Mechanical loading of cardiac and skeletal muscles in vivo and in vitro causes rapid activation of a number of immediate-early (IE) genes and hypertrophy of muscle cells. However, little is known as to how muscle cells sense mechanical load and transduce it into intracellular signals of gene regulation. We examined roles of putative cellular mechanotransducers, mechanosensitive ion channels, the cytoskeleton, and contractile activity in stretch-induced hypertrophy of cardiac myocytes grown on a deformable silicone sheet. Using the patch-clamp technique, we found a single class of stretchactivated cation channel that was completely blocked by gadolinium (Gd3+). Inhibition of this channel by Gd3+ did not affect either the stretch-induced expression of TE genes or the increase in protein synthesis. Neither disruption of microtubules with colchicine nor that of actin microfilaments by cytochalasin D prevented the stretch-induced IE gene expression and increase in protein synthesis. Arresting contractile activity of myocytes by high K+, tetrodotoxin, or Ba2+ did not affect the stretch-induced TE gene expression. Tetrodotoxinarrested myocytes could increase protein synthesis in response to stretch. These results suggest that Gd3+-sensitive ion channels, microtubules, microfflaments, and contractile activity may not be necessary for transduction of mechanical stretch into the IE gene expression and hypertrophy. The stimulus of membrane stretch may be transmitted to the cell nucleus through some mechanisms other than electrical or direct mechanical transduction in cardiac myocytes.In living animals, many types of cells are normally exposed to a variety of mechanical stimuli. Although it is a well-known fact that mechanical stimuli cause a variety of effects on the structure and function of the cell (1-3), little is known as to how cells sense the mechanical stimuli, transmit the information to second-messenger systems, and finally regulate gene expression.Cardiac and skeletal muscles rapidly change their mass and phenotype in response to the mechanical load imposed on them (4, 5), and they may be a suitable model system to study how mechanical stimuli regulate gene expression in nonsensory cells. It has been demonstrated that stretching cultured cardiac and skeletal muscle cells grown on a deformable silicone substrate increases protein synthesis (6-9); this result indicates that the ability to sense mechanical load is intrinsic to muscle cells and does not require exogenous neurohormonal factors. More recently, stretching cardiac muscle has been shown to increase inositol monophosphate and bisphosphate (10, 11) and to activate many other signal-transduction pathways (J.-i.S. and S.I., unpublished data), but how cells initially convert mechanical stimuli into biochemical signals is unknown. It has been postulated that mechanosensitive ion channels, the cytoskeleton, and contractile activity may act as mechanotransducers in muscle and other cell types (for reviews, see refs. 1-3, 12, and 13). However, experimenta...

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Although it is likely that a highly complex network of transcription factors acts in concert during mammalian brain development, relatively few such genes have been characterized to date. We describe here a novel murine homeobox gene, denoted Gtx, which in adult animals is specifically expressed within glial cells of the central nervous system, including the forebrain, and in germ cells of the testis. Gtx resides on chromosome 7 and does not cosegregate with any previously mapped homeobox gene. The amino acid sequence of the predicted protein encoded by Gtx is highly divergent from that of any other known homeobox genes. The Gtx homeodomain contains unique residues at positions predicted to contact DNA bases. It did not bind to known target sites for other homeobox genes in vitro but bound with high affinity to the MEF‐2 motif, a binding site for the serum response factor‐related proteins. GTX efficiently competed with RSRF to bind the MEF‐2 element in vitro. Co‐transfection of Gtx prevented the serum‐induced activation of the MEF‐2‐containing reporter genes. Although the true biological role of Gtx is not known, these results suggest that Gtx is a novel cell‐type specific homeobox gene that has the potential to act as a transcriptional repressor for a subset of serum‐inducible genes.

Enzymes involved in the metabolism nitric oxide (NO) and reactive oxygen species (ROS) may play a role for the decreased availability of NO in atherosclerosis. We, therefore, hypothesized that the pattern of gene expression of these enzymes is altered in atherosclerosis. Myocardial tissue from patients with coronary heart disease (CHD) or without CHD (control group) was investigated. The level of enzymes related to NO/ROS metabolism was determined both at mRNA level and protein level by rt-PCR, real-time PCR, and western blot. The expression of NOS1-3 (synthesis of NO), arginase1 (reduction of L-arginine), p22phox (active subunit of NADPH oxidase), GTPCH (rate limiting enzyme for tetrahydrobiopterin), SOD1-3 (scavengers of superoxide anions), PRTMT1-3, and DDAH2 (involved in the metabolism of ADMA) was determined. All enzymes were found to be expressed in human myocardium. NOS isoforms were decreased in CHD in protein level, but only the downregulation of NOS3 expression reached statistical significance. The expression of PRMT1 and PRMT3 was increased. In addition, the expression of DDAH2 was reduced, both theoretically leading to an increase of ADMA concentration. SOD3 was downregulated in tissue from patients with CHD. Taken together, in myocardial tissue from patients with atherosclerosis, the expression of genes increasing ADMA levels is enhanced in contrast to a reduced expression of genes promoting NO synthesis. These results may contribute to the explanation of increased oxidative stress in atherosclerosis on the level of gene expression.