Table 2.

PAR2 in obesity, diabetes, and metabolic syndrome: nonblood vessel function studies.

Model	Species	Sex	Tissues	Age	Metabolic phenotype			PAR2 tissue/cell target	Mechanism insights	PAR reagents	Article	Notes
					Glucose	Insulin	Body mass
Endocrine pancreas	Human	nr	Pancreas islets	—	—	—	—	Human islet-derived precursor cells (hIPC)	PAR2 is expressed in hIPCs; trypsin and PAR2-AP promote aggregation of hIPC which differentiate into islet-like aggregates	Trypsin; PAR2-AP: SLIGRL	[54]	Article identified while hand-searching the literature references
Insulin-deficient (type 1 diabetes)	Mouse C57B6	nr	Multiple	6–8 weeks	>3 g/dL urine	nr	nr	Mouse paw edema	Insulin signaling pathways may counter PAR2 mediated proinflammatory signaling in diabetic mice	PAR2-AP: SLIGRL; control AP: LRGILS	[55]	Diabetes is induced by T cell (effector Tc 1 cells with markers for CD8+ C3+ Vβ8.2+) mediated β-cell destruction. Metabolic phenotype monitoring was based on glycosuria > 3 g/dL. In-vitro data provided evidence that insulin reduced PAR2 stimulation of leukocyte adhesion to venular endothelium and global calcium influx in cell monolayers.
Obesity and diabetes	Mouse; β-arrestin 2 KO	M	Epididymal fat; liver	12–16 weeks	—	—	—	NIH3T3 fibroblasts; primary adipocytes; primary liver cells	PAR2 activation of Ca2+ signals increases cell metabolism by AMPK via CAMKKβ; PAR2 activation of β-arrestins inhibits AMPK	PAR2-AP: 2fLIGRLO; control AP: 2fLRGLO	[56]	PAR2 activation of AMPK occurred only in cells isolated from β-arrestin knockout (KO) mice. Authors proposed that changes in β-arrestin in db/db mice could contribute to changes in PAR2 signaling and, thus, alter AMPK activity. Changes in the ratio of phospho-Thr172-AMPK to total AMPK protein and the phosphorylation of AMPK substrate ACC were used to assay AMPK activity
Obesity high fat diet (HFD)	Mouse; PAR2 KO	M	Adipocytes and adipose macrophages	22–24 weeks	75% of control	33% of control	88% of control	Multiple	Distinct cell-specific TF-PAR2 signalling promotes insulin resistance and obesity	Tissue factor (TF)	[57]	Starting at 6–8 weeks of age, PAR2 knockout (KO) and wild-type (WT) were fed a HFD, which provided 60% of their caloric intake from fat. Controls (WT HFD at 22–24 weeks of age) mean estimates from graphs for fasting plasma glucose, 250 mg/dL; fasting plasma insulin, 3 ng/mL; body mass, ~48 g. After HFD, plasma free fatty acid concentrations were lower, and the responses to challenges with glucose and insulin were better in PAR2KO than in WT. Whole-body energy expenditure, normalized to account for body mass differences, was 15% higher in HFD PAR2KO than in HFD WT
Diabetic (type 1 diabetes)	Mouse ICR	M	Ileum	nr	>300 mg/dL	nd	nd	Ileum	Bromelain (a cysteine protease) reduces the hypermotility of ileum in diabetic mouse. Preliminary evidence indicating inhibition of bromelain's in vitro effects by ENMD-1068	Bromelain; PAR2 antagonist: ENMD-1068; peptide: PAR2C22-K36	[58]	The effects of ENMD-1068 on the metabolic phenotype of the mice were not determined. Study provides evidence extending the concept of PAR2 regulation by proteinases like elastase [23] disarming the activating tethered ligand sequence. ENMD-1068 has been shown to be a low potency inhibitor of enzyme-mediated but not small peptide-mediated activation of PAR2 [39]
Obese diabetic (type 2 diabetes)	Mouse db/db	nr	Kidney	9, 20, and 30 weeks	2-3 times control	nd	1.8 times control	Kidney tissues	Three-times at 20 weeks, and two times at 30 weeks more PAR2 positive-stained cells in glomerulus of db/db	none	[59]	Control (9 weeks of age db/db) group mean values: blood glucose, 429 mg/dL. Immunohistochemistry methods identified PAR2-specific staining in glomerulus of kidney tissue sections. Similarly, collagen and fibrin deposition increased in the same sections with age of db/db and reduction in kidney function
Adipose	Human	M F	Adipose-derived stem cell lines	42–58 years	—	—	—	—	PAR2-specific immunofluorescence identified on plasma membrane of adipose-derived stem cells in culture. Data obtained with trypsin alone and in combination with blocking antibody provides evidence suggesting a role for PAR2 mediating an upregulation of VEGF expression in these cells	Trypsin, antibody (SAM-11)	[60]	Cell lines were derived from 3 subjects [61], which were described as being without cardiovascular disease
Obesity	Human	M F	—	—	—	—	BMI >30 kg/m2	—	F2Rl1 on Chr 5 associated with BMI	none	[62]	Data collected from 1733 unrelated African Americans were combined in an admixture mapping study; F2Rl1 correlations with hypertension, systolic arterial blood pressures, diastolic arterial blood pressures, and high density lipoprotein C were not significant
Obesity	Human	nr	Omental and subcutaneous fat	—	—	—	BMI (kg/m2): lean, 21.4; overweight, 27.3; obese, 32.9.	Monocyte derived macrophages	Evidence indicated a positive linear correlation between increasing body-mass index and the levels of PAR2 mRNA expression in omental fat (n = 11 subjects); a twofold difference in PAR2 mRNA expression was seen over the range of BMI tested. Palmitic acid induced PAR2 expression in cultured monocyte-derived macrophages	PAR2 antagonist: GB88; PAR2AP: SLIGRL, 2fLIGRLO; antibodies: N19, SAM11	[63]	Rats (8-9 weeks of age) were fed a high-carbohydrate high-fat (HCHF) diet for a 16-week period. From weeks 8 to 16, rats were treated daily with either control (olive oil) or PAR2 antagonist GB88 (10 mg/kg/day). Control group (HCHF) means estimated from graphs for body mass at 24-25 weeks of age, 530 g; cumulative weight gain from weeks 8 to 16, 20%. GB88-treated rats showed better in vivo responses to challenges with glucose and insulin
Obesity/MetS treatment	Wistar rats	M	In vivo	24-25	—	—	Cumulative weight gain 50% of controls	Multiple nonvascular cells	Inhibition in vivo of PAR2 slowed weight gain, which seemed to be due decrease in the mass of fat accumulated during the period of the diet-induced obesity. Other beneficial effects of GB88 included normalizing plasma lipids, cholesterol, liver injury, and promoting metabolism gene expression in skeletal and adipose tissue
Insulin resistance	Human	M F	Skeletal myotubes and myoblasts	16–47 years	—	—	—	—	CHI3L1 protected cultured skeletal myoblasts from TNF-alpha induced insulin resistance. Evidence suggested CHI3L1 inhibition of TNF-alpha activation of NFkB was PAR2-dependent	CH3L1; trypsin; PAR2AP (SLIGKV); PAR2 inhibitory antibody: SAM11	[64]	The mechanism by which Chitinase-3 like protein 1 (CH3L1) interacts with PAR2 is not yet determined. PAR2 mRNA and protein expression were identified in the cell preparations; however, this study stopped short of directly testing known PAR2 activators in the cell culture model of insulin resistance. Alternate names for CH3L1 include mouse BRp39 (breast regression protein 39) and YKL-40
Metabolic syndrome	Human	nr	Coronary artery smooth muscle cells	—	—	—	—	Cultured cells	sDDP4 is a candidate adipokine, which may cause proliferation of coronary artery smooth muscle cells via PAR2	sDDP4; PAR2AP: SLIGKV; PAR2 antagonist: GB83	[65]	The mechanism by which soluble dipeptidyl peptidase 4 (sDDP4) activates PAR2 remains unclear. The authors speculated about nature of a four-amino-acid length conserved sequence between the human tethered ligand of PAR2 and sDDP4. Studies cited by the authors provide correlative evidence between sDDP4 expression and metabolic syndrome parameters
Diabetic nephropathy (DN)	Human	M F	Kidney	47–65 years (DN)	nr	nd	nr	Cortical sections	Increased immunohistochemistry staining for PAR2 in DN (2-3 times control), which was higher in vascular and tubular cells than in glomeruli	PAR2 antibody	[66]	Archival renal biopsy samples from 5 DN and 5 controls (normal portions from renal carcinoma cases). Average period of DN was 6.2 years at time of biopsy
Obesity (HFD)	Mouse tissue factor cytoplasmic tail deficient knock-in (TF-KI)	M	Liver	25–27 weeks	80% of controls	75% of controls	Same as controls	Liver and hematopoietic cells	TF-PAR2 signalling pathways in hepatocytes and hematopoietic cells independently contribute to steatosis	Antibody: 10H10 antibody	[67]	TF-KI were fed HFD for 19 weeks. From weeks 16–19, mice were administered 10H10 antibody or IgG (controls). Metabolic phenotype variables (means) are estimated from graph data in [67]. Control group: plasma glucose, 230 mg/dL; fasting plasma insulin, 5 ng/mL; body mass reported the same as wild-type mice, but data were not provided. PAR2 mRNA expression was 5 times higher in livers from HFD versus controls

nr, data values were not reported; nd, not determined; —, category is not directly applicable to study.