The Unexpected Role of A\u3b21-42 Monomers in the Pathogenesis of Alzheimer's Disease

Amyloid- (A) has been proposed as a biomarker and a drug target for the therapy of Alzheimer\u2019s disease (AD). The neurotoxic entity and relevance of each conformational form of A to AD pathology is still under debate; A oligomers are considered the major killer form of the peptide whereas monomers have been proposed to be involved in physiological process. Here we reviewed some different effects mediated by monomers and oligomers on mechanisms involved in AD pathogenesis such as autophagy and tau aggregation. Data reported in this review demonstrate that A monomers could have a major role in sustaining the pathogenesis of AD and that AD therapy should be focused not only in the removal of oligomers but also of monomers

The Decrease of Uch-L1 Activity Is a Common Mechanism Responsible for Aβ 42 Accumulation in Alzheimer’s and Vascular Disease

Alzheimer’s disease (AD) is a multifactorial pathology causing common brain spectrum disorders in affected patients. These mixed neurological disorders not only include structural AD brain changes but also cerebrovascular lesions. The main aim of the present issue is to find the factors shared by the two pathologies. The decrease of ubiquitin C-terminal hydrolase L1 (Uch-L1), a major neuronal enzyme involved in the elimination of misfolded proteins, was observed in ischemic injury as well as in AD, but its role in the pathogenesis of AD is far to be clear. In this study we demonstrated that Uch-L1 inhibition induces BACE1 up-regulation and increases neuronal and apoptotic cell death in control as well as in transgenic AD mouse model subjected to Bengal Rose, a light-sensitive dye inducing that induces a cortical infarction through photo-activation. Under the same conditions we also found a significant activation of NF-κB. Thus, the restoration of Uch-L1 was able to completely prevent both the increase in BACE1 protein levels and the amount of cell death. Our data suggest that the Uch-L1-mediated BACE1 up-regulation could be an important mechanism responsible for Aβ peptides accumulation in vascular injury and indicate that the modulation of the activity of this enzyme could provide new therapeutic strategies in AD

Neuroprotective and anti-inflammatory roles of the phosphatase and tensin homolog deleted on chromosome Ten (PTEN) Inhibition in a Mouse Model of Temporal Lobe Epilepsy.

Excitotoxic damage represents the major mechanism leading to cell death in many human neurodegenerative diseases such as ischemia, trauma and epilepsy. Caused by an excess of glutamate that acts on metabotropic and ionotropic excitatory receptors, excitotoxicity activates several death signaling pathways leading to an extensive neuronal loss and a consequent strong activation of astrogliosis. Currently, the search for a neuroprotective strategy is aimed to identify the level in the signaling pathways to block excitotoxicity avoiding the loss of important physiological functions and side effects. To this aim, PTEN can be considered an ideal candidate: downstream the excitatory receptors activated in excitotoxicity (whose inhibition was shown to be not clinically viable), it is involved in neuronal damage and in the first stage of the reactive astrogliosis in vivo. In this study, we demonstrated the involvement of PTEN in excitotoxicity through its pharmacological inhibition by dipotassium bisperoxo (picolinato) oxovanadate [bpv(pic)] in a model of temporal lobe epilepsy, obtained by intraperitoneal injection of kainate in 2-month-old C57BL/6J male mice. We have demonstrated that inhibition of PTEN by bpv(pic) rescues neuronal death and decreases the reactive astrogliosis in the CA3 area of the hippocampus caused by systemic administration of kainate. Moreover, the neurotoxin administration increases significantly the scanty presence of mitochondrial PTEN that is significantly decreased by the administration of the inhibitor 6 hr after the injection of kainate, suggesting a role of PTEN in mitochondrial apoptosis. Taken together, our results confirm the key role played by PTEN in the excitotoxic damage and the strong anti-inflammatory and neuroprotective potential of its inhibition

PTEN expression in the CA3 area of the hippocampus.

<p>Immunofluorescence showing PTEN expression in the CA3 area 1 day after kainic acid i.p. injection (B) and in control mice treated only by saline (A). Nuclei were stained with nuclear marker DAPI. Scale bar: 50 µm.</p

PTEN expression in mitochondrial and cytosolic fraction after the excitotoxic stimulus.

<p>Representative Western blot (A) and relative quantification (B) showing mitochondrial PTEN translocation in control (ctr), kainic treated group (KA) and kainic/bpv(pic) group (KA+I) 3, 6 and 12 h after the kainate treatment. As it can be observed, the excitotoxic stimulus leads to a significant increase in mitochondrial PTEN expression, significantly decreased 6 h after kainic acid injection in animals treated with bpv(pic). On the contrary, in the cytosolic fraction kainic acid or PTEN inhibitor does not lead to significant differences in PTEN levels in any time points considered as it can be observed from representative Western blots (C) and relative quantification (D). Data are expressed as mean ± S.E.M., *<i>P</i><0.05, #<i>P</i><0.05, **<i>P</i><0.01 with Two way ANOVA and Bonferroni post hoc test. Experiments were repeated three times.</p

PTEN inhibition protects CA3 neurons from kainate-induced excitotoxicity.

<p>Nissl-staining of hippocampus sections of mice treated with saline (A, control), with kainate (B, KA) or with both kainate and bpv(pic) (C, KA+I), killed one day after treatment (scale bar: 1 mm). A1. CA3 area of control animals (ctr) treated with saline only (scale bar: 50 µm). B1. CA3 area of animals treated with kainate (KA). Arrowheads point to apoptotic bodies and condensed nuclei as a consequence of kainate treatment. At higher magnification, a neuron that is degenerating. C1. CA3 area of animals treated with both kainate and PTEN inhibitor (KA+I). D. Immunostaining showing cleaved caspase-3 (in red) in neurons labeled with MAP-2 (in green) in the CA3 area of the hippocampus, one day after kainate administration. At higher magnification, arrowheads indicating neurons with a clear expression of cleaved caspase-3. Scale bar: 50 µm (30 µm at higher magnification). E. Surviving neurons in the hippocampal CA3 region. Histogram showing the linear density (cells/mm) of surviving neurons in the CA3 area of the hippocampus one day following kainic (KA) acid injection or kainic (KA) acid injection and PTEN inhibition (I) by bpv(pic) (KA+I). **<i>P</i><0.01, §§<i>P</i><0.01.</p

Astrogliosis in the CA3 area of the hippocampus following kainic acid injection.

<p>Glial fibrillary acidic protein (GFAP)-positive profiles in the hippocampi of control (A), kainic acid (KA)-treated, 1 day survival mice (B) and KA/bpv(pic)-treated, 1 day survival mice (C) (scale bar: 50 µm). D. Histogram showing the % of GFAP staining in the hippocampal CA3 area one day after kainic acid injection and PTEN inhibition by bpv(pic). The significant increase in GFAP immunoreactivity after kainate administration, expressed as a percentage of the whole area occupied by positive profiles, is significantly prevented by bpv(pic) treatment. *<i>P</i><0.05, §<0.05.</p

Activation of c-Jun after kainate stimulation in the CA3 area of the hippocampus.

<p>The P-c-Jun immunoreactivity, absent in control mice (A), can be observed in neurons of animals treated with kainate (B) or with both kainate and PTEN inhibitor (C), sacrificed one day after the treatment. At higher magnification, nuclei of neurons positive for P-c-Jun after kainate treatment. D. Immunostaining showing that P-c-Jun (red) is revealed in the nucleus of neurons labeled with NeuN (green) in the CA3 area of the hippocampus, one day after the kainate stimulation. Scale bar: 50 µm. E. Histogram showing the % of P-c-Jun staining in hippocampal CA3 subfield one day following KA injection and PTEN inhibition by bpv(pic). As it can be observed, bpv(pic) is unable to prevent the significant increase in the P-c-Jun immunoreactivity caused by kainate treatment. *<i>P</i><0.05.</p