Involvement of mu-calpain in human sperm capacitation for fertilization

PROBLEM

The distribution and physiological role of calpains in human sperm were investigated.

METHOD OF STUDY

Semen collected manually from healthy donors was liquefied then centrifuged by percoll gradient centrifugation. After exposure to different concentrations of Ca2+ ionophore A23187, the samples were used for immunostaining sodium dodecyl sulfate polyacrylamide gel electrophoresis, and western blot analysis. It was speculated from the results of the study using calpain-specific inhibitors that calpain contributes to the sperm motility and acrosome reaction.

RESULTS

With the anti-pro mu-calpain antibody, sperm were immunostained, whereas all were negative for anti-pro mu-calpain antibody binding. Stained sperm were classified into four types according to the staining pattern: acrosome type, equatorial segment type, whole head type, and neck and tail segments type. Western blot analysis of sperm homogenate revealed a single 80-kDa band using the anti-pro mu-calpain antibody, its dose-dependent reduction with Ca2+ ionophore A23187 suggesting activation by this treatment. In the presence of membrane permeable calpain inhibitors, sperm motility and acrosome reaction were significantly suppressed.

CONCLUSION

These results indicate that mu-calpain may play pivotal roles in the process of fertilization of human sperm.

Cataract formation by a semiquinone metabolite of acetaminophen in mice: possible involvement of Ca(2+)and calpain activation

Acetaminophen, an analgesic/antipyretic, is metabolized by hepatic cytochrome P450 to N -acetyl- p -benzoquinone imine (NAPQI), which is transported by blood circulation to the eye and induces anterior cortical cataract in mice. In this study we injected NAPQI into the anterior chamber of mouse eye and investigated time-dependent cellular responses in the lens. After a lag period of about 2 hr following NAPQI injection, lens opacification as determined by measurement of light scattering by the lens became evident and progressively increased thereafter. There was no difference in the profile of opacity development between a P450-inducer responsive mouse strain and a non-responsive strain. During the lag period, a marked increase in free intracellular Ca(2+)in the lens epithelium was observed at 1 hr by confocal fluorescence microscopy with a Ca(2+)probe. Concurrent with the free Ca(2+)increase, there was a 300% rise in the activity of the non-lysosomal neutral protease calpain in the lens at 1 hr after NAPQI injection. Evidence indicated degradation of vimentin in the lens in which calpain activity was enhanced. Co-injection of calpain inhibitors (N-Ac-Leu-Leu-norleucinol and N-Ac-Leu-Leu-methioninal) with NAPQI protected animals completely from cataract development, although a rise in free intracellular Ca(2+)in the lens epithelium was still observed. Lenses from the protected mice did not exhibit enhanced calpain activity. These results suggest the following sequence of events as a possible mechanism of NAPQI-induced cataract. NAPQI introduced in the anterior chamber of the eye enters the lens epithelial cells and disturbs Ca(2+)homeostasis with a resultant rise in free intracellular Ca(2+)which in turn activates calpain in the epithelium. The neutral protease then degrades cellular proteins (e.g. cytoskeletal proteins) and initiates anterior cortical cataract formation.

[A case of LGMD2A identified with both western blot analysis and immunostaining of calpain 3 in biopsied muscle]

A 45-year-old housewife had proximal dominant limb muscle weakness from around 25 years of age. Her parents were cousins. None of family members was affected. Progressive muscle weakness and atrophy were prominent at the posterior compartments of legs and trunk. Serum CK was moderately elevated. Muscle pathology revealed variation in fiber size, moderate increase in numbers of internal nuclei and abundant lobulated fibers. On immunostaining using by monoclonal antibody against human calpain 3 (NCL-CALP-2 C4; Novocastra) to the biopsied muscle, calpain 3 was completely absent in the sarcoplasm, while granular debris and in part positive striation were noted in control muscle. By Western blot analysis, a band corresponding to 94 kDa of calpain 3 was not detected. A genetic analysis of calpain 3 revealed homozygous C-565-G mutation (Leu189Val). From the present study. Western blot analysis and immunostaining by using calpain 3 antibody were suggested to be useful to diagnose LGMD2A in LGMD patients.

Downregulation of the calpain inhibitor protein calpastatin by caspases during renal ischemia-reperfusion

The interaction between the cysteine proteases calpain and caspases during renal ischemia-reperfusion (I/R) was investigated. An increase in the activity of calpain, as determined by 1) the appearance of calpain-mediated spectrin breakdown products and 2) the conversion of procalpain to active calpain, was demonstrated. Because intracellular calpain activity is regulated by calpastatin, the effect of I/R on calpastatin was determined. On immunoblot of renal cortex, there was a 50-100% decrease of a low molecular weight (LMW) form of calpastatin (41 kDa) after I/R. Calpastatin activity was also significantly decreased after I/R compared with sham-operated rats, indicating that the decreased protein expression had functional significance. In rats treated with the caspase inhibitor, z-Asp-2,6-dichlorobenzoyloxymethylketone (Z-D-DCB), the decrease in both calpastatin activity and protein expression was normalized, suggesting that caspases may be proteolyzing calpastatin. Caspase 3 activity increased significantly after I/R and was attenuated in ischemic kidneys from rats treated with the caspase inhibitor. In summary, during renal I/R injury, there is 1) calpain activation associated with downregulation of calpastatin protein and decreased calpastatin activity and 2) activation of caspase 3. In addition, in vivo caspase inhibition reverses the decrease in calpastatin activity. In conclusion, proteolysis of calpastatin by caspase 3 may regulate calpain activity during I/R injury. Although the protective effect of cysteine protease inhibition against hypoxic necrosis of proximal tubules has previously been demonstrated, the functional significance in ischemic acute renal failure in vivo merits further study.

Identification and characterization of a retina-specific calpain (Rt88) from rat

PURPOSE

To identify and characterize a newly discovered calpain termed Rt88 from rat retina.

METHODS

Rt88 in retina under normal physiological conditions was characterized in Sprague-Dawley rats of various ages by competitive RT-PCR, Northern blot analysis, cDNA cloning and sequencing. Recombinant Rt88 was expressed in the baculovirus system and characterized by casein zymography and immunoblotting.

RESULTS

Rt88 was sequenced and found to be similar to muscle calpain p94 except for three differences. A different exon 1 (as in lens Lp82 calpain) was present, and exons 15 and 16 in the unique IS2 region of muscle p94 were deleted. Of eleven tissues studied, mRNA for Rt88 was found only in retina where Rt88 increased with maturation and then remained constant. Casein zymography showed that rRt88 was proteolytically active after activation by calcium, but intact rRt88 was rapidly broken due to the presence of the IS1 region in domain II.

CONCLUSIONS

Rt88 is a retina-specific, calcium activated protease from the calpain superfamily (EC 3.4.22.17) of cysteine proteases. Rt88 is a recently identified member of the AX1 subfamily of calpains showing alternative exon 1 usage. So far, all AX1 subfamily members are from eye. Rt88 may perform specific proteolytic functions during development, normal turnover, or pathological degeneration of retinal proteins.

A BODIPY fluorescent microplate assay for measuring activity of calpains and other proteases

The use of 4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacene-3-propionic acid (BODIPY-FL) labeled casein in autoquenching assays of proteolytic activity has been recently described, and we have adapted this assay to measurement of calpain activity. BODIPY-FL coupled to casein at a ratio of 8 mol of BODIPY-FL/mol of casein or higher produces a BODIPY-FL-casein substrate that can be used in an autoquenching assay of calpain proteolytic activity. This assay has a number of advantages for measuring calpain activity. (1) The procedure does not require precipitation and removal of undegraded protein, so it is much faster than other procedures that require a precipitation step, and it can be used directly in kinetic assays of proteolytic activity. (2) The BODIPY-FL-casein assay is easily adapted to a microtiter plate format, so it can be used to screen large numbers of samples. (3) Casein is an inexpensive and readily available protein substrate that more closely mimics the natural substrates of endoproteinases, such as the calpains, than synthetic peptide substrates do. Casein has K(m) values for micro- and m-calpain that are similar to those of other substrates such as fodrin or MAP2 that may be "natural" substrates for the calpains, and there is no reason to believe that calpain hydrolysis of casein is inherently different from hydrolysis of fodrin or MAP2, which are much less accessible as substrates for protease assays. (4) The BODIPY-FL-casein assay is capable of detecting 10 ng ( approximately 5 nM) of calpain and is nearly as sensitive as the most sensitive calpain assay reported thus far. (5) The BODIPY-FL-casein assay is as reproducible as the FITC-casein assay, whose reproducibility is comparable to or better than the reproducibility of other methods used to assay calpain activity. The BODIPY-FL-casein assay is a general assay for proteolytic activity and can be used with any protease that cleaves casein.

Technical note: a rapid method for quantification of calpain and calpastatin activities in muscle

Stepwise and continuous gradient ion-exchange chromatography were compared for yield of calpains and calpastatin from ovine muscle in a study designed to quantify their activities for comparative purposes. In Exp. 1, a continuous (25 to 400 mM NaCl) gradient and a two-step gradient method (200 mM NaCl to coelute mu-calpain and calpastatin together and then 400 mM NaCl to elute mu-calpain) were compared. For the two-step method, mu-calpain activities were determined by subtracting calpastatin activities before and after heat inactivation of mu-calpain. Both the two-step and the continuous gradient method yielded similar results over a broad range of activities. The stepwise gradient method does not require the use of fraction collectors and pumps, and it can be completed in a fraction of the time required for the continuous gradient method. In Exp. 2, the two-step method was compared with a three-step method (100 mM NaCl to elute calpastatin, then 200 mM NaCl to elute mu-calpain, and then 400 mM NaCl to elute m-calpain). Unlike the continuous gradient method, calpastatin and mu-calpain could not be completely separated using the three-step chromatography method. Thus, the three-step gradient method should not be used to quantify the components of the calpain proteolytic system. The present results indicate that the two-step gradient method is a fast and inexpensive method to determine calpain and calpastatin activities in studies designed to quantify the components of the calpain proteolytic system in skeletal muscle.

A putative mechanism of demyelination in multiple sclerosis by a proteolytic enzyme, calpain

In autoimmune demyelinating diseases such as multiple sclerosis (MS), the degradation of myelin proteins results in destabilization of the myelin sheath. Thus, proteases have been implicated in myelin protein degradation, and recent studies have demonstrated increased expression and activity of a calcium-activated neutral proteinase (calpain) in experimental allergic encephalomyelitis, the corresponding animal model of MS. In the present study, calpain activity and expression (at translational and transcriptional levels) were evaluated in white matter from human patients with MS and Parkinson's and Alzheimer's diseases and compared with that of white matter from normal controls. Western blot analysis revealed that levels of the active form of calpain and calpain-specific degradation products (fodrin) were increased by 90.1% and 52.7%, respectively, in MS plaques compared with normal white matter. Calpain translational expression was up-regulated by 462.5% in MS plaques compared with controls, although levels of the specific endogenous inhibitor, calpastatin, were not altered significantly. At the transcriptional level, no significant changes in calpain or calpastatin expression were detected by reverse transcription-PCR. Using double immunofluorescent labeling, increased calpain expression was observed in reactive astrocytes, activated T cells, and activated mononuclear phagocytes in and adjacent to demyelinating lesions. Calpain activity and translational expression were not increased significantly in white matter from patients with Parkinson's or Alzheimer's diseases compared with that of normal controls. Because calpain degrades all major myelin proteins, the increased activity and expression of this proteinase may play a critical role in myelinolysis in autoimmune demyelinating diseases such as MS.

Externalization of calpain (calcium-dependent neutral cysteine proteinase) in human arthritic cartilage

OBJECTIVE

Calcium-dependent neutral cysteine proteinase (calpain) was originally referred to as an intracellular enzyme. However, recently it has come to be considered as an extracellular matrix proteinase, as well having a degrading effect on cartilage proteoglycan. In the present study we sought to determine whether human articular cartilage chondrocytes themselves have the capability to produce and secrete this interesting proteinase.

METHODS

Human articular cartilage tissue cultures from osteoarthritic (11 specimens from 7 patients) and rheumatoid arthritic (3 specimens from 2 patients) knee joints were established, and the m-calpain released into the culture medium was concentrated and detected by immunoelectrophoretic blotting. The presence of m-calpain in the arthritic cartilage was also examined by immunohistochemistry before and after culturing.

RESULTS

M-calpain was detectable in all of the cartilage tissue culture supernatants (conditioned medium) by western blotting. Positive intracellular immunostaining of m-calpain in chondrocytes was observed in all samples. Furthermore, m-calpain was found to be present in the matrix and on the articular surface of the cartilage in half of the specimens.

CONCLUSION

The findings of our experiment suggest that cartilage chondrocytes may actively take part in m-calpain production and that they may have the capacity to release it into the extracellular matrices.

Multiplex Western blotting system for the analysis of muscular dystrophy proteins

A multiplex system of Western blotting is presented in which most of the current muscular dystrophy proteins can be analyzed simultaneously on one pair of blots. This represents a significant improvement in efficiency and cost for this type of analysis. The final diagnosis is more quickly achieved in patients where several possible diagnoses are indicated after clinical appraisal, and those with unusual presentations may be quickly resolved. The method uses a biphasic polyacrylamide gel system, which enables the corresponding blot to be probed simultaneously with a cocktail of monoclonal antibodies. The gel is optimized so that large proteins of more than 200 kd (eg, dystrophin, dysferlin, and myosin heavy chain) can be analyzed in the top part, while smaller proteins under 150 kd (eg, calpain 3, the 80-kd fragment of laminin alpha2 chain, all of the sarcoglycans, and caveolin 3) are separated in the lower phase. This basic system could be used for different combinations of antibodies as new muscular dystrophy proteins are identified and require examination. In addition, analysis of the laminin alpha2 chain of merosin showed that this protein was expressed as a doublet or triplet set of bands in many patients with active muscle pathology. This may indicate the existence of an embryonic isoform, which is re-expressed in regenerating fibers.

Protective effects of calpain inhibitor for prolonged hypothermic cardiac preservation

PURPOSE

For successful organ transplantation, it is important to properly preserve the donor organ. This study was carried out to investigate tissue damage generated by the activation of calpain during prolonged hypothermic cardiac preservation using specific antibodies for mu- and m-calpain proenzymes, and to ensure the protective effect of calpain inhibitor 1 (N-acetyl-leucyl-leucyl-norleucinal).

METHODS

Excised rat hearts were divided into two groups: in Group I, the heart was arrested and immersed in University of Wisconsin solution with 20 microM of calpain inhibitor 1 (n = 28) and in Group N, the heart was arrested and immersed in University of Wisconsin solution without calpain inhibitor (n = 27). After a 12-hour preservation period at 4 degrees C, the hearts were reperfused on an isolated perfusion apparatus. Separation of the myocardial calpain isozymes was carried out by DEAE cellulose chromatography and both calpain proenzymes were detected by immunoblotting.

RESULTS

The cardiac function was more satisfactorily maintained in Group I in comparison with Group N. Remarkable leakage of creatine kinase, glutamic-oxaloacetic transaminase and lactate dehydrogenase was detected in Group N, while it was efficiently suppressed in Group I. During ischemia, mu-calpain proenzyme decreased in Group N (p < 0.01), but there was no significant change in m-calpain. However, during reperfusion, both mu- and m-calpains decreased more in Group N (p < 0.01).

CONCLUSION

Activation of calpain proenzymes and a decrease in cardiac function during preservation and reperfusion were demonstrated. The use of calpain inhibitor to protect against tissue damage was suggested as being useful for the prolonged preservation of the heart.

The role of calpain-mediated spectrin proteolysis in traumatically induced axonal injury

In animals and man, traumatic brain injury (TBI) results in axonal injury (AI) that contributes to morbidity and mortality. Such injured axons show progressive change leading to axonal disconnection. Although several theories implicate calcium in the pathogenesis of AI, experimental studies have failed to confirm its pivotal role. To explore the contribution of Ca2+-induced proteolysis to axonal injury, this study was undertaken in an animal model of TBI employing antibodies targeting both calpain-mediated spectrin proteolysis (CMSP) and focal neurofilament compaction (NFC), a marker of intra-axonal cytoskeletal perturbation, at 15-120 minutes (min) postinjury. Light microscopy (LM) revealed that TBI consistently evoked focal, intra-axonal CMSP that was spatially and temporally correlated with NFC. These changes were seen at 15 min postinjury with significantly increasing number of axons demonstrating CMSP immunoreactivity over time postinjury. Electron microscopy (EM) demonstrated that at 15 min postinjury CMSP was confined primarily to the subaxolemmal network. With increasing survival (30-120 min) CMSP filled the axoplasm proper. These findings provide the first direct evidence for focal CMSP in the pathogenesis of generalized/diffuse AI. Importantly, they also reveal an initial subaxolemmal involvement prior to induction of a more widespread axoplasmic change indicating a spatial-temporal compartmentalization of the calcium-induced proteolytic process that may be amenable to rapid therapeutic intervention.

Calpain mediates ischemic injury of the liver through modulation of apoptosis and necrosis

BACKGROUND & AIMS

Calpain proteases have been implicated in cell death by necrosis and more recently by apoptosis. Experiments were designed to determine the role of calpain proteases in ischemic rat liver injury by measurement of cytosolic calpain activity after different periods of ischemia-reperfusion and by evaluation of the effects of calpain inhibition on tissue injury and animal survival.

METHODS

Calpain activity was measured in the cytosol using Suc-Leu-Leu-Val-Try-7 amino-4 methyl coumarin, a specific fluorogenic substrate, and Cbz-Leu-Leu-Tyr-CHN2, a specific inhibitor.

RESULTS

Calpain activity increased significantly with the duration of ischemia-reperfusion and was inhibited more than 80% by the inhibitor. Calpain inhibition resulted in a significant decrease in transaminase release and tissue necrosis and converted nonsurvival ischemic conditions to survival conditions. When the in situ terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling assay for apoptosis was used, 35% +/- 6% of nonparenchymal cells and 16% +/- 3% of hepatocytes stained positively after 60 minutes of ischemia and 6 hours of reperfusion. In contrast, animals pretreated with the calpain inhibitor showed minimal evidence of apoptosis. This was further substantiated by gel electrophoresis assay for DNA fragmentation and by electron-microscopic evaluation.

CONCLUSIONS

These data suggest that calpain proteases play a pivotal role in warm ischemia-reperfusion injury of the rat liver through modulation of apoptosis and necrosis.

The neuronal cytoskeleton is at risk after mild and moderate brain injury

Recent studies have described alterations in cytoskeletal proteins such as microtubule-associated protein 2 (MAP-2) and neurofilament (NF) resulting from moderate and severe experimental brain injury; however, few have investigated the consequences of mild injury, which is associated clinically and experimentally with cognitive dysfunction and neuronal damage. To contrast cytoskeletal changes within 7 days following mild injury with those following moderate injury, we subjected anesthetized, adult rats to mild (1.1-1.3 atm) or moderate (2.3-2.5 atm) lateral fluid percussion brain injury or sham injury. Rats were sacrificed at 6 h (n=4 mild; n=4 moderate; n=2 sham), 24 h (n=4 mild; n=4 moderate; n=1 sham), or 7 days (n=5 mild; n=4 moderate; n=1 sham) following injury, and immunohistochemistry was performed for MAP-2 and NF. Both mild and moderate injury produced notable cytoskeletal changes in multiple brain regions; however, mild injury generally resulted in a lesser degree of MAP-2 and NF loss over a smaller spatial extent. When compared to moderately injured animals, animals subjected to mild injury showed substantially delayed MAP-2 and NF alterations within the cortex and hippocampal dentate gyrus and no evidence of MAP-2 loss in the hippocampal CA3 region. While mild and moderate injury resulted for the most part in similar patterns of axonal injury, tissue tears in the fimbria and loss of NF immunoreactivity in regions containing injured axons were only observed following moderate injury. Elucidating the effects of modulating injury severity may yield insight into the mechanisms involved in traumatic damage to the cytoskeleton and guide future treatment strategies.

A sensitive, continuously recording fluorogenic assay for calpain

We have developed a sensitive and continuously recording fluorogenic assay for the thiol protease calpain. This assay uses the dipeptide substrate Suc-Leu-Tyr-4-Methoxy-2-Naphthylamine (Suc-LY-MNA) in Tris buffer (pH 7.5) in the presence of 0.1% CHAPS. The assay is linear over a wide range of enzyme concentration and is capable of detecting 10 picomolar calpain making it more sensitive than any previously published method. Moreover, this assay gives a rate that is linear for over ten minutes making it useful for mechanistic studies of inhibitors. This assay can be easily adapted to a 96-well plate format facilitating the large scale screening of inhibitors.