R6/2 neurons with intranuclear inclusions survive for prolonged periods in the brains of chimeric mice

Abstract

The R6/2 mouse possesses mutant exon 1 of human Hdh, and R6/2 mice with 150 CAG repeats show neurological abnormalities by 10 weeks and die by 15 weeks. Few brain abnormalities, however, are evident at death, other than widespread ubiquitinated neuronal intranuclear inclusions (NIIs). We constructed R6/2t+/t- <--> wildtype (WT) chimeric mice to prolong survival of R6/2 cells and determine if neuronal death and/or neuronal injury become evident with longer survival. ROSA26 mice (which bear a lacZ transgene) were used as WT to distinguish between R6/2 and WT neurons. Chimeric mice consisting partly of R6/2 cells lived longer than pure R6/2 mice (up to 10 months), with the survival proportional to the R6/2 contribution. Genotypically R6/2 cells formed NIIs in the chimeras, and these NIIs grew only slightly larger than in 12-week pure R6/2 mice, even after 10 months. Additionally, neuropil aggregates formed near R6/2 neurons in chimeric mice older than 15 weeks. Thus, R6/2 neurons could survive well beyond 15 weeks in chimeras. Moreover, little neuronal degeneration was evident in either cortex or striatum by routine histological stains. Nonetheless, striatal shrinkage and ventricular enlargement occurred, and striatal projection neuron markers characteristically reduced in Huntington's disease were diminished. Consistent with such abnormalities, cortex and striatum in chimeras showed increased astrocytic glial fibrillary acidic protein. These results suggest that while cortical and striatal neurons can survive nearly a year with nuclear and extranuclear aggregates of mutant huntingtin, such lengthy survival does reveal cortical and striatal abnormality brought on by the truncated mutant protein.

BDNF regulation under GFAP promoter provides engineered astrocytes as a new approach for long-term protection in Huntington's disease

“…Importantly, HD patients show high levels of astrogliosis 3 and this pathological hallmark also shows a progressive increase in all tested animal models of HD in correlation with the degenerative process. [31][32][33]53 Interestingly, our study results show that pGFAP-BDNF transgenic astrocytes release high levels of this neurotrophin only on stimulation. We did not find differences in BDNF release between pGFAP-BDNF astrocytes and wt astrocytes in basal conditions.…”

Effect of early embryonic deletion of huntingtin from pyramidal neurons on the development and long-term survival of neurons in cerebral cortex and striatum

“…The anti-D1 antibody was a rat monoclonal directed against the 97-amino acid C-terminal fragment of human D1 (Sigma-Aldrich, D187), whose specificity has been demonstrated previously (Levey et al, 1993; Hersch et al, 1995). The anti-ENK used was a rabbit polyclonal antibody against leucine-enkephalin (ImmunoStar, 20066) whose specificity has also been shown previously (Reiner, 1987; Reiner et al, 2007; Tripathi et al, 2010). Immunolabeling for DARPP32 was carried out using an anti-DARPP32 (generously provided by P. Greengard and H. Hemmings), whose specificity has been previously documented (Ouimet et al, 1984).…”

The Neuropathology of Huntington’s Disease

“…8). It has been suggested that the toxic influence of these inclusions leads to a differential loss of specific subsets of neurons; however, this is still a topic of debate as there is evidence for both deleterious and protective effects of huntingtin aggregation (Davies et al 1999;Arrasate et al 2004;Reiner et al 2007). The important steps of the aggregate toxicity hypothesis may involve proteolysis, nuclear translocation, and aggregation.…”