NFC   Project Summary        Last Update: 040520

The Unit of Cellular Neurophysiology has been working at Dibit, HSR since 1992.
Updated info about current research can be found in the following official links:
Grohovaz Lab Home Page within the Department of Neurosciences
Daniele Zacchetti and Fabio Grohovaz pages within the Ph.D. Program in Molecular Medicine (Neuroscience section)

Molecular mechanisms of astrocyte activation

Changes in the phenotype of astrocytes (a process known as "activation") frequently occur in the central nervous system in order to preserve the brain function in response to physiological and pathological stimuli. Astrocytes exposed to cytokines (IL-1beta, TNFalpha, INFgamma), trophic factors (FGF2), autacoids (PGE2, NO, ATP), neurotransmitters (glutamate), and toxic molecules (ROS, beta-amyloid) react by changing morphology, proliferation rate, as well as secretion of biologically active molecules. Under pathological conditions, glial cells can retain this state of activation, amplifying tissue damage through a feedforward loop. We are characterizing the multiple ways in which physiological and pathological stimuli can activate astrocytes and the corresponding changes in the secretion of proteins and small molecules affecting neuronal activity and survival. In particular, during the last year, we analyzed the mechanisms of astrocyte activation leading to an increase in COX-2 with ensuing massive release of PGE2. In parallel, we have been investigating the role PGE2 plays on target cells and the transduction pathways activated upon binding of PGE2 to its cognate receptor.
a combined videoimaging-patch clamp approach, along with pharmacological strategies, we are studying a novel Ca2+ oscillatory activity in rat chromaffin cells. This activity is sustained by modulation of membrane permeability to Ca2+, not by its release from intracellular stores. We intend to characterise the ionic mechanism triggering fast oscillations and the cellular functions that are under their control.

Mechanisms of Protein Kinase C activation in neurons

Protein Kinase C (PKC) is a signaling molecule that has important implications in neurotransmitter release, synaptic plasticity and neurodegeneration. These roles appear to be mainly sustained by the neuronal specific isoform, PKC-gamma, which belongs to the conventional PKC family (cPKCs). We focused our research on the characterization of the cytosolic signaling steps that lead to translocation, and thus activation, of PKC-gamma in hippocampal pyramidal neurons. The plasma membrane translocation of GFP-tagged PKC-gamma, as well as minimal domains of cPKC (such us the diacylglycerol-binding C1 domain), was followed by total internal reflection microscopy (TIRM, also known as evanescent wave microscopy). Our results show that PKC activation requires either a strong stimulation of the NMDA receptors or co-activation of ionotropic and metabotropic glutamate receptors. We are currently defining these signaling pathways and, in particular, the possible activation of PLC and PLD by local calcium increases.


Translational control of BACE-1 expression: a possible role in Alzheimer’s disease

BACE-1 is the beta-secretase that triggers the amyloidogenic processing of the amyloid precursor protein and thus a key step in the production of the toxic beta-amyloid peptide that accumulates in the brain of Alzheimer’s disease patients leading to the neurodegenerative process. Experimental overexpression of BACE-1 is per se able to increase the cellular secretion of beta-amyloid. Based on these considerations, BACE-1 represents the most promising pharmacological target for prevention and cure of the disease. Within the context of the control of BACE-1 expression, we are investigating the post-transcriptional events, in light of the lack of correspondence between BACE-1 transcript expression and protein/activity levels. The analysis of the transcript leader of BACE-1, led us to discover a tissue-specific alternative splicing that increases the translation efficiency of the transcript. Differential expression of BACE-1 transcripts with leaders of different lengths might explain why, in some AD patients, a higher BACE-1 protein and activity is not paralleled by an increase in the transcript levels.


Role of sphingosylphosphorylcholine in Niemann-Pick type A disease

Niemann-Pick type A is a genetic disease characterized by the absence of a functional ASM gene. The consequent lack of acidic sphingomyelinase activity leads to abnormal accumulation of sphingomyelin. Under these conditions, also sphingosylphosphorylcholine (SPC, a sphingomyelin metabolite) accumulates in various tissues, including brain, where it might act as a toxic stimulus, contributing to the appearance of the neurological symptoms. We are currently studying the effects of SPC onto the main cellular targets in the central nervous system, i.e. astrocytes and neurons. In particular we investigate the activation of intracellular signaling pathways as well as the possibility that soluble factors might be released by astrocytes leading to neurodegeneration. Our preliminary results show that SPC promotes in astrocytes a Ca2+-dependent release of glutamate that, in turn, leads to Ca2+ elevation in neurons. The interplay between astrocytes and neurons in SPC-induced neurodegeneration will be further explored.