Muir-Torre syndrome: a case of unusual coexisting genetic mutations

Muir-Torre syndrome (MTS) is a rare autosomal dominant geno-dermatosis that was independently described by Muir in 1967 and Torre in 1968. MTS is a phenotypic subtype of Lynch syndrome and most commonly arises due to germline mutations in mismatch repair genes. MTS manifests with at least one cutaneous neoplasm and one visceral malignancy.

In Vivo Comparison of the Inflammatory Response Induced by Different Vascular Biomaterials

Biomaterial implants induce a local inflammatory response. A comparison of the inflammatory cell response was made between several biomaterials commonly used as vascular prostheses.

Disks of polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), aluminum, titanium, copper, and stainless steel were surgically placed into the peritoneum of mice. Recruited macrophage and neutrophil populations were measured after recovery from the disk surface and peritoneal lavage.

Following peritoneal biomaterial implants, there was no difference in total neutrophil or macrophage recruitment between mice implanted with PET, PTFE, aluminum, or titanium disks. However, there was significant attenuation of total neutrophil and macrophage recruitment to stainless steel compared with the other implants. Similarly, there was no significant difference in the percentage of leukocytes adherent to the PET, aluminum, or titanium disks. Macrophage adherence to the stainless steel disks was attenuated by 19.1%, and the number of neutrophils was attenuated by 69.1% when compared with PET implant mice. Mice implanted with copper disks universally expired.

Leukocyte recruitment did not differ between PET, PTFE, aluminum, or titanium disks, suggesting that these materials stimulate similar inflammatory responses. Stainless steel disks recruited both fewer neutrophils and fewer macrophages and support lower adherence of these cells than the other biomaterials. Copper incited an overwhelming and fatal response.

Control of organization and function of muscle and tendon by thrombospondin-4

Thrombospondins (TSPs) are multifunctional proteins that are deposited in the extracellular matrix where they directly affect the function of vascular and other cell types. TSP-4, one of the 5 TSP family members, is expressed abundantly in tendon and muscle. We have examined the effect of TSP-4 deficiency on tendon collagen and skeletal muscle morphology and function. In Thbs4(-/-) mice, tendon collagen fibrils are significantly larger than in wild-type mice, and there is no compensatory over-expression of TSP-3 and TSP-5, the two TSPs most highly homologous to TSP-4, in the deficient mice. TSP-4 is expressed in skeletal muscle, and higher levels of TSP-4 protein are associated with the microvasculature of red skeletal muscle with high oxidative metabolism. Lack of TSP-4 in medial soleus, red skeletal muscle with predominant oxidative metabolism, is associated with decreased levels of several specific glycosaminoglycan modifications, decreased expression of a TGFβ receptor beta-glycan, decreased activity of lipoprotein lipase, which associates with vascular cell surfaces by binding to glycosaminoglycans, and decreased uptake of VLDL. The soleus muscle is smaller and hind- and fore-limb grip strength is reduced in Thbs4(-/-) mice compared to wild-type mice. These observations suggest that TSP-4 regulates the composition of the ECM at major sites of its deposition, tendon and muscle, and the absence of TSP-4 alters the organization, composition and physiological functions of these tissues.

Macrophage gene expression and foam cell formation are regulated by plasminogen

BACKGROUND

Deciphering the molecular and cellular processes that govern macrophage foam cell formation is critical to understanding the basic mechanisms underlying atherosclerosis and other vascular pathologies.

METHODS AND RESULTS

Here, we identify a pivotal role of plasminogen (Plg) in regulating foam cell formation. Deficiency of Plg inhibited macrophage cholesterol accumulation on exposure to hyperlipidemic conditions in vitro, ex vivo, and in vivo. Gene expression analysis identified CD36 as a regulated target of Plg, and macrophages from Plg(-/-) mice had decreased CD36 expression and diminished foam cell formation. The Plg-dependent CD36 expression and foam cell formation depended on conversion of Plg to plasmin, binding to the macrophage surface, and the consequent intracellular signaling that leads to production of leukotriene B4. Leukotriene B4 rescued the suppression of CD36 expression and foam cell formation arising from Plg deficiency.

CONCLUSIONS

Our findings demonstrate an unanticipated role of Plg in the regulation of gene expression and cholesterol metabolism by macrophages and identify Plg-mediated regulation of leukotriene B4 as an underlying mechanism.

Thrombospondin-4 regulates fibrosis and remodeling of the myocardium in response to pressure overload

Thrombospondin-4 (TSP-4) expression increases dramatically in hypertrophic and failing hearts in rodent models and in humans. The aim of this study was to address the function of TSP-4 in the heart. TSP-4-knockout (Thbs4(-/-)) and wild-type (WT) mice were subjected to transverse aortic constriction (TAC) to increase left ventricle load. After 2 wk, Thbs4(-/-) mice had a significantly higher heart weight/body weight ratio than WT mice. The additional increase in the heart weight in TAC Thbs4(-/-) mice was due to increased deposition of extracellular matrix (ECM). The levels of interstitial collagens were higher in the knockout mice, but the size of cardiomyocytes and apoptosis in the myocardium was unaffected by TSP-4 deficiency, suggesting that increased reactive fibrosis was the primary cause of the higher heart weight. The increased ECM deposition in Thbs4(-/-) mice was accompanied by changes in functional parameters of the heart and decreased vessel density. The expression of inflammatory and fibrotic genes known to be influential in myocardial remodeling changed as a result of TSP-4 deficiency in vivo and as a result of incubation of cells with recombinant TSP-4 in vitro. Thus, TSP-4 is involved in regulating the adaptive responses of the heart to pressure overload, suggesting its important role in myocardial remodeling. Our study showed a direct influence of TSP-4 on heart function and to identify the mechanism of its effects on heart remodeling.

Thrombospondin-4 regulates vascular inflammation and atherogenesis

RATIONALE

Thrombospondin (TSP)-4 is an extracellular protein that has been linked to several cardiovascular pathologies. However, a role for TSP-4 in vascular wall biology remains unknown.

OBJECTIVE

We have examined the effects of TSP-4 gene (Thbs4) knockout on the development of atherosclerotic lesions in ApoE(-/-) mice.

METHODS AND RESULTS

Deficiency in TSP-4 reduced atherosclerotic lesions: at 20 weeks of age, the size of the aortic root lesions in Thbs4(-/-)/ApoE(-/-) mice was decreased by 48% in females and by 39% in males on chow diets; in mice on Western diets, lesions in the descending aorta were reduced by 30% in females and 33% in males. In ApoE(-/-) mice, TSP-4 was abundant in vessel areas prone to lesion development and in the matrix of the lesions themselves. TSP-4 deficiency reduced the number of macrophages in lesions in all groups by ≥ 2-fold. In addition, TSP-4 deficiency reduced endothelial cell activation (expression of surface adhesion molecules) and other markers of inflammation in the vascular wall (decreased production of monocyte chemoattractant protein-1 and activation of p38). In vitro, both the adhesion and migration of wild-type macrophages increased in the presence of purified recombinant TSP-4 in a dose-dependent manner (up to 7- and 4.7-fold, respectively). These responses led to p38-MAPkinase activation and were dependent on β(2) and β(3) integrins, which recognize TSP-4 as a ligand.

CONCLUSIONS

TSP-4 is abundant in atherosclerotic lesions and in areas prone to development of lesions and may influence the recruitment of macrophages by activating endothelial cells and directly interacting with macrophages to increase their adhesion and migration. Our observations suggest an important role for this matricellular protein in the local regulation of inflammation associated with atherogenesis.

Endoluminal arterial injury in plasminogen-deficient mice

BACKGROUND

Vascular remodeling following arterial injury is characterized by an initial inflammatory reaction. Prior experiments using peritoneal inflammatory models have shown that the plasminogen system plays a role in the intensity of the inflammatory response. This study was undertaken to test the hypothesis that an absence of plasminogen would lead to a decrease in vascular remodeling.

METHODS

A left carotid artery injury was created with a flexible guidewire in both wild-type [Plg(+/+)] and plasminogen deficient [Plg(-/-)] mice. The right carotid artery was uninjured and used as a control. Three weeks postinjury, the mice were sacrificed and perfusion fixed, and the bilateral carotid arteries were sectioned for histological examination and collection of morphometric data.

RESULTS

After arterial injury, electron microscopy of the acutely injured artery revealed that the endothelium was denuded, that there were breaks in the internal elastic membrane, and that there was disruption of the medial layer of smooth muscle cells. The intimal and medial areas were significantly increased between the uninjured and injured carotid arteries of both Plg(+/+) (+80% intimal, +41% medial, P < 0. 05) and Plg(-/-) [+48% intimal, +24% medial, P < 0.05) mice. However, although there was a significant increase in the adventitial area of Plg(+/+) mice (+18%, P < 0.05), there was no difference in Plg(-/-) mice (-6%). Interestingly, even after 3 weeks, four of six injured arteries in Plg(-/-) mice had persistent thrombus within the medial layer, whereas this was not found in any of the nine Plg(+/+) mouse arteries.

DISCUSSION

Plasminogen deficiency inhibited the increase in adventitial area seen after injury in Plg(+/+) mice, but not the increase in intimal or medial areas. Not surprisingly, plasminogen-deficient mice also demonstrated a severe alteration in intramural thrombus clearance. Thus, specific aspects of the vascular remodeling response are dependent on plasminogen.