Detection of <em>In Situ</em> Protein-protein Complexes at the <em>Drosophila</em> Larval Neuromuscular Junction Using Proximity Ligation Assay

Discs large (Dlg) is a conserved member of the membrane-associated guanylate kinase family, and serves as a major scaffolding protein at the larval ...

Simon Fraser University

Little is known regarding hepatic insulin-like growth factor-1 IGF-I signaling with aging despite the observation that other tissues demonstrate resistance to IGF-I with aging and declines in liver mass accompany aging. Our aim was to determine if the IGF-I-induced signaling process changes with aging. Young (5 months) and old (24 months) C57BL/6 mice hepatic tissues and blood samples were taken 20 min after an intraperitoneal injection of desIGF-I. Age had no significant effect on plasma glucose, insulin and total IGF-I levels. IRS-1 protein was significantly decreased (33%) with aging. Basal phosphorylation of IRS-1, PKB and ERK were unaffected whereas basal phosphorylation of CREB and FKHR were significantly increased (37 and 33%, respectively) with aging. desIGF-I caused a significant decrease in plasma glucose concentrations in both young (53%) and old (44%) mice. desIGF-I administration significantly increased the phosphorylation of IRS-1 in both young (104%) and old (89%) hepatic tissues. Similarly, the phosphorylation of PKB was dramatically enhanced in both young (527%) and old (350%) hepatic tissues after desIGF-I stimulation. By contrast, desIGF-I administration had no significant effects on the phosphorylation of ERK and phosphorylation of transcription factors CREB and FKHR in both young and old hepatic tissues. These data suggest that aging dose not impair IGF-I signaling in hepatic tissues.

Effects of aging on hepatic IGF-I signaling.

The ability of des IGF-I to activate Akt-1 and p70 S6K in skeletal muscle with or without acute endurance exercise was examined in young and old mice. Mice were sacrificed 12 h after a moderate intensity treadmill run following an interperitoneal injection of des-IGF-I or saline. Blood and skeletal muscle were collected and IGF-I receptor, Akt-1 and p70 S6K protein contents and their phosphorylation status were determined. Injection of des IGF-I similarly decreased plasma glucose concentration in both young (P<0.01) and old mice (P<0.01) whereas plasma insulin and total IGF-I levels of young and old mice were not significantly changed by des IGF-I. Total IGF-I receptor protein and IGF-1 receptor phosphorylation were lower in aged mice (P<0.05). Basal phosphorylation of Akt-1 was lower in aged skeletal muscle (P<0.01) and this was not caused by changes in Akt-1 protein. In both young (P<0.01) and aged (P<0.05) mice, des IGF-I significantly increased the phosphorylation of Akt-1 at Ser 473. However, a des IGF-I-mediated increase in the p70 S6K phosphorylation (P<0.01) was only seen in young mice. Prior exercise decreased the total plasma IGF-I level in the presence of des IGF-I in aged mice. Des IGF-I-mediated Akt-1 and p70 S6K phosphorylation was not changed by exercise in either young or old mice. It is concluded that there was an aging-related resistance at the p70 S6K level in mouse skeletal muscle that could not be restored by prior exercise and this resistance is associated with lower IGF-I receptor number and Akt-1 phosphorylation in the aged skeletal muscle.

Age-related differences in the des IGF-I-mediated activation of Akt-1 and p70 S6K in mouse skeletal muscle.

It is traditionally believed that worker productivity declines with age. The greatest contributor to this stereotype, particularly in physically demanding jobs, is that older workers can no longer maintain their sustained level of work due to the age-associated decline in physical capacity. The objective of this study was to determine the change in the frequency of task performance as a function of age in the power line technician (PLT) trade. The task requirements of the PLT occupation were determined through the use of a detailed job demands analysis (JDA) and the frequency at which these tasks were performed was acquired through a survey derived from the JDA. The results of the survey were assessed as a function of age. Older lineworkers (> or = 50 years) were found to spend more time working on the ground whereas the younger PLTs (< or = 39 years) more frequently performed the climbing tasks and the corresponding work on the poles and towers. In contrast the older PLTs performed all pushing/pulling tasks at a greater or equal frequency to that of the younger lineworkers. Despite these differences the frequency of task performance is similar across the age groups studied.

Task frequency as a function of age for the powerline technician trade.

The objective of this study was to assess the changes in the physical capacity as a function of age in power line technicians (PLTs). The physical test was designed to closely represent the essential physical tasks of the occupation that were identified through a detailed job demand analysis. The results from the physical test showed that six out of nine test variables did not demonstrate a statistical difference between the mean scores of young (< or = 39 years) and old age (50+ years) groups. However the older group scored significantly lower in the aerobic capacity test, one-handed pull down, and both right and left standard handgrip tests. Despite these differences the older PLT appears to meet and exceed the physical requirements necessary to carry out the essential tasks of this trade. However a physical test with a high level of content and construct validity is necessary to accurately evaluate the workers physical capacity in relation to the job demands. Based on the principal of specificity for muscle training and testing, this study has demonstrated that heavy manual work appears to maintain physical capacity specific to the task as age progresses.

Changes in physical capacity as a function of age in heavy manual work.

The objective of this study was to assess the neuroautonomic cardiovascular regulation in recently concussed athletes at rest and in response to low-moderate steady-state exercise, using heart rate variability (HRV).

Heart rate variability of recently concussed athletes at rest and exercise.

To better understand the interaction between motor neuron dysfunction and denervation in amyotrophic lateral sclerosis (ALS), we have evaluated motor neuron number and the retrograde uptake and transport of fluorogold by motor neurons in mice overexpressing mutant superoxide dismutase (mSOD), and wild-type controls. N-CAM immunoreactivity and protein kinase expression were determined in skeletal muscle during denervation. We found that in severely affected mSOD mice, motor neuron loss is moderate (approximate 40% reduction), whereas retrograde uptake/transport as assessed using fluorogold is profoundly impaired (approximately 90% reduction). The impairment in fluorogold uptake/transport corresponds to measures of progressive muscle denervation such as increased N-CAM immunoreactivity of muscle and increased expression of protein kinase B (PKB) in denervated muscle. These data suggest that the debility in the mSOD mouse model of ALS is produced, in part, by impaired retrograde uptake/transport in motor neuron axons in spite of regenerative support from muscle such as elevated expression of PKB.

Neuromuscular dysfunction in the mutant superoxide dismutase mouse model of amyotrophic lateral sclerosis.

Adducin is a ubiquitously expressed actin- and spectrin-binding protein involved in cytoskeleton organization, and is regulated through phosphorylation of the myristoylated alanine-rich C-terminal kinase (MARCKS)-homology domain by protein kinase C (PKC). We have previously shown that the Drosophila adducin, Hu-li tai shao (Hts), plays a role in larval neuromuscular junction (NMJ) growth. Here, we find that the predominant isoforms of Hts at the NMJ contain the MARCKS-homology domain, which is important for interactions with Discs large (Dlg) and phosphatidylinositol 4,5-bisphosphate (PIP2). Through the use of Proximity Ligation Assay (PLA), we show that the adducin-like Hts isoforms are in complexes with Dlg and PIP2 at the NMJ. We provide evidence that Hts promotes the phosphorylation and delocalization of Dlg at the NMJ through regulation of the transcript distribution of the PAR-1 and CaMKII kinases in the muscle. We also show that Hts interactions with Dlg and PIP2 are impeded through phosphorylation of the MARCKS-homology domain. These results are further evidence that Hts is a signaling-responsive regulator of synaptic plasticity in Drosophila.

Wade Parkhouse

Department of Biomedical Physiology and Kinesiology

Simon Fraser University

Detection of In Situ Protein-protein Complexes at the Drosophila Larval Neuromuscular Junction Using Proximity Ligation Assay

Wade Parkhouse

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Biomedical Physiology and Kinesiology

Simon Fraser University

Detection of In Situ Protein-protein Complexes at the Drosophila Larval Neuromuscular Junction Using Proximity Ligation Assay

Department of Biomedical Physiology and Kinesiology