Antiretroviral Therapy-Associated Acute Motor and Sensory Axonal Neuropathy

Guillain-Barré syndrome (GBS) has been reported in HIV-infected patients in association with the immune reconstitution syndrome whose symptoms can be mimicked by highly active antiretroviral therapy (HAART)-mediated mitochondrial toxicity. We report a case of a 17-year-old, HIV-infected patient on HAART with a normal CD4 count and undetectable viral load, presenting with acute lower extremity weakness associated with lactatemia. Electromyography/nerve conduction studies revealed absent sensory potentials and decreased compound muscle action potentials, consistent with a diagnosis of acute motor and sensory axonal neuropathy. Lactatemia resolved following cessation of HAART; however, neurological deficits minimally improved over several months in spite of immune modulatory therapy. This case highlights the potential association between HAART, mitochondrial toxicity and acute axonal neuropathies in HIV-infected patients, distinct from the immune reconstitution syndrome

Sites of monomeric actin incorporation in living PTK2 and REF-52 cells

The purpose of this study was to analyze where monomeric actin first becomes incorporated into the sarcomeric units of the stress fibers. We microinjected fluorescently labeled actin monomers into two cell lines that differ in the sarcomeric spacings of ␣-actinin and nonmuscle myosin II along their stress fibers: REF-52, a fibroblast cell line, and PtK2, an epithelial cell line. The cells were fixed at selected times after microinjection (30 s and longer) and then stained with an ␣-actinin antibody. Localization of the labeled actin and ␣-actinin antibody were recorded with low level light cameras. In both cell types, the initial sites of incorporation were in focal contacts, lamellipodia and in punctate regions of the stress fibers that corresponded to the ␣-actinin rich dense bodies. The adherent junctions between the epithelial PtK2 cells were also initial sites of incorporation. At longer times of incorporation, the actin fluorescence extended along the stress fibers and became almost uniform. We saw no difference in the pattern of incorporation in peripheral and perinuclear regions of the stress fibers. We propose that rapid incorporation of monomeric actin occurs at the cellular sites where the barbed ends of actin filaments are concentrated: at the edges of lamellipodia, the adherens junctions, the attachment plaques and in the dense bodies that mark out the sarcomeric subunits of the stress fibers. Cell Motil

Integrating an integrin: a direct route to actin

AbstractIntegrins were so named for their ability to link the extracellular and intracellular skeletons. Now almost 20 years into integrin research, numerous questions remain as to how this interaction is accomplished and how it is modified to achieve a desired phenotype. As the cell adhesion and actin assembly fields are merging in combined approaches, novel actin assembly mechanisms are being uncovered. Some of the earliest identified cytoplasmic linker molecules, believed to mediate integrin-actin binding, are once again the subject of scrutiny as potential dynamic mediators of cell anchorage. It seems plausible that each unique cellular morphology occurs as the result of activation of distinct actin assembly systems that are either stabilized by unique bundling and linker proteins or modified for progression to a new phenotype. While this research initiative is likely to continue rapidly in a forward fashion, it remains to be clarified how integrins assemble the most stable and basic cytoskeletal phenotype, the adherent cell with prominent stress fibers. Recent investigations point towards a shift in the current model of anchoring at the cell periphery by providing both mechanisms and evidence for de novo actin assembly orchestrated by the adhesion site. Lacking a complete pathway from integrin ligation to an integrated extracellular–intracellular skeleton in any single system, this review proposes a simple model of integrin-mediated stress fiber integration by drawing from work in multiple systems

Titin visualization in real time reveals an unexpected level of mobility within and between sarcomeres

Contrary to prior models in which titin serves as a stable scaffold in sarcomeres, sarcomeric and soluble titin exchange dynamically in myofibers when calcium levels are low

Heavy and light roles: myosin in the morphogenesis of the heart

Myosin is an essential component of cardiac muscle, from the onset of cardiogenesis through to the adult heart. Although traditionally known for its role in energy transduction and force development, recent studies suggest that both myosin heavy-chain and myosin lightchain proteins are required for a correctly formed heart. Myosins are structural proteins that are not only expressed from early stages of heart development, but when mutated in humans they may give rise to congenital heart defects. This review will discuss the roles of myosin, specifically with regards to the developing heart. The expression of each myosin protein will be described, and the effects that altering expression has on the heart in embryogenesis in different animal models will be discussed. The human molecular genetics of the myosins will also be reviewed

A cellular and molecular characterization of the Z-band portion of titin (zeugmatin)

Muscle contains a highly ordered array of proteins that must be meticulously organized. A study of myofibril development previously determined that one protein, zeugmatin, appeared to be involved in the formation of Z-bands, a key step in myofibril development. We employed molecular and biochemical approaches to characterize zeugmatin. Screening of a chicken heart lambda gt11 expression library with the zeugmatin antibody, mAb20, yielded an assembled 1.8 kb cDNA with high identity to the N-terminal region of human cardiac titin. This high homology and other experiments led us to conclude that zeugmatin was not a Z-band protein but the 2-band region of titin. Functional studies were done to determine if this region of titin has a role in Z-band formation. The protein product of the Z1.1 cDNAs were able to bind alpha-actinin, and this in vitro interaction is supported by the colocalization of mAb20 and alpha-actinin antibodies in vivo. In non-muscle cells, 24 hours after transfection, expressed Z1.1 localized to the alpha-actinin containing dense bodies of stress fibers, and 48 hours after transfection resulted in the disassembly of dense bodies and collapse of the cytoskeleton. The Z1.1 cDNA was inserted into a green fluorescent protein expression plasmid to yield a Z1.1GFP construct that produced a fragment of Z-band titin that was fluorescent. In living muscle cells, expressed Z1.1GFP was observed to incorporate into the Z-bands, and overexpression of Z1.1GFP resulted in the disassembly of Z-bands and myofibrils resulting in the loss of contractility. Z1.1 and other cDNAs isolated in this study will be useful in understanding the localization of full-length titin. The dominant negative phenotype we observed with overexpression of this Z-band fragment of titin allowed us to conclude that this region of titin plays an important role in maintaining and organizing the structure of the myofibril