Increased PKA signaling disrupts recognition memory and spatial memory: role in Huntington's disease

Huntington's disease (HD) patients and mouse models show learning and memory impairment even before the onset of motor symptoms. However, the molecular events involved in this cognitive decline are still poorly understood. Here, using three different paradigms, the novel object recognition test, the T-maze spontaneous alternation task and the Morris water maze, we detected severe cognitive deficits in the R6/1 mouse model of HD before the onset of motor symptoms. When we examined the putative molecular pathways involved in these alterations, we observed hippocampal cAMP-dependent protein kinase (PKA) hyper-activation in na?ve R6/1 mice compared with wild-type (WT) mice, whereas extracellular signal-regulated kinase 1/2 and calcineurin activities were not modified. Increased PKA activity resulted in hyper-phosphorylation of its substrates N-methyl-D-aspartate receptor subunit 1, Ras-guanine nucleotide releasing factor-1 and striatal-enriched protein tyrosine phosphatase, but not cAMP-responsive element binding protein or the microtubule-associated protein tau. In correlation with the over-activation of the PKA pathway, we found a down-regulation of the protein levels of some phosphodiesterase (PDE) 4 family members. Similar molecular changes were found in the hippocampus of R6/2 mice and HD patients. Furthermore, chronic treatment of WT mice with the PDE4 inhibitor rolipram up-regulated PKA activity, and induced learning and memory deficits similar to those seen in R6 mice, but had no effect on R6/1 mice cognitive impairment. Importantly, hippocampal PKA inhibition by infusion of Rp-cAMPS restored long-term memory in R6/2 mice. Thus, our results suggest that occlusion of PKA-dependent processes is one of the molecular mechanisms underlying cognitive decline in R6 animals.     

CD8+ cell depletion of donor lymphocyte infusions using cd8 monoclonal antibody-coated high-density microparticles (CD8-HDM) after allogeneic hematopoietic stem cell transplantation: a pilot study

A CD8 murine monoclonal antibody-coated high-density microparticle (HDM) has been developed, which allows for the rapid depletion of CD8+ T cells from apheresis products by gravity sedimentation. We conducted a study to determine the efficacy and safety of CD8 depletion of donor lymphocyte infusions (DLI) to treat relapse after stem cell transplantation using the Eligix CD8-HDM Cell Separation System. Patients were targeted to receive 3 x 10(7) CD4+ T cells/kg. Nine patients were enrolled, three with CML, three myeloma, two CLL, and one NHL. A median of 1 x 10(10) mononuclear cells were obtained by apheresis and processed. The median depletion of CD8+ cells was 99.3% (97.8->99.5%). CD8 depletion was highly specific, with a median recovery of CD4+ cells of 75%. A median of 2.9 x 10(7) CD4+ cells/kg was infused. No infusional toxicity was noted. All CML patients achieved a complete molecular remission. A CLL patient demonstrated a complete response. One patient developed GVHD (grade II acute GVHD and subsequently chronic GVHD). The CD8-HDM Cell Separation System appears to be highly selective and effective in depleting CD8+ T cells from DLI apheresis products, and CD8-depleted DLI is capable of mediating a graft-versus-leukemia effect while minimizing GVHD.     

Clinical outcomes with intensive therapy for patients with primary resistant multiple myeloma

Clinical outcomes were evaluated in 89 consecutive patients with multiple myeloma that had not responded to dexamethasone-based primary therapy, who received early intensive therapy supported by autologous stem cell transplantation. Results were compared with those of 45 comparable patients who refused or were unable to receive intensive treatment for socioeconomic reasons. Following high-dose therapy, the response rate was 69% including 16% with CR. Survival of 14 patients with CR (median >7.0 years) was significantly longer than those of 47 patients with PR (median 4.5 years) or of 28 patients who remained NR (median 2.2 years). CR occurred in 43% of patients with serum myeloma protein <1.5 gm/dl, in contrast to 7% of those with higher values, a finding similar to that observed previously for patients consolidated in PR. No prognostic factor was associated with PR and, in view of the high frequencies of PR or CR, all patients with primary resistant myeloma should be considered for early intensive therapy. The limited improvement of lifespan and disease-free survival for those in PR indicated the need for further treatment to achieve CR, the major surrogate marker for long survival.     

Evidence that the pituitary-adrenal axis does not cross-adapt to stressors: comparison to other physiological variables

The effects of previous chronic immobilization stress on the physiological responses of male rats to a novel chronic stressor (shock) were studied. Previous chronic exposure to immobilization reduced adrenocorticotropin (ACTH) and lactate responses to acute immobilization stress without altering the response to a novel acute stressor (tail shock). When subjected to chronic tail shock, body weight inhibition caused by chronic shock was greater in the rats not previously exposed to chronic immobilization, which suggests that there is cross-adaptation between different stressors. However, adrenocorticotropin adaptation to chronic shock was impaired by previous chronic immobilization. These data indicate that the existence of cross-adaptation to stressors might depend on the variable measured, the central nervous system pathways controlling the pituitary-adrenal axis being, apparently, resistant to cross-adaptation. This lack of cross-adaptation at certain levels can assure the maintenance of an adequate response to unknown environmental stimuli.     

Reduced calcineurin protein levels and activity in exon-1 mouse models of Huntington's disease: Role in excitotoxicity

Calcineurin is a serine/threonine phosphatase involved in the regulation of glutamate receptors signaling. Here, we analyzed whether the regulation of calcineurin protein levels and activity modulates the susceptibility of striatal neurons to excitotoxicity in R6/1 and R6/1:BDNF+/− mouse models of Huntington's disease. We show that calcineurin inhibition in wild-type mice drastically reduced quinolinic acid-induced striatal cell death. Moreover, calcineurin A and B were differentially regulated during disease progression with a specific reduction of calcineurin A protein levels and calcineurin activity at the onset of the disease in R6/1:BDNF+/− mice. Analysis of the conditional mouse model Tet/HD94 showed that mutant huntingtin specifically controls calcineurin A protein levels. Finally, calcineurin activation induced by intrastriatal quinolinic acid injection in R6/1 mouse was lower than in wild-type mice. Therefore, reduction of calcineurin activity by alteration of calcineurin A expression participates in the pathophysiology of Huntington's disease and contributes to the excitotoxic resistance observed in exon-1 mouse models.