No abstract

Treatment-induced changes in the plasma HIV-1 RNA level and the CD4+ lymphocyte count, taken together, are valid predictors of the clinical progression of HIV-related disease and can be used to assess the efficacy of zidovudine and possibly other antiretroviral drugs as well.

No abstract

Laminopathies are a group of disorders caused by mutations in the LMNA gene that encodes the nuclear lamina proteins, lamin A and lamin C; their pathophysiological basis is unknown. We report that lamin A/C-deficient (Lmna(-/-)) mice develop rapidly progressive dilated cardiomyopathy (DCM) characterized by left ventricular (LV) dilation and reduced systolic contraction. Isolated Lmna(-/-) myocytes show reduced shortening with normal baseline and peak amplitude of Ca(2+) transients. Lmna(-/-) LV myocyte nuclei have marked alterations of shape and size with central displacement and fragmentation of heterochromatin; these changes are present but less severe in left atrial nuclei. Electron microscopy of Lmna(-/-) cardiomyocytes shows disorganization and detachment of desmin filaments from the nuclear surface with progressive disruption of the cytoskeletal desmin network. Alterations in nuclear architecture are associated with defective nuclear function evidenced by decreased SREBP1 import, reduced PPARgamma expression, and a lack of hypertrophic gene activation. These findings suggest a model in which the primary pathophysiological mechanism in Lmna(-/-) mice is defective force transmission resulting from disruption of lamin interactions with the muscle-specific desmin network and loss of cytoskeletal tension. Despite severe DCM, defects in nuclear function prevent Lmna(-/-) cardiomyocytes from developing compensatory hypertrophy and accelerate disease progression.

Sympathetic neurons depend on nerve growth factor (NGF) for their survival both in vivo and in vitro; these cells die upon acute deprivation of NGF. We studied the effects of agents that cause membrane depolarization on neuronal survival after NGF deprivation. High-K+ medium (-33 mM) prevented cell death; the effect of K+ was dose-dependent (EC50 = 21 mM). The protection by high K+ was abolished either by withdrawal of extracellular Ca2+ or by preloading the cells with a Ca2+ chelator. The involvement of Ca21 flux across membranes in high-K+ saving of NGF-deprived neurons was also supported by experiments using Ca2+-channel antagonists and agonists. The Ca2' antagonists nimodipine and nifedipine effectively blocked the survival-promoting effect of high K+. The Ca2+ agonists Bay K 8644 and (S)-202-791 did not by themselves save neurons from NGF deprivation but did strongly augment the effect of high K+; EC50 was shifted from 21 mM to 13 mM. These data suggest that dihydropyridinesensitive L-type Ca2+ channels play a major role in the high-K+ saving. The depolarizing agents choline (EC50 = 1 mM) and carbamoylcholine (EC50 = 1 pM), acting through nicotinic cholinergic receptors, also rescued NGF-deprived neurons. The saving effect of nicotinic agonists was not blocked by withdrawal of extracellular Ca2+ but was counteracted by a chelator of intracellular Ca2+, suggesting the possible involvement of Ca2+ release from internal stores. Based on these findings we propose a "Ca2+ set-point hypothesis" for the degree of trophic-factor dependence of sympathetic neurons in vitro.There is ample evidence emphasizing the role of trophic factors in the establishment of neuron-target relationships so that only a restricted number of neurons will survive during the development of the nervous system (1, 2). Loss of sympathetic and sensory neurons occurs when endogenous nerve growth factor (NGF) is removed by administration of antiserum against NGF (3) or by making the animal autoimmune to NGF (4). Conversely, exogenously applied NGF has been shown to increase neuronal survival during development (5, 6) and after injury. Sympathetic neurons established in the presence of NGF die in vitro upon acute deprivation of NGF. This experimental model system mimics the physiological situation under which neurons die during development or after axotomy when trophic support becomes insufficient (7). Moreover, neuronal death caused by NGF deprivation in vitro (7) and naturally occurring death in vivo (8) are active processes requiring the synthesis of mRNA and protein.Neuronal survival is greatly influenced by electrical activity during certain stages of development (9). Chronic depolarization by elevated extracellular K+, explored originally by Scott and Fisher (10), improves the survival of various types of dissociated neurons in culture, including sympathetic neurons (11). Based on the observed effects of high K+ and choline on neuronal survival, Scott (12) argued that both agents were likely to act through depolarizing membrane pot...