Search

Matrix metalloproteinases (MMP) responsible for degradation of connective tissue are found in most tissues. The MMP are regulated at the levels of transcription, zymogen activation by plasmin or membrane-type- (MT) MMP, and control of enzyme activity by tissue inhibitors of metalloproteinases (TIMP). Whole bovine skeletal muscle showed multiple MMP activities on gelatin zymography and also expressed mRNA encoding MMP-1, -2, -9, -14, and -16, tissue inhibitors of metalloproteinase (TIMP)- 1, -2, and -3 and plasminogen activator and its receptor. Purified intra-muscular fibroblasts and myogenic cell culture derived from satellite cells expressed most or all of these elements. Statistical analysis (n = 35) revealed a strong positive correlation among the mRNA levels of several elements of the MMP system, including MMP-2, MMP-14, TIMP-1, -2, and -3 (r - 0.614 to 0.930, P [is less than] 0.0001). Our results provide an extensive profile of an extracellular proteolytic cascade involving MMP in skeletal muscle and suggest that 1) the activation cascades of muscle MMP may be initiated by both plasmin and membrane-type MMP; 2) a group of genes involved in the same 'arm' of zymogen activation are coexpressed in this tissue; and 3) skeletal muscle cells, in addition to the intramuscular fibroblasts, express an extensive complement of MMP and related proteins. Key Words: Connective Tissue, Fibroblasts, Metalloproteinases, Satellite Cells, Skeletal Muscle

Signal transducer and activator of transcription-5 (Stat5) is known to play a critical role in prolactin-induced [beta] -casein gene transcription in rodents. In nonmammary cells, Stat5 is activated by multiple hormones and cytokines, including growth hormone. We hypothesized that Stat5 may serve as a common point in the signal transduction pathways of hormones that promote milk protein gene expression in bovine mammary cells, which are regulated by GH and IGF-I in addition to prolactin. Assays for Stat5 DNA binding activity and protein were validated in mammary explant culture. The Stat5 protein abundance was not changed by any of the short-term hormonal treatments used in our study, suggesting that short-term regulation of Stat5 is predominantly at the level of protein activation. Both rat and bovine explant culture showed a rapid stimulation of Stat5 DNA binding activity by prolactin, GH, and IGF-I at the high concentrations typically used in explant cultures as well as at levels within physiologic ranges. Growth hormone stimulated Stat5 activity at a lower concentration in bovine than in rat cultures, but in both species the presence of GH increased the response of Stat5 activity to prolactin. These results suggest that transcription factor Stat5 may represent part of a common route by which different extracellular signals converge and are transduced intracellularly to coordinately regulate cell function in the mammary gland. Key Words: Bovidae, Insulin-Like Growth Factor, Mammary Glands, Prolactin, Signal Transduction, Somatotropin

Signal transducer and activator of transcription (Stat)5 has been implicated in the signal transduction pathways of several factors that are lactogenic or galactopoeitic in mammary cells, including prolactin, GH, and IGF-I. Data from cell or explant culture support the concept that Stat5 may represent part of a common route by which different extracellular signals converge and are transduced into the cell. There are few data on Stat5 activity and level in vivo, and we set out to determine whether physiological stimuli of milk synthesis, including GH, GH-releasing factor, and milking frequency, would be associated with alterations in Stat5 activity or protein. We measured Stat5 DNA binding activity using electrophoretic mobility shift assay and Stat5 protein by Western blot in bovine mammary tissue obtained by biopsy or slaughter. Stat5 activity was absent in nonlactating, nonpregnant cows and was present in late pregnancy and throughout lactation. Stat5 activity varied considerably among cows at similar stages of lactation. Mammary Stat5 activity and protein were determined in hormone-treated lactating cows and mammary quarters of cows milked at different frequencies. Infusion of GH and GH-releasing factor for 2 mo significantly raised levels of milk production and depressed mammary Stat5 activity without influencing Stat5 protein abundance. Mammary Stat5 was also influenced by milking frequency; once-daily milking reduced milk production, Stat5 activity, and protein abundance compared with twice-daily milking. Analysis of mammary Stat5 in relation to milk protein concentration in pooled data from lactating cows indicated that Stat5 activity was correlated (r = 0.505, P [is less than] 0.05) with average milk protein concentration and not related to milk protein yield (P [is less than] 0.05). These results show that both Stat5 protein and Stat5 activity are modulated by different physiological signals in vivo and suggest that Stat5 lies within in the zone where signal transduction cascades from a variety of factors are convergent. Further work is required to clarify the role of Stat5 in relation to other factors in regulation of milk protein gene expression. Key Words: Cows, Lactation, Milk, Protein, Somatotropin, Transcription Factors

Body composition, defined as the proportions and distribution of lean and fat tissues in the human body, is an emergent theme in clinical oncology. Severe muscle depletion (sarcopenia) is most easily overlooked in obese patients; the advent of secondary analysis of oncologic images provides a precise and specific assessment of sarcopenia. Here, we review the definitions, prevalence and clinical implications of sarcopenic obesity (SO) in medical and surgical oncology. Reported prevalence of SO varies due to the heterogeneity in the definitions and the variability in the cut points used to define low muscle mass and high fat mass. Prevalence of SO in advanced solid tumor patient populations average 9% (range 2.3%-14.6%) overall, and one in four (24.7%, range 5.9%-39.2%) patients with body mass index ≥30 kg/m2 are sarcopenic. SO is independently associated with higher mortality and higher rate of complications in systemic and surgical cancer treatment, across multiple cancer sites and treatment plans. These associations remain unexplained, however, it has been hypothesized that patients with sarcopenia are generally unfit and unable to tolerate stress. Another proposed mechanism relates to increased exposure to antineoplastic therapy, i.e. a large fat mass would be expected to inflate drug dose in BSA-based treatments, causing an increased rate of dose-limiting toxicity. Pharmacokinetic data are needed to confirm or refute this hypothesis. Old age, deconditioning, cancer progression, acute or chronic nonmalignant disease and drug side-effects are suggested causes of muscle loss, and it is unknown the degree to which this can be reversed. Sarcopenia can be readily detected before start of cancer treatment, however, clinical management protocols for SO patients require development. Studies of cancer treatment dose-modulation are in progress. [ABSTRACT FROM AUTHOR]