Age-dependent change in activities of lysosomal enzymes in rat brain

Cathepsin F is a potential marker for senescent human skin fibroblasts and keratinocytes associated with skin aging

Cellular senescence is characterized by cell cycle arrest and the senescence-associated secretory phenotype (SASP) and can be triggered by a variety of stimuli, including deoxyribonucleic acid (DNA) damage, oxidative stress, and telomere exhaustion. Cellular senescence is associated with skin aging, and identification of specific markers of senescent cells is essential for development of targeted therapies. Cathepsin F (CTSF) has been implicated in dermatitis and various cancers and participates in cell immortalization through its association with Bcl family proteins. It is a candidate therapeutic target to specifically label and eliminate human skin fibroblasts and keratinocytes immortalized by aging and achieve skin rejuvenation. In this study, we investigated whether CTSF is associated with senescence in human fibroblasts and keratinocytes. In senescence models, created using replicative aging, ionizing radiation exposure, and the anticancer drug doxorubicin, various senescence markers were observed, such as senescence-associated β-galactosidase (SA-β-gal) activity, increased SASP gene expression, and decreased uptake of the proliferation marker BrdU. Furthermore, CTSF expression was elevated at the gene and protein levels. In addition, CTSF-positive cells were abundant in aged human epidermis and in some parts of the dermis. In the population of senescent cells with arrested division, the number of CTSF-positive cells was significantly higher than that in the proliferating cell population. These results suggest that CTSF is a candidate for therapeutic modalities targeting aging fibroblasts and keratinocytes.

Characterization of Cysteine Cathepsin Expression in the Central Nervous System of Aged Wild-Type and Cathepsin-Deficient Mice

The association of cathepsin proteases in neurobiology is increasingly recognized. Our previous studies indicated that cathepsin-K-deficient (Ctsk−/−) mice have learning and memory impairments. Alterations in cathepsin expression are known to result in compensatory changes in levels of related cathepsins. To gain insight into the therapeutic usefulness of cathepsin inhibitors in aging individuals with osteoporosis or neurodegenerative diseases, we studied for variations in cathepsin expression and activity in aged (18–20 months) versus young (5–7 months) wild-type (WT) and cathepsin-deficient mice brains. There were age-dependent increases in cathepsin B, D, and L and cystatin C protein levels in various brain regions, mainly of WT and Ctsk−/− mice. This corresponded with changes in activity levels of cathepsins B and L, but not cathepsin D. In contrast, very little age-dependent variation was observed in cathepsin-B- and cathepsin-L-deficient mouse brain, especially at the protein level. The observed alterations in cathepsin protein amounts and activity are likely contributing to changes in important aging-related processes such as autophagy. In addition, the results provide insight into the potential impact of cathepsin inhibitor therapy in aged individuals, as well as in long-term use of cathepsin inhibitor therapy.

Myocardial cathepsin D is downregulated in sudden cardiac death

Cathepsins are the major lysosomal proteases that maintain intracellular homeostasis. Herein, we investigated the alterations in myocardial cathepsin expression during aging, cardiac hypertrophy, and sudden cardiac death (SCD). Cardiac tissue and blood were sampled from autopsy cases. Subjects were classified into three groups: SCD with cardiac hypertrophy (SCH), compensated cardiac hypertrophy (CCH), and control. Immunoblotting was performed for the major cardiac cathepsins and their targets: cathepsin B, D, and L (CTSB/D/L), p62, ATP synthase subunit c (ATPSC), and α-synuclein (ASNC). Immunohistochemical analysis and ELISA using serum samples were performed for CTSD. Cardiac CTSB and CTSD were upregulated with age (r = 0.63 and 0.60, respectively), whereas the levels of CTSL, p62, ATPSC, and ASNC remained unchanged. In age-matched groups, cardiac CTSD was significantly downregulated in SCH (p = 0.006) and CTSL was moderately downregulated in CCH (p = 0.021); however, p62, ATPSC, and ASNC were not upregulated in cardiac hypertrophy. Immunohistochemistry also revealed decreased myocardial CTSD levels in SCH, and serum CTSD levels were relatively lower in SCH cases. Overall, these results suggest that upregulation of cardiac CTSB and CTSD with age may compensate for the elevated proteolytic demand, and that downregulation of CTSD is potentially linked to SCH.

Influence of Normal Aging on Brain Autophagy: A Complex Scenario

Misfolded proteins are pathological findings in some chronic neurodegenerative disorders including Alzheimer's, Parkinson's, and Huntington's diseases. Aging is a major risk factor for these disorders, suggesting that the mechanisms responsible for clearing misfolded proteins from the brain, the ubiquitin-proteasome system and the autophagy-lysosomal pathway, may decline with age. Although autophagic mechanisms have been found to decrease with age in many experimental models, whether they do so in the brain is unclear. This review examines the literature with regard to age-associated changes in macroautophagy and chaperone-mediated autophagy (CMA) in the central nervous system (CNS). Beclin 1, LC3-II, and the LC3-II/LC3-I ratio have frequently been used to examine changes in macroautophagic activity, while lamp2a and HSPA8 (also known as hsc70) have been used to measure CMA activity. Three gene expression analyses found evidence for an age-related downregulation of macroautophagy in human brain, but no published studies were found of age-related changes in CMA in human brain, although cerebrospinal fluid concentrations of HSPA8 were reported to decrease with age. Most studies of age-related changes in brain autophagy in experimental animals have found age-related declines in macroautophagy, and macroautophagy is necessary for normal lifespan in Caenorhabditis elegans, Drosophila, and mice. However, the few studies of age-related changes in brain CMA in experimental animals have produced conflicting results. Investigations of the influence of aging on macroautophagy in experimental animals in systems other than the CNS have generally found an age-related decrease in Beclin 1, but conflicting results for LC3-II and the LC3-II/LC3-I ratio, while CMA decreases with age in most models. CONCLUSION: while indirect evidence suggests that brain autophagy may decrease with normal aging, this issue has not been investigated sufficiently, particularly in human brain. Measuring autophagic activity in the brain can be challenging because of differences in basal autophagic activity between experimental models, and the inability to include lysosomal inhibitors when measuring the LC3-II/LC3-I ratio in postmortem specimens. If autophagy does decrease in the brain with aging, then pharmacological interventions and/or lifestyle alterations to slow this decline could reduce the risk of developing age-related neurodegenerative disorders.

Lysosomal cathepsins and their regulation in aging and neurodegeneration

Lysosomes and lysosomal hydrolases, including the cathepsins, have been shown to change their properties with aging brain a long time ago, although their function was not really understood. The first biochemical and clinical studies were followed by a major expansion in the last 20 years with the development of animal disease models and new approaches leading to a major advancement of understanding of the role of physiological and degenerative processes in the brain at the molecular level. This includes the understanding of the major role of autophagy and the cathepsins in a number of diseases, including its critical role in the neuronal ceroid lipofuscinosis. Similarly, cathepsins and some other lysosomal proteases were shown to have important roles in processing and/or degradation of several important neuronal proteins, thereby having either neuroprotective or harmful roles. In this review, we discuss lysosomal cathepsins and their regulation with the focus on cysteine cathepsins and their endogenous inhibitors, as well as their role in several neurodegenerative diseases.

Lysosomes and lysosomal cathepsins in cell death

Lysosomes are the key degradative compartments of the cell. Lysosomal cathepsins, which are enclosed in the lysosomes, help to maintain the homeostasis of the cell's metabolism by participating in the degradation of heterophagic and autophagic material. Following the targeted lysosomal membrane's destabilization, the cathepsins can be released into the cytosol and initiate the lysosomal pathway of apoptosis through the cleavage of Bid and the degradation of the anti-apoptotic Bcl-2 homologues. Cathepsins can also amplify the apoptotic signaling, when the lysosomal membranes are destabilized at a later stage of apoptosis, initiated by other stimuli. However, the functional integrity of the lysosomal compartment during apoptosis enables efficient autophagy, which can counteract apoptosis by providing the energy source and by disposing the damaged mitochondria, which generate the ROS. Impairing autophagy by disabling the lysosome function is being investigated as an adjuvant therapeutic approach to sensitize cells to apoptosis-inducing agents. Destabilization of the lysosomal membranes by the lysosomotropic detergents seems to be a promising strategy in this context as it would not only disable autophagy, but also promote apoptosis through the initiation of the lysosomal pathway. In contrast, the impaired autophagy and lysosomal degradation linked with the increased oxidative stress underlie degenerative changes in the aging neurons. This further suggests that lysosomes and lysosomal cathepsins have a dual role in cell death. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Differential expression of cathepsin X in aging and pathological central nervous system of mice

Increasing evidence of a fundamental influence of cathepsins on inflammation has drawn interest in a thorough understanding of their role in physiological and pathological processes. Even though the number of identified cathepsins has more than doubled in the last years, information about their expression, regulation and function in the brain is still incomplete. In the present study we analyzed the regional, cellular and subcellular localization and the activity of the recently discovered cathepsin X in the normal, developing and pathological mouse brain. Our results show that CATX is: (i) is expressed in almost all cells in the mouse brain with a preference for glial cells; (ii) already widely expressed early in development and age-dependently upregulated in amount and activity; (iii) prominently localized in the lysosomal system but also scattered in the somal cytoplasm in the aged brain; (iv) upregulated in numerous glial cells of degenerating brain regions in a transgenic mouse model of amyotrophic lateral sclerosis; and (v) associated with plaques in a transgenic mouse model and in Alzheimer patients. These results strongly suggest that cathepsin X is an important player in degenerative processes during normal aging and in pathological conditions.

Identification and characterization of an increased glycoprotein in aging: Age-associated translocation of cathepsin D

We found that 14 N-glycosylated proteins were accumulated in the rat cerebral cortex cytosolic fraction in the aging process by a comparative study with two-dimensional gel electrophoresis and concanavalin A staining. All proteins had high mannose and/or hybrid-type N-glycans, as indicated by the fact that they were sensitive to endoglycosidase H digestion. Three of these cytosolic glycoproteins were identified as cathepsin D, a lysosomal protease, by tryptic digestion and nano liquid chromatography electrospray ionization quadrupole time of flight mass spectrometry. The increase of cytosolic cathepsin D during aging was not due to lysosomal membrane disruption, as shown by the fact that the activities of beta-hexosaminidase and beta-glucuronidase, other lysosomal enzymes, did not increase in the cytosolic fraction. Although the total amount of cathepsin D increased during aging, the amount of cathepsin D in the microsomal fraction did not change, indicating a selective increase of cytosolic cathepsin D. This phenomenon was also observed in the hippocampus, cerebellum, kidney, liver, and spleen. Based on these results, we propose that cytosolic cathepsin D is a new biomarker of aging.

Mechanisms of neural cell death: implications for development of neuroprotective treatment strategies

It has been increasingly recognized that cell death phenotypes and their molecular mechanisms are highly diverse. Necrosis is no longer considered a single entity, passively mediated by energy failure. Moreover, caspase-dependent apoptosis is not the only pathway involved in programmed cell death or even the only apoptotic mechanism. Recent experimental work emphasizes the diverse and interrelated nature of cell death mechanisms. Thus, there are both caspase-dependent and caspase-independent forms of apoptosis, which may differ morphologically as well as mechanistically. There are also necrotic-like phenotypes that require de novo protein synthesis and are, therefore, forms of programmed cell death. In addition, forms of cell death showing certain morphological features of both necrosis and apoptosis have been identified, leading to the term aponecrosis. Considerable experimental evidence also shows that modulation of one form of cell death may lead to another. Together, these observations underscore the need to substantially revise our conceptions about neuroprotection strategies. Use of multiple treatments that target different cell death cascades, or single agents that moderate multiple cell death pathways, is likely to lead to more effective neuroprotection for clinical disorders.

Dietary supplementation with melatonin reduces levels of amyloid beta-peptides in the murine cerebral cortex

Melatonin levels decrease with aging in mice. Dietary supplementation with melatonin has recently been shown to result in a significant rise in levels of endogenous melatonin in the serum and all other tissue samples tested. Herein, the effects of dietary melatonin on brain levels of nitric oxide synthase, synaptic proteins and amyloid beta-peptides (Abeta) were determined in mice. Melatonin supplementation did not significantly change cerebral cortical levels of nitric oxide synthase or synaptic proteins such as synaptophysin and SNAP-25. Increased brain melatonin concentrations however, led to a significant reduction in levels of toxic cortical Abeta of both short and long forms which are involved in amyloid depositions and plaque formation in Alzheimer's diseases. Thus, melatonin supplementation may retard neurodegenerative changes associated with brain aging. Depletion of melatonin in the brain of aging mice may in part account for this adverse change.

Age-related changes in murine CNS mRNA gene expression are modulated by dietary melatonin

Brain cellular functions decline with normal aging, accompanied by a changing profile of gene expression. Gene array analysis was used to quantitatively estimate messenger RNA (mRNA) expression levels in the cerebral cortex of both young (4-month) and old (27-month) B6C3F1 male mice. A stringent degree of significance was obtained by using multiple gene chips. Out of 12,423 mRNA levels, only 25 changed significantly with age. Nine of these genes coded for inflammatory proteins, all of which were elevated in aged, relative to younger mice. Melatonin (200 p.p.m.) included in the diet of aged animals for 8 wk elevated serum and cortical melatonin and reversed 13 of the 25 genes altered with age. In no case did melatonin potentiate age-related changes in gene expression. The restoration of a more youthful gene profile to brains of aged animals by melatonin, to a large extent, involves reversal of age-induced elevation of basal inflammatory parameters.

Lysosomes and brain aging in mammals

Hypotheses about the factors controlling the rate of brain aging are usually derived from 1) correlates of maximum life span across mammals or 2) investigations into the causes of age-related neuropathologies in humans. With regard to the former, the strong correlation between metabolic rate and longevity prompted a variety of free radical hypotheses of aging. There is also evidence that brain size affects life span independently of body metabolism rates. The second approach has led to a diverse array of pathogenic mechanisms and, importantly for the development of general hypotheses, the discovery of animal analogues. The present paper discusses the possibility that age-associated lysosomal dysfunction constitutes a generalized mammalian phenomenon that accounts for specific features of the aged human brain. Immunocytochemical studies using rats and dogs have identified lysosomal changes that begin early in adulthood and are most pronounced in brain areas known to be particularly vulnerable to age-related pathogenesis in humans. Experimentally induced lysosomal dysfunction in cultured brain slices from rats and mutant mice triggers a wide array of changes associated with the aged human brain, including meganeurites and intraneuronal tangles. Finally, there is evidence that at least some forms of proteolysis decrease with increasing brain size across the mammals. The above observations lead to the suggestion that the expansion of neuronal arborizations that occurred in conjunction with increases in brain size secondarily slowed both neuronal metabolism and protein turnover. These events could have served to reduce the rate at which lysosomes (and other organelles) fail.

Aberrant sphingomyelin/ceramide metabolic-induced neuronal endosomal/lysosomal dysfunction: potential pathological consequences in age-related neurodegeneration

Alterations in the trafficking and function of the endocytic pathway have been extensively documented to be one of the earliest pathological changes in sporadic Alzheimer's disease (AD). Although the pathophysiological consequences of these endosomal/lysosomal changes are currently unknown, several recent studies have suggested that such changes in endocytic function are able to cause a redistribution of several lysosomal hydrolases into early endosomes, leading to the overproduction of neurotoxic amyloid peptide. Recently, we and others have demonstrated that abnormal endocytic pathology within post-mitotic neurons can, in part, be attributed to alterations in sphingomyelin/ceramide metabolism, resulting in the intracellular accumulation of ceramide. Once inside the cell, the ability of ceramide to physically alter membrane structure, formation, and fusion, rather than serving solely as a lipid secondary messenger, may severely compromise normal endocytic trafficking. In this review, we will discuss the potential pathological effects of abnormal sphingomyelin/ceramide metabolism on intracellular vesicular transport in relation to both amyloid accumulation in AD and various neurodegenerative diseases associated with lysosomal abnormalities.

Neuronal endosomal/lysosomal membrane destabilization activates caspases and induces abnormal accumulation of the lipid secondary messenger ceramide

Impairment of endosomal/lysosomal functions are reported as some of the earliest changes in several age-related neurological disorders such as Alzheimer's disease. Dysregulation of the lysosomal system is also accompanied by the accumulation of age-associated pigments and several recent reports have indicated that this age-related lipofuscin accumulation can sensitize cells to oxidative stress and apoptotic cell death. In this study, we have established and evaluated an in vitro age-related pathology paradigm that models lipofuscin accumulation. Our model consists of the treatment of cultured primary mouse neurons with lysosomotropic detergents. We have observed that one of the earliest biochemical changes associated with lysosomotropic detergent-induced membrane instability is a loss of the endosomal/lysosomal proton gradient integrity, followed by an activation of sphingomyelin hydrolysis and ceramide accumulation within enlarged endosomal/lysosomal vesicles. In addition, we demonstrate that ceramide accumulation correlates with the activation of proximal procaspases-8 and -9 as well as distal caspase-3, prior to the appearance of cell death. Taken together, we propose that disturbances of the endosomal/lysosomal system, in addition to the activation of the sphingomyelinase hydrolysis cycle, play essential roles in the course of post-mitotic neuronal aging. The abnormal accumulation of undigested lipids and proteins within dysfunctional endosomal/lysosomal vesicle populations during the process of pathological aging may serve as triggers of the cell death programs that are associated with downstream neurodegeneration.

Structure-function relationships of acid ribonucleases: lysosomal, vacuolar, and periplasmic enzymes

It is surprising that only relatively recently has attention been directed to the characterization of the properties of acid ribonucleases (RNases), leading to some understanding of their biochemistry and their functional roles. The present review summarizes current progress in this field under the following general topics: (1) the wide distribution of acid RNases in organisms from viruses to animals; (2) recent findings concerning their primary and three-dimensional structure; (3) the structure-function relationship of acid RNases, with a fungal RNase from Rhizopus niveus as a model enzyme; (4) the unique localization of acid RNases in the periplasm of bacteria, vacuoles in plants, and lysosomes of animals and protozoa; and (5) the diversity of physiological roles, depending on the organism, such as self-incompatibility factors and defense proteins in some plants, the surface protein of an animal virus related to pathogenicity, and possible relationship to human cancer.

Porcine spleen deoxyribonuclease II. Covalent structure, cDNA sequence, molecular cloning, and gene expression

Porcine spleen DNase II, a lysosomal acid hydrolase, is a noncovalently linked alpha.beta heterodimer (Liao, T.-H. (1985) J. Biol. Chem. 260, 10708-10713). The alpha subunit, after disulfide cleavage, yields two chains, alpha1 and alpha2. The complete amino acid sequences of the alpha1, beta, and alpha2 chains were elucidated by protein sequencing, and the pairings of one interchain disulfide between alpha1 and alpha2 and of three intrachain disulfides in alpha2 were assigned. Six carbohydrate attachment sites, two in beta and four in alpha2, were detected by sugar analyses. The cDNA of DNase II was amplified using primers synthesized on the basis of the amino acid sequences determined. The amplified fragments shown to be a cDNA sequence of 1,292 bases. This cDNA sequence has an open reading frame encoding a 364-amino acid polypeptide containing a putative transmembrane peptide at the NH2-end, two small connecting peptides in the middle, and a peptide at the COOH terminus. These are evidently removed to form mature DNase II. Thus, all three chains in the sequence alpha1, beta, and alpha2 are coded by the same cDNA. When Chinese hamster ovary cells were transfected with a cloned plasmid with an inserted cDNA fragment encoding the entire reading frame, the expressed protein was released into the growth medium as an active form of DNase II.

A cellular stress model for the differential expression of glial lysosomal cathepsins in the aging nervous system

Activation of the endosomal-lysosomal system and altered expression of various lysosomal hydrolases have been implicated in several senescence-dependent neurodegenerative disorders and occurs, to a lesser extent, in the course of normal brain aging. The progressive accumulation of autofluorescent, peroxidase-positive astrocytic granules represents a highly consistent biomarker of aging in the vertebrate CNS. The sulfhydryl agent cysteamine greatly accelerates the accumulation of these glial inclusions in situ and in primary brain cell cultures. We previously determined that these glial inclusions are derived from abnormal mitochondria which undergo fusion with lysosomal elements in a complex autophagic process. In the present study, we demonstrate that cysteamine suppresses cathepsin B mRNA levels and immunoreactive protein in cultured astroglia, whereas cathepsin D mRNA and protein levels are significantly augmented by CSH exposure in these cells. Moreover, cathepsin D (but not cathepsin B) exhibits robust colocalization to the red autofluorescent inclusions. Concordant with our in vitro observations, cathepsin B immunoreactivity is prominent in the hypothalamic ventromedial nucleus which accumulates few autofluorescent glial inclusions during aging and is relatively inapparent in the heavily granulated hypothalamic arcuate nucleus. Conversely, cathepsin D is prominent in the aging arcuate nucleus where it colocalizes to the autofluorescent inclusions and exhibits scant immunoreactivity in the adjacent ventromedial nuclear complex. In senescent astroglia, oxidative stress may down-regulate the cathepsin B gene as part of a concerted cellular stress (heat shock) response. Glial cathepsin D, on the other hand, resists stress-related inhibition and may play an important role in disposing of oxidatively modified mitochondria in the aging and degenerating nervous system.

Expression of mRNAs of pancreatic and L type RNase inhibitors as a function of age in different tissues of SAMP8 and BDF1 mice

Turnover of mRNAs could be influenced not only by the synthesis of different mRNA species but also by the altered levels of mRNA-degrading enzymes such as RNases and their endogenous inhibitors. In the present work we evaluated possible age-related changes in the mRNA levels of pancreatic as well as L type RNase inhibitors in five different tissues of the BDF1, SAMR1 and SAMP8 using Northern blots. The mRNA levels varied depending on the tissues and mouse strains studied. In certain instances such as the RNase L inhibitor mRNA levels in the lung of SAMP8, there was a statistically significant (P < 0.05) increase of 40% if we compared the young (3 months old) and old (18 months old) animals. These changes could possibly contribute to a certain extent to the already lower levels of mRNAs due to decreased transcriptional activities in aged animals.

Cortical cathepsin D activity and immunolocalization in Alzheimer disease, critical coronary artery disease, and aging

The activity and immunocytochemical localization of cathepsin D in the frontal cortex were investigated in patients with Alzheimer disease (AD) and two groups of nondemented subjects; individuals with critical coronary artery disease (cCAD; > 75% stenosis) and non-heart disease controls (non-HD). The cathepsin D activity significantly increased with age in the non-HD population. No such age-related increase was observed in either AD or cCAD. Enzymatic activity was significantly increased in only the midaged, but not the older AD and cCAD subjects compared to controls. Immunocytochemical reactivity paralleled cathepsin D enzymatic activity. Frontal cortex neurons displayed an increased accumulation of cathepsin D immunoreactivity in aging (non-HD controls) with a further increase in cCAD, especially in the midaged group. Such immunoreactivity was markedly increased in AD. There was also an apparent age-related increase in the number of cathepsin D immunoreactive neurons in the non-HD population and a disease-related increase in only the mid-aged AD and cCAD subjects compared to controls. Senile plaques (SP) occurred in all AD patients, many cCAD, and a few of the oldest non-HD subjects, and they were immunoreactive to cathepsin D in each group. The data suggest a possible relationship between activation of cathepsin D and SP formation in AD, cCAD, and aging.

Calpain activity in adult and aged human brain regions

We assayed calpain activity in 27 human brain regions from adult (43-65 years of age) and aged (66-83 years of age) postmortem tissue samples. Calpain I (microM Ca-requiring) activity was 10% or less of the total activity; it was below detectable levels in a number of areas, and so data are are expressed as total (microM + mM Ca-dependent) calpain activity. The distribution of the enzyme was regionally heterogeneous. Highest activity was found in the spinal cord, followed by the amygdala, and levels in mesencephalic areas and in cerebellar grey matter were also high. Levels in cerebellar white matter, tegmentum, pons, and putamen were low, and activity in cortical areas was also relatively low. Although in some areas activity seemed higher with aging, the differences were not statistically significant. We previously found that the regional distribution of cathepsin D in human and in rat brain is similar, this seems to be true for calpain activity as well. The increase of protease activity with age found in rat brain is not found in human areas, as was shown previously with cathepsin D, and in the present study with calpain.

The distribution of cathepsin D activity in adult and aging human brain regions

We measured the activity of cathepsin D, the major cerebral protease, in 50 separate areas of the central nervous system of adult and aged humans, using hemoglobin as the substrate. The activity showed significant regional heterogeneity, with average differences of 50-100% between the lower and higher level areas, and a more than threefold difference between the lowest and highest levels. The forebrain, midbrain, and hindbrain each had areas of high and low activity; cerebellum and cord areas were among those with low activity. Cathepsin levels tended to increase with age in about half of the areas analyzed, and the increases were significant in 14. Statistically significant decreases with aging were observed in two areas. The increases varied between 30 and 60%, and the decreases were 20%. Enzyme activity in thalamus, hypothalamus, pons, medulla, and cerebellum increased with age. In the ventrolateral medulla, which contains the major portion of the cerebral noradrenergic cells, the cathepsin D levels increased with age; in the dorsal raphe area, which contains the major portion of the cerebral serotonergic cells, the enzyme levels decreased. The change with age in human brain seems to be less than what we observed in rat brain, where activity more than doubled in most areas. The changes in enzyme levels need to be tested at more ages to establish a pattern of changes in activity throughout life.

Abnormal distribution of cathepsins in the brain of patients with Alzheimer's disease

Formalin-fixed paraffin-embedded hippocampal sections of brains with early-onset and late-onset Alzheimer's disease were studied immunohistochemically with antisera against cathepsin D and cathepsin B. In addition to the staining of neuronal perikarya, some of the senile plaques visualized by Bielshowsky silver staining and some of reactive astrocytes were positively stained with the antisera against cathepsin D and cathepsin B in brains with Alzheimer's disease. Abnormal localization of cathepsin D and cathepsin B immunoreactivity in neuronal perikarya was observed in brains with early-onset Alzheimer's disease. These findings demonstrate that the distribution of lysosomal proteases was altered in brains with Alzheimer's disease, suggesting the primary and/or secondary involvement of the lysosomal proteases in the pathological process of Alzheimer's disease.