Non-Rodent Genetic Animal Models for Studying Tauopathy: Review of Drosophila, Zebrafish, and C. elegans Models.

Tauopathy refers to a group of progressive neurodegenerative diseases, including frontotemporal lobar degeneration and Alzheimer's disease, which correlate with the malfunction of microtubule-associated protein Tau (MAPT) due to abnormal hyperphosphorylation, leading to the formation of intracellular aggregates in the brain. Despite extensive efforts to understand tauopathy and develop an efficient therapy, our knowledge is still far from complete. To find a solution for this group of devastating diseases, several animal models that mimic diverse disease phenotypes of tauopathy have been developed. Rodents are the dominating tauopathy models because of their similarity to humans and established disease lines, as well as experimental approaches. However, powerful genetic animal models using Drosophila, zebrafish, and C. elegans have also been developed for modeling tauopathy and have contributed to understanding the pathophysiology of tauopathy. The success of these models stems from the short lifespans, versatile genetic tools, real-time in-vivo imaging, low maintenance costs, and the capability for high-throughput screening. In this review, we summarize the main findings on mechanisms of tauopathy and discuss the current tauopathy models of these non-rodent genetic animals, highlighting their key advantages and limitations in tauopathy research.

Short-term exposure to dim light at night disrupts rhythmic behaviors and causes neurodegeneration in fly models of tauopathy and Alzheimer's disease.

The accumulation and aggregation of phosphorylated tau proteins in the brain are the hallmarks for the onset of Alzheimer's disease (AD). In addition, disruptions in circadian rhythms (CRs) with altered sleep-wake cycles, dysregulation of locomotion, and increased memory defects have been reported in patients with AD. Drosophila flies that have an overexpression of human tau protein in neurons exhibit most of the symptoms of human patients with AD, including locomotion defects and neurodegeneration. Using the fly model for tauopathy/AD, we investigated the effects of an exposure to dim light at night on AD symptoms. We used a light intensity of 10 lux, which is considered the lower limit of light pollution in many countries. After the tauopathy flies were exposed to the dim light at night for 3 days, the flies showed disrupted CRs, altered sleep-wake cycles due to increased pTau proteins and neurodegeneration, in the brains of the AD flies. The results indicate that the nighttime exposure of tauopathy/AD model Drosophila flies to dim light disrupted CR and sleep-wake behavior and promoted neurodegeneration.

Loss of IP3 receptor function in neuropeptide secreting neurons leads to obesity in adult Drosophila.

BACKGROUND: Intracellular calcium signaling regulates a variety of cellular and physiological processes. The inositol 1,4,5 trisphosphate receptor (IP3R) is a ligand gated calcium channel present on the membranes of endoplasmic reticular stores. In previous work we have shown that Drosophila mutants for the IP3R (itprku) become unnaturally obese as adults with excessive storage of lipids on a normal diet. While the phenotype manifests in cells of the fat body, genetic studies suggest dysregulation of a neurohormonal axis. RESULTS: We show that knockdown of the IP3R, either in all neurons or in peptidergic neurons alone, mimics known itpr mutant phenotypes. The peptidergic neuron domain includes, but is not restricted to, the medial neurosecretory cells as well as the stomatogastric nervous system. Conversely, expression of an itpr+ cDNA in the same set of peptidergic neurons rescues metabolic defects of itprku mutants. Transcript levels of a gene encoding a gastric lipase CG5932 (magro), which is known to regulate triacylglyceride storage, can be regulated by itpr knockdown and over-expression in peptidergic neurons. Thus, the focus of observed itpr mutant phenotypes of starvation resistance, increased body weight, elevated lipid storage and hyperphagia derive primarily from peptidergic neurons. CONCLUSIONS: The present study shows that itpr function in peptidergic neurons is not only necessary but also sufficient for maintaining normal lipid metabolism in Drosophila. Our results suggest that intracellular calcium signaling in peptidergic neurons affects lipid metabolism by both cell autonomous and non-autonomous mechanisms.

The prominin-like Gene Expressed in a Subset of Dopaminergic Neurons Regulates Locomotion in Drosophila.

CD133, also known as prominin-1, was first identified as a biomarker of mammalian cancer and neural stem cells. Previous studies have shown that the prominin-like (promL) gene, an orthologue of mammalian CD133 in Drosophila, plays a role in glucose and lipid metabolism, body growth, and longevity. Because locomotion is required for food sourcing and ultimately the regulation of metabolism, we examined the function of promL in Drosophila locomotion. Both promL mutants and pan-neuronal promL inhibition flies displayed reduced spontaneous locomotor activity. As dopamine is known to modulate locomotion, we also examined the effects of promL inhibition on the dopamine concentration and mRNA expression levels of tyrosine hydroxylase (TH) and DOPA decarboxylase (Ddc), the enzymes responsible for dopamine biosynthesis, in the heads of flies. Compared with those in control flies, the levels of dopamine and the mRNAs encoding TH and Ddc were lower in promL mutant and pan-neuronal promL inhibition flies. In addition, an immunostaining analysis revealed that, compared with control flies, promL mutant and pan-neuronal promL inhibition flies had lower levels of the TH protein in protocerebral anterior medial (PAM) neurons, a subset of dopaminergic neurons. Inhibition of promL in these PAM neurons reduced the locomotor activity of the flies. Overall, these findings indicate that promL expressed in PAM dopaminergic neurons regulates locomotion by controlling dopamine synthesis in Drosophila.

UBE4B, a microRNA-9 target gene, promotes autophagy-mediated Tau degradation.

The formation of hyperphosphorylated intracellular Tau tangles in the brain is a hallmark of Alzheimer's disease (AD). Tau hyperphosphorylation destabilizes microtubules, promoting neurodegeneration in AD patients. To identify suppressors of tau-mediated AD, we perform a screen using a microRNA (miR) library in Drosophila and identify the miR-9 family as suppressors of human tau overexpression phenotypes. CG11070, a miR-9a target gene, and its mammalian orthologue UBE4B, an E3/E4 ubiquitin ligase, alleviate eye neurodegeneration, synaptic bouton defects, and crawling phenotypes in Drosophila human tau overexpression models. Total and phosphorylated Tau levels also decrease upon CG11070 or UBE4B overexpression. In mammalian neuroblastoma cells, overexpression of UBE4B and STUB1, which encodes the E3 ligase CHIP, increases the ubiquitination and degradation of Tau. In the Tau-BiFC mouse model, UBE4B and STUB1 overexpression also increase oligomeric Tau degradation. Inhibitor assays of the autophagy and proteasome systems reveal that the autophagy-lysosome system is the major pathway for Tau degradation in this context. These results demonstrate that UBE4B, a miR-9 target gene, promotes autophagy-mediated Tau degradation together with STUB1, and is thus an innovative therapeutic approach for AD.

Prominin-like Regulates Longevity and Glucose Metabolism via Insulin Signaling in Drosophila.

CD133, also called Prominin-1, is a biomarker for mammalian stem cells. It is involved in cell growth, development, and tumor biology. However, the function of CD133 at the organismal level has not been investigated. In this study, we found that prominin-like (promL) loss-of-function mutant flies show an extended life span and metabolic defects such as increased circulating carbohydrates, lipid storage, and starvation resistance. The messenger RNA expression levels of Drosophila insulin-like peptides (Dilps) were reduced in loss-of-function promL mutants. Furthermore, the level of phosphorylated AKT, a downstream component of insulin signaling, was lower in promL loss-of-function mutants than in the w- control flies. Importantly, the PromL protein is predominantly expressed in the pars intercerebralis region with insulin-producing cells of the adult brain. When we inhibited promL in insulin-producing cells, these flies showed an extended life span, metabolic defects, and reduced insulin signaling. These results indicate that the promL gene regulates longevity and glucose metabolism by controlling insulin signaling in Drosophila.

Altered lipid homeostasis in Drosophila InsP3 receptor mutants leads to obesity and hyperphagia.

Obesity is a complex metabolic disorder that often manifests with a strong genetic component in humans. However, the genetic basis for obesity and the accompanying metabolic syndrome is poorly defined. At a metabolic level, obesity arises from an imbalance between the nutritional intake and energy utilization of an organism. Mechanisms that sense the metabolic state of the individual and convey this information to satiety centers help achieve this balance. Mutations in genes that alter or modify such signaling mechanisms are likely to lead to either obese individuals, who in mammals are at high risk for diabetes and cardiovascular disease, or excessively thin individuals with accompanying health problems. Here we show that Drosophila mutants for an intracellular calcium signaling channel, the inositol 1,4,5-trisphosphate receptor (InsP3R) store excess triglycerides in their fat bodies and become unnaturally obese on a normal diet. Although excess insulin signaling can rescue obesity in InsP3R mutants to some extent, we show that it is not the only cause of the defect. Through mass spectrometric analysis of lipids we find that homeostasis of storage and membrane lipids are altered in InsP3R mutants. Possibly as a compensatory mechanism, InsP3R mutant adults also feed excessively. Thus, reduced InsP3R function alters lipid metabolism and causes hyperphagia in adults. Together, the metabolic and behavioral changes lead to obesity. Our results implicate altered InsP3 signaling as a previously unknown causative factor for metabolic syndrome in humans. Importantly, our studies also suggest preventive dietary interventions.

Insulin-like antigen of mangrove leaves and its anti-diabetic activity in alloxan-induced diabetic rats.

The objective of this study was to evaluate the anti-diabetic potential of three mangrove plants, Rhizophora mucronata, Rhizophora apiculata and Rhizophora annamalayana, and to detect the presence of their insulin-like protein. The in vivo anti-diabetic experiment was done on male albino Wister rats. Oral administration of 60 mg kg(-1) leaf powder extract of the three different mangrove plants for 30 days modulated the parameters such as blood glucose, plasma insulin, body weight, total haemoglobin, glycosylated haemoglobin, liver glycogen, plasma and tissue lipids, cholesterol, triglycerides, free fatty acids and phospholipids to normal levels in the alloxan-induced diabetic rats. The anti-diabetic activity of R. apiculata was more pronounced than that of the other mangrove extracts, but it was on a par with the commercial drug glibenclamide. The presence of an insulin-like protein in the mangrove extracts was detected by SDS-PAGE analysis and confirmed through ELISA. Hence, the anti-diabetic activity and the presence of an insulin-like protein in Rhizophora species were proved scientifically.

Effect of Mangrove Tea Extract from Ceriops decandra (Griff.) Ding Hou. on Salivary Bacterial Flora of DMBA Induced Hamster Buccal Pouch Carcinoma.

The objective of this study was to investigate the effects of mangrove tea on salivary bacterial flora in DMBA induced hamster buccal pouch carcinoma. Tea from mangrove plant Ceriops decandra was administered against DMBA induced buccal pouch carcinoma in hamster rats. The chemical constitutions and quality of mangrove tea is similar with the commercial tea Camellia sinensis. The Hamster rats were painted thrice a week with DMBA in their right buccal pouch, and also administrated orally with 1.25% of Ceriops tea extract, on alternate days of the DMBA treatment. Appropriate control animals were maintained. After 14 weeks of treatment, bacterial species in saliva were enumerated, tumor incidences were analyzed using histopathological section and tumor volume in the animals was quantified using water-displaced method. The decreased counts of beneficial bacteria and increased counts of harmful bacteria were associated with increased volume of tumors. The present study concluded that the tea extract from C. decandra prevents the oral cancer incidences and maintain the good health conditions of the animals.