ABSTRACT
GH is a well established regulator of growth, lipid, and glucose metabolism and therefore important for fuel utilization. However, little is known about the effects of macronutrients on the GH/IGF system. We used low-carbohydrate/high-fat diets (LC-HFD) as a model to study the impact of fat, protein, and carbohydrates on the GH/IGF-axis; 12-wk-old Wistar rats were fed either regular chow, a moderate, protein-matched LC-HFD, or a ketogenic LC-HFD (percentage of fat/protein/carbohydrates: chow, 16.7/19/64.3; LC-HF-1, 78.7/19.1/2.2; LC-HF-2, 92.8/5.5/1.7). After 4 wk, body and tibia length, lean body mass, and fat pad weights were measured. Furthermore, we investigated the effects of LC-HFD on 1) secretion of GH and GH-dependent factors, 2) expression and signaling of components of the GH/IGF system in liver and muscle, and 3) hypothalamic and pituitary regulation of GH release. Serum concentrations of IGF-I, IGF binding protein-1, and IGF binding protein-3 were lower with LC-HF-1 and LC-HF-2 (P < 0.01). Both LC-HFD-reduced hepatic GH receptor mRNA and protein expression, decreased basal levels of total and phosphorylated Janus kinase/signal transducers and activators of transcription signaling proteins and reduced hepatic IGF-I gene expression. Hypothalamic somatostatin expression was reduced only with LC-HF-1, leading to increased pituitary GH secretion, higher IGF-I gene expression, and activation of IGF-dependent signaling pathways in skeletal muscle. In contrast, despite severely reduced IGF-I concentrations, GH secretion did not increase with LC-HF-2 diet. In conclusion, lack of carbohydrates in LC-HFD induces hepatic GH resistance. Furthermore, central feedback mechanisms of the GH/IGF system are impaired with extreme, ketogenic LC-HFD.
Subject(s)
Diet, Carbohydrate-Restricted , Dietary Carbohydrates/pharmacology , Growth Hormone/metabolism , Liver/drug effects , Animals , Blotting, Western , Body Composition/drug effects , Body Weight/drug effects , Dietary Carbohydrates/administration & dosage , Dietary Fats/administration & dosage , Dietary Fats/pharmacology , Dietary Proteins/administration & dosage , Dietary Proteins/pharmacology , Gene Expression/drug effects , Glycogen Synthase Kinase 3/metabolism , Glycogen Synthase Kinase 3 beta , Growth Hormone/blood , Growth Hormone/genetics , Insulin-Like Growth Factor Binding Proteins/blood , Insulin-Like Growth Factor Binding Proteins/genetics , Insulin-Like Growth Factor Binding Proteins/metabolism , Insulin-Like Growth Factor I/genetics , Insulin-Like Growth Factor I/metabolism , Liver/metabolism , Male , Proto-Oncogene Proteins c-akt/metabolism , Rats , Rats, Wistar , Receptors, Somatotropin/genetics , Receptors, Somatotropin/metabolism , Reverse Transcriptase Polymerase Chain Reaction , STAT3 Transcription Factor/metabolism , STAT5 Transcription Factor/metabolismABSTRACT
Donor organ shortage is still the major obstacle for the clinical application of hepatocyte transplantation in the treatment of liver diseases. However, generation of hepatocyte-like cells from mesenchymal stem cells (MSCs) has become a real alternative to the isolation of primary hepatocytes. MSCs are extracted from the tissue by collagenase digestion and enriched by their capacity to grow on plastic surfaces. Enriched cells display distinct mesenchymal surface markers and are capable of multiple lineage differentiation. In the presence of specific growth conditions, the cells adopt functional features of differentiated hepatocytes. After orthotopic transplantation, differentiated human stem cells engraft in the host liver parenchyma of immunocompromised mice. This protocol describes the in vitro differentiation of stem cells from human bone marrow and their transplantation into livers of immunodeficient mice. The cell culture procedures take about 4-5 weeks, and cells engrafted in the mouse liver may be detected 2-3 months after transplantation.
Subject(s)
Hepatocytes/cytology , Hepatocytes/transplantation , Liver Transplantation/methods , Mesenchymal Stem Cells/cytology , Albumins/metabolism , Animals , Bone Marrow Cells/cytology , Cell Differentiation , Cell Separation , Hepatocytes/metabolism , Humans , Immunocompromised Host , Mice , Mice, Knockout , Models, Animal , Transplantation, HeterologousABSTRACT
OBJECTIVE: Acute hepatic fat accumulation appears to be crucial for liver regeneration after partial hepatectomy. Since fatty acids in the liver are provided by catecholamine-induced lipolysis in the adipose tissue, we investigated whether beta-adrenergic blockade of lipolysis might affect liver regeneration. MATERIAL AND METHODS: Mice were treated with propranolol prior to partial hepatectomy. Subsequently, liver regeneration was evaluated histologically, by determination of the relative liver weight and the mitotic index at different time points after surgery. RESULTS: Liver mass restoration was delayed by propranolol, which was associated with a lower hepatic triglyceride content. Ki-67 labelling indicated that liver regeneration was attenuated by propranolol through inhibition of mitosis. Hepatocytes were arrested in the G1 phase of the cell cycle, as shown by the expression of G1-related proteins such as proliferating cell nuclear antigen, cyclin D1 and cyclin-dependent kinase-2, and underwent apoptosis as indicated by detection of poly(adenosine diphosphate-ribose) polymerase fragments. beta-adrenergic blockade of the host animal did not provide transplanted hepatocytes with a growth advantage over host cells. CONCLUSION: Impairment of liver regeneration by propranolol is related to the inhibition of acute hepatic fat accumulation and to a predisposition of hepatocytes to apoptosis.
