Cellular Localization of Huntingtin in Striatal and Cortical Neurons in Rats: Lack of Correlation with Neuronal Vulnerability in Huntington’s Disease

Abstract

Immunohistochemistry and single-cell RT-PCR were used to characterize the localization of huntingtin and/or its mRNA in the major types of striatal neurons and in corticostriatal projection neurons in rats. Single-label immunohistochemical studies revealed that striatum contains scattered large neurons rich in huntingtin and more numerous medium-sized neurons moderate in huntingtin. Double-label immunohistochemical studies showed that the large huntingtin-rich striatal neurons include nearly all cholinergic interneurons and some parvalbuminergic interneurons. Somatostatinergic striatal interneurons, which are medium in size, rarely contained huntingtin. Calbindin immunolabeling showed that the vast majority of the medium-sized striatal neurons that contain huntingtin are projection neurons, but only approximately 65% of calbindin-labeled projection neurons (localized to the matrix compartment of striatum) were labeled for huntingtin. Calbindin-containing projection neurons of the matrix compartment and calbindin-negative projection neurons of the striatal patch compartment contained huntingtin with comparable frequency. Single-cell RT-PCR confirmed that striatal cholinergic interneurons contain huntingtin, but only approximately 65% of projection neurons contained detectable huntingtin message. The finding that huntingtin is not consistently found in striatal projection neurons [which die in Huntington's disease (HD)] but is abundant in striatal cholinergic interneurons (which survive in Huntington's disease) suggests that the mutation in huntingtin that causes HD may not directly kill neurons. In contrast to the heterogeneous expression of huntingtin in the different striatal neuron types, we found all corticostriatal neurons to be rich in huntingtin protein and mRNA. One possibility raised by our findings is that the HD mutation may render corticostriatal neurons destructive rather than render striatal neurons vulnerable.

Differential localization of the GluR1 and GluR2 subunits of the AMPA-type glutamate receptor among striatal neuron types in rats

“…Immunofluorescence double-labeling was carried out on tissue from the nine normal rats, as described previously (Chen, et al, 1996;Fusco, et al, 1999;Meade, et al, 2002;Deng et al, 2006). In brief, free-floating brain sections were incubated in a cocktail containing two primary antibodies, one directed against either GluR1 or GluR2 (Table 1), and the other against a marker for a given striatal neuron type.…”

“…et al, 1986(Beal. et al, ,1991Chesselet et al, 1990;DiFiglia, 1990;Uemura, et al, 1990;Figueredo-Cardenas, et al, 1994Ikonomidou and Turski, 1996;Paschen, 1996;Fusco et al, 1999;Meade et al, 2000), in particular by excess glutamate released from cortical terminals acting on striatal AMPA receptors (Schwarcz et al, 1984;Chen et al, 1999;Fusco et al, 1999;Popoli et al, 2002). Given the possible role of AMPA receptors in excitotoxic striatal injury (Chen et al, 1995), the question arises as to whether the differential localization of GluR1 and GluR2 contributes to differences in vulnerability among striatal neurons.…”

Genetic interaction between expanded murine Hdh alleles and p53 reveal deleterious effects of p53 on Huntington's disease pathogenesis

“…Although htt exhibits widespread distribution in both the brain and peripheral tissues, the GABAergic medium spiny neurons of the striatum and the large pyramidal neurons in layers III, V, and VI of the cerebral cortex undergo preferential degeneration (Sharp et al, 1995;Ho et al, 2001;Sieradzan and Mann, 2001). The abundance of huntingtin protein does not appear to confer vulnerability on striatal neurons, but rather, the expression of mutant htt in corticostriatal neurons seems to render them destructive to the striatal neurons that they innervate (Fusco et al, 1999). Both prior and subsequent to neuronal death, the indirect pathway of basal ganglia output is affected most severely, resulting in an increase in involuntary movements associated with loss of proenkephalin expression.…”

The Differential Susceptibility of Specific Neuronal Populations: Insights from Huntington's Disease

“…Htt and its mRNA are abundant in the striatum in keeping with the striatum being the focus of the neurodegeneration. However, Htt is also found in many other brain regions, including the cerebral cortex and cerebellum, as well as in many somatic tissues (3,8).…”