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Caspases play an important role in neurodegeneration in Huntington's disease (HD). Members of the Bcl-2 family are critical modulators of terminal cell death pathways. However, alterations of Bcl-2 family members and their functional role in an in vivo model of HD have not been documented. With the goal of gaining mechanistic insight, we used a transgenic mouse model of HD (R6/2) to investigate the chronology of caspase activation and functional alterations in members of the Bcl-2 family. In R6/2 mice caspase activation precedes proapoptotic changes in Bcl-2 family members. Of the caspases that we screened, caspase-1-like activation was the first to be detected in the disease process (7 weeks). Proapoptotic changes in members of the Bcl-2 family were first detected at 9 weeks. To demonstrate a potential functional/therapeutic role of Bcl-2 in HD, we crossed R6/2 mice with mice overexpressing Bcl-2 in neurons. Transgenic expression of Bcl-2 in R6/2 mice resulted in slight prolonged survival. Understanding the chronology of apoptotic events provides important information for appropriate therapeutic targeting in this devastating and untreatable disease.

Evidence indicates that both necrotic and apoptotic cell death contribute to tissue injury and neurological dysfunction following spinal cord injury. Caspases have been implicated as important mediators of apoptosis following acute central nervous system insults. We investigated whether caspase-1 and caspase-3 are involved in spinal cord injury-mediated cell death, and whether caspase inhibition may reduce tissue damage and improve outcome following spinal cord injury. We demonstrate a 17-fold increase in caspase-1 activity in traumatized spinal cord samples when compared with samples from sham-operated mice. Caspase-1 and caspase-3 activation were also detected by western blot following spinal cord injury, which was significantly inhibited by the broad caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. By immunofluorescence or in situ fluorogenic substrate assay, caspase-1 and caspase-3 expression were detected in neuronal and non-neuronal cells following spinal cord injury. N-Benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone treated mice, and transgenic mice expressing a caspase-1 dominant negative mutant, demonstrated a significant improvement of motor function and a reduction of lesion size compared with vehicle-treated mice. Our results demonstrate for the first time that both caspase-1 and caspase-3 are activated in neurons following spinal cord injury, and that caspase inhibition reduces post-traumatic lesion size and improves motor performance. Caspase inhibitors may be one of the agents to be used for the treatment of spinal cord injury.

Huntington disease is an autosomal dominant neurodegenerative disease with no effective treatment. Minocycline is a tetracycline derivative with proven safety. After ischemia, minocycline inhibits caspase-1 and inducible nitric oxide synthetase upregulation, and reduces infarction. As caspase-1 and nitric oxide seem to play a role in Huntington disease, we evaluated the therapeutic efficacy of minocycline in the R6/2 mouse model of Huntington disease. We report that minocycline delays disease progression, inhibits caspase-1 and caspase-3 mRNA upregulation, and decreases inducible nitric oxide synthetase activity. In addition, effective pharmacotherapy in R6/2 mice requires caspase-1 and caspase-3 inhibition. This is the first demonstration of caspase-1 and caspase-3 transcriptional regulation in a Huntington disease model.

Mutations in the copper/zinc superoxide dismutase (SOD1) gene produce an animal model of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. To test a new therapeutic strategy for ALS, we examined the effect of caspase inhibition in transgenic mice expressing mutant human SOD1 with a substitution of glycine to alanine in position 93 (mSOD1 G93A ). Intracerebroventricular administration of zVAD-fmk, a broad caspase inhibitor, delays disease onset and mortality. Moreover, zVAD-fmk inhibits caspase-1 activity as well as caspase-1 and caspase-3 mRNA up-regulation, providing evidence for a non–cell-autonomous pathway regulating caspase expression. Caspases play an instrumental role in neurodegeneration in transgenic mSOD1 G93A mice, which suggests that caspase inhibition may have a protective role in ALS.

Necrotic and apoptotic cell death both play a role mediating tissue injury following brain trauma. Caspase-1 (interleukin-1beta converting enzyme) is activated and oligonucleosomal DNA fragmentation is detected in traumatized brain tissue. Reduction of tissue injury and free radical production following brain trauma was achieved in a transgenic mouse expressing a dominant negative inhibitor of caspase-1 in the brain. Neuroprotection was also conferred by pharmacological inhibition of caspase-1 by intracerebroventricular administration of the selective inhibitor of caspase-1, acetyl-Tyr-Val-Ala-Asp-chloromethyl-ketone or the non-selective caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. These results indicate that inhibition of caspase-1-like caspases reduces trauma-mediated brain tissue injury. In addition, we demonstrate an in vivo functional interaction between interleukin-1beta converting enyzme-like caspases and free radical production pathways, implicating free radical production as a downstream mediator of the caspase cell death cascade.

Minocycline mediates neuroprotection in experimental models of neurodegeneration. It inhibits the activity of caspase-1, caspase-3, inducible form of nitric oxide synthetase (iNOS) and p38 mitogen-activated protein kinase (MAPK). Although minocycline does not directly inhibit these enzymes, the effects may result from interference with upstream mechanisms resulting in their secondary activation. Because the above-mentioned factors are important in amyotrophic lateral sclerosis (ALS), we tested minocycline in mice with ALS. Here we report that minocycline delays disease onset and extends survival in ALS mice. Given the broad efficacy of minocycline, understanding its mechanisms of action is of great importance. We find that minocycline inhibits mitochondrial permeability-transition-mediated cytochrome c release. Minocycline-mediated inhibition of cytochrome c release is demonstrated in vivo, in cells, and in isolated mitochondria. Understanding the mechanism of action of minocycline will assist in the development and testing of more powerful and effective analogues. Because of the safety record of minocycline, and its ability to penetrate the blood-brain barrier, this drug may be a novel therapy for ALS.

OBJECTIVE: Caspase-1 plays an important functional role mediating neuronal cell death and dysfunction after experimental traumatic brain injury (TBI) in mice. Minocycline, a derivative of the antibiotic tetracycline, inhibits caspase-1 expression. This study investigates whether minocycline can ameliorate TBI-mediated injury in mice. METHODS: Brains from mice subjected to traumatic brain injury underwent immunohistochemical analyses for caspase-1, caspase-3, and a neuronal specific marker (NeuN). Minocycline- and saline-treated mice subjected to traumatic brain injury were compared with respect to neurological function, lesion volume, and interleukin-1b production. RESULTS: Immunohistochemical analysis revealed that activated caspase-1 and caspase-3 are present in neurons 24 hours after TBI. Intraperitoneal administration of minocycline 12 hours before or 30 minutes after TBI in mice resulted in improved neurological function when compared with mice given saline control, as assessed by Rotarod performance 1 to 4 days after TBI. The lesion volume, assessed 4 days after trauma, was significantly decreased in mice treated with minocycline before or after trauma when compared with saline-treated mice. Caspase-1 activity, quantified by measuring mature interleukin-1b production by enzyme-linked immunosorbent assay, was considerably increased in mice that underwent TBI, and this increase was significantly diminished in minocycline-treated mice. CONCLUSION: We show for the first time that caspase-1 and caspase-3 activities localize specifically within neurons after experimental brain trauma. Further, these results indicate that minocycline is an effective pharmacological agent for reducing tissue injury and neurological deficits that result from experimental TBI, likely through a caspase-1-dependent mechanism. These results provide an experimental rationale for the evaluation of minocycline in human trauma patients. (Neurosurgery 48:1393‐1401, 2001)

Huntington's disease is an autosomal-dominant progressive neurodegenerative disorder resulting in specific neuronal loss and dysfunction in the striatum and cortex. The disease is universally fatal, with a mean survival following onset of 15-20 years and, at present, there is no effective treatment. The mutation in patients with Huntington's disease is an expanded CAG/polyglutamine repeat in huntingtin, a protein of unknown function with a relative molecular mass of 350,000 (M(r) 350K). The length of the CAG/polyglutamine repeat is inversely correlated with the age of disease onset. The molecular pathways mediating the neuropathology of Huntington's disease are poorly understood. Transgenic mice expressing exon 1 of the human huntingtin gene with an expanded CAG/polyglutamine repeat develop a progressive syndrome with many of the characteristics of human Huntington's disease. Here we demonstrate evidence of caspase-1 activation in the brains of mice and humans with the disease. In this transgenic mouse model of Huntington's disease, expression of a dominant-negative caspase-1 mutant extends survival and delays the appearance of neuronal inclusions, neurotransmitter receptor alterations and onset of symptoms, indicating that caspase-1 is important in the pathogenesis of the disease. In addition, we demonstrate that intracerebroventricular administration of a caspase inhibitor delays disease progression and mortality in the mouse model of Huntington's disease.

Caspases play an important role in neurodegeneration in Huntington's disease (HD). Members of the Bcl-2 family are critical modulators of terminal cell death pathways. However, alterations of Bcl-2 family members and their functional role in an in vivo model of HD have not been documented. With the goal of gaining mechanistic insight, we used a transgenic mouse model of HD (R6/2) to investigate the chronology of caspase activation and functional alterations in members of the Bcl-2 family. In R6/2 mice caspase activation precedes proapoptotic changes in Bcl-2 family members. Of the caspases that we screened, caspase-1-like activation was the first to be detected in the disease process (7 weeks). Proapoptotic changes in members of the Bcl-2 family were first detected at 9 weeks. To demonstrate a potential functional/therapeutic role of Bcl-2 in HD, we crossed R6/2 mice with mice overexpressing Bcl-2 in neurons. Transgenic expression of Bcl-2 in R6/2 mice resulted in slight prolonged survival. Understanding the chronology of apoptotic events provides important information for appropriate therapeutic targeting in this devastating and untreatable disease.