Jiusong Sun

Genetic deficiency and pharmacological stabilization of mast cells reduce diet-induced obesity and diabetes in mice

Although mast cell functions have classically been related to allergic responses, recent studies indicate that these cells contribute to other common diseases such as multiple sclerosis, rheumatoid arthritis, atherosclerosis, aortic aneurysm and cancer. This study presents evidence that mast cells also contribute to diet-induced obesity and diabetes. For example, white adipose tissue (WAT) from obese humans and mice contain more mast cells than WAT from their lean counterparts. Furthermore, in the context of mice on a Western diet, genetically induced deficiency of mast cells, or their pharmacological stabilization, reduces body weight gain and levels of inflammatory cytokines, chemokines and proteases in serum and WAT, in concert with improved glucose homeostasis and energy expenditure. Mechanistic studies reveal that mast cells contribute to WAT and muscle angiogenesis and associated cell apoptosis and cathepsin activity. Adoptive transfer experiments of cytokine-deficient mast cells show that these cells, by producing interleukin-6 (IL-6) and interferon-γ (IFN-γ), contribute to mouse adipose tissue cysteine protease cathepsin expression, apoptosis and angiogenesis, thereby promoting diet-induced obesity and glucose intolerance. Our results showing reduced obesity and diabetes in mice treated with clinically available mast cell-stabilizing agents suggest the potential of developing new therapies for these common human metabolic disorders.

Mast cells promote atherosclerosis by releasing proinflammatory cytokines.

Mast cells contribute importantly to allergic and innate immune responses by releasing various preformed and newly synthesized mediators. Previous studies have shown mast cell accumulation in human atherosclerotic lesions. This report establishes the direct participation of mast cells in atherogenesis in low-density lipoprotein receptor–deficient (Ldlr−/−) mice. Atheromata from compound mutant Ldlr−/− KitW-sh/W-sh mice showed decreased lesion size, lipid deposition, T-cell and macrophage numbers, cell proliferation and apoptosis, but increased collagen content and fibrous cap development. In vivo, adoptive transfer of syngeneic wild-type or tumor necrosis factor (TNF)-α-deficient mast cells restored atherogenesis to Ldlr−/−KitW-sh/W-sh mice. Notably, neither interleukin (IL)-6- nor interferon (IFN)-γ-deficient mast cells did so, indicating that the inhibition of atherogenesis in Ldlr−/−KitW-sh/W-sh mice resulted from the absence of mast cells and mast cell–derived IL-6 and IFN-γ. Compared with wild-type or TNF-α-deficient mast cells, those lacking IL-6 or IFN-γ did not induce expression of proatherogenic cysteine proteinase cathepsins from vascular cells in vitro or affect cathepsin and matrix metalloproteinase activities in atherosclerotic lesions, implying that mast cell–derived IL-6 and IFN-γ promote atherogenesis by augmenting the expression of matrix-degrading proteases. These observations establish direct participation of mast cells and mast cell–derived IL-6 and IFN-γ in mouse atherogenesis and provide new mechanistic insight into the pathogenesis of this common disease.

Lysosomal Cysteine Proteases in Atherosclerosis

Atherosclerosis is an inflammatory disease characterized by extensive remodeling of the extracellular matrix architecture of the arterial wall. Although matrix metalloproteinases and serine proteases participate in these pathologic events, recent data from atherosclerotic patients and animals suggest the participation of lysosomal cysteine proteases in atherogenesis. Atherosclerotic lesions in humans overexpress the elastolytic and collagenolytic cathepsins S, K, and L but show relatively reduced expression of cystatin C, their endogenous inhibitor, suggesting a shift in the balance between cysteine proteases and their inhibitor that favors remodeling of the vascular wall. Extracts of human atheromatous tissue show greater elastolytic activity in vitro than do those from healthy donors. The cysteinyl protease inhibitor E64d limits this increased elastolysis, indicating involvement of cysteine proteases in elastin degradation during atherogenesis. Furthermore, inflammatory cytokines augment expression and secretion of active cysteine proteases from cultured monocyte-derived macrophages, vascular smooth muscle cells, and endothelial cells and increase degradation of extracellular elastin and collagen. Cathepsin S–deficient cells or those treated with E64d show significantly impaired elastolytic or collagenolytic activity. Additionally, recent in vivo studies of atherosclerosis-prone, LDL receptor–null mice lacking cathepsin S show participation of this enzyme in the initial infiltration of leukocytes, medial elastic lamina degradation, endothelial cell invasion, and neovascularization, illustrating an important role for cysteine proteases in arterial remodeling and atherogenesis.

Cathepsin S Controls Angiogenesis and Tumor Growth via Matrix-derived Angiogenic Factors

The cysteine protease cathepsin S is highly expressed in malignant tissues. By using a mouse model of multistage murine pancreatic islet cell carcinogenesis in which cysteine cathepsin activity has been functionally implicated, we demonstrated that selective cathepsin S deficiency impaired angiogenesis and tumor cell proliferation, thereby impairing angiogenic islet formation and the growth of solid tumors, whereas the absence of its endogenous inhibitor cystatin C resulted in opposite phenotypes. Although mitogenic vascular endothelial growth factor, transforming growth factor-β1, and the anti-angiogenic endostatin levels in either serum or carcinoma tissue extracts did not change in cathepsin S- or cystatin C-null mice, tumor tissue basic fibroblast growth factor and serum type 1 insulin growth factor levels were higher in cystatin C-null mice, and serum type 1 insulin growth factor levels were also increased in cathepsin S-null mice. Furthermore, cathepsin S affected the production of type IV collagen-derived anti-angiogenic peptides and the generation of bioactive pro-angiogenic γ2 fragments from laminin-5, revealing a functional role for cathepsin S in angiogenesis and neoplastic progression.

Mast cells modulate the pathogenesis of elastase-induced abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA), an inflammatory disease, involves leukocyte recruitment, immune responses, inflammatory cytokine production, vascular remodeling, neovascularization, and vascular cell apoptosis, all of which contribute to aortic dilatation. This study demonstrates that mast cells, key participants in human allergic immunity, participate in AAA pathogenesis in mice. Mast cells were found to accumulate in murine AAA lesions. Mast cell-deficient KitW-sh/KitW-sh mice failed to develop AAA elicited by elastase perfusion or periaortic chemical injury. KitW-sh/KitW-sh mice had reduced aortic expansion and internal elastic lamina degradation; decreased numbers of macrophages, CD3+ T lymphocytes, SMCs, apoptotic cells, and CD31+ microvessels; and decreased levels of aortic tissue IL-6 and IFN-gamma. Activation of mast cells in WT mice via C48/80 injection resulted in enhanced AAA growth while mast cell stabilization with disodium cromoglycate diminished AAA formation. Mechanistic studies demonstrated that mast cells participated in angiogenesis, aortic SMC apoptosis, and matrix-degrading protease expression. Reconstitution of KitW-sh/KitW-sh mice with bone marrow-derived mast cells from WT or TNF-alpha-/- mice, but not from IL-6-/- or IFN-gamma-/- mice, caused susceptibility to AAA formation to be regained. These results demonstrate that mast cells participate in AAA pathogenesis in mice by releasing proinflammatory cytokines IL-6 and IFN-gamma, which may induce aortic SMC apoptosis, matrix-degrading protease expression, and vascular wall remodeling, important hallmarks of arterial aneurysms.

Cathepsin L activity controls adipogenesis and glucose tolerance.

Cysteine proteases play an important part in human pathobiology. This report shows the participation of cathepsin L (CatL) in adipogenesis and glucose intolerance. In vitro studies demonstrate the role of CatL in the degradation of the matrix protein fibronectin, insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF-1R), essential molecules for adipogenesis and glucose metabolism. CatL inhibition leads to the reduction of human and murine pre-adipocyte adipogenesis or lipid accumulation, protection of fibronectin from degradation, accumulation of IR and IGF-1R β-subunits, and an increase in glucose uptake. CatL-deficient mice are lean and have reduced levels of serum glucose and insulin but increased levels of muscle IR β-subunits, fibronectin and glucose transporter (Glut)-4, although food/water intake and energy expenditure of these mice are no less than their wild-type littermates. Importantly, the pharmacological inhibition of CatL also demonstrates reduced body weight gain and serum insulin levels, and increased glucose tolerance, probably due to increased levels of muscle IR β-subunits, fibronectin and Glut-4 in both diet-induced obese mice and ob/ob mice. Increased levels of CatL in obese and diabetic patients suggest that this protease is a novel target for these metabolic disorders.

Critical Role of Mast Cell Chymase in Mouse Abdominal Aortic Aneurysm Formation

Background— Mast cell chymase may participate in the pathogenesis of human abdominal aortic aneurysm (AAA), yet a direct contribution of this serine protease to AAA formation remains unknown. Methods and Results— Human AAA lesions had high numbers of chymase-immunoreactive mast cells. Serum chymase level correlated with AAA growth rate (P=0.009) in a prospective clinical study. In experimental AAA produced by aortic elastase perfusion in wild-type (WT) mice or those deficient in the chymase ortholog mouse mast cell protease-4 (mMCP-4) or deficient in mMCP-5 (Mcpt4−/−, Mcpt5−/−), Mcpt4−/− but not Mcpt5−/− had reduced AAA formation 14 days after elastase perfusion. Even 8 weeks after perfusion, aortic expansion in Mcpt4−/− mice fell by 50% compared with that of the WT mice (P=0.0003). AAA lesions in Mcpt4−/− mice had fewer inflammatory cells and less apoptosis, angiogenesis, and elastin fragmentation than those of WT mice. Although KitW-sh/W-sh mice had protection from AAA formation, reconstitution with mast cells from WT mice, but not those from Mcpt4−/− mice, partially restored the AAA phenotype. Mechanistic studies suggested that mMCP-4 regulates expression and activation of cysteine protease cathepsins, elastin degradation, angiogenesis, and vascular cell apoptosis. Conclusions— High chymase-positive mast cell content in human AAA lesions, greatly reduced AAA formation in Mcpt4−/− mice, and significant correlation of serum chymase levels with human AAA expansion rate suggests participation of mast cell chymase in the progression of human and mouse AAA.

Regulation of endothelial cell adhesion molecule expression by mast cells, macrophages, and neutrophils.

Background Leukocyte adhesion to the vascular endothelium and subsequent transendothelial migration play essential roles in the pathogenesis of cardiovascular diseases such as atherosclerosis. The leukocyte adhesion is mediated by localized activation of the endothelium through the action of inflammatory cytokines. The exact proinflammatory factors, however, that activate the endothelium and their cellular sources remain incompletely defined. Methods and Results Using bone marrow-derived mast cells from wild-type, Tnf−/−, Ifng−/−, Il6−/− mice, we demonstrated that all three of these pro-inflammatory cytokines from mast cells induced the expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), P-selectin, and E-selectin in murine heart endothelial cells (MHEC) at both mRNA and protein levels. Compared with TNF-α and IL6, IFN-γ appeared weaker in the induction of the mRNA levels, but at protein levels, both IL6 and IFN-γ were weaker inducers than TNF-α. Under physiological shear flow conditions, mast cell-derived TNF-α and IL6 were more potent than IFN-γ in activating MHEC and in promoting neutrophil adhesion. Similar observations were made when neutrophils or macrophages were used. Neutrophils and macrophages produced the same sets of pro-inflammatory cytokines as did mast cells to induce MHEC adhesion molecule expression, with the exception that macrophage-derived IFN-γ showed negligible effect in inducing VCAM-1 expression in MHEC. Conclusion Mast cells, neutrophils, and macrophages release pro-inflammatory cytokines such as TNF-α, IFN-γ, and IL6 that induce expression of adhesion molecules in endothelium and recruit of leukocytes, which is essential to the pathogenesis of vascular inflammatory diseases.

Cathepsin L Deficiency Reduces Diet-Induced Atherosclerosis in Low-Density Lipoprotein Receptor–Knockout Mice

Background— Remodeling of the arterial extracellular matrix participates importantly in atherogenesis and plaque complication. Increased expression of the elastinolytic and collagenolytic enzyme cathepsin L (Cat L) in human atherosclerotic lesions suggests its participation in these processes, a hypothesis tested here in mice. Methods and Results— We generated Cat L and low-density lipoprotein receptor (LDLr) double-deficient (LDLr−/−Cat L−/−) mice by crossbreeding Cat L-null (Cat L−/−) and LDLr-deficient (LDLr−/−) mice. After 12 and 26 weeks of a Western diet, LDLr−/−Cat L−/− mice had significantly smaller atherosclerotic lesions and lipid cores compared with littermate control LDLr−/−Cat L+/− and LDLr−/−Cat L+/+ mice. In addition, lesions from the compound mutant mice showed significantly reduced levels of collagen, medial elastin degradation, CD4+ T cells, macrophages, and smooth muscle cells. Mechanistic studies showed that Cat L contributes to the degradation of extracellular matrix elastin and collagen by aortic smooth muscle cells. Smooth muscle cells from LDLr−/−Cat L−/− mice or those treated with a Cat L-selective inhibitor demonstrated significantly less degradation of elastin and collagen and delayed transmigration through elastin in vitro. Cat L deficiency also significantly impaired monocyte and T-lymphocyte transmigration through a collagen matrix in vitro, suggesting that blood-borne leukocyte penetration through the arterial basement membrane requires Cat L. Cysteine protease active site labeling demonstrated that Cat L deficiency did not affect the activity of other atherosclerosis-associated cathepsins in aortic smooth muscle cells and monocytes. Conclusions— Cat L directly participates in atherosclerosis by degrading elastin and collagen and regulates blood-borne leukocyte transmigration and lesion progression.

Deficiency and Inhibition of Cathepsin K Reduce Body Weight Gain and Increase Glucose Metabolism in Mice

Objectives—Previous studies demonstrated increased levels of cysteine proteases cathepsins in serum and adipose tissues from obese patients. We now provide evidence from a mouse model of obesity to suggest a direct participation of cathepsin K (CatK) in mouse body weight gain and glucose metabolism. Methods and Results—Using real-time polymerase chain reaction, we detected 12-fold increase in CatK transcripts after adipogenesis of human preadipocytes. Using an immunohistology analysis, we consistently observed high levels of CatK expression in adipose tissues from obese humans and mice. Selective inhibition of CatK activity blocked the lipid accumulation in human and mouse preadipocytes. In mice, CatK deficiency reduced significantly diet-induced body weight gain and serum glucose and insulin levels. Similar results were obtained in diet-induced and genetically created (ob/ob) obese mice after animals were treated with a CatK-selective inhibitor. Mechanistic study demonstrated a role for CatK in degrading fibronectin, a matrix protein that controls adipogenesis. Deficiency or inhibition of CatK leads to fibronectin accumulation in muscle and adipose tissues. Conclusion—This study demonstrates an essential role of CatK in adipogenesis and mouse body weight gain, possibly via degradation of fibronectin, thus suggesting a novel therapeutic strategy for the control of obesity by regulating CatK activity.