Pan-Neuronal Expression of Human Mutant Huntingtin Protein in Drosophila Impairs Immune Response of Hemocytes

Huntington’s disease (HD) is a late-onset; progressive, dominantly inherited neurological disorder marked by an abnormal expansion of polyglutamine (poly Q) repeats in Huntingtin (HTT) protein. The pathological effects of mutant Huntingtin (mHTT) are not restricted to the nervous system but systemic abnormalities including immune dysregulation have been evidenced in clinical and experimental settings of HD. Indeed, mutant huntingtin (mHTT) is ubiquitously expressed and could induce cellular toxicity by directly acting on immune cells. However, it is still unclear if selective expression ofmHTT exon1 in neurons could induce immune responses and hemocyte function. In the present study, we intended to monitor perturbations in the hemocytes population and their physiological functions in Drosophila, caused by pan-neuronal expression of mHTT protein. We found that pan-neuronal expression of mHtt significantly alters crystal cells and plasmatocyte count in larvae and adults with disease progression. Interestingly, plasmatocytes isolated from diseased conditions exhibit a gradual decline in phagocytic activity ex vivo at progressive stages of the disease as compared to age-matched control groups. We also observed an increased production of reactive oxygen species (ROS) in plasmatocytes at advanced stages of the disease. In addition, diseased flies displayed elevated reactive oxygen species (ROS) in circulating plasmatocytes at the larval stage and in sessile plasmatocytes of hematopoietic pockets at of disease. All the parameters were monitored progressively, targeting the circulation at larvae stage and hematopoietic pockets in adults at different disease stages, and many alterations were documented in the early stage itself. These findings strongly implicate that neuronal expression of mHtt alone is sufficient to induce non-cell-autonomous immune dysregulation in vivo. Based on these findings, we propose that further insight into the mechanisms through which neuronal expression of mHtt might be inflicting the innate immune responses would facilitate therapeutic inventions aimed at amelioration of HD pathology and improving the quality of life of the patients.

Systemic AAV6-synapsin-GFP administration results in lower liver biodistribution, compared to AAV1&2 and AAV9, with neuronal expression following ultrasound-mediated brain delivery

Non-surgical gene delivery to the brain can be achieved following intravenous injection of viral vectors coupled with transcranial MRI-guided focused ultrasound (MRIgFUS) to temporarily and locally permeabilize the blood–brain barrier. Vector and promoter selection can provide neuronal expression in the brain, while limiting biodistribution and expression in peripheral organs. To date, the biodistribution of adeno-associated viruses (AAVs) within peripheral organs had not been quantified following intravenous injection and MRIgFUS delivery to the brain. We evaluated the quantity of viral DNA from the serotypes AAV9, AAV6, and a mosaic AAV1&2, expressing green fluorescent protein (GFP) under the neuron-specific synapsin promoter (syn). AAVs were administered intravenously during MRIgFUS targeting to the striatum and hippocampus in mice. The syn promoter led to undetectable levels of GFP expression in peripheral organs. In the liver, the biodistribution of AAV9 and AAV1&2 was 12.9- and 4.4-fold higher, respectively, compared to AAV6. The percentage of GFP-positive neurons in the FUS-targeted areas of the brain was comparable for AAV6-syn-GFP and AAV1&2-syn-GFP. In summary, MRIgFUS-mediated gene delivery with AAV6-syn-GFP had lower off-target biodistribution in the liver compared to AAV9 and AAV1&2, while providing neuronal GFP expression in the striatum and hippocampus.

Altered Brain Adiponectin Receptor Expression in the 5XFAD Mouse Model of Alzheimer’s Disease

Metabolic syndromes share common pathologies with Alzheimer’s disease (AD). Adiponectin, an adipocyte-derived protein, regulates energy metabolism via its receptors, AdipoR1 and AdipoR2. To investigate the distribution of adiponectin receptors (AdipoRs) in Alzheimer’s, we examined their expression in the aged 5XFAD mouse model of AD. In age-matched wild-type mice, we observed neuronal expression of both ARs throughout the brain as well as endothelial expression of AdipoR1. The pattern of receptor expression in the aged 5XFAD brain was significantly perturbed. Here, we observed decreased neuronal expression of both ARs and decreased endothelial expression of AdipoR1, but robust expression of AdipoR2 in activated astrocytes. We also observed AdipoR2-expressing astrocytes in the dorsomedial hypothalamic and thalamic mediodorsal nuclei, suggesting the possibility that astrocytes utilise AdipoR2 signalling to fuel their activated state in the AD brain. These findings provide further evidence of a metabolic disturbance and demonstrate a potential shift in energy utilisation in the AD brain, supporting imaging studies performed in AD patients.

An evolutionarily conserved metallophosphodiesterase is a determinant of lifespan in Drosophila

Evolutionarily conserved genes usually have a critical role to play during organismal aging and longevity. Here, we show that a previously uncharacterized Class III metallophosphoesterase in Drosophila, an ortholog of the MPPED1 and MPPED2 proteins in mammals, is necessary for optimal lifespan. dMPPED is the product of the gene CG16717 and hydrolyzed a variety of phosphodiester substrates in a metal-dependent manner. dMPPED was expressed widely during development and in the adult fly. Deletion of the gene in flies dramatically reduced lifespan, without affecting development or fecundity. Longevity was restored on ubiquitous expression of the protein, and neuronal expression of both wild type and the catalytically inactive form of dMPPED was also able to restore normal lifespan. Overexpression of the protein, both ubiquitously and neuronally in wild type flies extended lifespan by ~ 20%. RNA-seq analysis of dMPPEDKO flies revealed mis-regulation of innate immune pathways, a number of transcription factors and genes earlier reported to affect aging and lifespan. Importantly, neuronal expression of mammalian MPPED2 was able to rescue lifespan in dMPPEDKO flies, but not extend lifespan in wild type flies. This reports the first description of the biological role of an evolutionarily conserved metallophosphoesterase that may serve as a scaffolding protein in diverse signaling pathways to modulate longevity in the fly.