Homozygotes and heterozygotes for ciliary neurotrophic factor null alleles do not show earlier onset of Huntington's disease

Protease pathways in peptide neurotransmission and neurodegenerative diseases

1. Recent research demonstrates the critical importance of neuroproteases for the production of peptide neurotransmitters, and for the production of toxic peptides in major neurodegenerative diseases that include Alzheimer's (AD) and Huntington's diseases. This review describes the strategies utilized to identify the appropriate proteases responsible for producing active peptides for neurotransmission, with application of such approaches for defining protease mechanisms in neurodegenerative diseases. 2. Integration of multidisciplinary approaches in neurobiology, biochemistry, chemistry, proteomics, molecular biology, and genetics has been utilized for neuroprotease studies. These investigations have identified secretory vesicle cathepsin L for the production of the enkephalin opioid peptide neurotransmitter and other neuropeptides. Furthermore, new results using these strategies have identified secretory vesicle cathepsin B for the production of beta-amyloid (Abeta) in the major regulated secretory pathway that provides activity-dependent secretion of Abeta peptides, which accumulate in AD. 3. CNS neuroproteases that participate in peptide neurotransmission and in neurodegenerative diseases represent new candidate drug targets that may be explored in future research for the development of novel therapeutic agents for neurological conditions.

Neuroproteases in Peptide Neurotransmission and Neurodegenerative Diseases

The nervous system represents a key area for development of novel therapeutic agents for the treatment of neurological and neurodegenerative diseases. Recent research has demonstrated the critical importance of neuroproteases for the production of specific peptide neurotransmitters and for the production of toxic peptides in major neurodegenerative diseases that include Alzheimer, Huntington, and Parkinson diseases. This review illustrates the successful criteria that have allowed identification of proteases responsible for converting protein precursors into active peptide neurotransmitters, consisting of dual cysteine protease and subtilisin-like protease pathways in neuroendocrine cells. These peptide neurotransmitters are critical regulators of neurologic conditions, including analgesia and cognition, and numerous behaviors. Importantly, protease pathways also represent prominent mechanisms in neurodegenerative diseases, especially Alzheimer, Huntington, and Parkinson diseases. Recent studies have identified secretory vesicle cathepsin B as a novel beta-secretase for production of the neurotoxic beta-amyloid (Abeta) peptide of Alzheimer disease. Moreover, inhibition of cathepsin B reduces Abeta peptide levels in brain. These neuroproteases potentially represent new drug targets that should be explored in future pharmaceutical research endeavors for drug discovery.

Tissue-specific proteolysis of Huntingtin (htt) in human brain: evidence of enhanced levels of N- and C-terminal htt fragments in Huntington's disease striatum

Proteolysis of mutant huntingtin (htt) has been hypothesized to occur in Huntington's disease (HD) brains. Therefore, this in vivo study examined htt fragments in cortex and striatum of adult HD and control human brains by Western blots, using domain-specific anti-htt antibodies that recognize N- and C-terminal domains of htt (residues 181-810 and 2146-2541, respectively), as well as the 17 residues at the N terminus of htt. On the basis of the patterns of htt fragments observed, different "protease-susceptible domains" were identified for proteolysis of htt in cortex compared with striatum, suggesting that htt undergoes tissue-specific proteolysis. In cortex, htt proteolysis occurs within two different N-terminal domains, termed protease-susceptible domains "A" and "B." However, in striatum, a different pattern of fragments indicated that proteolysis of striatal htt occurred within a C-terminal domain termed "C," as well as within the N-terminal domain region designated "A". Importantly, striatum from HD brains showed elevated levels of 40-50 kDa N-terminal and 30-50 kDa C-terminal fragments compared with that of controls. Increased levels of these htt fragments may occur from a combination of enhanced production or retarded degradation of fragments. Results also demonstrated tissue-specific ubiquitination of certain htt N-terminal fragments in striatum compared with cortex. Moreover, expansions of the triplet-repeat domain of the IT15 gene encoding htt was confirmed for the HD tissue samples studied. Thus, regulated tissue-specific proteolysis and ubiquitination of htt occur in human HD brains. These results suggest that the role of huntingtin proteolysis should be explored in the pathogenic mechanisms of HD.