Passive immunotherapy of tauopathy targeting pSer413-tau: a pilot study in mice

Objective

Cellular inclusions of hyperphosphorylated tau are a hallmark of tauopathies, which are neurodegenerative disorders that include Alzheimer's disease (AD). Active and passive immunization against hyperphosphorylated tau has been shown to attenuate phenotypes in model mice. We developed new monoclonal antibodies to hyperphosphorylated tau and sought high therapeutic efficacy for future clinical use.

Methods

Using more than 20 antibodies, we investigated which sites on tau are phosphorylated early and highly in the tauopathy mouse models tau609 and tau784. These mice display tau hyperphosphorylation, synapse loss, memory impairment at 6 months, and tangle formation and neuronal loss at 15 months. We generated mouse monoclonal antibodies to selected epitopes and examined their effects on memory and tau pathology in aged tau609 and tau784 mice by the Morris water maze and by histological and biochemical analyses.

Results

Immunohistochemical screening revealed that pSer413 is expressed early and highly. Monoclonal antibodies to pSer413 and to pSer396 (control) were generated. These antibodies specifically recognized pathological tau in AD brains but not normal tau in control brains according to Western blots. Representative anti-pSer413 and anti-pSer396 antibodies were injected intraperitoneally into 10–11- or 14-month-old mice once a week at 0.1 or 1 mg/shot 5 times. The anti-pSer413 antibody significantly improved memory, whereas the anti-pSer396 antibodies showed less effect. The cognitive improvement paralleled a reduction in the levels of tau hyperphosphorylation, tau oligomer accumulation, synapse loss, tangle formation, and neuronal loss.

Interpretation

These results indicate that pSer413 is a promising target in the treatment of tauopathy.

The inflammatory response after an epidermal burn depends on the activities of mouse mast cell proteases 4 and 5

A second-degree epidermal scald burn in mice elicits an inflammatory response mediated by natural IgM directed to nonmuscle myosin with complement activation that results in ulceration and scarring. We find that such burn injury is associated with early mast cell (MC) degranulation and is absent in WBB6F1-Kit(W)/Kit(Wv) mice, which lack MCs in a context of other defects due to a mutation of the Kit receptor. To address further an MC role, we used transgenic strains with normal lineage development and a deficiency in a specific secretory granule component. Mouse strains lacking the MC-restricted chymase, mouse MC protease (mMCP)-4, or elastase, mMCP-5, show decreased injury after a second-degree scald burn, whereas mice lacking the MC-restricted tryptases, mMCP-6 and mMCP-7, or MC-specific carboxypeptidase A3 activity are not protected. Histologic sections showed some disruption of the epidermis at the scald site in the protected strains suggesting the possibility of topical reconstitution of full injury. Topical application of recombinant mMCP-5 or human neutrophil elastase to the scalded area increases epidermal injury with subsequent ulceration and scarring, both clinically and morphologically, in mMCP-5-deficient mice. Restoration of injury requires that topical administration of recombinant mMCP-5 occurs within the first hour postburn. Importantly, topical application of human MC chymase restores burn injury to scalded mMCP-4-deficient mice but not to mMCP-5-deficient mice revealing nonredundant actions for these two MC proteases in a model of innate inflammatory injury with remodeling.

Species Differences in Angiotensin II Generation and Degradation by Mast Cell Chymases

Although chymases are known to exhibit species differences in regard to angiotensin (Ang) II generation and degradation, their properties have never been compared under the same experimental conditions. We analyzed the processing of Ang I by chymases of a variety of species (human chymase, dog chymase, hamster chymase-1, rat mast cell protease-1 [rMCP-1], mouse mast cell protease-4 [mMCP-4]) at physiological ionic strength and under neutral pH conditions. Human chymase generated Ang II from Ang I without further degradation, whereas the chymases of other species generated Ang II, followed by degradation at the Tyr4-Ile5 site in a time-dependent manner. Kinetic analysis showed that in terms of Ang II generating activity (analyzed by cleavage of the Phe8-His9 bond using the model peptide Ang(5-10), Ile5-His6-Pro7-Phe8-His9-Leu10), the chymases ranked as follows: dog > human > hamster > mouse > rat (kcat/Km: 18, 11, 0.69, 0.059, 0.030 microM-1min-1), and that in terms of Ang II degrading activity (i.e., cleavage of the Tyr4-Ile5 bond of Ang II), the order was hamster > rat > mouse > dog (kcat/Km: 5.4, 4.8, 0.39, 0.29 microM-lmin-1). These results suggest species differences in the contribution of chymases to local Ang II generation and degradation.

Selective suppression of Th2-mediated airway eosinophil infiltration by low-molecular weight CCR3 antagonists

The effects of selective CC chemokine receptor (CCR)-3 antagonists on antigen-induced leukocyte accumulation in the lungs of mice adoptively transferred with in vitro-differentiated T(h)1 and T(h)2 were investigated. Inhalation of antigen by mice injected with T(h)1 and T(h)2 initiated the migration of T cells themselves into the lungs. Subsequently, neutrophils massively accumulated in T(h)1-transferred mice, whereas eosinophil infiltration was specifically induced by T(h)2. CCR3 antagonists, SB-297006 and/or SB-328437, suppressed antigen-induced accumulation of T(h)2 as well as eosinophils in the lungs, whereas they failed to affect T(h)1-mediated airway inflammation. Not only T(h)2 and eosinophil infiltration but also cellular mobilization in T(h)1-transferred mice was attenuated by an anti-CC chemokine ligand-11 antibody. CCR3 antagonists reduced chemokine production in the lungs of mice transferred with T(h)2 but not T(h)1, suggesting that down-regulation of chemokine synthesis is involved in the selective inhibition of T(h)2-mediated eosinophil infiltration by CCR3 antagonists.

Functional Chemokine Receptors in Allergic Diseases: Is CCR8 a Novel Therapeutic Target?

CC chemokine receptor (CCR) 8, which is expressed on Th2 cells and eosinophils, has been implicated in allergic diseases. This review represents an overview of the functional roles of CCR8 in the pathogenesis of eosinophilic inflammation and debates the potential of recently developed CCR8 antagonists to treat allergic disorders.

Generation and characterization of new monoclonal antibodies against human chymase

We have succeeded in producing monoclonal antibodies directed against a wide variety of epitopes of human chymase by using two different immunogens: a recombinant human chymase-heparin mixture, and chymase alone. Hybridomas were screened by ELISA, and 7 clones were selected based on antibody titers. Epitopes were localized by Western blotting with a C-terminal-deletion series of chymase-GST fusion proteins, and it was possible to use the antibodies for Western blotting and immunohistochemistry. Dot-blot analysis for species specificity revealed that the MAbs bound canine chymase as well as human chymase, and that two of them also bound rodent chymases. These results indicate that the antibodies can be used for various immunological analyses in further investigations of chymase.

Liver-expressed chemokine/CC chemokine ligand 16 attracts eosinophils by interacting with histamine H4 receptor

Liver-expressed chemokine (LEC)/CCL16 is a human CC chemokine that is constitutively expressed by the liver parenchymal cells and present in the normal plasma at high concentrations. Previous studies have shown that CCL16 is a low-affinity ligand for CCR1, CCR2, CCR5, and CCR8 and attracts monocytes and T cells. Recently, a novel histamine receptor termed type 4 (H4) has been identified and shown to be selectively expressed by eosinophils and mast cells. In this study, we demonstrated that CCL16 induced pertussis toxin-sensitive calcium mobilization and chemotaxis in murine L1.2 cells expressing H4 but not those expressing histamine receptor type 1 (H1) or type 2 (H2). CCL16 bound to H4 with a K(d) of 17 nM. By RT-PCR, human and mouse eosinophils express H4 but not H3. Accordingly, CCL16 induced efficient migratory responses in human and mouse eosinophils. Furthermore, the responses of human and mouse eosinophils to CCL16 were effectively suppressed by thioperamide, an antagonist for H3 and H4. Intravenous injection of CCL16 into mice induced a rapid mobilization of eosinophils from bone marrow to peripheral blood, which was also suppressed by thioperamide. Collectively, CCL16 is a novel functional ligand for H4 and may have a role in trafficking of eosinophils.

Rodent alpha-chymases are elastase-like proteases

Although the alpha-chymases of primates and dogs are known as chymotrypsin-like proteases, the enzymatic properties of rodent alpha-chymases (rat mast cell protease 5/rMCP-5 and mouse mast cell protease 5/mMCP-5) have not been fully understood. We report that recombinant rMCP-5 and mMCP-5 are elastase-like proteases, not chymotrypsin-like proteases. An enzyme assay using chromogenic peptidyl substrates showed that mast cell protease-5s (MCP-5s) have a clear preference for small aliphatic amino acids (e.g. alanine, isoleucine, valine) in the P1 site of substrates. We used site-directed mutagenesis and computer modeling approaches to define the determinant residue for the substrate specificity of mMCP-5, and found that the mutant possessing a Gly substitution of the Val at position 216 (V216G) lost elastase-like activity but acquired chymase activity, suggesting that the Val216 dominantly restricts the substrate specificity of mMCP-5. Structural models of mMCP-5 and the V216G mutant based on the crystal structures of serine proteases (rMCP-2, human cathepsin G, and human chymase) revealed the active site differences that can account for the marked differences in substrate specificity of the two enzymes between elastase and chymase. These findings suggest that rodent alpha-chymases have unique biological activity different from the chymases of other species.

Chymase is a potent chemoattractant for human monocytes and neutrophils

Chymase is a major chymotrypsin-like serine protease expressed in the secretory granules of mast cells in many mammalian species. In this study, we revealed the chemotactic activity of chymase for human mononuclear cells and neutrophils with a 48-well microchemotaxis chamber technique. Human chymase showed the potent chemotactic activity for monocytes and neutrophils dose-dependently in a concentration range from 0.1 to 10 microg/mL, corresponding to about 4-400 microM. The activity was as potent as that of N-formyl-methionyl-leucyl-phenylalanine. Chymase also stimulated cell migration of lymphocytes and purified T cells, but checkerboard analysis revealed that the effect was chemokinetic rather than chemotactic. Inhibition of chymase activities with chymase inhibitors, such as antileukoprotease and Bowman-Birk soybean trypsin inhibitor, significantly inhibited the chemotactic activity of chymase, suggesting that the proteolytic activity of chymase participates in the chemotactic activity. Our results suggest that mast cell chymase acts as a chemoattractant, and may play a role in the accumulation of inflammatory cells in development of the chronic inflammatory responses of allergic and nonallergic diseases.

Point mutations at glycine-121 of Escherichia coli dihydrofolate reductase: important roles of a flexible loop in the stability and function

To elucidate the role of a flexible loop in the stability and function of Escherichia coli dihydrofolate reductase, glycine-121 in a flexible loop (residues 117-131), separated by 19 A from active site Asp27, was substituted by site-directed mutagenesis with eight amino acids (Ala, Val, Leu, Asp, Ser, Cys, Tyr, and His). The free energy change of unfolding decreased in the order of G121A > G121D > G121C > G121S, wild-type > G121H > G121Y > G121L > G121V. The thermal denaturation temperature decreased with all mutations, accompanied by a decrease in the calorimetric enthalpy of denaturation. The steady-state kinetic parameter for the enzyme reaction, Km, was only slightly influenced, but kcat was significantly decreased by the mutations, there being 3- (G121C) to 42-fold (G121L) decreases in kcat/Km compared to that of the wild-type enzyme. The effects of mutations on the stability and enzyme activity were statistically examined as a function of the hydrophobicity and volume of amino acids introduced. The diminished stability and activity with increases in the hydrophobicity and volume of amino acids suggest that the main effect of the mutations would be modification of the flexibility of the loop due to overcrowding of the bulky side chains, overcoming the enhancement of the hydrophobic interaction.

Effects of point mutation in a flexible loop on the stability and enzymatic function of Escherichia coli dihydrofolate reductase

To elucidate the role of a flexible loop in the stability and function of Escherichia coli dihydrofolate reductase, glycine-121 in the flexible loop (117-131) was substituted to valine and leucine by site-directed mutagenesis. Despite the increased hydrophobicity of the side chains, the free energy changes of unfolding of the two mutants (G121V and G121L) determined by urea denaturation at 15 degrees C were decreased by 1.22 and 0.38 kcal/mol, respectively, compared with that of the wild-type. Thermal denaturation temperature, as monitored by differential scanning calorimetry, was decreased by 2.4 and 5.2 degrees C for G121V and G121L, respectively, accompanying the decrease in enthalpy change of denaturation. These findings indicate that the structure of DHFR is destabilized by the mutations, predominantly due to the large decrease in enthalpy change of denaturation relative to entropy change of denaturation. The steady-state kinetic parameter in the enzyme reaction, Km, was not influenced but kcat was greatly decreased by these mutations, resulting in 240- and 52-fold decreases in kcat/Km for G121V and G121L, respectively. The main effect of the mutations appeared to be modification of the flexibility of the loop due to overcrowding of the bulky side chains, overcoming the enhancement of hydrophobic interaction.