A major gene affecting age-related hearing loss in C57BL/6J mice

A major gene responsible for age-related hearing loss (AHL) in C57BL/6J mice was mapped by analyses of a (C57BL/6J x CAST/Ei) x C57BL/6J backcross. AHL, as measured by elevated auditory-evoked brainstem response (ABR) thresholds, segregated among backcross mice as expected for a recessive, primarily single-gene trait. Both qualitative and quantitative linkage analyses gave the same genetic map position for the AHL gene (Ahl on chromosome 10, near D10Mit5. Marker assisted selection was then used to produce congenic lines of C57BL/6J that contain different CAST-derived segments of chromosome 10. ABR test results and cochlear histopathology of aged progenitors of these congenic lines are presented. Ahl is the first gene causing late-onset, non-syndromic hearing loss that has been reported in the mouse.     

An antagonist for the leukemia inhibitory factor receptor inhibits leukemia inhibitory factor, cardiotrophin-1, ciliary neurotrophic factor, and oncostatin M

The leukemia inhibitory factor receptor (LIF-R) is activated not only by LIF, but also by cardiotrophin-1, ciliary neurotrophic factor with its receptor, and oncostatin M (OSM). Each of these cytokines induces the hetero-oligomerization of LIF-R with gp130, a signal-transducing subunit shared with interleukin-6 and interleukin-11. The introduction of mutations into human LIF that reduced the affinity for gp130 while retaining affinity for LIF-R has generated antagonists for LIF. In the current study, a LIF antagonist that was free of detectable agonistic activity was tested for antagonism against the family of LIF-R ligands. On cells that express LIF-R and gp130, all LIF-R ligands were antagonized. On cells that also express OSM receptor, OSM was not antagonized, demonstrating that the antagonist is specific for LIF-R. Ligand-triggered tyrosine phosphorylation of both LIF-R and gp130 was blocked by the antagonist. The antagonist is therefore likely to work by preventing receptor oligomerization.     

Total body irradiation and acute graft-versus-host disease: the role of gastrointestinal damage and inflammatory cytokines

The influence of bone marrow transplantation (BMT) conditioning regimens on the incidence and severity of graft-versus-host disease (GVHD) has been suggested in clinical BMT. Using murine BMT models, we show here an increase in GVHD severity in several donor-recipient strain combinations after intensification of the conditioning regimen by increasing the total body irradiation (TBI) dose from 900 cGy to 1,300 cGy. Increased GVHD was mediated by systemic increases in tumor necrosis factor alpha (TNF alpha). Histologic analysis of gastrointestinal tracts showed synergistic damage by increased TBI and allogeneic donor cells that permitted increased translocation of lipopolysacharide (LPS) into the systemic circulation. In vitro, LPS triggered excess TNF alpha from macrophages primed by the GVH reaction. In addition, macrophages isolated within 4 hours of conditioning were primed in proportion to the TBI dose itself to secrete TNF alpha. Thus, the higher TBI dose increased macrophage priming and increased gut damage after allogeneic BMT, causing higher systemic levels of inflammatory cytokines and subsequent severe GVHD. These data highlight the importance of conditioning in GVHD pathophysiology and suggest that interventions to prevent LPS stimulation of primed macrophages may limit the severity of GVHD after intensive conditioning for allogeneic BMT.     

Molecular recognition of human angiogenin by placental ribonuclease inhibitor--an X-ray crystallographic study at 2.0 A resolution

Human placental RNase inhibitor (hRI), a leucine-rich repeat protein, binds the blood vessel-inducing protein human angiogenin (Ang) with extraordinary affinity (Ki <1 fM). Here we report a 2.0 A resolution crystal structure for the hRI-Ang complex that, together with extensive mutagenesis data from earlier studies, reveals the molecular features of this tight interaction. The hRI-Ang binding interface is large and encompasses 26 residues from hRI and 24 from Ang, recruited from multiple domains of both proteins. However, a substantial fraction of the energetically important contacts involve only a single region of each: the C-terminal segment 434-460 of hRI and the ribonucleolytic active centre of Ang, most notably the catalytic residue Lys40. Although the overall docking of Ang resembles that observed for RNase A in the crystal structure of its complex with the porcine RNase inhibitor, the vast majority of the interactions in the two complexes are distinctive, indicating that the broad specificity of the inhibitor for pancreatic RNase superfamily proteins is based largely on its capacity to recognize features unique to each of them. The implications of these findings for the development of small, hRI-based inhibitors of Ang for therapeutic use are discussed.     

Food properties that influence neuromuscular activity during human mastication

The rate of breakdown of food in mastication depends on the ratio of two mechanical properties of the food--the toughness and modulus of elasticity (Agrawal et al., 1997)--a result which can be predicted by an analysis of the energetics of fracture. The work input to produce food fragmentation is provided by the masticatory muscles, the activity levels of which depend on sensory feedback from the mouth. Here, we test the hypothesis that the activity of a representative of this musculature is modulated by the above combination of food properties. The surface electrical activity (EMG) of the anterior temporalis muscles of ten human subjects was recorded while subjects chewed standardized volumes of 15 food types. The integrated EMG in these muscles was highly significantly related to the square root of the ratio of the above two food properties. Significant correlations were found between this food property index and integrated EMG, both when data for all chews and all subjects were lumped together (r = -0.86; p < 0.0001) and when correlation coefficients between the index and EMG were plotted for each chew made by each subject. Except for two subjects in the first chew, these coefficients reached and maintained highly significant levels throughout the masticatory sequence. Thus, a clear relationship between the electrical activity of a jaw-closing muscle and the mechanical properties of food has been found for the first time.     

Alterations in energy balance with exercise

The doubly labeled water method for measuring average daily metabolic rate (ADMR) in combination with resting metabolic rate (RMR) allows one to assess the relation between exercise and energy balance. Three topics were included in an analysis of available data: 1) the limits of energy turnover in relation to physical performance for the achievement of energy balance, 2) the effect of an exercise intervention on daily energy turnover and its components, and 3) the effect of exercise on body composition. In the general population, physical activity level (PAL: ADMR/RMR) ranges between 1.2 and 2.2-2.5. There is no sex difference in the level of physical activity. Higher PAL values can be maintained by training and supplementation of the diet with energy-dense, carbohydrate-rich formulas. Exercise training does not influence spontaneous activity except in the elderly. In sedentary subjects, exercise training does not influence RMR when body weight is maintained. An exercise-induced increase in ADMR is about twice the training load. Exercise induces an increase in fat-free mass, especially in women, and a decrease in fat mass. Women tend to preserve energy balance and consequently loss of fat mass is significantly less.