Mouse and rat cystatin C: Escherichia coli production, characterization and tissue distribution

Proteomic Analysis of a Rat Streptozotocin Model Shows Dysregulated Biological Pathways Implicated in Alzheimer's Disease

Alzheimer's Disease (AD) is an age-related neurodegenerative disorder characterized by progressive memory loss and cognitive impairment, affecting 35 million individuals worldwide. Intracerebroventricular (ICV) injection of low to moderate doses of streptozotocin (STZ) in adult male Wistar rats can reproduce classical physiopathological hallmarks of AD. This biological model is known as ICV-STZ. Most studies are focused on the description of behavioral and morphological aspects of the ICV-STZ model. However, knowledge regarding the molecular aspects of the ICV-STZ model is still incipient. Therefore, this work is a first attempt to provide a wide proteome description of the ICV-STZ model based on mass spectrometry (MS). To achieve that, samples from the pre-frontal cortex (PFC) and hippocampus (HPC) of the ICV-STZ model and control (wild-type) were used. Differential protein abundance, pathway, and network analysis were performed based on the protein identification and quantification of the samples. Our analysis revealed dysregulated biological pathways implicated in the early stages of late-onset Alzheimer's disease (LOAD), based on differentially abundant proteins (DAPs). Some of these DAPs had their mRNA expression further investigated through qRT-PCR. Our results shed light on the AD onset and demonstrate the ICV-STZ as a valid model for LOAD proteome description.

Injectable Peptide Hydrogels Loaded with Murine Embryonic Stem Cells Relieve Ischemia In Vivo after Myocardial Infarction

Myocardial infarction (MI) is a major cause of morbidity and mortality worldwide, especially in aging and metabolically unhealthy populations. A major target of regenerative tissue engineering is the restoration of viable cardiomyocytes to preserve cardiac function and circumvent the progression to heart failure post-MI. Amelioration of ischemia is a crucial component of such restorative strategies. Angiogenic β-sheet peptides can self-assemble into thixotropic nanofibrous hydrogels. These syringe aspiratable cytocompatible gels were loaded with stem cells and showed excellent cytocompatibility and minimal impact on the storage and loss moduli of hydrogels. Gels with and without cells were delivered into the myocardium of a mouse MI model (LAD ligation). Cardiac function and tissue remodeling were evaluated up to 4 weeks in vivo. Injectable peptide hydrogels synergized with loaded murine embryonic stem cells to demonstrate enhanced survival after intracardiac delivery during the acute phase post-MI, especially at 7 days. This approach shows promise for post-MI treatment and potentially functional cardiac tissue regeneration and warrants large-scale animal testing prior to clinical translation.

The Levels of Leptin, Cystatin C, Neuropilin-1 and Tau Protein in Relation to Dietary Habits in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in older people. Its prevalence is expected to increase, and therefore it poses a serious challenge to the healthcare system. The aim of the study was to assess the concentration of leptin, cystatin C, neuropilin-1 and tau protein, as well as the influence of dietary habits on these parameters, in a group of AD patients (n = 110) compared to 60 healthy people (n = 60). It has been shown that AD patients, compared to healthy people, are characterized by significantly higher median concentrations of leptin (9.97 vs. 3.08), cystatin c (1.53 vs. 0.56) and tau protein (8.46 vs. 4.19), but significantly lower median neuropilin-1 (69.94 vs. 167.28). Multiple regression analyses showed that leptin levels could be explained by dietary habits in 27%, cystatin C in 51%, neuropilin-1 in 41% and tau protein in 25% of cases. Modification of eating habits may contribute to improving the values of the discussed parameters.

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Identification of Proteins Responsible for High Activity of Cysteine Proteinase Inhibitor in the Blood of Nile Tilapia Oreochromis niloticus

Cysteine proteinase inhibitors (CPIs) protect tissues and organs against cysteine proteinases in animal blood and have attracted much attention for use in food processing and medical sciences for humans and animals. Several CPI proteins, which include stefins, cystatins, kininogens, histidine-rich glycoproteins (HRG) and fetuins, have been identified and characterized in mammals. Fish blood also contains high CPI activity, but the identity of the major protein responsible for this activity has not been clarified. This study was conducted to screen CPI activity by examining papain inhibitory activity from various different tissues in Nile tilapia Oreochromis niloticus and to identify major proteins for the activity in the blood. CPI activity was highest in the serum among the tissues screened in this study (at least fourfold higher than in other tissues)(P < 0.05). Major proteins for CPI activity in serum were purified using a CNBr-activated sepharose 4B column, gel filtration and an ion exchange FPLC column. From these purifications, two proteins with strong CPI activity were isolated and partially sequenced. Based on their molecular weights and partial amino sequences, the two major proteins with CPI activity from the blood in this species were found to be fetuin B (60 kDa) and kininogen (54 kDa).

Diagnostic circulating biomarkers to detect vision-threatening diabetic retinopathy: Potential screening tool of the future?

With the increasing prevalence of diabetes in developing and developed countries, the socio-economic burden of diabetic retinopathy (DR), the leading complication of diabetes, is growing. Diabetic retinopathy (DR) is currently one of the leading causes of blindness in working-age adults worldwide. Robust methodologies exist to detect and monitor DR; however, these rely on specialist imaging techniques and qualified practitioners. This makes detecting and monitoring DR expensive and time-consuming, which is particularly problematic in developing countries where many patients will be remote and have little contact with specialist medical centres. Diabetic retinopathy (DR) is largely asymptomatic until late in the pathology. Therefore, early identification and stratification of vision-threatening DR (VTDR) is highly desirable and will ameliorate the global impact of this disease. A simple, reliable and more cost-effective test would greatly assist in decreasing the burden of DR around the world. Here, we evaluate and review data on circulating protein biomarkers, which have been verified in the context of DR. We also discuss the challenges and developments necessary to translate these promising data into clinically useful assays, to detect VTDR, and their potential integration into simple point-of-care testing devices.

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

The Positive Side of the Alzheimer's Disease Amyloid Cross-Interactions: The Case of the Aβ 1-42 Peptide with Tau, TTR, CysC, and ApoA1

Alzheimer's disease (AD) represents a progressive amyloidogenic disorder whose advancement is widely recognized to be connected to amyloid-β peptides and Tau aggregation. However, several other processes likely contribute to the development of AD and some of them might be related to protein-protein interactions. Amyloid aggregates usually contain not only single type of amyloid protein, but also other type of proteins and this phenomenon can be rationally explained by the process of protein cross-seeding and co-assembly. Amyloid cross-interaction is ubiquitous in amyloid fibril formation and so a better knowledge of the amyloid interactome could help to further understand the mechanisms of amyloid related diseases. In this review, we discuss about the cross-interactions of amyloid-β peptides, and in particular Aβ1-42, with other amyloids, which have been presented either as integrated part of Aβ neurotoxicity process (such as Tau) or conversely with a preventive role in AD pathogenesis by directly binding to Aβ (such as transthyretin, cystatin C and apolipoprotein A1). Particularly, we will focus on all the possible therapeutic strategies aiming to rescue the Aβ toxicity by taking inspiration from these protein-protein interactions.

Cystatin C in adipose tissue and stimulation of its production by growth hormone and triiodothyronine in 3T3-L1 cells

Cystatin C (CysC) is a marker for estimation of glomerular filtration rate (GFR). CysC levels may depend not only on clearance/GFR but possibly also on changes in production. Our studies on tissue distribution of CysC protein in mice showed that adipose tissue expresses significant amounts of CysC, suggesting that adipocytes could contribute to circulating CysC levels in vivo. As growth hormone (GH) and triiodothyronine (T₃) increase both GFR and CysC (increased in acromegaly and hyperthyroidism) in vivo, we studied whether they could increase CysC production in 3T3-L1 adipocytes in vitro. CysC accumulated in culture media of 3T3-L1 adipocytes in a time-dependent fashion. GH and T₃ both (10 nmol/l) increased accumulation of CysC, to 373 ± 14 and 422 ± 20, respectively, vs 298 ± 10 ng per well over 4 days in controls. Thus, GH and T₃ enhance the production of CysC by adipocytes in vitro.

From Analysis of Ischemic Mouse Brain Proteome to Identification of Human Serum Clusterin as a Potential Biomarker for Severity of Acute Ischemic Stroke

Ischemic stroke is a devastating neurological disease that can cause permanent brain damage, but to date, few biomarkers are available to reliably assess the severity of injury during acute onset. In this study, quantitative proteomic analysis of ischemic mouse brain detected the increase in expression levels of clusterin (CLU) and cystatin C (CST3). Since CLU is a secretary protein, serum samples (n = 70) were obtained from acute ischemic stroke (AIS) patients within 24 h of stroke onset and together with 70 matched health controls. Analysis of CLU levels indicated significantly higher levels in AIS patients than healthy controls (14.91 ± 4.03 vs. 12.79 ± 2.22 ng/L; P = 0.0004). Analysis of serum CST3 also showed significant increase in AIS patients as compared with healthy controls (0.90 ± 0.19 vs. 0.84 ± 0.12 ng/L; P = 0.0064). The serum values of CLU were also positively correlated with the NIH Stroke Scale (NIHSS) scores, the time interval after stroke onset, as well as major stroke risk factors associated with lipid profile. These data demonstrate that elevated levels of serum CLU and CST3 are independently associated with AIS and may serve as peripheral biomarkers to aid clinical assessment of AIS and its severity. This pilot study thus contributes to progress toward preclinical proteomic screening by using animal models and allows translation of results from bench to bedside.

Serum cystatin C is associated with large cerebral artery stenosis in acute ischemic stroke

Large cerebral artery stenosis is a major cause of acute ischemic stroke (AIS); however, the correlation between serum cystatin C (CysC) and the stenosis of large cerebral arteries in patients with AIS has not been established. We performed a retrospective review of acute ischemic stroke patients, who were examined by cerebral digital subtraction angiography(DSA). Participants (252 cases) included 131 patients without stenosis and 121 patients with large cerebral artery stenosis. Serum CysC levels in patients with large cerebral artery stenosis were much higher than that of control subjects (p<0.001). However, serum CysC levels were not related to the location of stenosis. Further, logistic regression analyses showed that increased serum CysC was an independent risk factor of large cerebral artery stenosis in patients with acute ischemic stroke. Total participants were subdivided into quintiles based on serum CysC levels. Compared with the first quintile, the odds ratios of risk for large cerebral artery stenosis in the fourth and the fifth quintile were 1.26 (p<0.05) and 4.71(p<0.05) respectively, after the adjustment for age, sex, and smoking, hypertension, type 2 diabetes mellitus(DM), dyslipidemia, creatinine(Cr), urea, uric acid, and C reactive protein(CRP). Therefore, a significant positive correlation was observed between elevated serum CysC levels and large cerebral artery stenosis in patients with acute ischemic stroke. In summary, our findings provide new insights into the correlation between increased serum CysC and large cerebral artery stenosis in patients with acute ischemic stroke.

Insights into the mechanism of cystatin C oligomer and amyloid formation and its interaction with β-amyloid

Cystatin C (CysC) is a versatile and ubiquitously-expressed member of the cysteine protease inhibitor family that is present at notably high concentrations in cerebrospinal fluid. Under mildly denaturing conditions, CysC forms inactive domain-swapped dimers. A destabilizing mutation, L68Q, increases the rate of domain-swapping and causes a fatal amyloid disease, hereditary cystatin C amyloid angiopathy. Wild-type (wt) CysC will also aggregate into amyloid fibrils under some conditions. Propagated domain-swapping has been proposed as the mechanism by which CysC fibrils grow. We present evidence that a CysC mutant, V57N, stabilized against domain-swapping, readily forms fibrils, contradicting the propagated domain-swapping hypothesis. Furthermore, in physiological buffer, wt CysC can form oligomers without undergoing domain-swapping. These non-swapped oligomers are identical in secondary structure to CysC monomers and completely retain protease inhibitory activity. However, unlike monomers or dimers, the oligomers bind fluorescent dyes that indicate they have characteristics of pre-amyloid aggregates. Although these oligomers appear to be a pre-amyloid assembly, they are slower than CysC monomers to form fibrils. Fibrillation of CysC therefore likely initiates from the monomer and does not require domain-swapping. The non-swapped oligomers likely represent a dead-end offshoot of the amyloid pathway and must dissociate to monomers prior to rearranging to amyloid fibrils. These prefibrillar CysC oligomers were potent inhibitors of aggregation of the Alzheimer's-related peptide, β-amyloid. This result illustrates an example where heterotypic interactions between pre-amyloid oligomers prevent the homotypic interactions that would lead to mature amyloid fibrils.

Cystatin C Is a Crucial Endogenous Protective Determinant Against Stroke

BACKGROUND AND PURPOSE

Endogenous neuroprotection can be induced by ischemic and nonischemic preconditioning. However, not all subjects that undergo preconditioning exhibit similar favorable outcome. This study is to explore the molecules responsible for this phenomenon and find new therapeutic targets for stroke.

METHODS

Adult male Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion. High-throughput proteomic technique, isobaric tag for relative and absolute quantification, was used to screen differentially expressed proteins in the rats that developed ischemic tolerance from hyperbaric oxygen (HBO) preconditioning. The proteomic results were verified by Western blot and ELISA. Then, short interfering RNA and gene knockout rats were used to further determine the pivotal role of candidate proteins in HBO preconditioning-induced endogenous neuroprotection. Finally, lysosomal permeability was tested to elaborate the mechanism underlying this intrinsic neuroprotective effect.

RESULTS

Nine proteins differentially expressed in the serum of rats, which acquired benefits from HBO preconditioning, were screened and identified. Western blot and ELISA revealed that cystatin C (CysC) and mannose-binding lectin protein C were uniquely changed in rats with smaller infarction after HBO preconditioning and cerebral ischemia. Knockdown and knockout of CysC abolished HBO-induced neuroprotection. Moreover, HBO-induced endogenous CysC elevation preserved lysosomal membrane integrity after stroke in wild-type rats but not in CysC siRNA infusion or CysC^-/- rats. Most importantly, exogenous CysC also induced neuroprotection against ischemic/reperfusion injury.

CONCLUSIONS

CysC is a crucial determinant contributing to endogenous neuroprotection. It is also a novel candidate for stroke treatment through maintaining lysosomal membrane integrity.

Cystatin C in aging and in Alzheimer's disease

Under normal conditions, the function of catalytically active proteases is regulated, in part, by their endogenous inhibitors, and any change in the synthesis and/or function of a protease or its endogenous inhibitors may result in inappropriate protease activity. Altered proteolysis as a result of an imbalance between active proteases and their endogenous inhibitors can occur during normal aging, and such changes have also been associated with multiple neuronal diseases, including Amyotrophic Lateral Sclerosis (ALS), rare heritable neurodegenerative disorders, ischemia, some forms of epilepsy, and Alzheimer's disease (AD). One of the most extensively studied endogenous inhibitor is the cysteine-protease inhibitor cystatin C (CysC). Changes in the expression and secretion of CysC in the brain have been described in various neurological disorders and in animal models of neurodegeneration, underscoring a role for CysC in these conditions. In the brain, multiple in vitro and in vivo findings have demonstrated that CysC plays protective roles via pathways that depend upon the inhibition of endosomal-lysosomal pathway cysteine proteases, such as cathepsin B (Cat B), via the induction of cellular autophagy, via the induction of cell proliferation, or via the inhibition of amyloid-β (Aβ) aggregation. We review the data demonstrating the protective roles of CysC under conditions of neuronal challenge and the protective pathways induced by CysC under various conditions. Beyond highlighting the essential role that balanced proteolytic activity plays in supporting normal brain aging, these findings suggest that CysC is a therapeutic candidate that can potentially prevent brain damage and neurodegeneration.

Discordance in cathepsin B and cystatin C expressions in bronchoalveolar fluids between murine bleomycin-induced fibrosis and human idiopathic fibrosis

The activity of cysteine cathepsin B increased markedly in lung homogenates and in bronchoalveolar lavage fluids (BALF) of the mouse model of bleomycin-induced lung fibrosis after 14 days of challenge. In contrast the level of the cysteine cathepsin inhibitor cystatin C was unaffected in BALF of wild-type and cathepsin B-deficient mice. Therefore, murine cystatin C is not a reliable marker of fibrosis during bleomycin-induced lung fibrosis. Current data are in sharp contrast to previous analysis carried on human BALF from patients with idiopathic pulmonary fibrosis, for which the level of cathepsin B remained unchanged while cystatin C was significantly increased.

Cross-interactions between the Alzheimer Disease Amyloid-β Peptide and Other Amyloid Proteins: A Further Aspect of the Amyloid Cascade Hypothesis

Many protein folding diseases are intimately associated with accumulation of amyloid aggregates. The amyloid materials formed by different proteins/peptides share many structural similarities, despite sometimes large amino acid sequence differences. Some amyloid diseases constitute risk factors for others, and the progression of one amyloid disease may affect the progression of another. These connections are arguably related to amyloid aggregates of one protein being able to directly nucleate amyloid formation of another, different protein: the amyloid cross-interaction. Here, we discuss such cross-interactions between the Alzheimer disease amyloid-β (Aβ) peptide and other amyloid proteins in the context of what is known from in vitro and in vivo experiments, and of what might be learned from clinical studies. The aim is to clarify potential molecular associations between different amyloid diseases. We argue that the amyloid cascade hypothesis in Alzheimer disease should be expanded to include cross-interactions between Aβ and other amyloid proteins.

Cystatin C is an Independent Risk Factor and Therapeutic Target for Acute Ischemic Stroke

Cystatin C (CysC) has been used as a renal function indicator and a strong predictor of cardiovascular events. In this study, we determined the prognostic value of serum CysC in patients with acute ischemic stroke (AIS) and examined its protective role on ischemic brain injury. First-ever stroke patients (601 cases) and control subjects (325 cases) were recruited. Serum CysC level in patients with AIS were significantly higher than that in controls. Multivariate logistic regression analyses showed that elevated CysC is an independent risk factor of AIS; the odds ratio (95 % confidence interval) was 9.80 (3.12-30.83). The integrated population was divided into quintiles according to serum CysC. Compared with the first quintile, the odds ratios of risk for AIS in fourth quintile and fifth quintile were 1.92 (1.08-3.40) and 2.88 (1.49-5.54), respectively. Serum CysC was not associated with neurological deficits and the location of ischemic area; however, serum CysC in patients decreased after one-week therapy. This was consistent with CysC expression after ischemia/reperfusion injury in a mouse focal ischemia/reperfusion injury model. Exogenous CysC exerted neuroprotective effects by reducing infarct volume in this animal stroke model. Therefore, serum CysC is highly associated with AIS and is an independent prediction marker for AIS. Since our findings demonstrated the protection of exogenous CysC on ischemic brain injury, CysC is a novel and promising therapeutic target for AIS.

Cystatin C triggers neuronal degeneration in a model of multiple system atrophy

Multiple system atrophy is an intractable neurodegenerative disease caused by α-synuclein (α-syn) accumulation in oligodendrocytes and neurons. With the use of a transgenic mouse model overexpressing human α-syn in oligodendrocytes, we demonstrated that oligodendrocytic α-syn inclusions induce neuronal α-syn accumulation, resulting in progressive neuronal degeneration. The mechanism through which oligodendrocytic α-syn inclusions trigger neuronal α-syn accumulation leading to multiple system atrophy is unknown. In this study, we identified cystatin C, an oligodendrocyte-derived secretory protein that triggers α-syn up-regulation and insoluble α-syn accumulation, in neurons of the mouse central nervous system. Cystatin C was released by mouse oligodendrocytes overexpressing human α-syn, and extracellular cystatin C increased the expression of the endogenous α-syn gene in wild-type mouse neurons. These neurons then accumulate insoluble α-syn and may undergo apoptosis. Cystatin C is a potential pathogenic signal triggering neurodegeneration in multiple system atrophy.

Drug discovery for diabetic nephropathy: trying the leap from mouse to man

Diabetic nephropathy is the single major cause of kidney failure in the industrialized world and given the emerging global pandemic of diabetes mellitus, its prevalence is expected to only increase. Because of the lack of dynamic biomarkers that define the rate of kidney function loss, there are few proof-of-concept clinical trials for new therapeutics to treat diabetic nephropathy. A molecular understanding of the pathogenesis of diabetic nephropathy also is lacking. These deficiencies are magnified by the fact that most mouse models of diabetic nephropathy fail to show progressive kidney disease. Recently, some mouse models that showed requisite phenotypic changes of diabetic nephropathy have been identified. Validation of results obtained in these experimental models, and showing whether they accurately can predict clinical response to therapeutics in human diabetic nephropathy, must now be established.

Cystatin C in Alzheimer's disease

Changes in expression and secretion levels of cystatin C (CysC) in the brain in various neurological disorders and in animal models of neurodegeneration underscore a role for CysC in these conditions. A polymorphism in the CysC gene (CST3) is linked to increased risk for Alzheimer's disease (AD). AD pathology is characterized by deposition of oligomeric and fibrillar forms of amyloid β (Aβ) in the neuropil and cerebral vessel walls, neurofibrillary tangles composed mainly of hyperphosphorylated tau, and neurodegeneration. The implication of CysC in AD was initially suggested by its co-localization with Aβ in amyloid-laden vascular walls, and in senile plaque cores of amyloid in the brains of patients with AD, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), and cerebral infarction. CysC also co-localizes with Aβ amyloid deposits in the brains of non-demented aged individuals. Multiple lines of research show that CysC plays protective roles in AD. In vitro studies have shown that CysC binds Aβ and inhibits Aβ oligomerization and fibril formation. In vivo results from the brains and plasma of Aβ-depositing transgenic mice confirmed the association of CysC with the soluble, non-pathological form of Aβ and the inhibition of Aβ plaques formation. The association of CysC with Aβ was also found in brain and in cerebrospinal fluid (CSF) from AD patients and non-demented control individuals. Moreover, in vitro results showed that CysC protects neuronal cells from a variety of insults that may cause cell death, including cell death induced by oligomeric and fibrillar Aβ. These data suggest that the reduced levels of CysC manifested in AD contribute to increased neuronal vulnerability and impaired neuronal ability to prevent neurodegeneration. This review elaborates on the neuroprotective roles of CysC in AD and the clinical relevance of this protein as a therapeutic agent.

Urinary cystatin C as a biomarker for acute kidney injury and its immunohistochemical localization in kidney in the CDDP-treated rats

Cystatin C, a cysteine protease inhibitor, is a novel biomarker of renal damage. In the present study, we examined the urinary and plasma levels of cystatin C and how useful they are for the early detection of acute kidney injury (AKI) in CDDP-treated rats in comparison with other biomarkers (β2-microglobulin, calbindin, clusterin, EGF, GST-α, GST-μ, KIM-1, NGAL, osteopontin, TIMP-1, and VEGF). The urinary levels of cystatin C, GST-α, KIM-1, and EGF changed prior to proximal tubule damage and increases in plasma urea nitrogen and creatinine levels, suggesting their usefulness for predicting AKI. On the other hand, the plasma cystatin C level hardly changed. We also investigated the localization of cystatin C in the kidney according to the progression of renal damage. Cystatin C was predominantly localized in the proximal tubule of the cortex, and its immunohistochemical expression was not affected by CDDP treatment. In addition, cystatin C was observed in the lumen of the renal tubule in the cortex, cortico-medullary junction, and medulla during the progression of renal damage, although its immunoreactive area ratio was very low. In conclusion, urinary cystatin C measurements can detect CDDP-induced AKI as early as KIM-1, GST-α, and EGF in rats, although the change ratio of the cystatin C was smaller than others. Immunohistochemical cystatin C expression in the proximal tubule of the kidney was hardly changed by the CDDP treatment, but it was newly observed in the renal tubule lumen after CDDP treatment.

Cystatin E/M suppresses legumain activity and invasion of human melanoma

Background

High activity of cysteine proteases such as legumain and the cathepsins have been shown to facilitate growth and invasion of a variety of tumor types. In breast cancer, several recent studies have indicated that loss of the cysteine protease inhibitor cystatin E/M leads to increased growth and metastasis. Although cystatin E/M is normally expressed in the skin, its role in cysteine protease regulation and progression of malignant melanoma has not been studied.

Methods

A panel of various non-melanoma and melanoma cell lines was used. Cystatin E/M and C were analyzed in cell media by immunoblotting and ELISA. Legumain, cathepsin B and L were analyzed in cell lysates by immunoblotting and their enzymatic activities were analyzed by peptide substrates. Two melanoma cell lines lacking detectable secretion of cystatin E/M were transfected with a cystatin E/M expression plasmid (pCST6), and migration and invasiveness were studied by a Matrigel invasion assay.

Results

Cystatin E/M was undetectable in media from all established melanoma cell lines examined, whereas strong immunobands were detected in two of five primary melanoma lines and in two of six lines derived from patients with metastatic disease. Among the four melanoma lines secreting cystatin E/M, the glycosylated form (17 kD) was predominant compared to the non-glycosylated form (14 kD). Legumain, cathepsin B and L were expressed and active in most of the cell lines, although at low levels in the melanomas expressing cystatin E/M. In the melanoma lines where cystatin E/M was secreted, cystatin C was generally absent or expressed at a very low level. When melanoma cells lacking secretion of cystatin E/M were transfected with pCST6, their intracellular legumain activity was significantly inhibited. In contrast, cathepsin B activity was not affected. Furthermore, invasion was suppressed in cystatin E/M over-expressing melanoma cell lines as measured by the transwell Matrigel assay.

Conclusions

These results suggest that the level of cystatin E/M regulates legumain activity and hence the invasive potential of human melanoma cells.

Macrophage responses to interferon-gamma are dependent on cystatin C levels

The aim of the present investigation was to elucidate possible effects of cystatin C on inflammatory responses mediated by macrophages. Previously it has been shown that in vitro treatment of murine peritoneal macrophages with interferon-gamma (IFN-gamma) causes a down-regulation of cystatin C secretion. To investigate whether such changes in cystatin C expression in turn can affect inflammatory responses mediated by macrophages, we have compared effects of IFN-gamma on macrophages isolated from wild-type (cysC(+/+)) and cystatin C knockout (cysC(-/-)) mice. It was shown that IFN-gamma-primed cysC(-/-) macrophages exhibit significantly higher interleukin-10 (IL-10) but lower tumor necrosis factor-alpha (TNF-alpha) expression, and reduced nuclear factor (NF)-kappaB p65 activation, compared to similarly primed cysC(+/+) cells. Exogenously added cystatin C enhanced IFN-gamma-induced activation of NF-kappaB p65 and increased mRNA levels for inducible NO synthase (iNOS) in cysC(-/-) macrophages as well as levels of nitric oxide and TNF-alpha in the cell culture medium, in agreement with an enhanced pro-inflammatory response. Accordingly, IFN-gamma-induced IL-10 mRNA expression in cysC(-/-) macrophages was down-regulated by exogenously added cystatin C. Taken together, our data provide evidence that changes in cystatin C levels alter macrophage responses to IFN-gamma. The latter down-regulates the production of cystatin C, which leads to a suppressed inflammatory condition with enhanced IL-10 levels and down-regulated TNF-alpha and NF-kappaB. It is concluded that cystatin C through this effect can act as an immunomodulatory molecule.

Molecular and functional characterization of a cystatin analogue in large yellow croaker (Pseudosciaena crocea)

The cDNA of a cystatin analogue was isolated from the spleen Smart cDNA library of large yellow croaker Pseudosciaena crocea (Lyccys). The open reading frame (ORF) of 354 nucleotides (nt) of Lyccys encodes a protein of 118 amino acids (aa), containing a 21-aa signal peptide and a 97-aa mature polypeptide. The deduced Lyccys possessed structural features of the Family II cystatins, including three evolutionally conserved motifs known to interact with the active sites of cysteine peptidases: Gly at the N-terminus (Gly(25)), Gln-X-Val-X-Gly motif (Q(69)LVAG(73)) and Pro-Try pair at the C-terminus (P(106)W(107)). Genomic analysis revealed that Lyccys gene, spanning 2297 nt, consisted of three exons and two introns. The Lyccys gene was constitutively expressed in all eight tissues examined although at different levels. Real-time PCR analysis revealed that Lyccys transcript in spleen and kidney was obviously up-regulated by poly(I:C) or inactivated trivalent bacterial vaccine, while in blood its expression was down-regulated. Immuno-electron microscopy showed that Lyccys was mainly localized to the rough endoplasmic reticulum (rER) or in the vesicular structures in spleen and kidney cells. Recombinant Lyccys protein fused with glutathione S-transferase (rLyccys) was shown to have remarkable protease-inhibitory activity and well affinity binding to papain (with a K(i) of 1.3x10(-13) M). An in vivo administration of rLyccys could significantly up-regulate the expression levels of large yellow croaker tumor necrosis factor-alpha2 (TNF-alpha2) and interleukin-10 in spleen and kidney, but to a lesser extent increase TNF-alpha1 expression. These results suggest that the Lyccys is a secreted inhibitor of cysteine proteinases, which may have an immunomodulatory function in inflammation response.

Assessment of renal injury in vivo

The ICH S7A (Safety Pharmacology for Human Pharmaceuticals) guidelines specify that potential adverse pharmacologic effects of a test substance on renal function should be evaluated in supplemental studies when there is a cause for concern (ICH, 2001). For the most part, this can easily be accomplished by examination of the appropriate analytes in urine and blood collected as part of the routine preclinical safety studies. This review will serve as an overview of the selection, interpretation and limitations of standard clinical pathology methods (serum chemistry and urinalysis) for assessment of renal function in such studies, as well as provide some information on emerging biomarkers of renal function.

Cystatin C modulates neurodegeneration and neurogenesis following status epilepticus in mouse

Brain damaging insults cause alterations in neuronal networks that trigger epileptogenesis, and eventually lead to the appearance of spontaneous seizures. The present experiments were designed to study the cellular expression and functions of a cysteine proteinase inhibitor, cystatin C, whose gene expression is previously shown to be upregulated in the rat hippocampus during status epilepticus (SE)-induced epileptogenesis. The present data showed that the expression of cystatin C protein increased in the mouse hippocampus 7 days following SE and localized mainly to astrocytes and microglia. Acute neuronal death in the hippocampus at 24 h after SE was reduced in cystatin C-/- mice. Also, the basal level of neurogenesis in the subgranular layer of dentate gyrus was decreased in cystatin C-/- mice compared to wildtype littermates. Interestingly, migration of newly born neurons within the granule cell layer was attenuated in cystatin C-/- mice. These data demonstrate that cystatin C has a role in neuronal death and neurogenesis during SE-induced network reorganization.

Lack of the Cysteine Protease Inhibitor Cystatin C Promotes Atherosclerosis in Apolipoprotein E–Deficient Mice

OBJECTIVE

Degradation of extracellular matrix plays an important role in growth and destabilization of atherosclerotic plaques. Cystatin C, inhibitor of the collagen- and elastin-degrading cysteine proteases of the cathepsin family, is produced by virtually all cell types. It is present in the normal artery wall but severely reduced in human atherosclerotic lesions.

METHODS AND RESULTS

To determine the functional role of cystatin C in atherosclerosis, we crossed cystatin C-deficient (cysC(-/-)) mice with apolipoprotein E-deficient (apoE(-/-)) mice. After 25 weeks of atherogenic diet, mice lacking apoE and cystatin C (cysC(-/-) apoE(-/-)) had larger subvalvular plaques compared with cysC(+/+) apoE(-/-) mice (766,000+/-20,000 microm2 per section versus 662,000+/-19,000 microm2 per section; P=0.001), suggesting an atheroprotective role of cystatin C. The plaques from cysC(-/-) apoE(-/-) mice were characterized by increased total macrophage content. To determine which cellular source is important for the antiatherosclerotic effect of cystatin C, we performed bone marrow transplantations. ApoE(-/-) mice were transplanted with either cysC(-/-) apoE(-/-) or cysC(+/+) apoE(-/-) bone marrow. No significant differences in plaque area, macrophage, collagen, or lipid content of subvalvular lesions between the 2 groups were detected.

CONCLUSIONS

The result suggests that the protective role of cystatin C in atherosclerosis is dependent primarily on its expression in nonhematopoietic cell types.

Absence of the protease inhibitor cystatin C in inflammatory cells results in larger plaque area in plaque regression of apoE-deficient mice

Matrix remodelling plays an important role in regulating plaque stability. Cystatin C, an inhibitor of the elastin-degrading cysteine proteases of the cathepsin family, is believed to be one of the key protease inhibitors in this process. The aim of the present study was to investigate the role of leukocyte-specific cystatin C expression under conditions that favour plaque regression. Apolipoprotein E-deficient mice (apoE-/-) were given a Western-type diet 15 weeks prior transplantation with bone marrow from mice lacking cystatin C (cysC-/-) or cystatin C positive (cysC+/+) mice, in both cases apoE+/+ to create conditions favouring plaque regression. Transplantations were verified with PCR and Western analyses. Transplanted mice showed a 70% decrease in lipid content and reduction in plaque area compared to baseline ApoE-/- mice, demonstrating plaque regression due to apoE expression in macrophages. apoE-/- mice transplanted with cysC-/- bone marrow were then compared to mice transplanted with cysC+/+ bone marrow. Mice receiving cysC-/- bone marrow had a 30% larger plaque area, despite absence of significant differences in plasma cholesterol and lipid contents in plaque. Unexpectedly, mice transplanted with cystatin C-deficient bone marrow cells had increased elastin and collagen content in lesions. These observations suggest that leukocyte-specific expression of cystatin C is actively involved in matrix remodelling associated with plaque regression.

VAP1, with cystatin C motif, an oocyte protein encoded by a novel ovarian-specific gene during oogenesis in the common brushtail possum (Trichosurus vulpecula)

In the brushtail possum oocyte, vesicles accumulate in a polarized fashion at the vegetal pole and cytoplasm rich in mitochondria and containing the germinal vesicle comprise the animal pole. During cleavage to early blastocyst stages, animal pole cytoplasm locates to the cells of the embryonic hemisphere (pluriblast) and vegetal pole vesicular cytoplasm to cells of the abembryonic hemisphere (trophoblast). Previously identified 16 amino acid residues, associated with the vesicle-rich cytoplasm were used for molecular cloning and characterization of a vesicle associated protein, VAP1. The degenerate primer was used in a 3'RACE for vap1 gene cloning. The cDNA encoding VAP1 was 516 bp in length with no significant homologies and coded for 172 amino acid residues for the mature protein. The N-terminal domain of VAP1 showed a structural homology to the cysteine protease inhibitor, Cystatin. Gene expression studies during oogenesis revealed that vap1 had an ovary-specific, possibly oocyte-specific expression, which occurs during follicle formation and growth and in adult ovaries. Recombinant VAP1 fusion protein generated polyclonal antibodies in the mouse and in the brushtail possum.

Cystatin C uptake in the eye

BACKGROUND

As a secreted protein, cystatin C is assumed to play its role in the extracellular compartment, where it can inhibit virtually all cysteine proteases of families C1 (cathepsin B, L, S) and C13 (mammalian legumain-related proteases). Since many of its potential target enzymes in the eye reside in intracellular compartments, we sought evidence for a cellular uptake of the inhibitor in ocular tissues.

METHODS

Fluorescence-labeled human cystatin C was injected intravitreally into normal rat eyes. Ocular tissues were subsequently examined using ELISA, fluorescence microscopy, and immunohistochemistry. Cystatin C uptake was additionally studied in an in vitro retina model.

RESULTS

Cystatin C administered intravitreally in vivo is taken up into cells of the corneal endothelium and epithelium, the epithelial cells lining the ciliary processes, and into cells in the neuroretina (mostly ganglion cells) and the retinal pigment epithelium. The uptake is demonstrable also in vitro and was, in the neuroretina, found to be a high-affinity system, inhibited by cooling the specimens or by adding the microfilament polymerization inhibitor, cytochalasin D, to the medium.

CONCLUSIONS

There is an active, temperature-dependent uptake system for cystatin C into several cell types in the cornea, ciliary body, and retina. The cell types that take up cystatin C are generally the same that contain endogenous cystatin C, suggesting that much or all cystatin C seen intracellularly in the normal eye may have been taken up from the surrounding extracellular space. The uptake indicates that the inhibitor may exert biological functions in intracellular compartments. It is also possible that this uptake system may regulate the extracellular levels of cystatin C in the eye.

Gene deletion of cystatin C aggravates brain damage following focal ischemia but mitigates the neuronal injury after global ischemia in the mouse

Cystatin C is distributed in all human tissues and fluids with a particular abundance in the cerebrospinal fluid. Cystatin C is a strong endogenous inhibitor of lysosomal cysteine proteases, such as cathepsin B, L, H and S, that are involved in various biological processes such as degradation of cellular proteins and regulation of enzymes, as well as in pathological processes. Pharmacological inhibition of cathepsins has been shown to reduce neuronal damage after brain ischemia, suggesting that cystatin C is an endogenous neuroprotectant. Cystatin C has also amyloidogenic properties and is co-localized with beta-amyloid in degenerated neurons in Alzheimer's disease, suggesting a role in neuronal degeneration. To test the hypothesis that endogenous cystatin C is neuroprotective during brain ischemia, global and focal brain ischemia was induced in mice with the cystatin C gene knocked out. Following focal ischemia, larger brain infarcts were found in cystatin C knockout mice, probably due to a reduced inhibition of the cathepsins during ischemia. In contrast, brain damage after global ischemia was diminished in cystatin C knockout mice, suggesting that cystatin C has an aggravating effect on selective neuronal damage after global ischemia.

Up regulation of cathepsin K expression in articular chondrocytes in a transgenic mouse model for osteoarthritis

OBJECTIVES

To study the expression of cysteine proteinases, particularly cathepsin K, and their extracellular inhibitor cystatin C in articular cartilage of transgenic Del1 mice which harbour a short deletion mutation in a type II collagen transgene and are predisposed to early onset osteoarthritis.

METHODS

Northern analysis was used to measure mRNA levels of cathepsins B, H, K, L, and S, and cystatin C in total RNA extracted from knee joints of Del1 mice, using their non-transgenic litter mates as controls. Immunohistochemistry and morphometry was used to study the distribution of cathepsin K and cystatin C in the knee joints.

RESULTS

Up regulation of cathepsin K mRNA expression was seen in the knee joints of transgenic Del1 mice at the onset of cartilage degeneration. Cathepsin K was found near sites of matrix destruction in articular chondrocytes, particularly in clusters of proliferating cells, and in calcified cartilaginous matrix. In intact articular cartilage of control animals, cathepsin K was only seen in a small number of chondrocytes. Upon aging, control animals also developed osteoarthritis, which was accompanied by increased cathepsin K expression. Cystatin C was mostly localised in and around chondrocytes located in calcified cartilage, with no obvious association with the onset of cartilage degeneration.

CONCLUSION

The temporospatial distribution of cathepsin K in osteoarthritic cartilage suggests a role for this enzyme in the pathogenesis of osteoarthritis. Because cathepsin K can digest cartilage matrix components it may contribute to the development of osteoarthritic lesions. These data may provide new clues for the development of treatments aimed at preventing cartilage degeneration.

Cystatin C in the anterior segment of rat and mouse eyes

PURPOSE

Cystatin C is a mammalian cysteine protease inhibitor. This study describes the localization of cystatin C in the anterior segment of normal rat and mouse eyes. Cysteine proteases play an important role in protein degradation (e.g. of photoreceptor outer segments in the retinal pigment epithelium) and the balance between these proteases and their specific inhibitors is therefore of great interest.

METHODS

Cells containing cystatin C were identified by immunohistochemistry and quantified by ELISA. Messenger RNA levels were analysed by quantitative real-time polymerase chain reaction.

RESULTS

Cystatin C is present at biologically significant levels in the corneal epithelium, endothelium and stromal keratinocytes, lens epithelium, epithelial cells in the ciliary processes, aqueous humour and iris stromal cells. In the rat anterior segment, the highest cystatin C concentrations were found in the ciliary epithelium.

CONCLUSIONS

Cystatin C is present in several cell types and is probably locally produced. The inhibitor is likely to be an important regulator of cysteine proteases in the retinal pigment epithelium, ciliary epithelium, aqueous humour, lens epithelium and in the corneal endothelium and epithelium.

Salivary (SD-type) cystatins: over one billion years in the making--but to what purpose?

Human saliva contains relatively abundant proteins that are related ancestrally in sequence to the cystatin superfamily. Most, although not all, members of this superfamily are potent inhibitors of cysteine peptidases. Four related genes have been identified, CST1, 2, 4 and 5, encoding cystatins SN, SA, S, and D, respectively. CST1, 4, and probably CST5 are now known to be expressed in a limited number of other tissues in the body, primarily in exocrine epithelia, and the term SD-type cystatin is more appropriate than 'salivary cystatin'. These genes are co-ordinately regulated in the submandibular gland during post-natal development. The organization of these tissue-specifically-expressed genes in the genome, and their phylogeny, indicate that they evolved from an ancestral housekeeping gene encoding the ubiquitously expressed cystatin C, and are members of a larger protein family. Their relationship to rat cystatin S, a developmentally regulated rodent submandibular gland protein, remains to be established. In this review, the evolution of the SD-type cystatins in the cystatin superfamily, their genomics, expression, and structure-function relationships are examined and compared with known cystatin functions, with the goal of providing clues to their biological roles.

Cystatins C, E/M and F in human pleural fluids of patients with neoplastic and inflammatory lung disorders

Secretory type 2 cystatins, like cystatins C, E/M and F, are thought to be involved in many pathobiological processes, including vascular amyloidosis, rheumatoid arthritis, Alzheimer's disease, osteoporosis, viral and bacterial infections, inflammatory disorders and tumour invasion and metastasis. In order to define the levels of cystatins C, E/M, and F in pleural effusions and to investigate whether these cystatins correlate with diagnostic parameters of pleural and lung diseases, we determined their concentrations in 160 pleural effusions. The median concentration of cystatin C in pleural effusions was 1437 microg/l (95.8 nM), ranging between 18-3967 microg/l. Cystatin C did neither correlate with malignant nor with benign diseases. The concentration of cystatin E/M was significantly higher in effusions of primary pleural tumours (mesotheliomas) compared to secondary pleural tumours and benign diseases. Furthermore, there was a significant correlation between the concentration of cystatin E/M of mesotheliomas and the pleural fluid tumour cell count and of cystatin C. The median values of cystatin F were significantly increased in parapneumonic/empyema thoracis pleural effusions and tuberculous pleurisy compared to malignant pleural effusions, respectively. The concentration of cystatin F in benign effusions correlated significantly with diagnostic parameters and inflammation (total protein; lactate dehydrogenase; C-reactive protein). Finally, only in the group of parapneumonic/empyema thotatin F and the neutrophil count. In conclusion, pleural effusions of different origin contain high levels of cystatin C, perhaps constituting the major part of an inhibitor reservoir. The level of cystatin E/M appears to be significantly associated with primary pleural tumours and cystatin F correlates with inflammatory processes of lung disorders.

Comparison in localization between cystatin C and cathepsin K in osteoclasts and other cells in mouse tibia epiphysis by immunolight and immunoelectron microscopy

We compared the distribution of a cysteine proteinase inhibitor, cystatin C, with that of cathepsin K in osteoclasts of the mouse tibia by immunolight and immunoelectron microscopy. Light microscopically, strong immunoreactivity for cystatin C was found extracellularly along the resorption lacuna and intracellularly in the organelles of osteoclasts. In serial sections, various patterns of cystatin C and cathepsin K localization were seen, specifically: (1) some resorption lacuna were positive for both cystatin C and cathepsin K; (2) others were positive for either cystatin C or cathepsin K, but not both; and (3) some lacuna were negative for both. In osteoclasts, the localization of cystatin C was similar to that of cathepsin K. Furthermore, cystatin C immunoreactivity was detected in preosteoclasts and osteoblasts, whereas cathepsin K was seen only in preosteoclasts. Electron microscopically, cystatin C immunoreactive products were found in the rough endoplasmic reticulum (ER), Golgi apparatus, vesicles, granules, and vacuoles of osteoclasts. These cystatin C-positive vesicles had fused or were in the process of fusion with the ampullar vacuoles (extracellular spaces) containing cystatin C-positive, fragmented, fibril-like structures. The extracellular cystatin C was deposited on and between the cytoplasmic processes of ruffled borders, and on and between type I collagen fibrils. In the basolateral region of osteoclasts, cystatin C-positive vesicles and granules also fused with vacuoles that contained cystatin C-positive or negative fibril-like structures. These results indicate that osteoclasts not only synthesize and secrete cathepsin K from the ruffled border into the bone resorption lacunae, but also a cysteine proteinase inhibitor, cystatin C. Therefore, it is suggested that cystatin C regulates the degradation of bone matrix by cathepsin K, both extracellularly and intracellularly.

cDNA and genomic cloning of lacritin, a novel secretion enhancing factor from the human lacrimal gland

Multiple extracellular factors are hypothesized to promote the differentiation of unstimulated and/or stimulated secretory pathways in exocrine secretory cells, but the identity of differentiation factors, particularly those organ-specific, remain largely unknown. Here, we report on the identification of a novel secreted glycoprotein, lacritin, that enhances exocrine secretion in overnight cultures of lacrimal acinar cells which otherwise display loss of secretory function. Lacritin mRNA and protein are highly expressed in human lacrimal gland, moderately in major and minor salivary glands and slightly in thyroid. No lacritin message or protein is detected elsewhere among more than 50 human tissues examined. Lacritin displays partial similarity to the glycosaminoglycan-binding region of brain-specific neuroglycan C (32 % identity over 102 amino acid residues) and to the possibly mucin-like amino globular region of fibulin-2 (30 % identity over 81 amino acid residues), and localizes primarily to secretory granules and secretory fluid. The lacritin gene consists of five exons, displays no alternative splicing and maps to 12q13. Recombinant lacritin augments unstimulated but not stimulated acinar cell secretion, promotes ductal cell proliferation, and stimulates signaling through tyrosine phosphorylation and release of calcium. It binds collagen IV, laminin-1, entactin/nidogen-1, fibronectin and vitronectin, but not collagen I, heparin or EGF. As an autocrine/paracrine enhancer of the lacrimal constitutive secretory pathway, ductal cell mitogen and stimulator of corneal epithelial cells, lacritin may play a key role in the function of the lacrimal gland-corneal axis.

Cystatin C in a rat model of end-stage renal failure

BACKGROUND

Cystatin C (MW 13kDa) serum concentration reflects glomerular filtration rate better than creatinine. Like other low-molecular weight proteins it is not eliminated by dialysis. Still, cystatin C serum concentrations do not rise progressively in end-stage renal failure and rarely exceed 10 mg/L (i.e. 8 times the upper limit of normal).

OBJECTIVE

To study cystatin C kinetics in a rat model of end-stage renal failure.

METHODS

Sequential bilateral nephrectomy was performed seven days apart in 13 male Sprague-Dawley rats as described by Levine and Saltzman. Serum cystatin C (Cystatin C PET-kit, DAKO), creatinine and total protein were measured in daily intervals after the second nephrectomy. Linearity of the anti-human cystatin C assay for rat cystatin C was tested using dilutions of uremic rat serum. Rats were sacrificed for signs of severe uremia on days 10 (n=5), 11 (n=4) and 12 (n = 5).

RESULTS

At baseline, mean (+/- SE) cystatin C was 1.59+/-0.041 mg/L, creatinine 19.6+/-1.2 micromol/L. Following bilateral nephrectomy, cystatin C immediately rose to 3.82+/-0.15 mg/L, creatinine to 312+/-20 micromol/L. During the following days, cystatin C concentration stabilized to 4 mg/L approximately whereas creatinine continued to rise to 822+/-185 kmol/L on day 12. Correction for the decrease in serum total protein concentration from 48.9+/-2.3 g/L to 37.4+/-3.6 g/L did not alter these results.

CONCLUSION

The kinetics of cystatin C and creatinine in this rat model of end-stage renal failure are in accordance with human data suggesting a change in cystatin C production or extra-renal elimination in severe chronic uremia.

FGF-2-responsive neural stem cell proliferation requires CCg, a novel autocrine/paracrine cofactor

We have purified and characterized a factor, from the conditioned medium of neural stem cell cultures, which is required for fibroblast growth factor 2's (FGF-2) mitogenic activity on neural stem cells. This autocrine/paracrine cofactor is a glycosylated form of cystatin C (CCg), whose N-glycosylation is required for its activity. We further demonstrated that, both in vitro and in vivo, neural stem cells undergoing cell division are immunopositive for cystatin C. Finally, we showed in vivo functional activity of CCg by demonstrating that the combined delivery of FGF-2 and CCg to the adult dentate gyrus stimulated neurogenesis. We propose that the process of neurogenesis is controlled by the cooperation between trophic factors and autocrine/paracrine cofactors, of which CCg is a prototype.

Rainbow trout (Oncorhynchus mykiss) cystatin C: expression in Escherichia coli and properties of the recombinant protease inhibitor

Cystatins are a superfamily of low Ki cysteine proteinase inhibitors found in both plants and animals. Cystatin C, a secreted molecule of this family, is of interest from biochemical and evolutionary points of view, and also has biotechnological applications. Recently we cloned and sequenced the cDNA for rainbow trout (Oncorhynchus mykiss) cystatin C [Li et al., 1998. Molecular cloning, sequence analysis and expression distribution of rainbow trout (Oncorhynchus mykiss) cystatin C. Comp. Biochem. Phys. B 121, 135-143]. To explore the relationship between protein structure and function of trout cystatin C, we established a bacterial system for expression of the protein. Trout cystatin C expressed in the cytoplasm of bacterial cells did not have detectable protease inhibitory activity. Activity was regained by Ni-NTA chromatography under denaturing conditions followed by dialysis-based refolding. Titration of purified cystatin C preparations with papain indicated that approximately 20% of the total protein had been converted to the active form after one refolding cycle. Expression levels were 3-5 mg/l. The protease-inhibitory properties of recombinant trout cystatin C were similar to those of human and chicken cystatin C derived from biological sources and recombinant cystatin C derived from rat and mouse genes. The Ki for papain was 1.2 x 10(-15) M, exhibiting the high affinity binding unique to this family of protease inhibitors.

Decreased metastatic spread in mice homozygous for a null allele of the cystatin C protease inhibitor gene

AIMS

Increased or altered activities of cysteine proteases have been implicated in serious human disorders such as cancer, rheumatoid arthritis, sepsis, and osteoporosis. To improve the current knowledge of the regulatory role of a major mammalian cysteine protease inhibitor, cystatin C, in such disease processes, a cystatin C deficient mouse was generated and characterized.

METHODS

The mouse cystatin C gene was inactivated by insertion of a bacterial neo gene through homologous recombination in 129/Sv embryonic stem cells. Embryonic stem cell clones were injected into C57BL/6J blastocysts followed by injection of the blastocysts into pseudopregnant female mice. F1 offspring with agouti coat colour after mating of chimaeric males with C57BL/6J females were examined by DNA analysis, and mice carrying the targeted mutation were intercrossed to obtain homozygous cystatin C deficient (CysC-/-) mice. To study the role of cysteine proteases and their inhibitors in metastasis, the spread of B16-F10 melanoma cells in CysC-/- and wild-type mice was compared. Analysis of the formation of remote metastases was carried out by intravenous injection of beta-galactosidase transfected B16-F10 cells and subsequent determination of cancer cell colonies in the lungs.

RESULTS

Cystatin C deficient mice were fertile and showed no gross pathological abnormality up to 6 months of age. Compared with wild-type mice, seven times fewer large metastatic colonies were counted by means of a dissecting microscope in CysC-/- mice two weeks after tail vein injection of B16-F10 cells. At all of eight time points from 15 minutes to two weeks after intravenous injection of tumour cells, the CysC-/- mice had significantly fewer lung metastases. The observed differences were smaller when beta-galactosidase transfected cells were used to allow counting of small colonies. Subcutaneous and intracerebral tumour growth was not different in the CysC-/- mice.

CONCLUSIONS

Cystatin C concentrations in vivo might influence metastasis in some tissues. The decreased metastatic spread of B16-F10 cells in CysC-/- mice is the result of both reduced seeding and reduced growth of tumour cells in their lungs.

Modulation of invasive properties of murine squamous carcinoma cells by heterologous expression of cathepsin B and cystatin C

Murine SCC-VII squamous carcinoma cells have the capacity to penetrate reconstituted basement membranes (Matrigel) in vitro. The invasion of Matrigel layers by SCC-VII cells was significantly reduced by E-64, a specific inhibitor of lysosomal cysteine proteinases. The cathepsin-B-selective E-64 derivative, CA-074, inhibited penetration of Matrigel by SCC-VII cells to the same extent, indicating a major role for this particular lysosomal enzyme in extracellular-matrix degradation during squamous-carcinoma-cell invasion. SCC-VII cells were stably transfected with a cDNA encoding human procathepsin B, in an attempt to modulate the invasive properties of the cell line. The transfected cells expressed the heterologous gene, secreted increased amounts of procathepsin B and displayed enhanced invasive potential. In vivo, the activity of cathepsin B is strictly regulated by endogenous inhibitors. SCC-VII cells were therefore also stably transfected with a cDNA encoding human cystatin C, the most potent cysteine-proteinase inhibitor in mammalian tissues. The expression of this transgene resulted in the production of active recombinant cystatin C and a pronounced reduction in Matrigel invasion. These studies demonstrate that the invasive properties of squamous-cell carcinomas can be changed by modulation of the balance between cathepsin B and its endogenous inhibitors, and provide further evidence for the involvement of this lysosomal cysteine proteinase in tumour invasion and metastasis.

Intracellular accumulation of the amyloidogenic L68Q variant of human cystatin C in NIH/3T3 cells

AIM

To study the cellular transport of L68Q cystatin C, the cystatin variant causing amyloidosis and brain haemorrhage in patients suffering from hereditary cystatin C amyloid angiopathy (HCCAA).

METHODS

Expression vectors for wild-type and L68Q cystatin C were constructed and used to transfect mouse NIH/3T3 cells. Stable cell clones were isolated after cotransfection with pSV2neo. Clones expressing human wild-type and L68Q cystatin C were compared with respect to secreted cystatin C by enzyme linked immunosorbent assay (ELISA), and for intracellular cystatin C by western blotting and immunofluorescence cytochemistry. Colocalisation studies in cells were performed by double staining with antibodies against human cystatin C and marker proteins for lysosomes, the Golgi apparatus, or the endoplasmic reticulum, and evaluated by confocal microscopy.

RESULTS

Concentrations of human cystatin C secreted from transfected NIH/3T3 cells were similar to those secreted from human cells in culture. In general, clones expressing the gene encoding L68Q cystatin C secreted slightly lower amounts of the protein than clones expressing wild-type human cystatin C. Both immunofluorescence cytochemistry and western blotting experiments showed an increased accumulation of cystatin C in cells expressing the gene encoding L68Q cystatin C compared with cells expressing the gene for the wild-type protein. The intracellularly accumulating L68Q cystatin C was insoluble and located mainly in the endoplasmic reticulum.

CONCLUSIONS

The cellular transport of human cystatin C is impeded by the pathogenic amino acid substitution Leu68-->Gln. The resulting intracellular accumulation and increased localised concentration of L68Q cystatin C might be an important event in the molecular pathophysiology of amyloid formation and brain haemorrhage in patients with HCCAA.

Cystatin F is a glycosylated human low molecular weight cysteine proteinase inhibitor

A previously undescribed human member of the cystatin superfamily called cystatin F has been identified by expressed sequence tag sequencing in human cDNA libraries. A full-length cDNA clone was obtained from a library made from mRNA of CD34-depleted cord blood cells. The sequence of the cDNA contained an open reading frame encoding a putative 19-residue signal peptide and a mature protein of 126 amino acids with two disulfide bridges and enzyme-binding motifs homologous to those of Family 2 cystatins. Unlike other human cystatins, cystatin F has 2 additional Cys residues, indicating the presence of an extra disulfide bridge stabilizing the N-terminal region of the molecule. Recombinant cystatin F was produced in a baculovirus expression system and characterized. The mature recombinant protein processed by insect cells had an N-terminal segment 7 residues longer than that of cystatin C and displayed reversible inhibition of papain and cathepsin L (Ki = 1.1 and 0.31 nM, respectively), but not cathepsin B. Like cystatin E/M, cystatin F is a glycoprotein, carrying two N-linked carbohydrate chains at positions 36 and 88. An immunoassay for quantification of cystatin F showed that blood contains low levels of the inhibitor (0.9 ng/ml). Six B cell lines in culture secreted barely detectable amounts of cystatin F, but several T cell lines and especially one myeloid cell line secreted significant amounts of the inhibitor. Northern blot analysis revealed that the cystatin F gene is primarily expressed in peripheral blood cells and spleen. Tissue expression clearly different from that of the ubiquitous inhibitor, cystatin C, was also indicated by a high incidence of cystatin F clones in cDNA libraries from dendritic and T cells, but no clones identified by expressed sequence tag sequencing in several B cell libraries and in >600 libraries from other human tissues and cells.

Leukocystatin, a new Class II cystatin expressed selectively by hematopoietic cells

We describe a new cystatin in both mice and humans, which we termed leukocystatin. This protein has all the features of a Class II secreted inhibitory cystatin but contains lysine residues in the normally hydrophobic binding regions. As determined by cDNA library Southern blots, this cystatin is expressed selectively in hematopoietic cells, although fine details of the distribution among these cell types differ between the human and mouse mRNAs. In addition, we have determined the genomic organization of mouse leukocystatin, and we found that in contrast to most cystatins, the leukocystatin gene contains three introns. The recombinant proteins corresponding to these cystatins were expressed in Escherichia coli as N-terminal glutathione S-transferase or FLAGTM fusions, and studies showed that they inhibited papain and cathepsin L but with affinities lower than other cystatins. The unique features of leukocystatin suggests that this cystatin plays a role in immune regulation through inhibition of a unique target in the hematopoietic system.

Differential localization of cysteine protease inhibitors and a target cysteine protease, cathepsin B, by immuno-confocal microscopy

The cystatin superfamily of cysteine protease inhibitors and target cysteine proteases such as cathepsin B have been implicated in malignant progression. The respective cellular/extracellular localization of cystatins and cysteine proteases in tumors may be critical in regulating activity of the enzymes. Confocal microscopy has enabled us to demonstrate the differential localization of cystatins and cathepsin B in an embryonic liver cell line and an invasive hepatoma cell line. In both, stefins A and B were distributed diffusely throughout the cytoplasm, whereas cystatin C was distributed in juxtanuclear vesicles. Stefin A and cystatin C, but not stefin B, were present on the cell surface. Cystatin C was found on the top surfaces of both cell lines, whereas stefin A was found only on the top surface of the embryonic liver cells. Cathepsin B staining was concentrated in perinuclear vesicles in the embryonic liver cells. In the hepatoma cells, staining for cathepsin B was also present in vesicles adjacent to the cell membrane and on localized regions of the bottom surface. Such a disparate distribution of cathepsin B and its endogenous inhibitors may facilitate proteolysis by the hepatoma cells and thereby contribute to their invasive phenotype.

Molecular cloning and N-terminal analysis of bovine cystatin C. Identification of a full-length N-terminal region

The N-terminal region of human cystatin C has been shown to be of crucial importance for the interaction of the inhibitor with cysteine proteinases. However, several studies have been unable to identify the corresponding region in bovine cystatin C, indicating that the binding of proteinases to the bovine inhibitor may not be dependent on this region. With the aim to resolve this apparent discrepancy and to elucidate the relation of bovine cystatin C to other cystatins, we have isolated a cDNA clone encoding bovine precystatin C. The sequence of this cDNA was similar to that of the human inhibitor and showed a putative signal peptidase cleavage site consistent with the N-terminal regions of the bovine and human inhibitors being of comparable size. This suggestion was verified by determination of the relative molecular mass of the mature bovine inhibitor isolated from cerebrospinal fluid under conditions minimising proteolysis. The N-terminal of the purified inhibitor was blocked, but the sequence of the N-terminal peptide produced by digestion with endopeptidase LysC could be unequivocally determined by tandem mass spectroscopy. Together, these results show that bovine cystatin C has 118 residues, in contrast with 110-112 residues reported previously, and has an N-terminal region analogous to that of human cystatin C. This region presumably is of similar importance for tight binding of target proteinases as in the human inhibitor.