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Tissue inhibitor of metalloproteases (TIMPs) are inhibitors of matrix metalloproteinases (MMPs) that regulate tissue extracellular matrix (ECM) turnover. TIMP4 is highly expressed in adipose tissue, its levels are further elevated following high-fat diet, but its role in obesity is unknown. Eight-week old wild-type (WT) and Timp4-knockout (Timp4 -/- ) mice received chow or high fat diet (HFD) for twelve weeks. Timp4 -/- mice exhibited a higher food intake but lower body fat gain. Adipose tissue of Timp4 -/- -HFD mice showed reduced hypertrophy and fibrosis compared to WT-HFD mice. Timp4 -/- -HFD mice were also protected from HFD-induced liver and skeletal muscle triglyceride accumulation and dyslipidemia. Timp4 -/- -HFD mice exhibited reduced basic metabolic rate and energy expenditure, but increased respiratory exchange ratio. Increased free fatty acid excretion was detected in Timp4 -/- -HFD compared to WT-HFD mice. CD36 protein, the major fatty acid transporter in the small intestine, increased with HFD in WT but not in Timp4 -/- mice, despite a similar rise in Cd36 mRNA in both genotypes. Consistently, HFD increased enterocyte lipid content only in WT but not in Timp4 -/- mice. Our study reveals that absence of TIMP4 can impair lipid absorption and the high fat diet-induced obesity in mice possibly by regulating the proteolytic processing of CD36 protein in the intestinal enterocytes.

Background: The development of atherosclerosis is strongly linked to disorders of cholesterol metabolism. Matrix metalloproteinases (MMPs) are dysregulated in patients and animal models with atherosclerosis. Whether systemic MMP activity influences cholesterol metabolism is unknown., Methods and Results: We examined MMP-9-deficient (Mmp9 -/- ) mice and found them to have abnormal lipid gene transcriptional responses to dietary cholesterol supplementation. As opposed to Mmp9 +/+ (wild-type) mice, Mmp9 -/- mice failed to decrease the hepatic expression of sterol regulatory element binding protein 2 pathway genes, which control hepatic cholesterol biosynthesis and uptake. Furthermore, Mmp9 -/- mice failed to increase the expression of genes encoding the rate-limiting enzymes in biliary cholesterol excretion (eg, Cyp7a and Cyp27a). In contrast, MMP-9 deficiency did not impair intestinal cholesterol absorption, as shown by the 14 C-cholesterol and 3 H-sitostanol absorption assay. Similar to our earlier study on Mmp2 -/- mice, we observed that Mmp9 -/- mice had elevated plasma secreted phospholipase A 2 activity. Pharmacological inhibition of systemic circulating secreted phospholipase A 2 activity (with varespladib) partially normalized the hepatic transcriptional responses to dietary cholesterol in Mmp9 -/- mice. Functional studies with mice deficient in other MMPs suggested an important role for the MMP system, as a whole, in modulation of cholesterol metabolism., Conclusions: Our results show that MMP-9 modulates cholesterol metabolism, at least in part, through a novel MMP-9-plasma secreted phospholipase A 2 axis that affects the hepatic transcriptional responses to dietary cholesterol. Furthermore, the data suggest that dysregulation of the MMP system can result in metabolic disorder, which could lead to atherosclerosis and coronary heart disease., (© 2016 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.)

Background: Endocrine functions of the heart have been well established. We investigated the hypothesis that cardiac secretion of a unique phospholipase A2 recently identified by our laboratory (cardiac secreted phospholipase A2 [sPLA2]) establishes a heart-liver endocrine axis that is negatively regulated by matrix metalloproteinase-2 (MMP-2)., Methods and Results: In Mmp2(-/-) mice, cardiac (but not hepatic) sPLA2 was elevated, leading to hepatic inflammation, immune cell infiltration, dysregulation of the sterol regulatory element binding protein-2 and liver X receptor-α pathways, abnormal transcriptional responses to dietary cholesterol, and elevated triglycerides in very low-density lipoprotein and in the liver. Expression of monocyte chemoattractant protein-3, a known MMP-2 substrate, was elevated at both mRNA and protein levels in the heart. Functional studies including in vivo antibody neutralization identified cardiac monocyte chemoattractant protein 3 as a possible agonist of cardiac sPLA2 secretion. Conversely, systemic sPLA2 inhibition almost fully normalized the cardiohepatic phenotype without affecting monocyte chemoattractant protein-3. Finally, wild-type mice that received high-performance liquid chromatography-isolated cardiac sPLA2 from Mmp2(-/-) donors developed a cardiohepatic gene expression profile similar to that of Mmp2(-/-) mice., Conclusions: These findings identified the novel MMP-2/cardiac sPLA2 pathway that endows the heart with important endocrine functions, including regulation of inflammation and lipid metabolism in the liver. Our findings could also help explain how MMP2 deficiency leads to cardiac problems, inflammation, and metabolic dysregulation in patients., (© 2015 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.)

Previously, we reported that cardiac matrix metalloproteinase (MMP)-2 is upregulated in hypertensive mice. How MMP-2 affects the development of cardiac disease is unclear. Here, we report that MMP-2 protects from hypertensive cardiac disease. In mice infused with angiotensin II, the lack of MMP-2 (Mmp2(-/-)) did not affect the severity of the hypertension but caused cardiac hypertrophy to develop earlier and to a greater extent versus wild-type (Mmp2(+/+)) mice, as measured by heart weight:body weight ratio and upregulation of hypertrophy and fibrosis markers. We further found numerous metabolic and inflammatory gene expression abnormalities in the left ventricle of Mmp2(-/-) mice. Interestingly, Mmp2(-/-) mice expressed greater amounts of sterol regulatory element-binding protein-2 and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (a target of sterol regulatory element-binding protein-2-mediated transcription and rate limiting enzyme in cholesterol and isoprenoids biosynthesis) in addition to markers of inflammation including chemokines of the C-C motif ligand family. We focused on the functionally related genes for sterol regulatory binding protein-2 and 3-hydroxy-3-methylglutaryl-coenzyme A reductase. The 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, lovastatin, attenuated angiotensin II-induced cardiac hypertrophy and fibrosis in Mmp2(-/-) and wild-type (Mmp2(+/+)) mice, with Mmp2(-/-) mice showing resistance to cardioprotection by lovastatin. MMP-2 deficiency predisposes to cardiac dysfunction as well as metabolic and inflammatory gene expression dysregulation. This complex phenotype is, at least in part, because of the cardiac sterol regulatory element-binding protein-2/3-hydroxy-3-methylglutaryl-coenzyme A reductase pathway being upregulated in MMP-2 deficiency., (© 2015 American Heart Association, Inc.)

As a transient receptor potential (TRP) superfamily member, polycystic kidney disease 2-like-1 (PKD2L1) is also called TRPP3 and has similar membrane topology as voltage-gated cation channels. PKD2L1 is involved in hedgehog signaling, intestinal development, and sour tasting. PKD2L1 and PKD1L3 form heterotetramers with 3:1 stoichiometry. C-terminal coiled-coil-2 (CC2) domain (G699-W743) of PKD2L1 was reported to be important for its trimerization but independent studies showed that CC2 does not affect PKD2L1 channel function. It thus remains unclear how PKD2L1 proteins oligomerize into a functional channel. By SDS-PAGE, blue native PAGE and mutagenesis we here identified a novel C-terminal domain called C1 (K575-T622) involved in stronger homotrimerization than the non-overlapping CC2, and found that the PKD2L1 N-terminus is critical for dimerization. By electrophysiology and Xenopus oocyte expression, we found that C1, but not CC2, is critical for PKD2L1 channel function. Our co-immunoprecipitation and dynamic light scattering experiments further supported involvement of C1 in trimerization. Further, C1 acted as a blocking peptide that inhibits PKD2L1 trimerization as well as PKD2L1 and PKD2L1/PKD1L3 channel function. Thus, our study identified C1 as the first PKD2L1 domain essential for both PKD2L1 trimerization and channel function, and suggest that PKD2L1 and PKD2L1/PKD1L3 channels share the PKD2L1 trimerization process.

Background: Matrix metalloproteinase (MMP)-2 deficiency makes humans and mice susceptible to inflammation. Here, we reveal an MMP-2-mediated mechanism that modulates the inflammatory response via secretory phospholipase A2 (sPLA2), a phospholipid hydrolase that releases fatty acids, including precursors of eicosanoids., Methods and Results: Mmp2(-/-) (and, to a lesser extent, Mmp7(-/-) and Mmp9(-/-)) mice had between 10- and 1000-fold elevated sPLA2 activity in plasma and heart, increased eicosanoids and inflammatory markers (both in the liver and heart), and exacerbated lipopolysaccharide-induced fever, all of which were blunted by adenovirus-mediated MMP-2 overexpression and varespladib (pharmacological sPLA2 inhibitor). Moreover, Mmp2 deficiency caused sPLA2-mediated dysregulation of cardiac lipid metabolic gene expression. Compared with liver, kidney, and skeletal muscle, the heart was the single major source of the Ca(2+)-dependent, ≈20-kDa, varespladib-inhibitable sPLA2 that circulates when MMP-2 is deficient. PLA2G5, which is a major cardiac sPLA2 isoform, was proinflammatory when Mmp2 was deficient. Treatment of wild-type (Mmp2(+/+)) mice with doxycycline (to inhibit MMP-2) recapitulated the Mmp2(-/-) phenotype of increased cardiac sPLA2 activity, prostaglandin E2 levels, and inflammatory gene expression. Treatment with either indomethacin (to inhibit cyclooxygenase-dependent eicosanoid production) or varespladib (which inhibited eicosanoid production) triggered acute hypertension in Mmp2(-/-) mice, revealing their reliance on eicosanoids for blood pressure homeostasis., Conclusions: A heart-centric MMP-2/sPLA2 axis may modulate blood pressure homeostasis, inflammatory and metabolic gene expression, and the severity of fever. This discovery helps researchers to understand the cardiovascular and systemic effects of MMP-2 inhibitors and suggests a disease mechanism for human MMP-2 gene deficiency., (© 2015 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.)

Low-density lipoprotein receptor (LDLR) catalyzes the uptake of LDL-cholesterol by liver and peripheral organs. The function of the LDLR is antagonized by pro-protein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR at the plasma membrane inducing LDLR degradation. Here, we report that matrix metalloproteinase-2 (MMP-2) interacts with and cleaves PCSK9, as evidenced by proteomic, chemical cross-linkage, blue native-PAGE and domain-specific antibodies Western blot analyses. Furthermore, MMP-2 overexpression renders Hepa1-c1c7 cells resistant to PCSK9-induced LDLR degradation. The data suggest that pathological MMP-2 overexpression may protect the LDLR from PCSK-9-induced degradation., (Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)