[Show abstract][Hide abstract] ABSTRACT: Transglutaminases (TG) form a family of enzymes that catalyse various post-translational modifications of glutamine residues in proteins and peptides including intra- and intermolecular isopeptide bond formation, esterification and deamidation. We have characterized a novel member of the mammalian TG family, TG6, which is expressed in a human carcinoma cell line with neuronal characteristics and in mouse brain. Besides full-length protein, alternative splicing results in a short variant lacking the second β-barrel domain in man and a variant with truncated β-sandwich domain in mouse. Biochemical data show that TG6 is allosterically regulated by Ca(2+) and guanine nucleotides. Molecular modelling indicates that TG6 could have Ca(2+) and GDP-binding sites related to those of TG3 and TG2, respectively. Localization of mRNA and protein in the mouse identified abundant expression of TG6 in the central nervous system. Analysis of its temporal and spatial pattern of induction in mouse development indicates an association with neurogenesis. Neuronal expression of TG6 was confirmed by double-labelling of mouse forebrain cells with cell type-specific markers. Induction of differentiation in mouse Neuro 2a cells with NGF or dibutyryl cAMP is associated with an upregulation of TG6 expression. Familial ataxia has recently been linked to mutations in the TGM6 gene. Autoantibodies to TG6 were identified in immune-mediated ataxia in patients with gluten sensitivity. These findings suggest a critical role for TG6 in cortical and cerebellar neurons.
[Show abstract][Hide abstract] ABSTRACT: Adipose tissue is an important endocrine and metabolic tissue that is actively involved in cross-talk with peripheral organs such as skeletal muscle. It is likely that adipose-derived factors may underlie the development of insulin resistance in muscle. Thus, the cross-talk between adipose and muscle may be important for the propagation of obesity-related diseases. Visfatin (Pre-B-cell colony-enhancing factor 1 homolog/Nampt) is a recently discovered adipokine with pleiotropic functions. The aim of this study was to examine the effect of visfatin on cellular stress responses and signalling pathways in skeletal muscle. Visfatin treatment of differentiated C2C12 myotubes generated reactive oxygen species (ROS) comprising both superoxide and hydrogen peroxide that was dependent on de novo transcription and translation. In differentiated C2C12 myoblasts, visfatin had no effects on insulin-stimulated Akt phosphorylation nor on activation of the Akt signalling pathway. Additionally, visfatin-induced oxidative stress occurred independent of activation of the stress-activated protein kinases (MAPKs) ERK and p38. In contrast, phosphorylation of NFkB was associated with visfatin-mediated generation of ROS and blockade of this pathway via selective IKK inhibition led to a partial reduction in oxidative stress. Furthermore, the generation of ROS following visfatin treatment was highly dependent on both de novo transcription and translation. Taken together, these findings provide novel insights for the unique pathophysiological role of visfatin in skeletal muscle.
Pflügers Archiv - European Journal of Physiology 11/2009; 459(4):619-30. · 4.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: One of the most conserved methods to significantly increase lifespan in animals is through dietary restriction (DR). The mechanisms by which DR increases survival are controversial but are thought to include improvements in mitochondrial function concomitant with reductions in reactive oxygen species production and alterations in the insulin signalling pathway, resulting in global metabolic adaptation. In order to identify novel genes that may be important for lifespan extension of Brown Norway rats, we compared gene expression profiles from skeletal muscle of 28-month-old animals fed ad libitum or DR diets using whole-genome arrays. Following DR, 426 transcripts were significantly down-regulated whilst only 52 were up-regulated. Included in the up-regulated transcripts were three functionally related previously unidentified DR-regulated genes: Nr4a1, Nr4a2, and Nr4a3. Up-regulation of all three Nr4a receptors was also observed in liver - but not brain - of DR-fed animals. Furthermore, RT-PCR revealed up-regulation of several NR4A transcriptional targets (Ucp-3, Ampk-gamma3, Pgc-1alpha and Pgc-1beta) in skeletal muscle of DR animals. Due to the proposed roles of the NR4A nuclear receptors in sensing and responding to changes in the nutritional environment and in regulating glucose and lipid metabolism and insulin sensitivity, we hypothesise that these proteins may contribute to DR-induced metabolic adaptation.
Mechanisms of ageing and development 04/2009; 130(4):240-7. · 4.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A number of physiological changes follow prolonged skeletal muscle unloading as occurs in spaceflight, bed rest, and hindlimb suspension (HLS) and also in aging. These include muscle atrophy, fiber type switching, and loss of the ability to switch between lipid and glucose usage, or metabolic inflexibility. The signaling and genomic events that precede these physiological manifestations have not been investigated in detail, particularly in regard to loss of metabolic flexibility. Here we used gene arrays to determine the effects of 24-h HLS on metabolic remodeling in mouse muscle. Acute unloading resulted in differential expression of a number of transcripts in soleus and gastrocnemius muscle, including many involved in lipid and glucose metabolism. These include the peroxisome proliferator-activated receptors (PPARs). In contrast to Ppar-alpha and Ppar-gamma, which were downregulated by acute HLS, Ppar-delta was upregulated concomitant with increased expression of its downstream target, uncoupling protein-3 (Ucp-3). However, differential expression of Ppar-delta was both acute and transient in nature, suggesting that regulation of PPARdelta may represent an adaptive, compensatory response aimed at regulating fuel utilization and maintaining metabolic flexibility.
[Show abstract][Hide abstract] ABSTRACT: Ageing is associated with an activation of the innate immune system which manifests in a chronic, low-grade, inflammatory
status common in elderly individuals. Age-related inflammatory activity, as measured by increased serum levels of proinflammatory
cytokines and activation of inflammatory signalling pathways, leads to long-term tissue damage and is thought to contribute
to—and occur as a consequence of—immunosenescence. In addition to immune system deregulation, this elevated inflammatory status
is associated with a number of age-related diseases and conditions, including neurodegeneration, atherosclerosis, sarcopenia,
and diabetes, and is a main contributor to the age-related decline in physical function and vitality known as frailty. Inflammation
is also an important component of the insulin resistance syndrome. In addition to age, a major risk factor for the development
of the insulin resistance syndrome is obesity. Obesity is associated with increased proinflammatory cytokine production and
altered regulation of both pro and antiinflammatory molecules, including a class of adipose-derived signalling molecules termed
adipocytokines. The increased production of inflammatory mol- ecules in obese and nonobese insulin resistant elderly individuals
may contribute to age-related decline in health, including dysfunction of the immune system. Antiinflammatory strategies for
the treatment of the insulin resistance syndrome may promote remodelling of the immune system thereby contributing to remediation
of immunity and prevention of frailty in the elderly population.