| 1. |
- Li, Mingxin, 1964-
(författare)
-
Celluar and Molecular Mechanisms Underlying Regulation of Skeletal Muscle Contraction in Health and Disease
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Morphological changes, genetic modifications, and cell functional alterations are not always parallel. Therefore, assessment of skeletal muscle function is an integral part of the etiological approach. The general objective of this thesis was to look into the cellular and molecular events occurring in skeletal muscle contraction in healthy and diseased condition, using a single fiber preparation and a single fiber in vitro motility assay, in an attempt to approach the underlying mechanisms from different physiological angles. In a body size related muscle contractility study, scaling of actin filament sliding speed and its temperature sensitivity has been investigated in mammals covering a 5,500-fold difference in body mass. A profound temperature dependence of actin filament sliding speed over myosin head was demonstrated irrespective of MyHC isoform expression and species. However, the expected body size related scaling within orthologus myosin isoforms between species failed to be maintained at any temperature over 5,500-fold range in body mass, with the larger species frequently having faster in vitro motility speeds than the smaller species. This suggest that apart from the MyHC iso-form expression, other factors such as thin filament proteins and myofilament lattice spacing, may contribute to the scaling related regulation of skeletal muscle contractility. A study of a novel R133W β-tropomyosin mutation on regulation of skeletal muscle contraction in the skinned single fiber prepration and single fiber in vitro motility assay suggested that the mutation induced alteration in myosin-actin kinetics causing a reduced number of myosin molecules in the strong actin binding state, resulting in overall muscle weakness in the absence of muscle wasting. A study on a type IIa MyHC isoform missense mutation at the motor protein level demonstrated a significant negative effect on the function of the IIa MyHC isoform while other myosin isoforms had normal function. This provides evidence that the pathogenesis of the MyHC IIa E706K myopathy involves defective function of the mutated myosin as well as alterations in the structural integrity of all muscle irrespective of MyHC isoform expression.
|
|
| 2. |
- Llano-Diez, Monica
(författare)
-
Mechanisms Underlying Intensive Care Unit Muscle Wasting : Intervention Strategies in an Experimental Animal Model and in Intensive Care Unit Patients
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Critically ill patients admitted to the intensive care unit (ICU) commonly develop severe muscle wasting and weakness and consequently impaired muscle function. This not only delays respirator weaning and ICU discharge, but has deleterious effects on morbidity, mortality, financial costs, and quality of life of survivors. Acute Quadriplegic Myopathy (AQM) is one of the most common neuromuscular disorders underlying ICU muscle wasting and paralysis, and is a consequence of modern intensive care interventions, although the exact causes remain unclear. Muscle gene/protein expression, intracellular signalling, post-translational modifications, muscle membrane excitability, and contractile properties at the single muscle fibre level were explored in order to unravel the mechanisms underlying the muscle wasting and weakness associated with AQM and how this can be counteracted by specific intervention strategies. A unique experimental rat ICU model was used to address the mechanistic and therapeutic aspects of this condition, allowing time-resolved studies for a period of two weeks. Subsequently, the findings obtained from this model were translated into a clinical study. The obtained results showed that the mechanical silencing of skeletal muscle, i.e., absence of external strain (weight bearing) and internal strain (myosin-actin activation) due to the pharmacological paralysis or sedation associated with the ICU intervention, is likely to be the primary mechanism triggering the preferential myosin loss and muscle wasting, features specifically characteristic of AQM. Moreover, mechanical silencing induces a specific gene expression pattern as well as post-translational modifications in the motor domain of myosin that may be critical for both function and for triggering proteolysis. The higher nNOS expression found in the ICU patients and its cytoplasmic dislocation are indicated as a probable mechanism underlying these highly specific modifications. This work also demonstrated that passive mechanical loading is able to attenuate the oxidative stress associated with the mechanical silencing and induces positive effects on muscle function, i.e., alleviates the loss of force-generating capacity that underlie the ICU intervention, supporting the importance of early physical therapy in immobilized, sedated, and mechanically ventilated ICU patients.
|
|
| 3. |
- Valsecchi, Isabel, 1973-
(författare)
-
AtZDP, a Plant 3' DNA Phosphatase, Involved in DNA Repair
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- DNA bases can be modified by endogenous agents (e.g. oxidized by products of respiration and photosynthesis or methylated by gene silencing processes) as well as by environmental agents (e.g. oxidized by UV light). In the process of removing modified bases, a 3’-phosphate group is sometimes left in the resulting gap, and has to be removed since it blocks the incorporation of a new nucleotide by DNA polymerase. The aim of this thesis was the characterization of AtZDP, a plant enzyme with a DNA 3’-phosphatase activity.By homologous modeling, the existence of four domains was predicted in AtZDP, three independent zinc-finger and one DNA 3’-phosphatase domains. AtZDP was found to be localized in the nucleus by bimolecular fluorescence complementation. Western blotting analysis showed that the enzyme was ubiquitously expressed in plant tissues.AtZDP was found in a 600,000 molecular-weight protein complex by gel chromatography and glycerol gradient sedimentation centrifugation. The fractions containing AtZDP in the complex displayed 3’-DNA phosphatase activity as shown by desphosphorylation of a DNA oligonucleotide with a 3’-phosphate terminus. Also fractions of the gel chromatography corresponding to lower molecular weight showed 3’-DNA phosphatase activity, but antibodies against AtZDP did not recognize this fraction inferring that in plants, at least another protein with similar activity exists.In mammals, polynucleotide kinase, an enzyme with the same activity phosphatase activity as AtZDP, is involved in single-strand and double-strand repair pathways. To elucidate if AtZDP could be part of similar pathways, different double strand and single-strand oligonucleotides with 3’-phosphate termini were separately incubated with AtZDP. All substrates were dephosphorylated by AtZDP, assuming that this enzyme could potentially be involved in double-strand DNA repair. A double-strand oligonucleotide containing a one-bp gap with a 3’-phosphate terminus was repaired by a leaf protein extract. The activities of a 3’-DNA phosphatase, a flap 5’ to 3’ endonuclease-like, a DNA polymerase and a DNA ligase were observed. The presence of these enzymes revealed that these damages are in plants predominantly repaired by long-patch base excision repair.
|
|
| 4. |
- Xu, Wenqian, 1992-, et al.
(författare)
-
Media Representation of Life Stages : Analysis of Photographs Posted on Norrköping Municipal Facebook Accounts
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Aim: It has been found by researchers that older adults are statistically underrepresented and associated with negative stereotypes in the mass media. Older adults are generally viewed as incompetent from stereotyped media content, which may make them socially excluded from a set of opportunities and resources. The media portrayals are conceived as value-expressive and constructing the image of older adults and ageing. The purpose of this study is to investigate how Norrköping municipality portrays citizens at different life stages in social media with a special emphasis on the use of age stereotypes in the photos used.Method: The material consists of the photos collected from 32 Facebook accounts produced by municipal bodies during the entire year of 2018. The analysis is based on a categorization of various features of the photos in order to statistically describe the relation between signs, activities and contexts associated with distinct life stages. Further, the meaning of frequently-used symbols in the photographs is analysed.Result: The study concludes that old age persons are numerically underrepresented in the material. A number of signs and activities in the photographs, and contexts beyond the photographs, that stereotypically corresponded to five distinct life stages (infancy, childhood, adolescence, adulthood and old age) are identified. Old age is repetitively portrayed in the context of coffee drinking and foot bathing on Norrköping municipality’s Facebook page, while adolescence is depicted with practical training at high schools to an excessive degree. Besides, the result suggests that certain minorities of citizens did not show up in the municipal social media: people with disabilities, migrants, people with dementia and on forth.Conclusion: The municipality communicates stereotypical images of life stages through associating with specific contexts in the photographic coverage. Therefore, communication professionals need to be aware of the stereotypical construction of life stages in the media.
|
|
