Background Previously, we found that mast cell tryptases and carboxypeptidase A3 (CPA3) are differentially expressed in the airway epithelium in asthmatic subjects. We also found that asthmatic subjects can be divided into 2 subgroups (“TH2 high” and “TH2 low” asthma) based on epithelial cell gene signatures for the activity of TH2 cytokines. Objectives We sought to characterize intraepithelial mast cells (IEMCs) in asthma. Methods We performed gene expression profiling in epithelial brushings and stereology-based quantification of mast cell numbers in endobronchial biopsy specimens from healthy control and asthmatic subjects before and after treatment with inhaled corticosteroids (ICSs). We also performed gene expression and protein quantification studies in cultured airway epithelial cells and mast cells. Results By means of unsupervised clustering, mast cell gene expression in the airway epithelium related closely to the expression of IL-13 signature genes. The levels of expression of mast cell genes correlate positively with lung function improvements with ICSs. IEMC density was 2-fold higher than normal in subjects with TH2-high asthma compared with that seen in subjects with TH2-low asthma or healthy control subjects (P = .015 for both comparisons), and these cells were characterized by expression of tryptases and CPA3 but not chymase. IL-13 induced expression of stem cell factor in cultured airway epithelial cells, and mast cells exposed to conditioned media from IL-13–activated epithelial cells showed downregulation of chymase but no change in tryptase or CPA3 expression. Conclusion IEMC numbers are increased in subjects with TH2-high asthma, have an unusual protease phenotype (tryptase and CPA3 high and chymase low), and predict responsiveness to ICSs. IL-13–stimulated production of stem cell factor by epithelial cells potentially explains mast cell accumulation in TH2-high asthmatic epithelium.

Human mast cell tryptases vary strikingly in secretion, catalytic competence, and inheritance. To explore the basis of variation, we compared genes from a range of primates, including humans, great apes (chimpanzee, gorilla, orangutan), Old- and New-World monkeys (macaque and marmoset), and a prosimian (galago), tracking key changes. Our analysis reveals that extant soluble tryptase-like proteins, including α- and β-like tryptases, mastins, and implantation serine proteases, likely evolved from membrane-anchored ancestors because their more deeply rooted relatives (γ tryptases, pancreasins, prostasins) are type I transmembrane peptidases. Function-altering mutations appeared at widely separated times during primate speciation, with tryptases evolving by duplication, gene conversion, and point mutation. The α-tryptase Gly216Asp catalytic domain mutation, which diminishes activity, is present in macaque tryptases, and thus arose before great apes and Old World monkeys shared an ancestor, and before the αβ split. However, the Arg−3Gln processing mutation appeared recently, affecting only human α. By comparison, the transmembrane γ-tryptase gene, which anchors the telomeric end of the multigene tryptase locus, changed little during primate evolution. Related transmembrane peptidase genes were found in reptiles, amphibians, and fish. We identified soluble tryptase-like genes in the full spectrum of mammals, including marsupial (opossum) and monotreme (platypus), but not in nonmammalian vertebrates. Overall, our analysis suggests that soluble tryptases evolved rapidly from membrane-anchored, two-chain peptidases in ancestral vertebrates into soluble, single-chain, self-compartmentalizing, inhibitor-resistant oligomers expressed primarily by mast cells, and that much of present numerical, behavioral, and genetic diversity of α- and β-like tryptases was acquired during primate evolution.

Mice homozygous for the STAT4-null mutation were sensitized to cockroach Ag, challenged intratracheally 21 days later, and compared with STAT4-competent allergic mice. The STAT4−/− mice showed significant decreases in airway hyperreactivity (AHR) and peribronchial eosinophils compared with wild-type controls. In addition, pulmonary levels of chemokines were decreased in the STAT4−/− mice, including CC chemokine ligand (CCL)5, CCL6, CCL11, and CCL17. However, levels of Th2-type cytokines, such as IL-4 and IL-13, as well as serum IgE levels were similar in the two groups. Transfer of splenic lymphocytes from sensitized wild-type mice into sensitized STAT4−/− mice did not restore AHR in the mutant mice. Furthermore, chemokine production and peribronchial eosinophilia were not restored during the cellular transfer experiments. Thus, it appears that STAT4 expression contributes to a type 2 process such as allergen-induced chemokine production and AHR. In additional studies, competent allergic mice were treated with anti-IL-12 locally in the airways at the time of allergen rechallenge. These latter studies also demonstrated a decrease in AHR. Altogether, these data suggest that STAT4-mediated pathways play a role locally within the airway for the exacerbation of the allergen-induced responses.

Background: Vertebrate marapsins can be either type I transmembrane proteases or unanchored. Results: Point mutations liberated marapsins from transmembrane peptides independently in human-related primates and other mammalian clades. Soluble marapsins are active and inhibitor-resistant. Conclusion: Mutational tail loss transformed transmembrane marapsins and related proteins into soluble proteases. Significance: These findings suggest a general evolutionary mechanism for evolving proteases with new properties and functions.

Salt forms of pharmaceutical compounds can have unique pharmacokinetic and toxicity properties. MDV1634 was evaluated for neurology indication and also demonstrated blood pressure (BP)-lowering effects in nonclinical studies. During the chemistry manufacturing campaign, 2 salt forms, dihydrochloride (2HCl) and maleate (MAL), which improved chemical stability and water solubility of the free base were identified. MDV1634.MAL showed better chemical attributes and was evaluated in toxicology studies for further development. A 28-day oral toxicity study in dogs with MDV1634.MAL demonstrated partially reversible renal toxicity. Although MAL salt is generally regarded as safe, renal toxicity is sometimes observed in rats and dogs. To evaluate contribution of each salt form to renal toxicity and BP lowering, an additional 28-day study was conducted with MDV1634.2HCL and MDV1634.MAL, which included toxicokinetics, continuous BP measurement in a subset of dogs, and sensitive urinary biomarker evaluation for temporal monitorability and reversibility of potential renal findings. In the repeat study, both salt forms showed similar exposures during the dosing period, but renal tubular toxicity was observed only with MDV1634.MAL and not with MDV1634.2HCl. The renal findings with MDV1634.MAL included early urinary biomarker changes (increase in albumin, clusterin, β2 microglobulin, and neutrophil gelatinase-associated lipocalin); elevations in serum blood urea nitrogen and creatinine; and microscopic findings of partially reversible tubular basophilia, single cell necrosis, pigmentation, and mineralization. The renal findings in contrast to the BP findings were MAL-specific and considered not related to MDV1634, thereby under scoring the importance of salt forms in pharmaceutical development.

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