Specific PI3K Isoform Modulation in Heart Failure: Lessons from Transgenic Mice

Cardiac pathophysiology heavily relies on receptor-mediated signal transduction, and pharmacologic control of such biological processes has proven successful in preventing and treating multiple heart diseases. Recent progress in the study of receptor-mediated signal transduction events in the heart highlighted the role of a family of lipid kinases known as phosphoinositide 3-kinases (PI3Ks). These enzymes are involved downstream different receptors in the production of a lipid second messenger molecule (namely phosphatidylinositol (3,4,5)-trisphosphate [PIP₃]), which mediates a large number of biological responses critical for the heart, including cardiomyocyte growth, survival, and contractility as well as cardiovascular inflammation. This review focuses on the recent advances in the understanding of PI3K function in cardiac pathophysiology obtained by studying mouse mutants for different PI3K genes and by validating the effects of PI3K pharmacologic inhibition in preclinical models of critical cardiac diseases like heart failure.     

Effects of nerve growth factor in experimental model of focal microgyria

Aim

The effects on neural repair of intraparenchymal nerve growth factor (NGF) administration were evaluated in neonate Wistar rats with experimentally induced focal microgyria.

Methods

A freezing focal polymicrogyric lesion was induced on the frontal cortex in 35 newborn Wistar rats on postnatal day?1. NGF was administered in 15 cases, with 20 pups as controls. Animals were sacrificed at 72?h and 7?days after NGF administration. Real-time PCR was used for the quantification of the expression of TrkA, p75, and doublecortin (DCX) at the level of the cortical lesion in seven different groups of animals: control 72?h (n?=?5), control 7?days (n?=?5), microgyria 72?h (n?=?5), microgyria 7?days (n?=?5), microgyria + NGF 72?h (n?=?5), microgyria + NGF 7?days (n?=?5), and control + NGF (n?=?5).

Results

A significant increase in TrkA expression was found in the microgyria + NGF 7?days group compared to the others. TrkA upregulation was already visible 72?h after NGF administration. Unlike TrkA, p75 expression increased in animals subjected to the experimental focal microgyria and decreased markedly after NGF administration. DCX expression in injured animals was observed to increase strongly 7?days after NGF administration compared with other groups.

Conclusions

NGF administration interferes with neural repair mechanisms at the polymicrogyric lesion site by means of TrkA and DCX upregulation which possibly counteracts the process of apoptosis caused by the brain injury.     

Activation of Rho GTPases triggers structural remodeling and functional plasticity in the adult rat visual cortex

A classical example of age-dependent plasticity is ocular dominance (OD) plasticity, triggered by monocular deprivation (MD). Sensitivity of cortical circuits to a brief period of MD is maximal in juvenile animals and downregulated in adult age. It remains unclear whether a reduced potential for morphological remodeling underlies this downregulation of physiological plasticity in adulthood. Here we have tested whether stimulation of structural rearrangements is effective in promoting experience-dependent plasticity in adult age. We have exploited a bacterial protein toxin, cytotoxic necrotizing factor 1 (CNF1), that regulates actin dynamics and structure of neuronal processes via a persistent activation of Rho GTPases. Injection of CNF1 into the adult rat visual cortex triggered a long-lasting activation of the Rho GTPase Rac1, with a consequent increase in spine density and length in pyramidal neurons. Adult rats treated with CNF1, but not controls, showed an OD shift toward the open eye after MD. CNF1-mediated OD plasticity was selectively attributable to the enhancement of open-eye responses, whereas closed-eye inputs were unaffected. This effect correlated with an increased density of geniculocortical terminals in layer IV of monocularly deprived, CNF1-treated rats. Thus, Rho GTPase activation reinstates OD plasticity in the adult cortex via the potentiation of more active inputs from the open eye. These data establish a direct link between structural remodeling and functional plasticity and demonstrate a role for Rho GTPases in brain plasticity in vivo. The plasticizing effects of Rho GTPase activation may be exploited to promote brain repair.     

CRMP2 hyperphosphorylation is characteristic of Alzheimer's disease and not a feature common to other neurodegenerative diseases

Collapsin response mediator protein 2 (CRMP2) is an abundant brain-enriched protein that regulates neurite outgrowth. It is phosphorylated by Cdk5 and GSK3, and these modifications are abnormally high in the brains of Alzheimer's disease (AD) patients. Increased phosphorylation of CRMP2 is also apparent in mouse models of AD that express mutated AβPP and PSEN1, but not AβPP or tau alone, where it is detectable before the appearance of amyloid plaques and neurofibrillary tangles, suggesting it is an early event in AD pathogenesis. Here, we have extended these observations by showing that CRMP2 is not hyperphosphorylated in mice overexpressing mutated PSEN1 alone, or in cultured neurons treated with soluble, oligomeric Aβ42 peptide. Similarly, CRMP2 phosphorylation was not increased in a mouse model of severe neurodegeneration (PMSC-1 knockout) or in cultured neurons subjected to neurotoxic concentrations of NMDA or staurosporine. Most interestingly, CRMP2 phosphorylation was not increased in frontal cortex from patients with frontotemporal lobar degeneration associated with mutations in MAPT or with Pick bodies. Together, these observations are consistent with the hypothesis that abnormal phosphorylation of CRMP2 is specific to AD and occurs downstream of excessive processing of AβPP, but that neither excessive Aβ42 peptide nor neurotoxicity alone are sufficient to promote hyperphosphorylation.     

One-year evaluation of factors affecting the biological activity of interferon beta in multiple sclerosis patients

MxA is an antiviral protein induced by type I interferons (IFN) and some viruses; MxA gene expression is an appropriate marker for measuring biologic activity of exogenous IFNβ, as its induction indicates IFNAR receptor stimulation. A recent study has shown that measurement of MxA mRNA, after 1 year of treatment, predicts clinical responsiveness to IFNβ therapy. Loss of IFNβ bioactivity is mostly due to anti-IFNβ antibodies (both neutralizing and binding), non-compliance and receptor saturation. The aim of this study was to evaluate all possible causes of loss of IFNβ bioactivity after 1 year in treated patients. One hundred sixty-seven multiple sclerosis (MS) patients were included. One year after beginning IFNβ therapy, each patient underwent a blood test; MxA gene expression was measured by real time PCR, antiviral CPE assay to detect neutralizing antibodies (NAbs), and capture-ELISA (cELISA) to measure binding antibodies (BAbs). For MxA an upper normal threshold of 87 (RE) was considered, 20 TRU/mL was the threshold for NAbs, and 1 U for BAbs positivity. Thirty-seven out of 167 patients (22%) were MxA-negative; of these, 22 were both BAbs and NAbs+, whereas 12 were BAbs+ but Nabs−, and three were both BAbs and NAbs−. The following conclusions were drawn from the study: (1) MxA mRNA should be measured after 1 year of IFNβ therapy; (2) after 1 year of IFNβ treatment, absence of IFNβ bioactivity was detected in 22% of the patients; (3) different biological phenomena and reduced compliance explain this absence; (4) identification of the reason for absence of IFN bioactivity improves patients’ management.