Effect of inhibitors of cholesterol synthesis on muscle differentiation

Angiotensin-II-induced Muscle Wasting is Mediated by 25-Hydroxycholesterol via GSK3β Signaling Pathway

While angiotensin II (ang II) has been implicated in the pathogenesis of cardiac cachexia (CC), the molecules that mediate ang II's wasting effect have not been identified. It is known TNF-α level is increased in patients with CC, and TNF-α release is triggered by ang II. We therefore hypothesized that ang II induced muscle wasting is mediated by TNF-α. Ang II infusion led to skeletal muscle wasting in wild type (WT) but not in TNF alpha type 1 receptor knockout (TNFR1KO) mice, suggesting that ang II induced muscle loss is mediated by TNF-α through its type 1 receptor. Microarray analysis identified cholesterol 25-hydroxylase (Ch25h) as the down stream target of TNF-α. Intraperitoneal injection of 25-hydroxycholesterol (25-OHC), the product of Ch25h, resulted in muscle loss in C57BL/6 mice, accompanied by increased expression of atrogin-1, MuRF1 and suppression of IGF-1/Akt signaling pathway. The identification of 25-OHC as an inducer of muscle wasting has implications for the development of specific treatment strategies in preventing muscle loss.

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Ang II induced muscle wasting is mediated by TNF-α, which in turn up regulates Ch25h

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Knockout of TNFR1 inhibits the production of 25-OHC and blocks ang II induced muscle loss in mice

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25-OHC injection induces muscle wasting in mice by activating GSK3β

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A GSK3β inhibitor blocks ang II induced muscle atrophy, which paves the way for targeted therapy to treat muscle wasting

Cardiac cachexia (CC), a condition characterized by weight loss and muscle wasting, is a serious complication that occurs in patients with chronic heart failure. This condition impairs patient's daily physical activity and their quality of life. Specific therapy for CC is currently unavailable because the pathogenesis remains unknown. Previous studies have identified angiotensin II (ang II) as an important mediator of CC. We now report a previously unrecognized role of 25-hydroxycholesterol (25-OHC) in mediating ang II induced muscle loss. The identification of 25-OHC as a muscle wasting inducer has implications for the development of therapeutic intervention in preserving muscle mass.

Cytoskeleton and Adhesion in Myogenesis

The function of muscle is to contract, which means to exert force on a substrate. The adaptations required for skeletal muscle differentiation, from a prototypic cell, involve specialization of housekeeping cytoskeletal contracting and supporting systems into crystalline arrays of proteins. Here I discuss the changes that all three cytoskeletal systems (microfilaments, intermediate filaments, and microtubules) undergo through myogenesis. I also discuss their interaction, through the membrane, to extracellular matrix and to other cells, where force will be exerted during contraction. The three cytoskeletal systems are necessary for the muscle cell and must exert complementary roles in the cell. Muscle is a responsive system, where structure and function are integrated: the structural adaptations it undergoes depend on force production. In this way, the muscle cytoskeleton is a portrait of its physiology. I review the cytoskeletal proteins and structures involved in muscle function and focus particularly on their role in myogenesis, the process by which this incredible muscle machine is made. Although the focus is on skeletal muscle, some of the discussion is applicable to cardiac and smooth muscle.

Cholesterogenesis and cell division in phytohemagglutinin-stimulated human lymphocytes: a comparative study with several inhibitors

It has been shown that when lymphocytes are stimulated by phytohemagglutinin the expected stimulation of DNA synthesis is preceded by stimulation of cholesterol synthesis. This confirms the existence of a relation between cell division and cholesterol synthesis. We studied the effect on cell division of six inhibitors of cholesterol biosynthesis, previously shown to interfere with different steps of the process: 7 beta-hydroxycholesterol, 25-hydroxycholesterol, lanost-7-en-3 beta, 32-diol, mevinolin, propiconazole, dodecylimidazole. Since experiments were performed in the presence of a high percentage of human serum, which provided cells with exogenous cholesterol via the LDL-receptor pathway, our investigation was focused on the role of newly synthesized cholesterol. The biosynthesis was evaluated by labeling cells with [14C]sodium acetate; to take into account variations of cell permeability to sodium acetate, the results were expressed as the percentage of total cellularly incorporated radioactivity transformed into cholesterol, after separation from all other labeled metabolites. These data were compared with the percentage of transformation into nonsaponifiable lipids, which varied in parallel with HMG-CoA reductase activity, as confirmed by direct enzymatic measurement. Cell division was assessed by simultaneous measurements of three parameters: thymidine incorporation into DNA, cell proliferation and cellular protein content. All the effectors strongly inhibited the conversion of labeled acetate into cholesterol, but cell division was not inhibited by two of them: propiconazole and 7 beta-hydroxycholesterol. These compounds only slightly inhibited the synthesis of nonsaponifiable lipids, which mainly consisted of methylsterols resulting from a blockage of lanosterol demethylation. Thus, it can be concluded that the nonsaponifiable metabolite essential for cell growth is not newly synthesized cholesterol. It was also found that inhibitors affected cell division only when they were added to the culture medium before the decline of cholesterol synthesis stimulation.

The role of enterocyte cholesterol metabolism in intestinal cell growth and differentiation

Cholesterol is an essential constituent of all mammalian cell membranes, and its availability is therefore a prerequisite for cellular growth and other functions. To define further the role of cholesterol metabolism in the intestine both in vitro and in vivo, studies were performed. Several lines of evidence based on these studies suggest that the main purpose of local cholesterol synthesis in the gut is the support of rapid enterocyte proliferation: 1) growth was inhibited during pharmacologic suppression of cholesterol synthesis in intestinal organ or cell culture; 2) the endocrine regulation of intestinal growth was in most but not all instances accompanied by appropriate changes in cholesterol synthesis; 3) most of cholesterol synthesis and lipoprotein uptake was localized predominantly in the crypt and lower villus region; and 4) very little of the sterol synthesized by the intestinal mucosa was exported into lymph but seems rather to be incorporated into cell membranes.

The fusion of myoblasts

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