Diversity of rat brain cysteine proteinase inhibitors: isolation of low-molecular-weight cystatins and a higher-molecular weight T-kininogen-like glycoprotein

Transcriptome analysis of the hippocampal CA1 pyramidal cell region after kainic acid-induced status epilepticus in juvenile rats

Molecular mechanisms involved in epileptogenesis in the developing brain remain poorly understood. The gene array approach could reveal some of the factors involved by allowing the identification of a broad scale of genes altered by seizures. In this study we used microarray analysis to reveal the gene expression profile of the laser microdissected hippocampal CA1 subregion one week after kainic acid (KA)-induced status epilepticus (SE) in 21-day-old rats, which are developmentally roughly comparable to juvenile children. The gene expression analysis with the Chipster software generated a total of 1592 differently expressed genes in the CA1 subregion of KA-treated rats compared to control rats. The KEGG database revealed that the identified genes were involved in pathways such as oxidative phosporylation (26 genes changed), and long-term potentiation (LTP; 18 genes changed). Also genes involved in Ca²⁺ homeostasis, gliosis, inflammation, and GABAergic transmission were altered. To validate the microarray results we further examined the protein expression for a subset of selected genes, glial fibrillary protein (GFAP), apolipoprotein E (apo E), cannabinoid type 1 receptor (CB1), Purkinje cell protein 4 (PEP-19), and interleukin 8 receptor (CXCR1), with immunohistochemistry, which confirmed the transcriptome results. Our results showed that SE resulted in no obvious CA1 neuronal loss, and alterations in the expression pattern of several genes during the early epileptogenic phase were comparable to previous gene expression studies of the adult hippocampus of both experimental epileptic animals and patients with temporal lobe epilepsy (TLE). However, some changes seem to occur after SE specifically in the juvenile rat hippocampus. Insight of the SE-induced alterations in gene expression and their related pathways could give us hints for the development of new target-specific antiepileptic drugs that interfere with the progression of the disease in the juvenile age group.

Comparison of cathepsin protease activities in brain tissue from normal cases and cases with Alzheimer's disease, Lewy body dementia, Parkinson's disease and Huntington's disease

Recent evidence, based upon immunocytochemical and histochemical analysis of brain cortical tissue from alzheimer's disease patients, has suggested that altered activity and/or distribution of the lysosomal proteases cathepsins B and D may be implicated in the abnormal protein processing pathway resulting in formation of the neurotoxic amyloid A4 peptide, characteristic of this neurodegenerative disorder. We have therefore compared, via biochemical assay techniques using conventional or specially synthesised (corresponding to protein cleavage points of relevant to A4 peptide formation) fluorogenic substrates, the levels of activity of the lysosomal proteases cathepsins B, D, H and L, and dipeptidyl aminopeptidases I and II in frontal cortex (grey/white matter) from control and Alzheimer's disease patients. For comparative purposes, activity levels of the above enzymes were also determined in frontal cortex tissue from cases with Lewy body dementia and Parkinson's disease, and in caudate tissue from control and Huntington's disease cases. There was no significant difference in activity for any protease types in tissue from control cases and cases with Alzheimer's disease, Lewy body dementia or Parkinson's disease, with the exception of reduced dipeptidyl aminopeptidase II activity in Lewy body dementia and Parkinson's cases. We have therefore been unable to confirm a potential role for lysosomal cathepsins in the characteristic neurodegeneration associated with Alzheimer's disease; however the finding of significant increases in activity of dipeptidyl aminopeptidase II, cathepsin H and cathepsin D specifically in cases with Huntington's disease is of particular note. We therefore suggest the potential role of the latter enzymes in the pathogenesis of Huntington's disease requires further investigation.

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.

Distribution of immunoreactive T-kininogen in rat nervous tissues

The distribution in the nervous system of T-kininogen, the third kallikrein-resistant kininogen of the rat, was determined using bioassays and a radioimmunoassay system. In rat brain homogenates, trypsin released large amounts of a kinin-like myostimulating activity while urinary kallikrein released small amounts. The kinins released by trypsin were identified by HPLC as mostly T-kinin. Radioimmunoassays showed that a T-kininogen-like immunoreactive factor was uniformly distributed throughout the central nervous system. Higher levels were found in female rats than in male rats. Maximum levels were observed in newborn animals. A slight increase of T-kininogen content of the brain was observed after turpentine injection while T-kininogen level in liver was dramatically increased. T-kininogen plasma contamination to the nervous tissues was estimated by injecting 125I-labelled T-kininogen. The T-kininogen content of rat cultured cells and neurons was also examined. Highest levels were found in dorsal root ganglia neurons, lower levels in Schwann cells, phaeochromocytoma cells, mixed cells from spinal ganglion and in astrocytes. Immunocytochemistry showed the presence of T-kininogen in the cytoplasm of cultured dorsal root ganglia neurons and embryonic hippocampal neurons. The distribution of T-kininogen throughout the central and peripheral nervous system of the rat, the variations of its level during the life span suggest that T-kininogen would play the role of a cysteine proteinase inhibitor and not that of a T-kinin-releasing substrate in nervous tissues.

Immunolocalization of High Molecular Weight Kininogen (HKg) and T Kininogen (TKg) in the Rat Hypothalamus

Specific HKg immunostaining detected with antiserum against the light chain (LC) of HKg was restricted to SRIF neurons of the hypothalamic periventricular area projecting to median eminence (ME). Heavy chain (HC) immunoreactivity related to HKg and/or low molecular weight kininogen (LKg) was found in some other hypothalamic territories. Specific TKg was mainly associated with vasopressin in neurons of suprachiasmatic (SCN), supraoptic (SON) and paraventricular (PVN) nuclei. By direct RIA, hypothalamus was found to contain the highest level of TKg (10ng/mg protein) and after trypsin hydrolysis and HPLC separation of kinins, 10.3 pg BK and 7.3 pg T-kinin/mg protein.

Brain cysteine proteinase inhibitors II: evidence that a 21-kDa papain-binding component resembles ras p21

A 21-kDa protein extracted from rat or bovine brain at high pH was purified on alkylated-papain and shown to have dual ras-like and cysteine proteinase inhibitory (CPI) properties. This was demonstrated by its GTP-binding activity, cross-reactivity toward pan-reactive ras p21 monoclonal antibody, and inhibition of papain. The material eluted earlier than cystatins or kininogens on the alkylated papain-affinity column and was devoid of other CPIs based on immunoblot analysis. In a second procedure, ras p21s isolated from rat or bovine brain membranes by cholate extraction and purified by gel-permeation and hydrophobic interaction were shown to act also as potent CPIs, inhibiting rat brain cathepsin L, papain, or rat brain cathepsin B with Ki values of 3, 11, and 167 nM, respectively. This component cross-reacted with the monospecific anti-ras, but not with other anti-CPIs, and represented 3-4% of total GTP binding present in homogenates. The specific activity of the purified 21 kDa component was 4.7 nmol GTP-gamma-S bound per mg protein. The data support the notion that brain ras p21s constitute a separate group of CPIs and are available for regulating some aspects of brain protein turnover.

The kallikrein-kinin system in the rat hypothalamus. Immunohistochemical localization of high molecular weight kininogen and T kininogen in different neuronal systems

High molecular weight kininogen (HKg) and T kininogen (TKg) were detected and localized by immunocytochemistry in adult rat hypothalamus. In addition, kininogens were measured by their direct radioimmunoassay (RIA) or by indirect estimation of kinins released after trypsin hydrolysis and high pressure liquid chromatography (HPLC) separation of bradykinin (BK) and T kinin. A specific HKg immunoreactivity demonstrated with antibodies directed against the light chain (LC) of HKg was colocated with SRIF in neurons of hypothalamic periventricular area (PVA) projecting to external zone (ZE) of median eminence (ME). Heavy chain (HC) immunoreactivity which could be related to HKg or to low molecular weight kininogen (LKg) was detected in some other systems: i) parvocellular neurons of suprachiasmatic (SCN) and arcuate nuclei containing SRIF, ii) magnocellular neurons (mostly oxytocinergic) of paraventricular (PVN) and supraoptic (SON) nuclei, iii) neurons of dorsomedian and lateral hypothalamic areas. TKg immunostaining was restricted to magnocellular neurons of PVN, SON, accessory nuclei (mostly vasopressinergic) and to parvocellular neurons of SCN (vasopressinergic). TKg projections are directed towards the internal zone (ZI) of ME, but very few immunoreactive terminals are detectable in neurohypophysis. TKg staining parallels with vasopressin during water deprivation, and is undetectable in homozygous Brattleboro rats. In some magnocellular neurons, TKg and HC (related to HKg or LKg) are coexpressed. TKg, was also detected in hypothalamus and cerebellum extracts by direct RIA, and BK and T kinin were identified after trypsin hydrolysis. HKg and LKg can act as precursor of BK which can play a physiological role as releasing factor, neuromodulator--neurotransmitter,--or modulator of local microcirculation in hypothalamus. The three kininogens are also potent thiolprotease inhibitors which could modulate both the maturation processes of peptidic hormones and their inactivation and catabolism.

Enkephalin analogs as substrates for the assay of brain cysteine proteinase (Cathepsin L) and its endogenous inhibitors

A series of enkephalin-like peptides (X-Tyr-Gly-Gly-R-Pro) were synthesized for assay of cathepsin L and papain. Enzymes acted only at the Gly-Gly bond to release N-terminal dipeptides. When X = dansyl and R = Phe(NO2) the substrate was suited for continuous fluorimetric assay of rat brain cathepsin L (Km 45 microM, kcat/Km 1333 mM-1 sec-1). The substituted pentapeptides provided information on the influence of P2, P2' residues on rates of Gly-Gly cleavage. The synthetic substrate provided rapid and sensitive assays for the brain cathepsin L and its interaction with 13-14 kDa (cerebrocystatin) and 70 kDa (T-kininogen) rat brain inhibitors. The suppression of cathepsin L- or papain-mediated hydrolysis of substrates by inhibitors may be the result of competition between their binding domains at the enzyme catalytic center.

A rapid two-step purification of rat cystatin C, one major inhibitor of cysteine proteinases

Rat cystatin C was purified to apparent homogeneity from rat urine after induction of a tubular dysfunction with sodium chromate. Twentyfold concentrated urine was chromatographed by a rapid purification procedure. A two-step purification including affinity chromatography on carboxymethyl papain- Sepharose and high-resolution anion exchange chromatography was developed. The purified protein has an apparent molecular mass of 15 kDa and pI of 10.2; its aminoacid composition was similar to human cystatin C. As opposed to previous data, purified urinary rat cystatin C did not contain significant amounts of carbohydrate. Antisera against rat cystatin C, raised in rabbits, partially cross-reacted with human and mouse cystatin C, indicating their antigenic similarities. Like human cystatin C, native rat cystatin C, named slow form, is degraded into a more acidic form, called fast form, by a loss of N-terminal amino acids; fast form displayed a pI of 9.4.