A novel aspect of calpain activation

Calpain, a Ca2+-dependent biomodulator, alters the properties of substrate proteins by cleaving them at a limited number of specific sites. Recent studies of the structure-function relationship of calpain and X-ray analysis of its Ca2+-binding domain have revealed hitherto unknown features of the regulation of calpain activity. A novel dissociation/autolysis mechanism for the activation of calpain at the membrane is proposed, which incorporates recent findings from structure-function studies of calpain, and its implications are discussed.

The Dorothy Russell Memorial Lecture. The molecular and cellular sequelae of experimental traumatic brain injury: pathogenetic mechanisms

The mechanisms underlying secondary or delayed cell death following traumatic brain injury (TBI) are poorly understood. Recent evidence from experimental models of TBI suggest that diffuse and widespread neuronal damage and loss is progressive and prolonged for months to years after the initial insult in selectively vulnerable regions of the cortex, hippocampus, thalamus, striatum, and subcortical nuclei. The development of new neuropathological and molecular techniques has generated new insights into the cellular and molecular sequelae of brain trauma. This paper will review the literature suggesting that alterations in intracellular calcium with resulting changes in gene expression, activation of reactive oxygen species (ROS), activation of intracellular proteases (calpains), expression of neurotrophic factors, and activation of cell death genes (apoptosis) may play a role in mediating delayed cell death after trauma. Recent data suggesting that TBI should be considered as both an inflammatory and/or a neurodegenerative disease is also presented. Further research concerning the complex molecular and neuropathological cascades following brain trauma should be conducted, as novel therapeutic strategies continue to be developed.

Temporal ordering of pathogenic events following transient global ischemia

Rats were subjected to transient global ischemia (four vessel occlusion) and time-related changes in the selectively vulnerable hippocampal field CA1 were characterized. The assessment included ex vivo field responses to afferent stimulation, silver staining, calpain-induced spectrin breakdown, chromatolysis, and cell death, beginning at 6 h post-ischemia and continuing until total disintegration of the pyramidal cells occurred several days later. The earliest change observed was a modest increase in the slope and amplitude of field CA1 potentials (at 6 h). The hyperresponsiveness was most apparent at higher stimulation currents and persisted unchanged at 16 h post-ischemia. Three effects became detectable within 24 h, post-ischemia: (a) an increase in concentrations of calpain-mediated, spectrin breakdown products; (b) enhanced silver staining in the deep pyramidal neurons of the field CA1 with lesser, though still apparent, staining of stratum radiatum, and (c) a decrease in amplitude and slope of field CA1 responses to afferent stimulation. Both the concentration of spectrin breakdown products and the intensity of silver staining progressively increased to a maximum at four days post ischemia, while the amplitude and slope of the field responses dropped to a very low level between 24 and 48 h. Disturbances of Nissl staining were finally evident at 48 h, with nearly complete disappearance of staining at five days post-ischemia. This study provides the first demonstration of a close and early temporal relationship between calpain proteolysis, subcellular damage to the pyramidal cells and their loss of function following global ischemia, prior to their eventual death.

New inhibitors of calpain prevent degradation of cytoskeletal and myelin proteins in spinal cord in vitro

We have determined the effects of the calpain inhibitors AK275 and AK295 upon purified m-calpain and calcium-mediated degradation of neurofilament protein (NFP) in rat spinal cord in vitro. After incubation, the soluble radioactivity and/or extent of myelin basic protein (MBP) or NFP degradation was determined. Fifty percent of caseinolytic activity was inhibited by both inhibitors at 0.6 microM concentration, while more than 90% inhibition was seen at 1.6 microM. In contrast, 37% and 64% inhibition of MBP degradation was seen with AK295 and AK275, respectively, at 10 microM concentration. The extent of NFP degradation in spinal cord was quantified from immunoblot enhanced chemiluminescence. The calcium-mediated breakdown of NFP was inhibited by both AK275 and AK295, and the inhibition was dose-dependent. A 50% inhibition of NFP degradation was seen with AK295 at 10 microM and was almost completely inhibited at 25-50 microM. AK295 was slightly more potent than AK275. These studies suggest that these potent calpain inhibitors may be used therapeutically to provide neuroprotection in vivo in experimental central nervous system trauma and ischemia.