A novel transgenic mouse expressing double mutant tau driven by its natural promoter exhibits tauopathy characteristics

The neurofibrillary-tangles (NTFs), characteristic of tauopathies including Alzheimer's-disease (AD), are the pathological features which correlate best with dementia. The objective of our study was to generate an authentic transgenic (tg) animal model for NFT pathology in tauopathy/AD. Previous NFT-tg mice were driven by non-related/non-homologous promoters. Our strategy was to use the natural tau promoter for expressing the human-tau (htau) gene with two mutations K257T/P301S (double mutant, DM) associated with severe phenotypes of frontotemporal-dementia in humans. Cellular, biochemical, behavioral and electrophysiological studies were subsequently conducted. The tg mice showed a tolerated physiological level of the DM-htau protein, mostly in cortex and hippocampus. The mice demonstrated tauopathy-like characteristics, which increased with age, that included NFT-related pathology, astrogliosis, argyrophilic plaque-like (amyloid-free) structures in brain, with memory deficits and signs of anxiety. Moreover, the tg mice showed a robust synaptic plasticity deficit selectively expressed in a severe impairment in their ability to maintain hippocampal long-term-potentiation (LTP) in response to stimulation of the perforant path, providing evidence that “tau-pathology only” is sufficient to cause this memory and learning-associated deficit. This is a unique mutant-htau-tg model which presents a wide spectrum of features characteristic of tauopathy/AD, which does not show unrelated motor deficits described in other models of tauopathy. In addition, expressing the DM-htau in a neuronal cell model resulted in tau-aggregation, as well as impaired microtubule arrangement. Both animal and cell models, which were regulated under the natural tau promoter (of rat origin), provide authentic and reliable models for tauopathy, and offer valuable tools for understanding the molecular events underlying tauopathies including AD.     

Astrocytes facilitate melanoma brain metastasis via secretion of IL‐23

Melanoma is the leading cause of skin cancer mortality. The major cause of melanoma mortality is metastasis to distant organs, frequently to the brain. The microenvironment plays a critical role in tumourigenesis and metastasis. In order to treat or prevent metastasis, the interactions of disseminated tumour cells with the microenvironment at the metastatic organ have to be elucidated. However, the role of brain stromal cells in facilitating metastatic growth is poorly understood. Astrocytes are glial cells that function in repair and scarring of the brain following injury, in part via mediating neuroinflammation, but the role of astrocytes in melanoma brain metastasis is largely unresolved. Here we show that astrocytes can be reprogrammed by human brain‐metastasizing melanoma cells to express pro‐inflammatory factors, including the cytokine IL‐23, which was highly expressed by metastases‐associated astrocytes in vivo. Moreover, we show that the interactions between astrocytes and melanoma cells are reciprocal: paracrine signalling from astrocytes up‐regulates the secretion of the matrix metalloproteinase MMP2 and enhances the invasiveness of brain‐metastasizing melanoma cells. IL‐23 was sufficient to increase melanoma cell invasion, and neutralizing antibodies to IL‐23 could block this enhanced migration, implying a functional role for astrocyte‐derived IL‐23 in facilitating the progression of melanoma brain metastasis. Knocking down the expression of MMP2 in melanoma cells resulted in inhibition of IL‐23‐induced invasiveness. Thus, our study demonstrates that bidirectional signalling between melanoma cells and astrocytes results in the formation of a pro‐inflammatory milieu in the brain, and in functional enhancement of the metastatic potential of disseminated melanoma cells. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

The role of the heterochronic microRNA let-7 in the progression of aging

Aging results in reduced tissue homeostasis and declined ability to replace damaged cells by new functional ones. In many tissues, homeostasis and repair are supported by tissue-specific stem cells that induce to generate differentiated cells in accordance with physiological requirements. Heterochronic genes, initially described in worms, specify the timing of fate decisions in each cell type and thus ensure a synchronized program of development throughout the animal. The heterochronic let-7 microRNA plays an important role in development by repressing cell fate regulators to promote stage progression. Recent studies reveal a new role of let-7 which occurs much later in life and regulates aging of several tissues, across species. In this article I review the current knowledge on the fate mechanisms of tissue stem cells during aging that are modulate by let-7, as well as its co-partners and its target genes. I also discuss the therapeutic potential of controlling heterochronic events as a possible treatment for aging‐related disorders. Timing is a clear dimension of organisms' development that may be difficult to witness in aging stages that are not as defined as in embryonic development. Exploring the regulation of stem cell aging by let-7 may ultimately reveal novel timing mechanisms.     

Histamine-2 receptor antagonists at night improve gastroesophageal reflux disease symptoms for patients on proton pump inhibitor therapy

While night-time symptoms of gastroesophageal reflux disease (GERD) are common, considerable controversy exists regarding the use of histamine-2 receptor antagonists (H2Ras) for night-time reflux control. Some studies have suggested possible tolerance to H2RA while others have suggested that long-term efficacy of gastric acid control can be maintained with night-time H2RA use. The aim of this study was to identify if GERD patients have sustained symptom improvement with long-term use of night-time H2RA. Records of 56 consecutive GERD patients on twice daily proton pump inhibitor (PPI) and night-time H2RA therapy were reviewed. During a phone interview patients were asked a 5-item questionnaire, which included overall assessment of symptoms, night-time symptoms, sleep disturbance, duration and frequency of therapy. Of the 56 patients, 39 (31 women, mean age 56) completed the questionnaire (15 were not reached and 2 did not recall enough information). All respondents had taken night-time H2RA for at least 1 month (28/39 patients with > 6 months duration) with 33/39 patients taking H2RAs every night. The addition of H2RA led to an improvement in overall symptoms in 28/39 (72%) patients, improvement in night-time reflux symptoms in 25/34 (74%) patients and improvement of GERD-associated sleep disturbance in 18/27 (67%) patients. Five (13%) patients had stopped the H2RA on their own, stating that its efficacy waned after 1 month. Our results suggest that the majority of patients report persistent improvement in GERD symptoms from night-time H2RA use and that possible clinically important tolerance to H2RAs occurs in a small number of patients. Further prospective, placebo-controlled studies may help confirm that there is a role for night-time H2RAs in GERD symptom control.     

Gout and hyperlipidaemia. Effect of overweight on the levels of circulating lipids

A study of the serum lipids in 90 patients with gout and 90 controls matched for age and weight index demonstrated that in gout there was a significant elevation of the mean serum levels of cholesterol (282 +/- 55 mg/100 ml), triglycerides (183 +/- 161 mg/100 ml) and phospholipids (270 +/- 61 mg/100 ml) compared with the controls whose mean values were respectively 243 +/- 41 mg, 95 +/- 53 mg and 245 +/- 36 mg. Hyperlipidaemia of mixed type was the most common lipid defect in the patients with gout; there was no difference in the frequency of pure hypercholesterolaemia (without hypertriglyceridaemia) between gout and the controls. The frequency of anomalies of blood lipid levels in gout does not result from (or not solely from) obesity since patients with gout and controls were matched for their weight and height. There was a correlation between the serum lipid levels and obesity in the controls but this was not demonstrable in the patients with gout.     

Multiple adaptive mechanisms to chronic liver disease revealed at early stages of liver carcinogenesis in the Mdr2-knockout mice

Molecular events preceding the development of hepatocellular carcinoma were studied in the Mdr2-knockout (Mdr2-KO) mice. These mice lack the liver-specific P-glycoprotein responsible for phosphatidylcholine transport across the canalicular membrane. Portal inflammation ensues at an early age followed by hepatocellular carcinoma development after the age of 1 year. Liver tissue samples of Mdr2-KO mice in the early and late precancerous stages of liver disease were subjected to histologic, biochemical, and gene expression profiling analysis. In an early stage, multiple protective mechanisms were found, including induction of many anti-inflammatory and antioxidant genes and increase of total antioxidant capacity of liver tissue. Despite stimulation of hepatocyte DNA replication, their mitotic activity was blocked at this stage. In the late stage of the disease, although the total antioxidant capacity of liver tissue of Mdr2-KO mice was normal, and inflammation was less prominent, many protective genes remained overexpressed. Increased mitotic activity of hepatocytes resulted in multiple dysplastic nodules, some of them being steatotic. Expression of many genes regulating lipid and phospholipid metabolism was distorted, including up-regulation of choline kinase A, a known oncogene. Many other oncogenes, including cyclin D1, Jun, and some Ras homologues, were up-regulated in Mdr2-KO mice at both stages of liver disease. However, we found no increase of Ras activation. Our data suggest that some of the adaptive mechanisms induced in the early stages of hepatic disease, which protect the liver from injury, could have an effect in hepatocarcinogenesis at later stages of the disease in this hepatocellular carcinoma model.