The herbal compound geniposide rescues formaldehyde-induced apoptosis in N2a neuroblastoma cells

The herbal medicine Tong Luo Jiu Nao （TLJN） contains geniposide （GP） and ginsenoside Rgl at a molar ratio of i0：1. Rgl 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 amyloi- dogenic 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 in- gredient 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, mor- phology 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 signifi- cantly 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 ef- ficacy. This presents purified GP as a drug or lead compound for the treatment of AD.

Visualizing the microtubule-associated protein tau in the nucleus

Although tau is mainly known as an axonal microtubule-associated protein,many studies indicate that it is not restricted to this subcellular compartment.Assessing tau’s subcellular distribution,however,is not trivial as is evident from transgenic mouse studies.When human tau is over-expressed,it can be immunohistochemically localized to axons and the somatodendritic domain,modeling what is found in neurodegenerative diseases such as Alzheimer’s disease.Yet,in wild-type mice,despite its abundance,tau is difficult to visualize even in the axon.It is even more challenging to detect this protein in the nucleus,where tau has been proposed to protect DNA from damage.To establish a framework for future studies into tau’s nuclear functions,we compared several methods to visualize endogenous nuclear tau in cell lines and mouse brain.While depending on the fixation and permeabilization protocol,we were able to detect nuclear tau in SH-SY5Y human neuroblastoma cells,we failed to do so in N2a murine neuroblastoma cells.As a second method we used subcellular fractionation of mouse tissue and found that in the nucleus tau is mainly present in a hypophosphorylated form.When either full-length or truncated human tau was expressed,both accumulated in the cytoplasm,but were also found in the nuclear fraction.Because subcellular fractionation methods have their limitations,we finally isolated nuclei to probe for nuclear tau and found that the nuclei were free of cytoplasmic contamination.Together our analysis identifies several protocols for detecting tau in the nucleus where it is found in a less phosphorylated form.