Changes in the expression of extracellular regulated kinase (ERK 1/2) in the R6/2 mouse model of Huntington's disease after phosphodiesterase IV inhibition

The mitogen-activated protein kinases (MAPKs) superfamily comprises three major signaling pathways: the extracellular signal-regulated protein kinases (ERKs), the c-Jun N-terminal kinases or stress-activated protein kinases (JNKs/SAPKs) and the p38 family of kinases.ERK 1/2 signaling has been implicated in a number of neurodegenerative disorders, including Huntington's disease (HD). Phosphorylation patterns of ERK 1/2 and JNK are altered in cell models of HD. In this study, we aimed at studying the correlations between ERK 1/2 and the neuronal vulnerability to HD degeneration in the R6/2 transgenic mouse model of HD. Single and double-label immunofluorescence for phospho-ERK (pERK, the activated form of ERK) and for each of the striatal neuronal markers were employed on perfusion-fixed brain sections from R6/2 and wild-type mice. Moreover, Phosphodiesterase 4 inhibition through rolipram was used to study the effects on pERK expression in the different types of striatal neurons. We completed our study with western blot analysis. Our study shows that pERK levels increase with age in the medium spiny striatal neurons and in the parvalbumin interneurons, and that rolipram counteracts such increase in pERK. Conversely, cholinergic and somatostatinergic interneurons of the striatum contain higher levels of pERK in the R6/2 mice compared to the controls. Rolipram induces an increase in pERK expression in these interneurons. Thus, our study confirms and extends the concept that the expression of phosphorylated ERK 1/2 is related to neuronal vulnerability and is implicated in the pathophysiology of cell death in HD. (C) 2012 Elsevier Inc. All rights reserved

DISC1 and Huntington's disease-overlapping pathways of vulnerability to neurological disorder?

We re-annotated the interacting partners of the neuronal scaffold protein DISC1 using a knowledge-based approach that incorporated recent protein interaction data and published literature to. This revealed two highly connected networks. These networks feature cellular function and maintenance, and cell signaling. Of potentially greatest interest was the novel finding of a high degree of connectivity between the DISC1 scaffold protein, linked to psychiatric illness, and huntingtin, the protein which is mutated in Huntington's disease. The potential link between DISC1, huntingtin and their interacting partners may open new areas of research into the effects of pathway dysregulation in severe neurological disorders

Immunohistochemical localization of TRPC6 in the rat substantia nigra.

Transient receptor potential channels (TRPC) are plasma membrane, nonselective cationic channels and have been proposed as candidates involved in the regulation of cellular Ca2+ influx [D.E. Clapham, L.W. Runnels, C., Strubing, The TRP ion channel family, Nat. Rev. Neurosci. 2 (2001) 387-396; A. Martorana, C. Giampa, Z. DeMarch, M.T. Viscomi, S. Patassini, G. Sancesario, G. Bernardi, F.R. Fusco, Distribution of TRPC1 receptors in dendrites of rat substantia nigra: a confocal and electron microscopy study, Eur. J. Neurosci. 24 (2006) 732-738]. Studies on regional localization patterns of TRPCs are necessary to provide helpful guidelines for correlating current types with particular channels. In this study, we examined the distribution of one particular member of TRPC superfamily, namely, TRPC6, in the substantia nigra of normal rat brain. Single and double label immunohistochemistry were employed to perform both light and confocal microscopy observations. Our single label studies showed that, in the substantia nigra, TRPC6 labeled the perikarya with a diffuse and intense immunoreaction product distributed throughout cell cytoplasm whereas only a light immunostaining was observed in the cell nuclei. No labeling of axon or terminals was observed, although TRPC6 was evenly distributed in the neuropil. Our dual label studies showed a TRPC6 immunoreactivity pattern that was localized into the proximal dendrites and axon hillock of the large dopaminergic neurons identified by TH immunoreaction. Furthermore, our double label immunofluorescence study for TRPC6 and mGluR1 showed a complete co-localization of the two markers in the substantia nigra. Moreover, TRPC6 did not co-localize with synaptophysin. Thus, our study shows the postsynaptic localization of TRPC6 and its association with mGluR1 in the midbrain dopamine neurons

Effects of phosphodiesterase inhibition on ERK phosphorylation in the R6/2 mouse model of Huntington’s disease

Introduction: ERK signaling has been implicated in a number of neurodegenerative disorders, including Huntington’s Disease(HD). Phosphorylation patterns of ERK and JNK are altered in cell models of HD. We have studied the correlations between ERK and the neuronal vulnerability to HD degeneration in the R6/2 transgenic mouse model of HD treated with the phosphodiesterase 4 inhibitor rolipram. Materials and methods: Immunohistochemistry for phospho-ERK (p-ERK, the activated form of ERK) and dual label immunofluorescence for p-ERK and each of the striatal neuronal markers were employed on perfusion-fixed brain sections from R6/2 and wild-tipe mice. Results: Striatal neurons, both spiny projection and interneurons, are completely devoid of p-ERK immunoreactivity in the wild-type mouse. Conversely, parvalbuminlabeled GABAergic interneurons of the striatum are highly enriched in p-ERK in the R6/2 mice, cholinergic and somatostatinergic interneurons are devoid of it. With rolipram treatment, p-ERK decreases in the parvaminergic neurons and in thecalbindin projection neurons of R6/2 mice. Discussion and conclusions: Our study confirms and extend the concept that the expression of phosphorilated ERK is related to neuronal vulnerability and is implicated in the pathophysiology of cell death in HD. Such concept is confirmed by the beneficial effects of rolipram in decreasing the levels of p-ERK in the more vulnerable neurons

Systemic delivery of recombinant Brain Derived Neurotrophic Factor (BDNF) in the R6/2 mouse model of Huntington's disease

Loss of huntingtin-mediated BDNF gene transcription has been shown to occur in HD and thus contribute to the degeneration of the striatum. Several studies have indicated that an increase in BDNF levels is associated with neuroprotection and amelioration of neurological signs in animal models of HD. In a recent study, an increase in BDNF mRNA and protein levels was recorded in mice administered recombinant BDNF peripherally. Chronic, indwelling osmotic mini-pumps containing either recombinant BDNF or saline were surgically placed in R6/2 or wild-type mice from 4 weeks of age until euthanasia. Neurological evaluation (paw clasping, rotarod performance, locomotor activity in an open field) was performed. After transcardial perfusion, histological and immunohistochemical studies were performed. We found that BDNF- treated R6/2 mice survived longer and displayed less severe signs of neurological dysfunction than the vehicle treated ones. Primary outcome measures such as brain volume, striatal atrophy, size and morphology of striatal neurons, neuronal intranuclear inclusions and microglial reaction confirmed a neuroprotective effect of the compound. BDNF was effective in increasing significantly the levels of activated CREB and of BDNF the striatal spiny neurons. Moreover, systemically administered BDNF increased the synthesis of BDNF as demonstrated by RT-PCR, and this might account for the beneficial effects observed in this model

Nuclear localization of phosphodiesterase 10A (PDE10A) in the R6/2 mouse striatal interneurons

Introduction: Cyclic nucleotides play an important role as second messengers in the CNS. Intracellular concentrations of cAMP and cGMP are modulated by the rate of degradation by a variety of phosphodiesterases (PDEs). PDE10A is the single member of one of the newest PDE gene families. PDE10A has been observed in the brain mostly in the striatal projec- tion neurons [1]. However, we have previously observed [unpublished data], in the striatum, a number of PDE10 immunoreactive neurons that were not projection neurons. Methods: R6/2 mice and their wild type littermates were sacrificed at 5, 9, 13 weeks of age, and single and double label immunohistochemis- try were performed to identify the different neuronal subtypes of the striatum (medium spiny, choliner- gic, parvalbuminergic, somatos- tatinergic). Results: PDE10A was observed in all subtypes of striatal neurons. In the spiny projection neurons, PDE10A localized in the cytoplasm, whereas in the striatal interneurons, regardless of the sub- type, PDE10A displayed a clearly nuclear localization. This was true both for the wild type and for the R6/2 mice. Conclusions: Our study demonstrates that PDE10A is con- tained not only in the medium spiny neurons, but also in the striatal in- terneurons. Moreover, the different compartmentalization might be ex- plained by a different activity exert- ed by PDE10A between projection neurons and interneurons. Reference [1] Seeger TF, Bartlett B, Coskran TM, Culp JS, James LC, Krull DL, Lanfear J, Ryan AM, Schmidt CJ, Strick CA, Var- ghese AH, Williams RD, Wylie PG, Men- niti FS. Immunohistochemical localiza- tion of PDE10A in the rat brain. Brain Res. 2003; 985: 113-126