The cDNA structure and expression analysis of the genes for the cysteine proteinase inhibitor cystatin C and for beta 2-microglobulin in rat brain

Identification and prediction model of placenta-brain axis genes associated with neurodevelopmental delay in moderate and late preterm children

BACKGROUND

Moderate and late preterm (MLPT) birth accounts for the vast majority of preterm births, which is a global public health problem. The association between MLPT and neurobehavioral developmental delays in children and the underlying biological mechanisms need to be further revealed. The "placenta-brain axis" (PBA) provides a new perspective for gene regulation and risk prediction of neurodevelopmental delays in MLPT children.

METHODS

The authors performed multivariate logistic regression models between MLPT and children's neurodevelopmental outcomes, using data from 129 MLPT infants and 3136 full-term controls from the Ma'anshan Birth Cohort (MABC). Furthermore, the authors identified the abnormally regulated PBA-related genes in MLPT placenta by bioinformatics analysis of RNA-seq data and RT-qPCR verification on independent samples. Finally, the authors established the prediction model of neurodevelopmental delay in children with MLPT using multiple machine learning models.

RESULTS

The authors found an increased risk of neurodevelopmental delay in children with MLPT at 6 months, 18 months, and 48 months, especially in boys. Further verification showed that APOE and CST3 genes were significantly correlated with the developmental levels of gross-motor domain, fine-motor domain, and personal social domain in 6-month-old male MLPT children.

CONCLUSIONS

These findings suggested that there was a sex-specific association between MLPT and neurodevelopmental delays. Moreover, APOE and CST3 were identified as placental biomarkers. The results provided guidance for the etiology investigation, risk prediction, and early intervention of neurodevelopmental delays in children with MLPT.

Identification, expression profiling, and functional characterization of cystatin C from big-belly seahorse (Hippocampus abdominalis)

Cystatins are natural inhibitors of lysosomal cysteine proteases, including cathepsins B, L, H, and S. Cystatin C (CSTC) is a member of the type 2 cystatin family and is an essential biomarker in the prognosis of several diseases. Emerging evidence suggests the immune regulatory roles of CSTC in antigen presentation, the release of different inflammatory mediators, and apoptosis in various pathophysiologies. In this study, the 390-bp cystatin C (HaCSTC) cDNA from big-belly seahorse (Hippocampus abdominalis) was cloned and characterized by screening the pre-established cDNA library. Based on similarities in sequence, HaCSTC is a homolog of the teleost type 2 cystatin family with putative catalytic cystatin domains, signal peptides, and disulfide bonds. HaCSTC transcripts were ubiquitously expressed in all tested big-belly seahorse tissues, with the highest expression in ovaries. Immune challenge with lipopolysaccharides, polyinosinic:polycytidylic acid, Edwardsiella tarda, and Streptococcus iniae caused significant upregulation in HaCSTC transcript levels. Using a pMAL-c5X expression vector, the 14.29-kDa protein of recombinant HaCSTC (rHaCSTC) was expressed in Escherichia coli BL21 (DE3), and its protease inhibitory activity against papain cysteine protease was determined with the aid of a protease substrate. Papain was competitively blocked by rHaCSTC in a dose-dependent manner. In response to viral hemorrhagic septicemia virus (VHSV) infection, HaCSTC overexpression strongly decreased the expression of VHSV transcripts, pro-inflammatory cytokines, and pro-apoptotic genes; while increasing the expression of anti-apoptotic genes in fathead minnow (FHM) cells. Furthermore, HaCSTC overexpression protected VHSV-infected FHM cells against VHSV-induced apoptosis and increased cell viability. Our findings imply the profound role of HaCSTC against pathogen infections by modulating fish immune responses.

Association between cystatin C gene polymorphism and the prevalence of white matter lesion in elderly healthy subjects

Cystatin C (CST3) is a cysteine protease inhibitor abundant in the central nervous system, and demonstrated to have roles in several pathophysiological processes including vascular remodeling and inflammation. Previously, we showed a relation of CST3 gene polymorphisms with deep and subcortical white matter hyperintensity (DSWMH) in a small case-control study. In this study, we aimed to investigate the relation in a larger cross-sectional study. Participants of a brain health examination program were recruited (n = 1795) in the study, who underwent routine blood tests and cognitive function tests. Cerebral white matter changes were analyzed by MRI. Additionally, 7 single nucleotide polymorphisms (SNPs) (−82G/C, −78T/G, −5G/A, +4A/C, +87C/T, +148G/A and +213G/A) in the promoter and coding regions of CST3 gene were examined. Among them, carriers of the minor allele haplotype −82C/+4C/+148A were significantly associated with decreased CST3 concentration in the plasma. Unadjusted analysis did not show significant relation between carriers of the minor allele haplotype and periventricular hyperintensity (PVH), but DSWMH was marginally (p < 0.054) increased in this group. After adjusting the effects of other variables like age and kidney function, logistic regression analysis revealed that carriers of the minor allele haplotype were at a significantly increased risk of developing both PVH and DSWMH. Thus, our results suggest that carriers of the minor allele haplotype −82C/+4C/+148A of CST3 gene could be at an increased risk to develop cerebral white matter disturbance.

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.

Mass spectrometric analysis of rat cerebrospinal fluid proteins following exposure to the neurotoxicant carbonyl sulfide

RATIONALE

Using a proteomic-based approach we have investigated possible altered expression of a range of cerebral spinal fluid (CSF) proteins following exposure to the neurotoxicant carbonyl sulfide (COS). CSF is ideal for the investigation of markers of brain injury or disease since it is secreted from several central nervous system structures and changes in the CSF composition may reflect brain insult and many pathological processes.

METHODS

Animals were placed in exposure chambers and were exposed to 0 ppm or 500 ppm COS for 1, 2 or 3 days, 6 h per day. After the last inhalation exposure, 50-70 μL CSF sample was obtained by lumbar puncture. CSF samples were analyzed by electrospray ionization mass spectrometry (ESI-MS) on either a Premier quadrupole time-of-flight (QTOF) or an Agilent 6340 ion trap and by matrix-assisted laser desorption/ionization (MALDI)-MS on a 4800 MALDI-TOF/TOF analyzer.

RESULTS

The dynamic range of abundance of the identified proteins spanned over more than three orders of magnitude. The four most abundant proteins identified (albumin, cystatin C, serotransferrin, transthyretin) are major proteins that are present in both CSF and blood at high levels but the fifth most abundant protein identified (prostaglandin H2D isomerase) is the second most abundant protein in human CSF and is secreted and synthesized in the rat central nervous system. No significant differences were observed between COS-treated CSF samples and the control CSF samples because of blood contamination.

CONCLUSIONS

Quantitative MS protein analyses of rat CSF is limited by the low sample volumes that can practicably be obtained from rats and the low protein concentrations in rat CSF. Results of this work suggest a clear need for CSF collection that would minimize blood contamination. Published in 2014. This article is a U.S. Government work and is in the public domain in the USA.

Restoration by Dietary Glutamine of Reduced Tumor Necrosis Factor Production in a Low-Protein-Diet-Fed Rat Model

Tumor necrosis factor-alpha (TNF) production by peritoneal macrophages and its dietary modification were investigated by using rats fed on a low-protein diet. The rats were given a 20% casein (control) diet or a 3% casein diet for 21 days, and TNF production was measured in activated macrophages of these animals. TNF production was significantly lower in macrophages from rats fed on the low-protein diet than that in macrophages from rats fed on the control diet. Oral administration of a cabbage extract, a known modulator of TNF production, to the low-protein-diet-fed rats significantly enhanced TNF production by macrophages. Glutamine supplementation to the low-protein diet significantly enhanced TNF production as well as TNF mRNA expression. These results indicate that the 3%-casein-diet-fed rat would be useful as a model for reduced TNF production in protein malnutrition. These results also suggest that glutamine administration restored the reduced TNF production associated with protein malnutrition.

Characterization of the functional domain of β2-microglobulin from the Asian seabass, Lates calcarifer

Background

β2-Microglobulin (β₂M) is the light chain of major histocompatibility class I (MHC I) that binds non-covalently with the α heavy chain. Both proteins attach to the antigen peptide, presenting a complex to the T cell to be destroyed via the immune mechanism.

Methodology/Principal Findings

In this study, a cDNA sequence encoding β₂M in the Asian seabass (Lates calcarifer) was identified and analyzed using in silico approaches to predict and characterize its functional domain. The β₂M cDNA contains an open reading frame (ORF) of 351 bases with a coding capacity of 116 amino acids. A large portion of the protein consists of the IG constant domain (IGc1), similar to β₂M sequences from other species studied thus far. Alignment of the IGc1 domains of β₂M from L. calcarifer and other species shows a high degree of overall conservation. Seven amino acids were found to be conserved across taxa whereas conservation between L. calcarifer and other fish species was restricted to 14 amino acids at identical conserved positions.

Conclusion/Significance

As the L. calcarifer β₂M protein analyzed in this study contains a functional domain similar to that of β₂M proteins in other species, it can be postulated that the β₂M proteins from L. calcarifer and other organisms are derived from a common ancestor and thus have a similar immune function. Interestingly, fish β₂M genes could also be classified according to the ecological habitat of the species, i.e. whether it is from a freshwater, marine or euryhaline environment.

Cystatin C in macular and neuronal degenerations: implications for mechanism(s) of age-related macular degeneration

Cystatin C is a strong inhibitor of cysteine proteinases expressed by diverse cells. Variant B cystatin C, which was associated with increased risk of developing age-related macular degeneration, differs from the wild type protein by a single amino acid (A25T) in the signal sequence responsible for its targeting to the secretory pathway. The same variant conveys susceptibility to Alzheimer disease. Our investigations of the trafficking and processing of variant B cystatin C in living RPE cells highlight impaired secretion of extracellular modulators and inappropriate protein retention in RPE cells as potential molecular mechanisms underpinning macular, and possibly neuronal, degeneration.

Biochemistry and Clinical Role of Human Cystatin C

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Expression of Cystatin C in the rat endometrium during the peri-implantation period

Endometrial receptivity for embryo implantation in the rat is a transient state occurring on day 5 of pregnancy or pseudopregnancy and is controlled by estrogen and progesterone. To identify genes potentially involved in receptivity, a uterine cDNA library was screened. An interesting pattern for Cystatin C (Cst3) expression was discovered with a peak in abundance just prior to embryo implantation (day 4 of pregnancy) followed by a significant drop the following day when implantation is initiated. Histology localized Cst3 mRNA and CST3 protein to the glandular epithelium on day 4 of pregnancy suggesting that it is secreted into the uterine lumen at this time. In ovariectomized rats endometrial Cst3 mRNA levels decreased within 3h of treatment with estradiol; this effect was inhibited by the anti-estrogen, ICI 182, 780. The data suggest that the endometrial expression of the cysteine protease inhibitor, Cst3, is modulated by estrogen during the peri-implantation period.

Variable expression of cystatin C in cultured trans-differentiating rat hepatic stellate cells

AIM: To study the expression of cystatin C (CysC), its regulation by transforming growth factor-β1 (TGF-β1) and platelet-derived growth factor (PDGF) and the potential interference of CysC with TGF-β1 signaling in this special cell type.

METHODS: We evaluated the CysC expression in cultured, profibrogenic hepatic stellate cells and trans-differentiated myofibroblasts by Northern and Western blotting and confocal laser scanning microscopy.

RESULTS: CysC was increased significantly in the course of trans-differentiation. Both TGF-β1 and PDGF-BB suppressed CysC expression. Furthermore, CysC secretion was induced by the treatment with TGF-β1. Although CysC induced an increased binding affinity of TGF-β receptor type III (beta-glycan) as assessed by chemical cross-linking with [¹²⁵I]-TGF-β1, it did not modulate TGF-β1 signal transduction as shown by evaluating the Smad2/3 phosphorylation status and [CAGA]-MLP-luciferase reporter gene assay. Interestingly, the shedding of type III TGF-β receptor beta-glycan was reduced in CysC-treated cells. Our data indicated that CysC expression was upregulated during trans-differentiation.

CONCLUSION: Increased CysC levels in the serum of patients suffering from liver diseases are at least partially due to a higher expression in activated hepatic stellate cells. Furthermore, TGF-β1 influences the secretion of CysC, highlighting a potentially important role of cysteine proteases in the progression of hepatic fibrogenesis.

The use of cystatin C to inhibit epithelial-mesenchymal transition and morphological transformation stimulated by transforming growth factor-beta

Introduction

Transforming growth factor-β (TGF-β) is a potent suppressor of mammary epithelial cell (MEC) proliferation and is thus an inhibitor of mammary tumor formation. Malignant MECs typically evolve resistance to TGF-β-mediated growth arrest, enhancing their proliferation, invasion, and metastasis when stimulated by TGF-β. Recent findings suggest that therapeutics designed to antagonize TGF-β signaling may alleviate breast cancer progression, thereby improving the prognosis and treatment of breast cancer patients. We identified the cysteine protease inhibitor cystatin C (CystC) as a novel TGF-β type II receptor antagonist that inhibits TGF-β binding and signaling in normal and cancer cells. We hypothesized that the oncogenic activities of TGF-β, particularly its stimulation of mammary epithelial–mesenchymal transition (EMT), can be prevented by CystC.

Method

Retroviral infection was used to constitutively express CystC or a CystC mutant impaired in its ability to inhibit cathepsin protease activity (namely Δ14CystC) in murine NMuMG MECs and in normal rat kidney (NRK) fibroblasts. The effect of recombinant CystC administration or CystC expression on TGF-β stimulation of NMuMG cell EMT in vitro was determined with immunofluorescence to monitor rearrangements of actin cytoskeletal architecture and E-cadherin expression. Soft-agar growth assays were performed to determine the effectiveness of CystC in preventing TGF-β stimulation of morphological transformation and anchorage-independent growth in NRK fibroblasts. Matrigel invasion assays were performed to determine the ability of CystC to inhibit NMuMG and NRK motility stimulated by TGF-β.

Results

CystC and Δ14CystC both inhibited NMuMG cell EMT and invasion stimulated by TGF-β by preventing actin cytoskeletal rearrangements and E-cadherin downregulation. Moreover, both CystC molecules completely antagonized TGF-β-mediated morphological transformation and anchorage-independent growth of NRK cells, and inhibited their invasion through synthetic basement membranes. Both CystC and Δ14CystC also inhibited TGF-β signaling in two tumorigenic human breast cancer cell lines.

Conclusion

Our findings show that TGF-β stimulation of initiating metastatic events, including decreased cell polarization, reduced cell–cell contact, and elevated cell invasion and migration, are prevented by CystC treatment. Our findings also suggest that the future development of CystC or its peptide mimetics hold the potential to improve the therapeutic response of human breast cancers regulated by TGF-β.

Enhanced Anti-Rotavirus Action of Human Cystatin C by Site-Specific Glycosylation in Yeast

The cDNA encoding human cystatin C (HCC) was subjected to site-specific substitution of alanine for serine at the position 37, to obtain the Asn(35)-Lys(36)-Ser(37) sequence that is a signal for asparagine-linked (N-linked) glycosylation of protein in eukaryotes, and was transformed into Pichia pastoris X33. As a result, 1.2 mg/L oligomannosyl HCC with a carbohydrate chain of Man(10)GlcNAc(2) was produced by the Pichia transformant. The oligomannosyl HCC was more stable at the low ionic strength condition of 50 mM potassium phosphate buffer, pH 7.0, than the wild-type. In addition, the oligomannosylation substantially improved the molecular stability of cystatin against an aspartic proteinase, cathepsin D, in which the susceptibility decreased to less than 50% of nonglycosylated one. The anti-rotavirus activity of HCC was substantially enhanced by the site-directed glycosylation using the yeast expression system. A MA-104 cell line was used as a host cell for human rotavirus type-2 Wa strain in this study, to which both the wild-type and oligomannosyl HCCs did not show cytotoxicity at a concentration of 100 mug/mL. More than 80% viability of the host cell infected with 1.0 x 10(5) PFU/mL of rotavirus was conserved under the condition coexisting with 75 mug/mL of the oligomannosyl HCC, which was 15.2% higher than that of wild-type HCC. Thus, the in vitro anti-rotavirus assay indicated that the supplement of a proper amount of the oligomannosyl HCC could be used as an anti-rotavirus agent.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Interactive effects of microbial transglutaminase and recombinant cystatin on the mackerel and hairtail muscle protein

Interactive effects of microbial transglutaminase (MTGase) and recombinant cystatin on the mackerel and hairtail water soluble protein (WSP), salt soluble protein (SSP), and muscle protein (MP) were investigated. According to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and enzymic activity analyses, cross-linking of mackerel and hairtail myosin heavy chain and low molecular mass compounds and formation of epsilon-(gamma-glutamyl)lysine cross-links were observed on samples with MTGase, while the recombinant cystatin could effectively inhibit the cathepsins and subsequently prevent degradation of proteins during setting. The cathepsins and MTGase activities in WSP, SSP, and MP solutions decreased, but the recombinant cystatin activity increased during setting at 45 degrees C.

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.

Demonstration of multiple novel glycoforms of the stem cell survival factor CCg

We have investigated the presence of different glycoforms of cystatin C secreted by adult hippocampal rat-derived stem/progenitor cells (AHPs) into conditioned medium. A glycosylated form of cystatin C (CCg) has been identified previously in conditioned medium from AHPs as an autocrine/paracrine cofactor. Fibroblast growth factor-2 (FGF2) requires cooperation with CCg to support AHP survival at low density in vitro. The purpose of the present study was to investigate further if cystatin C consists of one glycoform or if several different glycoforms are secreted by AHPs in vitro. The presence of the glycoforms was studied using enzymatic deglycosylation in conjunction with gel electrophoresis and Western blotting. The glycoforms of cystatin C were isolated with a combination of gel electrophoresis and electroelution, yielding the intact glycoforms in liquid phase before enzymatic deglycosylation. Our results revealed several novel glycoforms, in contrast to previous publication. The results suggest that N- and O-linked glycans with sialic acid are attached to cystatin C. Furthermore, we have demonstrated that all glycoforms are present in conditioned medium after only 48 hr of culturing and that all nestin-positive AHPs are immunopositive against cystatin C. These findings suggest secretion of the glycoforms by cultured AHPs.

Human brain cathepsin H as a neuropeptide and bradykinin metabolizing enzyme

Highly purified human brain cathepsin H (EC 3.4.22.16) was used to study its involvement in degradation of different brain peptides. Its action was determined to be selective. On Leu-enkephalin, dynorphin (1-6), dynorphin (1-13), alpha-neoendorphin, and Lys-bradykinin, it showed a preferential aminopeptidase activity by cleaving off hydrophobic or basic amino acids. It showed no aminopeptidase activity on bradykinin, which has Pro adjacent to its N-terminal amino acid, on neurotensin with blocked N-terminal amino acid, or on dermorphin with second amino acid D-alanine. After prolonged incubation, cathepsin H acted as an endopeptidase. Dermorphin and dynorphin (1-13) were cleaved at bonds with Phe in the P2 position, while dynorphin (1-6), alpha-neoendorphin, bradykinin and Lys-bradykinin were cleaved at bonds with Gly in the P2 position. Further on, it was shown that human brain cathepsin H activity could be controlled in vivo by cystatin C in its full-length form or its [delta1-10] variant, already known to be co-localized in astrocytes, since the Ki values for the inhibition are in the 10(-10) M range.

Alzheimer disease-associated cystatin C variant undergoes impaired secretion

CST3 is the coding gene for cystatin C (CysC). CST3 B/B homozygosity is associated with an increased risk of developing Alzheimer disease. We performed CysC analysis on human primary skin fibroblasts obtained from donors carrying A/A, A/B, and B/B CST3. Pulse-chase experiments demonstrated that the release of the B variant of CysC has a different temporal pattern compared to that of the A one. Fibroblasts B/B homozygous displayed a reduced secretion of CysC due to a less efficient cleavage of the signal peptide, as suggested by high-resolution Western blot analysis and by in vitro assay. In the brain, the reduced level of CysC may represent the molecular factor responsible for the increased risk of Alzheimer disease.

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.

Up-regulation of cystatin C expression in the murine hippocampus following perforant path transections

Cystatins are endogenous cysteine protease inhibitors that modulate the turnover of intracellular and extracellular proteins. These inhibitors are strongly implicated in a variety of pathological processes such as tumor metastasis and many degenerating CNS disorders. Here we report the expression of cystatin C, a major cysteine protease inhibitor of mammalian animals, in the murine hippocampus at 3, 7, 15 and 30 days following perforant path transections. Northern blot analysis showed that cystatin C transcripts were up-regulated in a transient manner with a significant increase at 7 and 15 days post-lesion (219% and 185% of control, respectively) in the rat hippocampus after entorhinal deafferentation. In situ hybridization and immunohistochemistry confirmed the time-dependent up-regulation of both cystatin C mRNA and protein expressions in a mouse model which initiated at 3 days post-lesion, reached maximal levels 7-15 days post-lesion, and remained slightly elevated by day 30 post-lesion. The modulation of cystatin C expression was observed to occur specifically in the entorhinally denervated zones: the stratum lacunosum-moleculare of the hippocampus and the outer molecular layer of the dentate gyrus. Double labeling by either a combination of in situ hybridization for cystatin C with immunohistochemistry for glial fibrillary acidic protein or double immunofluorescence staining for both proteins in mouse hippocampus at 7 and 15 days post-lesion revealed that most cystatin C-expressing cells are astrocytes. From these results we suggest that the spatiotemporal up-regulation of cystatin C in the hippocampus is induced by entorhinal deafferentation and that cystatin C may be involved in the astroglia-mediated neural plasticity events in the hippocampus following perforant path transections.

Cystatin 11: a new member of the cystatin type 2 family

Cystatin (CST)11, a novel member of the CST type 2 family of cysteine protease inhibitors, was identified in Macaca mulatta epididymis by subtractive hybridization cloning. The human CST11 gene on chromosome 20p11.2 is located near three other CST genes expressed predominantly in the male reproductive tract. The CST11 gene spans three exons, a structure similar to that of other CST family 2 genes. An exon 2-deleted alternative transcript (CST11Delta2) was also identified. CST11 mRNA is expressed only in the epididymis as judged by Northern blot hybridization and is androgen regulated. The protein is most abundant in the initial segment, but is detected throughout the epididymis and on ejaculated human sperm. The calculated tertiary structure of CST11 reveals that the three regions corresponding to the protease inhibitory wedge of CST3 are similarly juxtaposed in CST11, consistent with protease inhibitor function. Intact and exon 2-deleted CST11 recombinant proteins were tested for antibacterial activity. After a 2-h incubation of Escherichia coli with 50 microg/ml recombinant CST11 or CST11Delta2, bacterial colony-forming units were reduced to 30% of control, indicating that both forms have antimicrobial activity.

Characterization of a cysteine proteinase inhibitor induced during neuronal cell differentiation

A rat homolog of human cystatin E/M was identified by differential display of transcripts induced during neuronal cell differentiation. A member of the family 2 cystatins, rat cystatin E/M is secreted, glycosylated and developmentally regulated. Rat cystatin E/M is expressed in brain, and is induced during differentiation of a conditionally immortalized E17 rat hippocampal cell line (H19-7) by bFGF or activated Raf via MEK-dependent and -independent signaling pathways. Rat cystatin E/M protein is increased post-transcriptionally in PC12 cells, and the protein is secreted into the medium of primary embryonal hippocampal cultures. Analysis of the K (i) of recombinant His-tagged rat cystatin E/M toward cathepsins B and H revealed that rat cystatin E/M has an inhibitor profile distinct from that of other members of the cystatin family. Motif swapping between rat cystatin E/M and human cystatin C, a well-characterized cystatin, identified some residues that can contribute to the specificity of inhibition. Taken together, these results describe a member of the cystatin family that has a distinct inhibitor profile and may play a role in neuronal development.

Elevation of cystatin C in susceptible neurons in Alzheimer's disease

A common polymorphism in the cystatin C gene is associated with increased risk of developing Alzheimer's disease (AD). To explore possible neuropathological consequences of this genetic association, we examined expression of cystatin C in brains from 22 AD and 11 control patients by immunohistochemistry. In the temporal cortex of all AD brains, there was strong cystatin C immunostaining of neurons and activated glia, whereas staining was absent or minimal in 7 of the 11 control brains. Neuronal staining of cystatin C in AD brains was primarily limited to pyramidal neurons in cortical layers III and V, which are the neurons most susceptible to cell death in AD. The increase in cystatin C staining in AD was independent of cystatin C genotype. Immunostaining of cystatin C within neurons showed a punctate distribution, which co-localized with the endosomal/lysosomal proteinase, cathepsin B. A primarily glial source for cystatin C was suggested by parallel studies using in situ hybridization of mouse brain. In human AD brain, there was little co-localization of cystatin C with parenchymal Abeta deposits, although a small fraction of cerebral blood vessels and neurofibrillary tangles were cystatin C-positive. The regional distribution of cystatin C neuronal immunostaining also duplicated the pattern of neuronal susceptibility in AD brains: the strongest staining was found in the entorhinal cortex, in the hippocampus, and in the temporal cortex; fewer pyramidal neurons were stained in frontal, parietal, and occipital lobes. These neuropathological observations reinforce the association between cystatin C and AD, and support a model of cystatin C involvement in the process of neuronal death in AD.

Dynamics of brain-derived proteins in cerebrospinal fluid

BACKGROUND

The recent theory of blood-cerebrospinal fluid (CSF) barrier function and dysfunction connects molecular flux and CSF flow rate. A reduced CSF flow rate is sufficient to account for the observed hyperbolic relation between different blood-derived protein concentrations in CSF in cases of a blood-CSF barrier dysfunction.

METHODS

The dynamics of brain-derived proteins in CSF are investigated with reference to the CSF flow rate measured by CSF/serum albumin concentration quotient.

RESULTS

Proteins from neurons or glial cells, tau protein, neuron-specific enolase, S-100 protein, all enter CSF primarily in the ventricular and cisternal space. Their concentration between normal ventricular and lumbar CSF is decreasing (in contrast to blood-derived proteins), and in the case of pathologically decreasing CSF flow rate, the concentration in lumbar CSF remains invariantly constant. Concentrations of the primarily leptomeningeal proteins, beta-trace protein and cystatin C, increase between normal ventricular and lumbar CSF, and in the case of pathologically decreased CSF flow rate they increase linearly in lumbar CSF (concentrations of blood-derived proteins increase non-linearly).

CONCLUSIONS

A satisfactory physiological explanation can now be given for the dynamics of proteins in CSF consisting of both brain- and blood-derived fractions (transthyretin, soluble intercellular adhesion molecule (s-ICAM)), as well as the disputed decrease of leptomeningeal protein concentrations (beta-trace protein, cystatin C) in cases of bacterial meningitis is also explained. The biophysical treatment of dynamics in the ventricular and lumbar CSF extends the new theory and shows that CSF flow rate is the most relevant parameter for understanding the pathological changes of both blood- and brain-derived proteins in CSF. The impact on diagnosis of neuro-degenerative diseases is discussed.

Serum cystatin C in patients with myeloma

BACKGROUND

Cystatin C is a low molecular weight protein thought to be synthesised by all nucleated cells and freely filtered by the kidney. It has been proposed as a marker for GFR; however, it has been suggested that there may be limitations to its use, because it may be over-expressed in some tumour cells and the abnormal tissue growth may also lead to an increased circulating level.

METHODS

We investigated the serum cystatin C levels in 60 patients with myeloma, comparing results with those for serum creatinine, beta(2)-microglobulin and the paraprotein concentration.

RESULTS

We found no correlation between cystatin C and the paraprotein concentration in these patients.

CONCLUSION

These results suggest that disease burden does not correlate to the circulating level of cystatin C in patients with myeloma.

Spinal cord genes enriched in rat dorsal horn and induced by noxious stimulation identified by subtraction cloning and differential hybridization

Persistent nociceptive input increases neuronal excitability and induces a program of gene expression in the dorsal spinal cord. The alteration in gene expression commences with phosphorylation and induction of immediate early genes and proceeds to target genes. Only a few target genes have been identified as yet. The present report uses a polymerase chain reaction-based subtraction cloning procedure to obtain an "anatomically focused" complementary DNA library enriched in transcripts related to sensory spinal cord (rat dorsal horn minus ventral horn). A subset of clones from this library (n=158) was screened to verify dorsal horn enrichment and to identify those regulated by carrageenan-induced peripheral inflammation. Molecular classes which displayed enriched expression included a proto-oncogene not previously associated with sensory processes, two regulators of the Rho/Rac pathway which controls cell shape, and three genes involved in cytoskeletal regulation and scaffolding. Additional transcripts coded for proteins involved in intercellular communication or intracellular function. Within the set of 158 transcripts, one known and two unknown genes were induced by persistent noxious input. The known gene codes for the secreted cysteine proteinase inhibitor, cystatin C, suggesting that modulation of extracellular proteolytic activity occurs. Since it is secreted, cystatin C may also provide a cerebrospinal fluid bio-marker for persistent pain states. Using a combined anatomical and functional approach, we have extended the molecular repertoire of genes expressed and induced in second-order neurons or supporting glial cells in several new directions, with particular emphasis on regulation of cell morphology and plasma membrane dynamics. Some of these proteins reveal new pathways for information signaling in the sensory half of the spinal cord and require further research to understand their role in the adult spinal cord. The induced genes may provide new molecular targets for therapeutic development and provide new probes for investigating the dynamic state of cellular activity that occurs during persistent pain states.

Up-regulation of MUC5AC mRNA expression in endotoxin-induced otitis media

We investigated the expression levels of MUC5AC in endotoxin-induced otitis media with effusion (OME) in the rat using competitive polymerase chain reaction (PCR) and the morphology of middle ear mucosa using transmission electron microscopy (TEM). Experimental OME in the rat was induced after middle ear instillation of Escherichia coli lipopolysaccharides (LPS). Middle ear mucosa were obtained at 0 h, 12 h, Day 1, Day 3, Day 7 and Day 14 and reverse transcriptase (RT)-PCRs were then performed for the identification of MUC1, MUC2, MUC5AC and submandibular mucin 1 expression, followed by competitive PCRs for MUC5AC and beta2-microglobulin expression. Normal middle ear mucosa revealed no expression of mucin genes, whereas endotoxin upregulated the expression of MUC5AC mRNA between 12 h and Day 7, with maximal expression at Days 1 and 3. Middle ears treated three times with LPS upregulated more MUC5AC mRNA expression, by a factor of approximately 3.5, than those 1 day after one instillation. On TEM, dark granulated cells were observed at Day 3 after endotoxin instillation, but mixed granulated cells were seen on the ears treated three times with LPS. These results suggest that MUC5AC could be one of the major mucin genes in the middle ear mucosa related to otitis media.

Involvement of cystatin C in oxidative stress-induced apoptosis of cultured rat CNS neurons

Oxidative stress is involved in neuronal degeneration in cerebrovascular injury, neuropathology and aging. When rat CNS neurons were cultured in a high (50%) oxygen atmosphere, the neurons died. This high oxygen-induced cell death showed features of apoptotic cell death, characterized by DNA fragmentation, and was blocked by inhibitor of protein synthesis. We found that cystatin C and HuC mRNA, the products of which are an inhibitor of cysteine proteases and an RNA binding protein, respectively, were up-regulated in neurons cultured in the high oxygen atmosphere. In the present study, we focused on cystatin C. Cystatin C protein levels were also increased in neurons cultured in the high oxygen atmosphere. In situ hybridization with an RNA probe for rat cystatin C and immunocytochemistry with anti-human cystatin C antibody showed that microtubule-associated protein 2 (MAP2)-positive neurons expressed cystatin C mRNA and protein, respectively, in the high oxygen atmosphere. These results indicated that oxidative stress stimulates an increase in cystatin C expression in cultured neurons, and that cystatin C might have important roles in regulation of apoptosis elicited by oxidative stress.

Analysis of expressed sequence tags of retinal pigment epithelium: cystatin C is an abundant transcript

In order to identify genes that are expressed in the retinal pigment epithelium (RPE), randomly chosen clones of a cDNA library of cultured human foetal RPE cells were analyzed by sequencing. Of 164 informative expressed sequence tags (ESTs), 88 matched the sequences of 74 genes for proteins of known or presumed function. Approximately a third of these represented genes with involvement in gene/protein expression, with a major subcategory concerned with protein turnover. In particular, the gene coding for precursor cystatin C was represented by 3 independent ESTs, and plaque hybridization estimated the frequency of cystatin C clones in the library to be 1.3%. Cystatin C mRNA in cultured RPE cells was confirmed by Northern blotting and by reverse transcription polymerase chain reaction (RT-PCR) with identification of the cystatin C sequence as the product of the reaction. The survey also revealed 25 novel human sequences representing genes that are active in RPE. One of these was localized near a recently identified, new autosomal recessive retinitis pigmentosa locus. In conclusion, the findings specifically demonstrate the unexpected presence of cystatin C mRNA at fairly high abundance in cultured human RPE cells, and, more generally, serve as a model study establishing the usefulness of the EST approach for further characterizing the molecular basis of the activities of the RPE.

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.

Postnatal changes of gene expression for tissue inhibitors of metalloproteinase-1 and -2 and cystatins S and C, in rat submandibular gland demonstrated by quantitative reverse transcription-polymerase chain reaction

The rat submandibular gland is not fully developed at birth and definitive differentiation takes place postnatally. The steady-state mRNA expression for the four proteinase inhibitor molecules, tissue inhibitors of metalloproteinase (TIMP)-1 and -2, and cystatins S and C, and for a housekeeping gene, glyceraldehyde-3-phosphate dehydrogenase (G3PDH), in rat submandibular glands was measured by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) at different stages of postnatal development. The gene-expression patterns of TIMP-1 and -2 relative to G3PDH were similar to each other. The TIMP-2 and cystatin C genes were more highly expressed than those of TIMP-1 and cystatin S at all stages. Moreover, the gene expressions of TIMP-1 and -2, and of cystatins S and C, were predominant between 1 and 7, and 7 and 12 weeks of age, respectively, and coincided developmentally with the regression of terminal tubule cells and the differentiation of granular convoluted tubule cells, respectively. Quantitative competitive RT-PCR allowed accurate measurement of small changes in the steady-state concentrations of these proteinase-inhibitor mRNA molecules.

Molecular cloning, sequence analysis and expression distribution of rainbow trout (Oncorhynchus mykiss) cystatin C

Cystatin C is one of a family of proteinase inhibitors of cathepsins and other cysteine proteinases. Among warm-blooded vertebrates, small functional regions of cystatin amino acid sequences are well conserved among species, but major portions of cystatin amino acid sequences vary evolutionarily. Although considerable attention has been given to mammalian and avian cystatins, little data exist on cystatins from other vertebrates. A cDNA clone for trout cystatin C was isolated from a lambda gt11 cDNA library of rainbow trout (Oncorhynchus mykiss) liver. An apparently full-length cDNA clone of 674 bp encoding 132 amino acid residues was obtained. Sequence analysis indicated that trout cystatin C contains an N-terminal signal sequence extension of 21 amino acids and a mature sequence of 111 amino acid residues, with amino acid residues conserved in functional regions relative to mammalian and avian cystatin C. Using cloned cDNA as a probe, we investigated expression of the cystatin C gene in trout tissues, several cell lines of trout liver or liver tumor, and cell cultures of liver tumor origin. Cystatin C mRNA was in high abundance in trout embryo tissue, a tumor-derived liver cell line and some normal adult tissues. Southern hybridization analysis indicated one copy of the trout cystatin C gene per haploid genome, and sequence comparisons indicated considerable divergence in large portions of the coding region of the trout cystatin C gene relative to a variety of species.

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.

Interactions between ovine cathepsin L, cystatin C and alpha 2-macroglobulin. Potential role in the genital tract

The specific inhibitor of cysteine proteinases, cystatin C, was purified from ram rete testis fluid and the conditioned medium of Sertoli cells. This molecule associated with sheep liver cathepsin L at one of the fastest rates ever described for a proteinase/inhibitor interaction (1.75 +/- 0.20 x 10(8) M-1.s-1). But the association rate constant for the interaction of cathepsin L with alpha 2-macroglobulin, a non-specific inhibitor of proteinases, was also extremely high (8.8 +/- 0.75 x 10(6) M-1.s-1). Cathepsin L complexed with alpha 2-macroglobulin was protected from inhibition by type 2 and type 3 cystatins. The data indicate that cystatin C is the most potent inhibitor of cathepsin L in mammalian male genital tract fluids, whereas alpha 2-macroglobulin may act as a terminal acceptor of this enzyme. These inhibitors could therefore inhibit the activated form of procathepsin L which may appear during the complex process of spermatozoa production and maturation in the testis and epididymis.

Purification and cellular localization of beta2-microglobulin in the testis

Using multiple high performance liquid chromatography (HPLC) steps, a protein of 12 kDa was purified to apparent homogeneity from rat Sertoli cell-enriched culture medium (SCCM). Partial N-terminal amino acid sequence analysis revealed a sequence of NH2-IQKTPQIQVYS which is identical to beta2-microglobulin (beta2MG) previously identified in the brain. Studies by sequential reverse transcription and polymerase chain reaction (RT-PCR) indicated that beta2MG mRNA was expressed in Sertoli but not in germ cells suggesting that Sertoli cells are the source of this protein in the seminiferous epithelium behind the blood-testis barrier. The steady-state beta2MG mRNA level in Sertoli cells cultured in vitro was not affected by either follicle stimulating hormone (FSH), testosterone, estradiol, dexamethasone or several cytokines such as interleukin-1beta (IL-1beta), interleukin 6 (IL-6), and transforming growth factor beta (TGF-beta), with the exception of interferon-gamma (INFgamma) which induced a dose-dependent stimulation of beta2MG mRNA. The possible physiological significance of this protein in the male reproductive tract is discussed.

Microvascular degeneration in hereditary cystatin C amyloid angiopathy of the brain

Hereditary cystatin C amyloid angiopathy (HCCAA), an autosomal dominant form of cerebral amyloid angiopathy (CAA) occurring primarily in Iceland, is characterized by a variant cystatin C amyloid deposition in the walls of cerebral parenchymal and leptomeningeal vessels. Cystatin C is also found to colocalize with amyloid beta/A4 protein in cerebral vessel walls of patients with Alzheimer's disease (AD), sporadic CAA, and hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D). The abundance of cystatin C deposition in cerebral blood vessel walls suggests that cellular elements of the vessel wall itself may play a role in its deposition. Microvascular changes in the brains of HCCAA patients were investigated by single- and double-label immunohistochemistry. We found that cystatin C amyloid immunoreactivity was present not only in cerebral cortical and leptomeningeal vessels, but also in white matter parenchymal vessels. Cystatin C deposition was more prominent in the media of parenchymal vessels and in the adventitia of leptomeningeal vessels. Smooth muscle (sm) cells were few or could not be identified within vessel walls showing extensive cystatin C deposition, suggesting progressive loss of these cells as cystatin C accumulates. However, in less severely affected vessels, cystatin C was present in cells that also had the phenotype of sm, suggesting that sm cells synthesize or process cystatin C. Cystatin C immunoreactivity was in addition, detected in some neuronal cell bodies throughout the cortex in patients with HCCAA and AD-related CAA. Our results indicate that cellular components of the vessel walls may play an important role in cystatin C deposition, as they do in beta/A4 deposition in AD-related CAA. Cystatin C deposition within the vascular media and adventitia, with associated vessel wall injury as manifested by sm cell loss, represents microvascular degeneration that leads to cerebral hemorrhage.

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

Recombinant mouse (Mus musculus) and rat (Rattus norvegicus) cystatin C were produced by expression in Escherichia coli, isolated and functionally characterized. The mouse and rat inhibitors were both fully active in titrations of papain. Determination of equilibrium constants for dissociation (Ki) for their complexes with the target proteinase, cathepsin B, produced values not largely different from that for human cystatin C (Ki 0.07-0.13 nM). Rabbit antisera against mouse and rat cystatin C were produced and used for improved affinity purification of the recombinant inhibitors. Affinity purified immunoglobulins isolated from the antiserum against mouse cystatin C were used for construction of a sensitive enzyme-linked immunosorbent assay. The assay was used to demonstrate a high degree of immunological cross-reactivity between mouse and rat cystatin C and could be used for cystatin C quantification in mouse and rat tissue homogenates. All tissues analyzed contained cystatin C, with a relative content very similar to that of human tissues. For all species, brain tissue contained the highest cystatin C amounts and liver the lowest, whereas kidney, spleen and muscle tissues were intermediate in content. In the mouse, a notable high cystatin C content in parotid gland tissue was observed. The high degree of similarity in distribution pattern and functional properties for mouse, rat and human cystatin C indicates that a murine model should be relevant for studies of the human disease, hereditary cystatin C amyloid angiopathy.

Up-regulation of cystatin C by microglia in the rat facial nucleus following axotomy

Cystatin C, a cysteine proteinase inhibitor, is expressed in the central nervous system (CNS) as well as many other organs of mammals. However, little is known concerning whether its expression is regulated under pathological conditions of the CNS and what types of cells are responsible for this regulation. We performed differential hybridization screening of cDNA libraries derived from the rat facial nucleus and found a cDNA of rat cystatin C to be up-regulated following facial nerve axotomy. In situ hybridization using an RNA probe for rat cystatin C revealed that cystatin C mRNA in the facial nucleus was markedly increased in amount by day 7 after axotomy and was then decreased to the normal level by day 50. The intense signal for cystatin C mRNA in the damaged facial nucleus was localized in the glial cells which had the morphological characteristics of microglia. Light and electron microscopic immunohistochemistry using a rabbit antibody specific for cystatin C confirmed that microglia in the damaged facial nucleus were strongly positive for cystatin C. The immunoreactivity was also found in the extracellular space, consistent with the fact that cells producing cystatin C generally secrete this protein. These results demonstrate that cystatin C is markedly up-regulated by microglia in response to axotomy and is probably secreted by these cells into the extracellular space, suggesting that this proteinase inhibitor has (a) significant function(s) in the processes of neuronal degeneration, regeneration, and/or repair subsequent to axotomy.

Comparisons of P-glycoprotein expression in isolated rat brain microvessels and in primary cultures of endothelial cells derived from microvasculature of rat brain, epididymal fat pad and from aorta

In vivo expression of P-glycoprotein in isolated rat brain microvessels is compared with that in vitro in primary cultures of brain endothelial cells. More P-glycoprotein is detected by Western immunoblotting in microvessels than in cultured endothelium. RT-PCR with isoform-specific primers and immunoblotting with a mdr1b-specific antibody reveals only mdr1a in vivo but both mdr1a and mdr1b in vitro. Thus mdr1a decreases whereas mdr1b increases during culture. P-Glycoprotein activity is evident in vitro, with resistance modulators, e.g. verapamil, producing increases in intracellular [3H]vincristine accumulation. Endothelial cells cultured from epididymal fat pad microvasculature and aorta contain little or no P-glycoprotein. Here, resistance modulators are less effective.

Cystatin C, a protease inhibitor, in degenerating rat hippocampal neurons following transient forebrain ischemia

Cystatin C, a cysteine protease inhibitor produced by the choroid plexus and found in CSF at high concentrations, may have an important role in brain injury. We used the two-vessel occlusion model with hypotension to induce transient forebrain ischemia (TFI) in rats for 10 min and then examined cystatin C immuno-like reactivity (CC-IR) after 1, 3, 7 and 14 days of recovery. Our results reveal that CC-IR was minimal or absent in the hippocampus of normal and 1 day post-ischemic animals. However, CC-IR was present in CA1 pyramidal cells and a small number of reactive glia of the stratum radiatum (SR) and stratum oriens (SO) at 3, 7 and 14 days post-ischemia. Histological assessment of the hippocampus indicates that CC-IR was localized in morphologically degenerative neurons. This distinct temporal expression of cystatin C in the rat hippocampus is concurrent with delayed neuronal death following TFI. Thus, these results indicate that cystatin C and/or its substrates may be important components of the post-ischemic neurodegenerative and repair process.

The cerebral expression of plasma protein genes in different species

The cerebrospinal fluid (CSF) contains the same proteins as blood plasma, but with a different pattern of concentrations. Protein concentrations in CSF are much lower than those in blood. CSF proteins are derived from blood or synthesized within the brain. The choroid plexus is an important source of CSF proteins. Transthyretin is the protein most abundantly synthesized and secreted by choroid plexus. It determines the distribution of thyroxine in the cerebral compartment. Synthesis of transthyretin first evolved in the brain, then later it became a plasma protein synthesized in the liver. Other proteins secreted by choroid plexus are serum retinol-binding protein, transferrin, caeruloplasmin, insulin-like growth factors, insulin-like growth factor binding proteins, cystatin C, alpha 1-antichymotrypsin, alpha 2-macroglobulin, prothrombin, beta 2-microglobulin and prostaglandin D synthetase. Species differences in expression of the genes for these proteins are outlined, and their developmental pattern, regulation and roles in the cerebral extracellular compartment are discussed.

Evolution of transthyretin in marsupials

The evolution of the expression and the structure of the gene for transthyretin, a thyroxine-binding plasma protein formerly called prealbumin, was studied in three marsupial species: the South American polyprotodont Monodelphis domestica, the Australian polyprotodont Sminthopsis macroura and the Australian diprotodont Petaurus breviceps. The transthyretin gene was found to be expressed in the choroid plexus of all three species. In liver it was expressed in P. breviceps and in M. domestica, but not in S. macroura. This, together with previous studies [Richardson, S. J., Bradley, A. J., Duan, W., Wettenhall, R. E. H., Harms, P. J., Babon, J. J., Southwell, B. R., Nicol, S., Donnellan, S. C. & Schreiber, G. (1994) Am. J. Physiol. 266, R1359-R1370], suggests the independent evolution of transthyretin synthesis in the liver of the American Polyprotodonta and the Australian Diprotodonta. The results obtained from cloning and sequencing of the cDNA for transthyretin from the three species suggested that, in the evolution of the structure of transthyretin in vertebrates, marsupial transthyretin structures are intermediate between bird/reptile and eutherian transthyretin structures. In marsupials, as in birds and reptiles, a hydrophobic tripeptide beginning with valine and ending with histidine was found in transthyretin at a position which has been identified in eutherians as the border between exon 1 and intron 1. In humans, rats and mice, the nine nucleotides, coding for this tripeptide in marsupials/reptiles/birds, are found at the 5' end of intron 1. They are no longer present in mature transthyretin mRNA. This results in a change in character of the N-termini of the subunits of transthyretin from hydrophobic to hydrophilic. This change might affect the accessibility of the thyroxine-binding site in the central channel of transthyretin, since, at least in humans, the N-termini of the subunits of transthyretin are located in the vicinity of the channel entrance [Hamilton, J. A., Steinrauf, L. K., Braden, B. C., Liepnieks, J., Benson, M. D., Holmgren, G., Sandgren, O. & Steen, L. (1993) J. Biol. Chem. 268, 2416-2424].

Expression of the cysteine proteinase inhibitor cystatin C mRNA in rat eye

BACKGROUND

Cystatin C, a naturally occurring inhibitor of cysteine proteinases, belongs to family 2 of the cystatin superfamily. While cystatins in general, and cystatin C specifically, are expressed in various cell types and found in biological fluids, cystatins in ocular structures have not been investigated. In the present study, the expression of cystatin C mRNA in the eye of the rat was studied.

METHODS

Total RNA was extracted from eyes as well as from pooled corneae, retinas, lenses, sclerae, and corneae of adult rats. Cystatin C mRNA was detected in the RNA samples by reverse transcriptase--polymerase chain reaction and Northern blot hybridization. In addition, in situ hybridizations of formalin-fixed cryostat sections were carried out using a digoxigenin-labeled cystatin C probe.

RESULTS

Cystatin C mRNA was demonstrated in total RNAs extracted from the eye, sclera, and retina, but not in RNAs isolated from the cornea and lens. In situ hybridizations revealed cystatin C mRNA in most of the stromal cells of the sclera. In the retina, a strong signal was localized in the outer nuclear layer. The distribution of the reaction product suggested that in the retina Müller cells and rod cells are the primary sites of expression of cystatin C. In addition, some glial cells in the inner nuclear and ganglion cell layers were stained. No specific signal for cystatin C mRNA was detected in the cornea, lens, iris, ciliary body, and choroid.

CONCLUSIONS

In the eye of the rat, significant levels of cystatin C mRNA are detected in the sclera and retina. In the sclera cystatin C may play a role in modulating the activities of cysteine proteinases, mostly cathepsins, involved in the turnover and remodeling of the stroma. In the retina, cystatins synthesized and presumably released by Müller cells and rod cells may have a protective function against the harmful effects of cysteine proteinases released under physiologic and pathologic conditions.

Localization of mRNAs by in-situ hybridization to the residual body at stages IX-X of the cycle of the rat seminiferous epithelium: fact or artefact?

Several recent articles have reported localization of specific mRNAs in the rat testis to stage IX and X seminiferous tubules using in-situ hybridization. In all cases the expression was located basally in the tubules and appeared as discrete round clusters of grains close to the lamina propria. The localization was interpreted as being in Sertoli cells or leptotene spermatocytes. In this study we demonstrate that this pattern is most probably due to artefactual binding of probes to the residual body (RB). In the present study testicular tissue, perfusion-fixed with Bouin's and embedded in paraffin, was used, as this resulted in excellent morphological preservation such that RBs within tubules at stages VIII-X were clearly distinguishable. RNA content of the RBs was demonstrated at stages VIII-X using methyl green pyronin staining, and could be eliminated by pretreatment with RNAse or trichloroacetic acid. Localization of mRNAs for 11 seminiferous tubule proteins was assessed using 35S-labelled and digoxigenin-labelled riboprobes (activin receptor-II, alpha-inhibin, transferrin, androgen-binding protein (ABP), cyclic protein-2 (CP-2), CREM, sulphated glycoproteins 1 and 2 (SGP-1 and SGP-2), transition protein 2 (TP-2) and cystatin-C), and digoxigenin-labelled oligonucleotide probes (transition protein-1 (TP-1), TP-2 and protamine-1). All of these probes showed localization to the correct cell type(s) within the seminiferous epithelium. In addition, six antisense riboprobes (activin receptor-II, CREM, SGP-2, CP-2, cystatin C and alpha-inhibin) showed hybridization to basally located residual bodies in tubules at stages IX-X on one or more occasions, whereas residual bodies around the edge of the lumen (stage VIII) or in transit through the seminiferous epithelium showed no hybridization; sense probes showed no localization to residual bodies. A common feature of the probes which localized to the basal RBs was that they had been prepared using cDNA cloned into Bluescript SK- vector such that the antisense strand was generated from the T7 polymerase promotor. A cRNA prepared using T7 polymerase and Bluescript vector alone and a GC-rich 27mer oligonucleotide corresponding to the region of the multiple cloning site of Bluescript adjacent to the T7 site both localized uniquely to basal RB. It is concluded that the hybridization seen within RBs is probably a subtle artefact unique to RBs undergoing dissolution following fusion with Sertoli cell lysosomes, and may reflect nonspecific hybridization to GC-rich fragments of RNA.