Background-Neutrophils may be an important source of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9), two matrix-degrading enzymes thought to be critical in the formation of an abdominal aortic aneurysm (AAA). The purpose of this investigation was to test the hypothesis that neutrophil depletion would limit experimental AAA formation by altering one or both of these enzymes. Methods and Results-Control, rabbit serum-treated (RS; nϭ27) or anti-neutrophil-antibody-treated (anti-PMN; nϭ25) C57BL/6 mice underwent aortic elastase perfusion to induce experimental aneurysms. Anti-PMN-treated mice became neutropenic (mean, 349 cells/L), experiencing an 84% decrease in the circulating absolute neutrophil count (PϽ0.001) before elastase perfusion. Fourteen days after elastase perfusion, control mice exhibited a mean aortic diameter (AD) increase of 104Ϯ14% (PϽ0.0001), and 67% developed AAAs, whereas anti-PMN-treated mice exhibited a mean AD increase of 42Ϯ33%, with 8% developing AAAs. The control group also had increased tissue neutrophils (20.3 versus 8.6 cells per 5 high-powered fields [HPFs]; Pϭ0.02) and macrophages (6.1 versus 2.1 cells per 5 HPFs, Pϭ0.005) as compared with anti-PMN-treated mice. There were no differences in monocyte chemotactic protein-1 or macrophage inflammatory protein-1␣ chemokine levels between groups by enzyme-linked immunosorbent assay. Neutrophil collagenase (MMP-8) expression was detected only in the 14-day control mice, with increased MMP-8 protein levels by Western blotting (Pϭ0.017), and MMP-8 -positive neutrophils were seen almost exclusively in this group. Conversely, there were no statistical differences in MMP-2 or MMP-9 mRNA expression, protein levels, enzyme activity, or immunostaining patterns between groups. When C57BL/6 wild-type (nϭ15) and MMP-8 -deficient mice (nϭ17) were subjected to elastase perfusion, however, ADs at 14 days were no different in size (134Ϯ7.9% versus 154Ϯ9.9%; Pϭ0.603), which suggests that MMP-8 serves only as a marker for the presence of neutrophils and is not critical for AAA formation. Conclusions-Circulating

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Objective-It is hypothesized that a male predominance, similar to that in humans, persists in a rodent model of experimental abdominal aortic aneurysm (AAA) via alterations in matrix metalloproteinases (MMPs). Methods and Results-Group I experiments were as follows: elastase perfusion of the infrarenal aorta was performed in male (M) and female (F) rats. At 14 days, aortas were harvested for immunohistochemistry, real-time polymerase chain reaction (PCR), and zymography. Group II experiments were the following: abdominal aorta was transplanted from F or M donors into F or M recipients. At 14 days, rodents that had undergone transplantation underwent elastase perfusion. In group III, male rats were given estradiol or sham 5 days before elastase perfusion. In group I, M rats had larger AAAs with higher frequency than did F rats. M rat aortas had more significant macrophage infiltrates and increased matrix metalloproteinase (MMP)-9 production and activity. In group II, M-to-M aortic transplants uniformly developed aneurysms after elastase perfusion, whereas F-to-F aortic transplants remained resistant to aneurysm formation. F aortas transplanted into M recipients, however, lost aneurysm resistance. In group III, estradiol-treated rats demonstrated smaller aneurysms and less macrophage infiltrate and MMP-9 compared with M controls after elastase. Conclusions-These data provide evidence of gender-related differences in AAA development, which may reflect an estrogen-mediated reduction in macrophage MMP-9 production.

Aging in rodents and humans is characterized by loss of muscle mass (sarcopenia). Testosterone supplementation increases muscle mass in healthy older men. Here, using a mouse model, we investigated the molecular mechanisms by which testosterone prevents sarcopenia and promotes muscle growth in aging. Aged mice of 22 months of age received a single sc injection of GnRH antagonist every 2 wk to suppress endogenous testosterone production and were implanted subdermally under anesthesia with 0.5 or 1.0 cm testosterone-filled implants for 2 months (n ϭ 15/ group). Young and old mice (n ϭ 15/group), of 2 and 22 months of age, respectively, received empty implants and were used as controls. Compared with young animals, a significant (P Ͻ 0.05) increase in muscle cell apoptosis coupled with a decrease in gastrocnemius muscles weight (by 16.7%) and muscle fiber cross-sectional area, of both fast and slow fiber types, was noted in old mice. Importantly, such age-related changes were fully reversed by higher dose (1 cm) of testosterone treatment. Testosterone treatment effectively suppressed age-specific increases in oxidative stress, processed myostatin levels, activation of c-Jun NH 2 -terminal kinase, and cyclin-dependent kinase inhibitor p21 in aged muscles. Furthermore, it restored age-related decreases in glucose-6-phosphate dehydrogenase levels, phospho-Akt, and Notch signaling. These alterations were associated with satellite cell proliferation and differentiation. Collectively these results suggest involvement of multiple signal transduction pathways in sarcopenia. Testosterone reverses sarcopenia through stimulation of cellular metabolism and survival pathway together with inhibition of death pathway. (Endocrinology 151: 628 -638, 2010) S arcopenia is defined as the progressive decline of skeletal muscle mass and strength, which occurs with aging (1, 2). The rate of muscle loss is estimated to be 1-2% per year after the age of 50 yr and can affect even healthy physically active adults. Secondary to loss of skeletal muscle mass, there is a corollary decrease in functional independence and the ability to perform activities of daily living within the elderly population (2). Approximately 25% of people above the age of 70 yr and 40% of those who have reached the age of 80 yr are clinically sarcopenic (2, 3). Additionally, aging-associated skeletal muscle loss also leads to an increased risk of falls, fractures, dependency, and all-cause mortality (3-5).Mechanisms that regulate age-related loss of skeletal muscle mass are not well defined, but the pathogenesis is likely multifactorial. With age, in a process similar to that