CNF1 Improves Astrocytic Ability to Support Neuronal Growth and Differentiation In vitro

Abstract

Modulation of cerebral Rho GTPases activity in mice brain by intracerebral administration of Cytotoxic Necrotizing Factor 1 (CNF1) leads to enhanced neurotransmission and synaptic plasticity and improves learning and memory. To gain more insight into the interactions between CNF1 and neuronal cells, we used primary neuronal and astrocytic cultures from rat embryonic brain to study CNF1 effects on neuronal differentiation, focusing on dendritic tree growth and synapse formation, which are strictly modulated by Rho GTPases. CNF1 profoundly remodeled the cytoskeleton of hippocampal and cortical neurons, which showed philopodia-like, actin-positive projections, thickened and poorly branched dendrites, and a decrease in synapse number. CNF1 removal, however, restored dendritic tree development and synapse formation, suggesting that the toxin can reversibly block neuronal differentiation. On differentiated neurons, CNF1 had a similar effacing effect on synapses. Therefore, a direct interaction with CNF1 is apparently deleterious for neurons. Since astrocytes play a pivotal role in neuronal differentiation and synaptic regulation, we wondered if the beneficial in vivo effect could be mediated by astrocytes. Primary astrocytes from embryonic cortex were treated with CNF1 for 48 hours and used as a substrate for growing hippocampal neurons. Such neurons showed an increased development of neurites, in respect to age-matched controls, with a wider dendritic tree and a richer content in synapses. In CNF1-exposed astrocytes, the production of interleukin 1β, known to reduce dendrite development and complexity in neuronal cultures, was decreased. These results demonstrate that astrocytes, under the influence of CNF1, increase their supporting activity on neuronal growth and differentiation, possibly related to the diminished levels of interleukin 1β. These observations suggest that the enhanced synaptic plasticity and improved learning and memory described in CNF1-injected mice are probably mediated by astrocytes.

Long-lasting efficacy of the cognitive enhancer Cytotoxic Necrotizing Factor 1

“…However, some evidences support the second mechanisms (Cerri et al, 2011;Diana et al, 2007). To this regard, it is also worth mentioning that increase in synaptic connections induced by CNF1 seems to be strictly dependent on astrocytes (Malchiodi-Albedi et al, 2012).…”

The Cytotoxic Necrotizing Factor 1 from E. Coli: A Janus Toxin Playing with Cancer Regulators

“…Furthermore, the above hypothesis is also reinforced by the interesting effect of CNF1 in non transformed brain cells [74] and in vivo on the central nervous system of pathological mouse models [75,76]. On primary brain cells, the CNF1 effect is characterized by an increased development of neuritis with a wider dendritic tree and richer synapse content [74]. In vivo , a single intracerebroventricular injection of CNF1 is able to modulate Rho GTPases activity and to improve cognitive performances in animal models of Alzheimer’s disease [76] and Rett syndrome [75].…”

“…This finding entails the risk to maintain the Rho GTPases permanently activated in cancer cells challenged with CNF1. Furthermore, the above hypothesis is also reinforced by the interesting effect of CNF1 in non transformed brain cells [74] and in vivo on the central nervous system of pathological mouse models [75,76]. On primary brain cells, the CNF1 effect is characterized by an increased development of neuritis with a wider dendritic tree and richer synapse content [74].…”

Deamidase toxins

“…Several reports have demonstrated the first proofs of concept that bacterial toxins activating Rho GTPases are endowed with the ability to treat or prevent cognitive and infectious diseases. For example, a series of studies now report that the injection of CNF1 into the brain has a positive impact on the development and differentiation of astrocytes, a phenomenon that likely underlies the cognition-enhancing properties of the toxin [92,93]. The link between Rho GTPases and innate immunity has been established through the discovery of a dominant negative mutation of Rac2 D57N in a patient with a neutrophil immunodeficiency syndrome [94].…”