Background-The striated preferentially expressed gene (Speg) generates 4 different isoforms through alternative promoter use and tissue-specific splicing. Depending on the cell type, Speg isoforms may serve as markers of striated or smooth muscle differentiation. Methods and Results-To elucidate function of Speg gene isoforms, we disrupted the Speg gene locus in mice by replacing common exons 8, 9, and 10 with a lacZ gene. ␤-Galactosidase activity was detected in cardiomyocytes of the developing heart starting at day 11.5 days post coitum (dpc). ␤-Galactosidase activity in other cell types, including vascular smooth muscle cells, did not begin until 18.5 dpc. In the developing heart, protein expression of only Speg␣ and Speg␤ isoforms was present in cardiomyocytes. Homozygous Speg mutant hearts began to enlarge by 16.5 dpc, and by 18.5 dpc, they demonstrated dilation of right and left atria and ventricles. These cardiac abnormalities in the absence of Speg were associated with a cellular hypertrophic response, myofibril degeneration, and a marked decrease in cardiac function. Moreover, Speg mutant mice exhibited significant neonatal mortality, with increased death occurring by 2 days after birth. Conclusions-These findings demonstrate that mutation of the Speg locus leads to cardiac dysfunction and a phenotype consistent with a dilated cardiomyopathy. Key Words: cardiomyopathy Ⅲ hypertrophy Ⅲ myocytes Ⅲ genes M yosin light chain kinases (MLCK) are a family of proteins that are important for myocyte function, including structure and regulation of the actin-based cytoskeleton. 1,2 One member of this family, striated preferentially expressed gene (Speg), has isoforms in both striated and smooth muscle cells. 3 The Speg locus contains 2 transcriptional start sites, and through alternative promoter use and splicing in a tissue-specific manner, it generates 4 different isoforms. 3 Speg␣ and Speg␤ are expressed in striated muscle (cardiac and skeletal), aortic preferentially expressed gene (Apeg-1) is expressed in smooth muscle (predominantly vascular), and brain preferentially expressed gene (Bpeg) is expressed in the brain and aorta. [3][4][5] Speg␣ and Speg␤ share homology with MLCK family members. Specifically, the Speg isoforms, along with obscurin-MLCK, are unique members of the MLCK family, because they contain 2 tandemly arranged serine/threonine kinase (MLCK) domains. 2 Beyond the MLCK domains, Speg␣ and Speg␤ also contain immunoglobulin and fibronectin domains that are characteristic of the MLCK family of proteins. Prior investigations in our laboratory revealed that Speg␣ and Speg␤ are sensitive markers of striated muscle differentiation and that Speg colocalizes with desmin in the sarcomeric Z disc 3 ; however, the functional significance of Speg isoforms is yet to be elucidated. Editorial p 213 Clinical Perspective p 268In contrast to smooth muscle cells, striated muscle cells of both cardiac and skeletal origin undergo terminal differenti- Received June 15, 2008; accepted October 14, 2008. From Pulmona...

The purpose of this study was to evaluate the differences that occur within the plasma compartment of normolipidemic men, classified on the basis of their response to prolonged consumption of additional dietary cholesterol. Using a crossover design, 40 men aged 18-57 y were randomly allocated to an egg (640 mg/d additional dietary cholesterol) or placebo group (0 mg/d additional dietary cholesterol), for two 30-d periods, which were separated by a 3-wk washout period. Subjects were classified as hypo- [increase in plasma total cholesterol (TC) of <0.05 mmol/L for each additional 100 mg of dietary cholesterol consumed] or hyperresponders (increase in TC of > or =0.06 mmol/L for each additional 100 mg of dietary cholesterol consumed) on the basis of their plasma reaction to the additional dietary cholesterol provided. Male hyporesponders did not experience an increase in LDL cholesterol (LDL-C) or HDL cholesterol (HDL-C) during the egg period, whereas both lipoproteins were significantly (P < 0.0001 and P < 0.05, respectively) elevated in hyperresponders. Although the LDL/HDL ratio was increased in male hyperresponders after the high cholesterol period, the mean increase experienced by this population was still within National Cholesterol Education Program guidelines. Furthermore, male hyperresponders had higher lecithin cholesterol acyltransferase (P < 0.05) and cholesteryl ester transfer protein (P < 0.05) activities during the egg period, which suggests an increase in reverse cholesterol transport. These data suggest that additional dietary cholesterol does not increase the risk of developing an atherogenic lipoprotein profile in healthy men, regardless of their response classification.

These data revealed that excess dietary cholesterol does not increase the risk of developing an atherogenic lipoprotein profile in pre-menopausal women, regardless of their response classification. Although the addition of 640 mg of cholesterol to the diet did result in an increase in plasma cholesterol in hyperresponders, the LDL/HDL ratio was maintained. This result, accompanied by increases in CETP activity, leads to the speculation that hyper-responders may process the excess cholesterol in the plasma compartment through an enhancement of the reverse cholesterol transport pathway. With this mechanism identified, further measurement of additional parameters is needed to verify this conclusion.

Male Hartley guinea pigs (10/group) were assigned either to a control diet (no drug treatment) or to diets containing 0.4, 2.2, or 7.3 mg/day of an ileal apical sodium-codependent bile acid transporter (ASBT) inhibitor, 1-[4-[4[(4R,5R) . Based on food consumption, guinea pigs received 0, 0.8, 3.7, or 13.4 mg/kg/day of the ASBT inhibitor. The amount of cholesterol in the four diets was maintained at 0.17%, equivalent to 1200 mg/day in the human situation. Guinea pigs treated with 13.4 mg/kg/day SC-435 had 41% lower total cholesterol and 44% lower low-density lipoprotein (LDL)-cholesterol concentrations compared with control (P Ͻ 0.01), whereas no significant differences were observed with either of the lower doses of SC-435. Hepatic cholesterol esters were significantly reduced by 43, 56, and 70% in guinea pigs fed 0.8, 3.7, and 13.4 mg/kg/day of the ASBT inhibitor, respectively (P Ͻ 0.01). In addition, the highest dose of the inhibitor resulted in a 42% increase in the number of very low-density lipoprotein (VLDL) triacylglycerol molecules and a larger VLDL diameter compared with controls (P Ͻ 0.05). Acyl-CoA cholesterol/acyltransferase activity was 30% lower with the highest dose treatment, whereas cholesterol 7␣-hydroxylase, the regulatory enzyme of bile acid synthesis, was 30% higher with the highest ASBT inhibitor dose (P Ͻ 0.05). Furthermore, bile acid excretion increased 2-fold with the highest dose of SC-435 compared with the control group (P Ͻ 0.05). These results suggest that the reduction in total and LDL-cholesterol concentrations by the ASBT inhibitor is a result of alterations in hepatic cholesterol metabolism due to modifications in the enterohepatic circulation of bile acids.

To evaluate some of the mechanisms involved in the hypocholesterolemic effects of corn fiber oil (CFO), male Hartley guinea pigs were fed diets containing increasing doses of CFO [0 (control), 5, 10 or 15 g/100 g]. Total fat was adjusted to 15 g/100 g in all diets with regular corn oil. Diets contained 0.25 g/100 g cholesterol. A positive control group (LC) with low dietary cholesterol (0.04 g/100 g) was also included. Plasma LDL cholesterol concentrations were 32, 55 and 57% (P Ͻ 0.0005) lower with increasing doses of CFO. Compared with controls, intake of CFO resulted in 27-32% lower hepatic microsomal cholesterol (P Ͻ 0.0001), the regulatory pool of LDL receptor (LDL-R) expression. CFO intake resulted in favorable plasma and hepatic cholesterol concentrations, similar to those in guinea pigs fed the LC diet. Hepatic cholesterol 7␣-hydroxylase (CYP7) activity was ϳ88% higher in guinea pigs fed the two higher dosages of CFO (P Ͻ 0.05). In parallel, CYP7 mRNA abundance was ϳ88% higher in guinea pigs fed all three CFO diets. CFO treatment also induced hepatic LDLR mRNA by 66 -150% with significant differences at the highest CFO dose. These results suggest that CFO, as a result of decreased bile acid absorption, increased mRNA abundance and activity of CYP7. Because hepatic cholesterol is the substrate for CYP7, a lowering of cholesterol concentrations in the total and microsomal pools was observed. As a response to the depleted microsomal free cholesterol pool, the LDL receptor was up-regulated, drawing more cholesterol from plasma, thus leading to the observed decrease in plasma LDL cholesterol concentrations. J. Nutr. 132: 335-340, 2002.

These studies were undertaken to assess guinea pigs as potential models for early atherosclerosis development. For that purpose, male, female, and ovariectomized (to mimic menopause) guinea pigs were fed a control or a TEST diet for 12 wk. Differences between diets were the type of protein (60% casein/40% soybean vs. 100% soybean) and the type of fiber (12.5% cellulose vs. 2.5% cellulose/5% pectin/5% psyllium) for control and TEST diets, respectively. Diet had no effect on plasma cholesterol or triacylglycerol (TAG) concentrations; however, there were significant effects related to sex/hormonal status. Ovariectomized guinea pigs had higher plasma cholesterol and TAG concentrations than males or females (P < 0.01). In contrast to effects on plasma lipids, hepatic cholesterol and TAG were 50% lower in the TEST groups (P < 0.01) compared to controls. Low density lipoproteins (LDL) from guinea pigs fed the TEST diet had a lower number of cholesteryl ester (CE) molecules and a smaller diameter than LDL from controls. Atherosclerotic lesions were modulated by both diet (P < 0.0001) and sex (P < 0.0001). Guinea pigs fed the TEST diet had 25% less lesion extension whereas males had 20% larger occlusion of the arteries compared to both female and ovariectomized guinea pigs. Significant positive correlations were found between LDL CE and atherosclerotic lesions (r = 0.495, P < 0.05) and LDL size and fatty streak area (r = 0.56, P < 0.01). In addition, females fed the TEST diet had the lowest plasma and hepatic cholesterol concentrations, the smallest LDL particles, and the least atherosclerosis involvement compared to the other groups. These data indicate that dietary factors and sex/hormonal status play a role in determining plasma lipids and atherosclerosis in guinea pigs.

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To evaluate some of the mechanisms involved in the plasma cholesterol lowering of sitostanol (SI), male Hartley guinea pigs were fed diets containing cholesterol (0´25 g/100 g) and four doses of SI: either 0 (control), 0´75, 1´5 or 2´25 g/100 g. In addition a negative control (2C) group with dietary cholesterol (0´04 g/100 g) was included. Corn oil was used as the source of fat and the contribution of fat energy was 35 %. Plasma total cholesterol was 43, 49 and 53 % P , 0´0001 lower after SI intake compared to the control. Plasma LDL concentrations were 47, 53 and 61 % lower with increasing doses of SI. In addition, intake of SI resulted in 26±42 % lower hepatic total cholesterol. Hepatic esterified cholesterol and triacylglycerols were 32± 60 % and 55±61 % lower after SI intake. SI intake resulted in favourable plasma and hepatic cholesterol concentrations similar to those in guinea pigs fed low levels of dietary cholesterol (2C). The LDL obtained from the control group had a higher number of molecules of free and esterified cholesterol than the SI groups. SI intake resulted in 69±71 % higher cholesterol excretion compared to the control. SI treatment enhanced the total faecal neutral sterol excretion by 54±58 % compared to control and by 70±76 % compared to the (2C) group. These results suggest that SI might have its hypocholesterolaemic effect by reducing cholesterol absorption, which results in lower concentration of cholesterol in liver. This reduction in hepatic cholesterol might possibly alter hepatic cholesterol metabolism and affect lipoprotein concentration and composition.