Citations

The effect of environmental perturbations on a system of two-level atoms is to alter the coupling between the atoms and their surroundings, which manifests itself as a change in the relaxation rates of the atoms. One of the ways in which environmental fluctuations can affect an atom is to modulate its transition frequency in a stochastic manner. We study the response of such two-level atoms to irradiation by a monochromatic laser, and report the results of numerical experiments on the spectrum of scattered light. It is observed that this spectrum is a sensitive indicator of the parameters that describe the stochastic modulation. In addition, the spectra exhibit substantially different features depending on whether the stochastic process follows a diffusion or a jump mechanism. The numerical results are based on a Monte Carlo procedure, which can be applied to stochastic processes in a wide variety of biological, chemical, and physical processes.

Inclusion body myositis (IBM), the most common age-related muscle disease in the elderly population, is an incurable disorder leading to severe disability. Sporadic IBM has an unknown etiology, although affected muscle fibers are characterized by many of the pathobiochemical alterations traditionally associated with neurodegenerative brain disorders such as Alzheimer's disease. Accumulation of the amyloid-β peptide, which is derived from proteolysis of the larger amyloid-β precursor protein (βAPP), seems to be an early pathological event in Alzheimer's disease and also in IBM, where in the latter, it predominantly occurs intracellularly within affected myofibers. To elucidate the possible role of βAPP mismetabolism in the pathogenesis of IBM, transgenic mice were derived in which we selectively targeted βAPP overexpression to skeletal muscle by using the muscle creatine kinase promoter. Here we report that older (>10 months) transgenic mice exhibit intracellular immunoreactivity to βAPP and its proteolytic derivatives in skeletal muscle. In this transgenic model, selective overexpression of βAPP leads to the development of a subset of other histopathological and clinical features characteristic of IBM, including centric nuclei, inflammation, and deficiencies in motor performance. These results are consistent with a pathogenic role for βAPP mismetabolism in human IBM.

Choline acetyltransferase (ChAT; EC 2.3.1.6 ) catalyzes the reversible synthesis of acetylcholine (ACh) from acetyl CoA and choline at cholinergic synapses. Mutations in genes encoding ChAT affecting motility exist in Caenorhabditis elegans and Drosophila , but no CHAT mutations have been observed in humans to date. Here we report that mutations in CHAT cause a congenital myasthenic syndrome associated with frequently fatal episodes of apnea (CMS-EA). Studies of the neuromuscular junction in this disease show a stimulation-dependent decrease of the amplitude of the miniature endplate potential and no deficiency of the ACh receptor. These findings point to a defect in ACh resynthesis or vesicular filling and to CHAT as one of the candidate genes. Direct sequencing of CHAT reveals 10 recessive mutations in five patients with CMS-EA. One mutation (523insCC) is a frameshifting null mutation. Three mutations (I305T, R420C, and E441K) markedly reduce ChAT expression in COS cells. Kinetic studies of nine bacterially expressed ChAT mutants demonstrate that one mutant (E441K) lacks catalytic activity, and eight mutants (L210P, P211A, I305T, R420C, R482G, S498L, V506L, and R560H) have significantly impaired catalytic efficiencies.

Heat shock protein (hsp)90 functions in a complex chaperoning pathway where its activity is modulated by ATP and by interaction with several co-chaperones. One co-chaperone, p23, binds selectively to the ATP-bound state of hsp90. However, the isolated ATP-binding domain of hsp90 does not bind p23. In an effort to identify the p23-binding domain, we have constructed a series of hsp90 deletion mutants fused with glutathione- S -transferase (GST). Full-length GST-hsp90 is able to bind p23, and also, to chaperone assembly of progesterone receptor complexes. Truncations from the C terminus of GST-hsp90 reveal a C-terminal boundary for the p23-binding domain at approximately residue 490. This fragment contains, in order, the ATP-binding domain, a highly charged region, and 203 residues beyond the charged region. p23 binding is unaffected by deletion of the charged region, indicating that two noncontiguous regions of hsp90 are involved in p23 binding. These regions are only effective when hsp90 is in a dimeric state as shown by loss of p23 binding upon removal of GST or as shown by use of FK506-binding protein12-hsp90 constructs that form dimers and bind p23 only in the presence of a bivalent drug. Thus, p23 binding requires an hsp90 dimer with close proximity between N-terminal regions of hsp90 and a conformation specified by ATP.

Transduction of energetic signals into membrane electrical events governs vital cellular functions, ranging from hormone secretion and cytoprotection to appetite control and hair growth. Central to the regulation of such diverse cellular processes are the metabolism sensing ATP-sensitive K + (K ATP ) channels. However, the mechanism that communicates metabolic signals and integrates cellular energetics with K ATP channel-dependent membrane excitability remains elusive. Here, we identify that the response of K ATP channels to metabolic challenge is regulated by adenylate kinase phosphotransfer. Adenylate kinase associates with the K ATP channel complex, anchoring cellular phosphotransfer networks and facilitating delivery of mitochondrial signals to the membrane environment. Deletion of the adenylate kinase gene compromised nucleotide exchange at the channel site and impeded communication between mitochondria and K ATP channels, rendering cellular metabolic sensing defective. Assigning a signal processing role to adenylate kinase identifies a phosphorelay mechanism essential for efficient coupling of cellular energetics with K ATP channels and associated functions.

Dendritic cells (DCs) play a central role in regulating immune activation and responses to self. DC maturation is central to the outcome of antigen presentation to T cells. Maturation of DCs is inhibited by physiological levels of 1α,25 dihydroxyvitamin D 3 [1α,25(OH) 2 D 3 ] and a related analog, 1α,25(OH) 2 -16-ene-23-yne-26,27-hexafluoro-19-nor-vitamin D 3 (D 3 analog). Conditioning of bone marrow cultures with 10 −10 M D 3 analog resulted in accumulation of immature DCs with reduced IL-12 secretion and without induction of transforming growth factor β1. These DCs retained an immature phenotype after withdrawal of D 3 analog and exhibited blunted responses to maturing stimuli (CD40 ligation, macrophage products, or lipopolysaccharide). Resistance to maturation depended on the presence of the 1α,25(OH) 2 D 3 receptor (VDR). In an in vivo model of DC-mediated antigen-specific sensitization, D 3 analog-conditioned DCs failed to sensitize and, instead, promoted prolonged survival of subsequent skin grafts expressing the same antigen. To investigate the physiologic significance of 1α,25(OH) 2 D 3 /VDR-mediated modulation of DC maturity we analyzed DC populations from mice lacking VDR. Compared with wild-type animals, VDR-deficient mice had hypertrophy of subcutaneous lymph nodes and an increase in mature DCs in lymph nodes but not spleen. We conclude that 1α,25(OH) 2 D 3 /VDR mediates physiologically relevant inhibition of DC maturity that is resistant to maturational stimuli and modulates antigen-specific immune responses in vivo .

Peptides derived from proteolytic processing of the β-amyloid precursor protein (APP), including the amyloid-β peptide (Aβ), play a critical role in the pathogenesis of Alzheimer's dementia. We report that transgenic mice overexpressing APP and Aβ have a profound attenuation in the increase in neocortical blood flow elicited by somatosensory activation. The impairment is highly correlated with brain Aβ concentration and is reproduced in normal mice by topical neocortical application of exogenous Aβ1–40 but not Aβ1–42. Overexpression of M146L mutant presenilin-1 in APP mice enhances the production of Aβ1–42 severalfold, but it does not produce a commensurate attenuation of the hyperemic response. APP and Aβ overexpression do not diminish the intensity of neural activation, as reflected by the increase in somatosensory cortex glucose usage. Thus, Aβ-induced alterations in functional hyperemia produce a potentially deleterious mismatch between substrate delivery and energy demands imposed by neural activity.