Incorporation and degradation by kidney lysosomes of cystatin alpha injected intravenously

Isolation of lysosomes from tissues and cells by differential and density gradient centrifugation

This unit covers the use of Percoll, Nycodenz, and iodixanol for purification of lysosomes from a light mitochondrial pellet or postnuclear supernatant. The first protocol describes isolation of lysosomes from rat liver using a Percoll gradient; it includes some comments on using brain and kidney tissue as source material. Alternatively, this protocol can be modified to enhance the separation of lysosomes by organelle density perturbation. Another alternative uses a discontinuous gradient of Nycodenz to purify lysosomes from a rat liver light mitochondrial pellet. A continuous iodixanol gradient, which can be used to purify other organelles in the light mitochondrial fraction, is yet another alternative for purifying lysosomes. Lysosomes can also be isolated from some of the more commonly used cultured cells. The unit also includes assays for common lysosome marker enzymes.

Cathepsin L plays an important role in the lysosomal degradation of L-lactate dehydrogenase

A cystatin alpha-sensitive cysteine proteinase that plays an important role in the lysosomal inactivation and degradation of L-lactate dehydrogenase (LDH) was purified by column chromatography from an ammonium sulfate precipitate of lysosome extract prepared from rat livers. It was eluted with marked delay from cathepsins B and H in a Sephacryl S-200 column by its specific interaction with the gel, and then effectively separated from cathepsins B and H and other proteins. It was eluted with 0.5 M NaCl after washing with 0.2 M NaCl in a CM-Sephadex column, indicating that it showed the same elution behavior as cathepsin L from the CM-Sephadex column. It had activity to hydrolyze z-Phe-Arg-NH-Mec, a synthetic substrate for cysteine proteinases, including cathepsins B and L. The N-terminal sequences of the final preparation of LDH-inactivating enzyme were identical with those of rat cathepsin L. Inactivation and degradation of LDH by the final preparation were observed and effectively inhibited by a low level of cystatin alpha as well as a general cysteine proteinase inhibitor, leupeptin or (L-3-trans-carboxyoxirane-2-carbonyl)-L-leucine (3-methylbutyl)amide (E-64-c). From these results, it is concluded that cathepsin L plays a critical role in the lysosomal degradation of native LDH.

Native and acid-denatured L-lactate dehydrogenase are different in the lysosomal proteinases involving in their overall degradation

When native and (LDH) acid-denatured lactate dehydrogenase were incubated with total lysosomal enzymes in vitro, amino acids from their degradation were produced at various acidic pH. The pH profile in the overall degradation of native LDH was markedly different from that of acid-denatured LDH. Disappearance of the 35-kDa subunit of native LDH was markedly suppressed by a low level of cystatin alpha as well as by a general cysteine proteinase inhibitor, N-(L3-trans-carboxyoxirane-2-carbonyl)-L-leucine-3-methylbutylamid e (E-64-c). On the other hand, the degradation of acid-denatured LDH was only slightly suppressed by these inhibitors. It was concluded that at least a part of the proteinases involved in the overall degradation of native LDH is different from the proteinases involved in the degradation of acid-denatured form and a role of a cystatin alpha-sensitive cysteine proteinase is critical in the lysosomal degradation of native LDH, but not in that of acid-denatured form.

Immunocytochemical study of cathepsin L and rat salivary cystatin-3 in rat osteoclasts treated with E-64 in vivo

The localization of cathepsin L and rat salivary cystatin-3 (RSC-3) in rat osteoclasts (rat femoral and alveolar bones) treated with or without E-64 (control) was examined immunocytochemically. In osteoclasts pretreated with E-64, immunoreactivity for cathepsin L was very weak extracellularly compared to that in the control osteoclasts. However, it was strong intracellularly. The localization of RSC-3 was unclear in the control osteoclasts, while in E-64 treated osteoclasts, both the clear zone and ruffled border areas showed a very strong immunoreaction. At the electron-microscopic level, in normal osteoclasts, numerous immunoreaction products for cathepsin L were found extracellularly in the bone matrix under the ruffled border, while few intracellular products were observed. In contrast, in the E-64-treated osteoclasts, only a few immunoreaction products were found extracellularly, while intracellularly cathepsin L was found in numerous endosome-lysosomal vacuoles. In the immunoreaction for RSC-3, the cytoplasm of the ruffled border was positive, and the tips of the RSC-3-positive ruffled border appeared to enter deeply into the bone matrix. Intracellularly, the granular reaction products of RSC-3 were found in the vacuoles (probably autophagolysosomes). Thus, in E-64-treated osteoclasts, inhibition of the extracellular release of cathepsin L was demonstrated. In addition, intralysosomal accumulation of RSC-3 and deep penetration of the RSC-3-positive ruffled border into the bone matrix were found. These findings suggest that RSC-3 is associated with the inhibition of cathepsin L in both the lysosomes (in the osteoclasts) and bone matrix.

Clearance of chicken cystatin from the rat circulation

Chicken cystatin (mixed form) was prepared from egg white. Radioactively labeled preparations were administered intravenously to rats. 125I-cystatin disappeared from the rat circulation with a half-life of approximately 73 min. The radiolabeled inhibitor was rapidly taken up by the kidneys. Percoll density gradient analysis showed that it was incorporated into lysosomes. Within 24 hr after the injection of 125I-cystatin, 25% of the administered radioactivity was recovered in the urine, but only 2% was in the protein-bound form.

Translocation of orally administered rat salivary cystatin into serum and kidney

This translocation was followed by means of a sensitive enzyme immunoassay. Salivary cystatin could be detected in serum, oesophagus, stomach, small intestine and kidney 15 min after oral administration. The salivary cystatin level in serum and kidney extract was maximal 15-60 and 30-60 min, respectively, after its administration and increased dose-dependently. Chromatography showed that the cystatin molecule in serum was identical to that in the submandibular saliva used for oral administration, but differed from that in kidney extract. These results suggest that salivary cystatin is absorbed intact by the gastrointestinal tract and reaches the bloodstream, from which it is taken up by the kidney and modified.

Involvement of a cystatin-alpha-sensitive cysteine proteinase in the degradation of native L-lactate dehydrogenase and serum albumin by rat liver or kidney lysosomes

A lysosomal cysteine proteinase plays a critical role in the lysosomal degradation of native L-lactate dehydrogenase. The effects of a recombinant cystatin alpha and other cysteine proteinase inhibitors on the degradation of unlabeled native L-lactate dehydrogenase by total lysosomal enzymes were examined in vitro. L-Lactate dehydrogenase was inactivated, its 35-kDa subunit disappeared and the final amino acid degradation products were produced during an incubation with disrupted lysosomes in vitro. These processes were all markedly suppressed by a small amount of cystatin alpha without inhibiting the activities of the known lysosomal cysteine proteinases, cathepsins B, H, L, and J. These results suggest that a cysteine proteinases, which is highly sensitive to cystatin alpha and distinct from other known lysosomal cysteine proteinases, is involved in the lysosomal degradation of native L-lactate dehydrogenase. An L-lactate-dehydrogenase-inactivating enzyme in the extracts of lysosomes was partially purified. It was separated from cathepsin J using a Sephacryl S-200 gel-filtration column and was further separated from cathepsin H by DEAE-Sephadex A-50 anion-exchange column chromatography. The inactivation and degradation of L-lactate dehydrogenase by this partially purified enzyme were all markedly suppressed by a low level of cystatin alpha without inhibiting the activities of both cathepsins B and L. The degradation of rat serum albumin by the partially purified enzyme was also inhibited by the same concentration of cystatin alpha. It is concluded that a cystatin-alpha-sensitive cysteine proteinase, other than cathepsins B, H, L and J, is present in lysosomes and functions in the lysosomal degradation of at least native L-lactate dehydrogenase and serum albumin.

Participation of cathepsin L on bone resorption

The proteinase responsible for bone collagen degradation in osteo-resorption was examined. The bone pit formation induced by parathyroid hormone (PTH) was markedly suppressed by leupeptin, E-64 and cystatin A, while no inhibition was observed by CA-074, a specific inhibitor of cathepsin B. Pig leucocyte cysteine proteinase inhibitor (PLCPI), a specific inhibitor of cathepsin L, and chymostatin, a selective inhibitor of cathepsin L, completely inhibited the pit formation. Cathepsin L activity in osteoclasts was much higher than the other cathepsin activities. Serum calcium in rats placed on a low calcium diet was decreased by treatment of E-64 or cystatin A, but not by CA-074. These findings suggest that cathepsin L is the main proteinase responsible for bone collagen degradation.

Effects of selective inhibition of cathepsin B and general inhibition of cysteine proteinases on lysosomal proteolysis in rat liver in vivo and in vitro

Intraperitoneal administration of N-(L-trans-propylcarbamoyloxirane-2-carbonyl)-L-isoleucyl-L-prolin e (CA-074) to rats at a dose of 4 mg/100 g greatly inhibited cathepsin-B activity in both liver and kidney for at least 4 h. Its inhibitory effect was selective for cathepsin-B activity in the liver but not in the kidney. The effects of selective inhibition of cathepsin-B activity by CA-074 treatment, and general inhibition of cysteine proteinases by N-(L-3-trans-carboxyoxirane-2-carbonyl)-L-leucyl-3-methylbutylamid e (E-64-c) on the degradation of fluorescein isothiocyanate (FITC)-labeled asialofetuin in liver lysosomes, were examined in vivo. Undegraded or partially degraded FITC-labeled asialofetuin and its FITC-labeled degradation products were both found in the lysosomes and were easily separated by Sephadex G-25' column chromatography. The FITC-labeled degradation products were mainly lysine with an FITC-labeled epsilon-amino group. Accumulation of undegraded or partially degraded FITC-labeled asialofetuin in the lysosomes was marked after E-64-c treatment, but slight after CA-074 treatment. Under the marked inhibition of general lysosomal cysteine-proteinase activity by E-64-c or marked selective inhibition of cathepsin-B activity by CA-074 in vitro, degradation of FITC-labeled asialofetuin by disrupted lysosomes was analyzed on the basis of measurement of FITC-labeled degradation products by Sephadex G-25 column chromatography. It was suppressed markedly but incompletely by E-64-c as well as by CA-074, but more weakly than by E-64-c. These results shows that E-64-sensitive cysteine proteinases are important in lysosomal protein degradation, but cathepsin B has only a role in part and that an E-64-resistant proteinase(s) may also be important.