Time-resolved endogenous chlorophyll fluorescence sensitivity to pH: study on Chlorella sp. algae.

To better understand pH-dependence of endogenous fluorescence of algae, we employed spectroscopy and microscopy methods, including advanced time-resolved fluorescence imaging microscopy (FLIM), using green algae Chlorella sp. as a model system. Absorption spectra confirmed two peaks, at 400-420 nm and 670 nm. Emission was maximal at 680 nm, with smaller peaks between 520 and 540 nm. Acidification led to a gradual decrease in the red fluorescence intensity with the maximum at 680 nm when excited by 450 nm laser. FLIM measurements, performed using 475 nm picoseconds excitation, uncovered that this effect is accompanied by a shortening of the tau1 fluorescence lifetime. Under severe acidification, we also noted an increase in the green fluorescence with a maximum between 520-540 nm and a shift toward 690-700 nm of the red fluorescence, accompanied by prolongation of the tau2 fluorescence lifetime. Gathered data increase our knowledge on the responsiveness of algae to acidification and indicate that endogenous fluorescence derived from chlorophylls can potentially serve as a biosensing tool for monitoring pH change in its natural environment.

Inhibition of NF-kappaB potentiates amyloid beta-mediated neuronal apoptosis.

One mechanism leading to neurodegeneration during Alzheimer's disease (AD) is amyloid beta peptide (Abeta) neurotoxicity. Abeta elicits in cultured central nervous system neurons a biphasic response: a low-dose neurotrophic response and a high-dose neurotoxic response. Previously we reported that NF-kappaB is activated by low doses of Abeta only. Here we show that NF-kappaB activation leads to neuroprotection. In primary neurons we found that a pretreatment with 0.1 microM Abeta-(1-40) protects against neuronal death induced with 10 microM Abeta-(1-40). As a known neuroprotective agent we next analyzed the effect of tumor necrosis factor alpha (TNF-alpha). Maximal activation of NF-kappaB was found with 2 ng/ml TNF-alpha. Pretreatment with TNF-alpha protected cerebellar granule cells from cell death induced by 10 microM Abeta-(1-40). This protection is described by an inverted U-shaped dose response and is maximal with a NF-kappaB-activating dose. The molecular specificity of this protective effect was analyzed by specific blockade of NF-kappaB activation. Overexpression of a transdominant negative IkappaB-alpha blocks NF-kappaB activation and potentiates Abeta-mediated neuronal apoptosis. Our findings show that activation of NF-kappaB is the underlying mechanism of the neuroprotective effect of low-dose Abeta and TNF-alpha. In accordance with these in vitro data we find that nuclear NF-kappaB immunoreactivity around various plaque stages of AD patients is reduced in comparison to age-matched controls. Taken together these data suggest that pharmacological NF-kappaB activation may be a useful approach in the treatment of AD and related neurodegenerative disorders.

Transcription factor NF-kappaB is activated in primary neurons by amyloid beta peptides and in neurons surrounding early plaques from patients with Alzheimer disease.

Amyloid beta peptide (A beta)-containing plaques are a hallmark of Alzheimer disease. Here, we show that the neurotoxic A beta, a major plaque component, is a potent activator of the transcription factor NF-kappaB in primary neurons. This activation required reactive oxygen intermediates as messengers because an antioxidant prevented A beta-induced NF-kappaB activation. Maximal activation of NF-kappaB was found with 0.1 microM A beta-(1-40) and 0.1 microM A beta-(25-35) fragments, making a role for NF-kappaB in neuroprotection feasible. Using an activity-specific mAb for the p65 NF-kappaB subunit, activation of NF-kappaB also was observed in neurons and astroglia of brain sections from Alzheimer disease patients. Activated NF-kappaB was restricted to cells in the close vicinity of early plaques. Our data suggest that the aberrant gene expression in diseased nervous tissue is at least in part due to A beta-induced activation of NF-kappaB, a potent immediate-early transcriptional regulator of numerous proinflammatory genes.