To reveal the putative cellular factors involved in SARS coronavirus replication, the helicase (Hel, nsp13) of SARS coronavirus was used to screen the cDNA library of rat pulmonary epithelial cells using the yeast two-hybrid system. Positively interacting proteins were further tested using a mammalian cell hybrid system and co-immunoprecipitation in the human A549 cell line, which has been shown to support SARS coronavirus replication. Out of the seven positive clones observed by yeast two-hybrid assay, only the Ddx5 (Asp-Glu-Ala-Asp box polypeptide 5) protein showed specific interaction with SARS-CoV helicase. When expression of DdX5 was knocked down by small interfering RNA (siRNA), SARS coronavirus replication was significantly inhibited in fetal rhesus kidney (FRhK-4) cells. Since Ddx5 is a multifunctional protein that plays important roles in transcriptional regulation, its interaction with SARS coronavirus helicase provides interesting clues for studying virus-host cell interactions in SARS-CoV infections.
The herbal medicine Tong Luo Jiu Nao (TLJN) contains geniposide (GP) and ginsenoside Rg1 at a molar ratio of 10:1. Rg1 is the major component of another herbal medicine, panax notoginseng saponin (PNS). TLJN has been shown to strengthen brain function in humans, and in animals it improves learning and memory. We have previously shown that TLJN reduces amyloidogenic processing in Alzheimer's disease (AD) mouse models. Together this suggests TLJN may be a potential treatment for patients with dementia. Because chronic damage of the central nervous system by formaldehyde (FA) has been presented as a risk factor for age-associated cognitive dysfunction, in the present study we investigated the protective effect of both TLJN and GP in neuron-like cells exposed to FA. FA-exposed murine N2a neuroblastoma cells were incubated with TLJN, its main ingredient GP, as well as PNS, to measure cell viability and morphology, the rate of apoptosis and expression of genes encoding Akt, FOXO3, Bcl2 and p53. The CCK-8 assay, cytoskeletal staining and flow cytometry were used to test cell viability, morphology and apoptosis, respectively. Fluorescent quantitative real-time PCR (qRT-PCR) was used to monitor changes in gene expression, and HPLC to determine the rate of FA clearance. Treatment of N2a cells with 0.09 mmol L 1 FA for 24 h significantly reduced cell viability, changed cell morphology and promoted apoptosis. Both TLJN and GP conferred neuroprotection to FA-treated N2a cells, whereas PNS, which had to be used at lower concentrations because of its toxicity, did not. Our data demonstrate that TLJN can rescue neuronal damage caused by FA and that its main ingredient, GP, has a major role in this efficacy. This presents purified GP as a drug or lead compound for the treatment of AD. FA is a colorless, irritating gas with a high oxidation capa-
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