Specific caspase interactions and amplification are involved in selective neuronal vulnerability in Huntington's disease

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder resulting in selective neuronal loss and dysfunction in the striatum and cortex. The molecular pathways leading to the selectivity of neuronal cell death in HD are poorly understood. Proteolytic processing of full-length mutant huntingtin (Htt) and subsequent events may play an important role in the selective neuronal cell death found in this disease. Despite the identification of Htt as a substrate for caspases, it is not known which caspase(s) cleaves Htt in vivo or whether regional expression of caspases contribute to selective neuronal cells loss. Here, we evaluate whether specific caspases are involved in cell death induced by mutant Htt and if this correlates with our recent finding that Htt is cleaved in vivo at the caspase consensus site 552. We find that caspase-2 cleaves Htt selectively at amino acid 552. Further, Htt recruits caspase-2 into an apoptosome-like complex. Binding of caspase-2 to Htt is polyglutamine repeat-length dependent, and therefore may serve as a critical initiation step in HD cell death. This hypothesis is supported by the requirement of caspase-2 for the death of mouse primary striatal cells derived from HD transgenic mice expressing full-length Htt (YAC72). Expression of catalytically inactive (dominant-negative) forms of caspase-2, caspase-7, and to some extent caspase-6, reduced the cell death of YAC72 primary striatal cells, while the catalytically inactive forms of caspase-3, -8, and -9 did not. Histological analysis of post-mortem human brain tissue and YAC72 mice revealed activation of caspases and enhanced caspase-2 immunoreactivity in medium spiny neurons of the striatum and the cortical projection neurons when compared to controls. Further, upregulation of caspase-2 correlates directly with decreased levels of brain-derived neurotrophic factor in the cortex and striatum of 3-month YAC72 transgenic mice and therefore suggests that these changes are early events in HD pathogenesis. These data support the involvement of caspase-2 in the selective neuronal cell death associated with HD in the striatum and cortex.

Soy-derived antiapoptotic fractions protect gastrointestinal epithelium from damage caused by methotrexate treatment in the rat

The ability of a previously described soy-derived antiapoptotic fraction (SDAAF), a soy water extract (Lexirin), and raw soy flour to inhibit methotrexate (MTX)-induced gastrointestinal damage was evaluated by histological examination of duodenal/jejunal sections from MTX-treated rats. Male Sprague-Dawley rats were fed diets containing casein as a sole protein source or diets supplemented with fractions isolated from soy (SDAAF or Lexirin) before and after MTX treatment. The soy fractions were also shown to inhibit serum deprivation-induced programmed cell death (apoptosis) in mouse embryonic C3H10T1/2 cells. Protein sequence (Lexirin) and enzyme activity (Lexirin and SDAAF) were also analyzed. Rats that received SDAAF- and Lexirin-supplemented diets had significantly reduced necrotic and apoptotic damage in the duodenal mucosa, as demonstrated by difference in villi height, mitotic activity, epithelial cell height, and inflammatory response.