcylation, and reduce AD-related hallmarks and decreased protein nitration, possibly as effect of induced autophagy

Targeted acetylation of NF-kappaB/RelA and histones by epigenetic drugs reduces post-ischemic brain injury in mice with an extended therapeutic window.

Nuclear factor-kappaB (NF-κB) p50/RelA is a key molecule with a dual effect in the progression of ischemic stroke. In harmful ischemia, but not in preconditioning insult, neurotoxic activation of p50/RelA is characterized by RelA-specific acetylation at Lys310 (K310) and deacetylation at other Lys residues. The derangement of RelA acetylation is associated with activation of Bim promoter. Objective: With the aim of producing neuroprotection by correcting altered acetylation of RelA in brain ischemia, we combined the pharmacological inhibition of histone deacetylase (HDAC) 1-3, the enzymes known to reduce global RelA acetylation, and the activation of sirtuin 1, endowed with a specific deacetylase activity on the K310 residue of RelA. To afford this aim, we tested the clinically used HDAC 1-3 inhibitor entinostat (MS-275) and the sirtuin 1 activator resveratrol. Methods: We used the mouse model of transient middle cerebral artery occlusion (MCAO) and primary cortical neurons exposed to oxygen glucose deprivation (OGD). Results: The combined use of MS-275 and resveratrol, by restoring normal RelA acetylation, elicited a synergistic neuroprotection in neurons exposed to OGD. This effect correlated with MS-275 capability to increase total RelA acetylation and resveratrol capability to reduce RelA K310 acetylation through the activation of an AMP-activated protein kinase-sirtuin 1 pathway. The synergistic treatment reproduced the acetylation state of RelA peculiar of preconditioning ischemia. Neurons exposed to the combined drugs totally recovered the optimal histone H3 acetylation.Neuroprotection was reproduced in mice subjected to MCAO and treated with MS-275 (20μg/kg and 200μg/kg) or resveratrol (6800μg/kg) individually. However, the administration of lowest doses of MS-275 (2μg/kg) and resveratrol (68μg/kg) synergistically reduced infarct volume and neurological deficits. Importantly, the treatment was effective even when administered 7h after the stroke onset. Chromatin immunoprecipitation analysis of cortices harvested from treated mice showed that the RelA binding and histone acetylation increased at the Bcl-x L promoter and decreased at the Bim promoter. Conclusion: Our study reveals that epigenetic therapy shaping acetylation of both RelA and histones may be a promising strategy to limit post-ischemic injury with an extended therapeutic window

Protein oxidative damage in UV-related skin cancer and dysplastic lesions contributes to neoplastic promotion and progression

The ultraviolet (UV) component of solar radiation is the major driving force of skin carcinogenesis. Most of studies on UV carcinogenesis actually focus on DNA damage while their proteome-damaging ability and its contribution to skin carcinogenesis have remained largely underexplored. A redox proteomic analysis of oxidized proteins in solar-induced neoplastic skin lesion and perilesional areas has been conducted showing that the protein oxidative burden mostly concerns a selected number of proteins participating to a defined set of functions, namely: chaperoning and stress response; protein folding/refolding and protein quality control; proteasomal function; DNA damage repair; protein-and vesicle-trafficking; cell architecture, adhesion/extracellular matrix (ECM) interaction; proliferation/oncosuppression; apoptosis/survival, all of them ultimately concurring either to structural damage repair or to damage detoxication and stress response. In peri-neoplastic areas the oxidative alterations are conducive to the persistence of genetic alterations, dysfunctional apoptosis surveillance, and a disrupted extracellular environment, thus creating the condition for transformant clones to establish, expand and progress. A comparatively lower burden of oxidative damage is observed in neoplastic areas. Such a finding can reflect an adaptive selection of best fitting clones to the sharply pro-oxidant neoplastic environment. In this context the DNA damage response appears severely perturbed, thus sustaining an increased genomic instability and an accelerated rate of neoplastic evolution. In conclusion UV radiation, in addition to being a cancer-initiating agent, can act, through protein oxidation, as a cancer-promoting agent and as an inducer of genomic instability concurring with the neoplastic progression of established lesions

Glutamatergic Reinnervation and Assembly of Glutamatergic Synapses in Adult Rat Skeletal Muscle Occurs at Cholinergic Endplates

After denervation of adult rat abdominal muscles, the postsynaptic apparatus of neuromuscular junctions (NMJs) retains its original architecture and clustering of acetylcholine receptors (AChRs). When descending fibers of the spinal cord are surgically diverted to this muscle by a nerve grafting procedure, supraspinal glutamatergic neurons can innervate muscle fibers and restore motor function; the newly formed NMJs switch from a cholinergic to a glutamatergic-type synapse. We show here that regenerating nerve endings contact the fibers in an area occupied by cholinergic endplates. These NMJs are morphologically indistinguishable from those in controls, but they differ in the subunit composition of AChRs. Moreover, by immunofluorescence and immunoelectron microscopy, new NMJs express glutamatergic synapse markers. The \u3b1-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR1 partially colocalizes with AChRs, and vesicular glutamate transporter 2 is localized in the presynaptic compartment. Immunoprecipitation analysis of membranes from reinnervated muscle showed that AMPA receptor subunits GluR1 and GluR2 coimmunoprecipitate with rapsyn, the AChR-anchoring protein at the NMJ. Taken together, these results indicate that cholinergic endplates can be targeted by new glutamatergic projections and that the clustering of AMPA receptors occurs there