Calcium-induced alteration of mitochondrial morphology and mitochondrial-endoplasmic reticulum contacts in rat brown adipocytes.

Mitochondria are key organelles maintaining cellular bioenergetics and integrity, and their regulation of [Ca2+]i homeostasis has been investigated in many cell types. We investigated the short-term Ca-SANDOZ® treatment on brown adipocyte mitochondria, using imaging and molecular biology techniques. Two-month-old male Wistar rats were divided into two groups: Ca-SANDOZ® drinking or tap water (control) drinking for three days. Alizarin Red S staining showed increased Ca2+ level in the brown adipocytes of treated rats, and potassium pyroantimonate staining localized electron-dense regions in the cytoplasm, mitochondria and around lipid droplets. Ca-SANDOZ® decreased mitochondrial number, but increased their size and mitochondrial cristae volume. Transmission electron microscopy revealed numerous enlarged and fusioned-like mitochondria in the Ca-SANDOZ® treated group compared to the control, and megamitochondria in some brown adipocytes. The Ca2+ diet affected mitochondrial fusion as mitofusin 1 (MFN1) and mitofusin 2 (MFN2) were increased, and mitochondrial fission as dynamin related protein 1 (DRP1) was decreased. Confocal microscopy showed a higher colocalization rate between functional mitochondria and endoplasmic reticulum (ER). The level of uncoupling protein-1 (UCP1) was elevated, which was confirmed by immunohistochemistry and Western blot analysis. These results suggest that Ca-SANDOZ® stimulates mitochondrial fusion, increases mitochondrial-ER contacts and the thermogenic capacity of brown adipocytes.

Endothelial cell apoptosis in brown adipose tissue of rats induced by hyperinsulinaemia: the possible role of TNF-α.

The aim of the present study was to investigate whether hyperinsulinaemia, which frequently precedes insulin resistance syndrome (obesity, diabetes), induces apoptosis of endothelial cells (ECs) in brown adipose tissue (BAT) and causes BAT atrophy and also, to investigate the possible mechanisms underlying ECs death. In order to induce hyperinsulinaemia, adult male rats of Wistar strain were treated with high dose of insulin (4 U/kg, intraperitonealy) for one or three days. Examinations at ultrastructural level showed apoptotic changes of ECs, allowing us to point out that changes mainly but not exclusively, occur in nuclei. Besides different stages of condensation and alterations of the chromatin, nuclear fragmentation was also observed. Higher number of ECs apoptotic nuclei in the BAT of hyperinsulinaemic rats was also confirmed by propidium iodide staining. Immunohistochemical localization of tumor necrosis factor-alpha (TNF-α) revealed increased expression in ECs of BAT of hyperinsulinaemic animals, indicating its possible role in insulin-induced apoptotic changes. These results suggest that BAT atrophy in hyperinsulinaemia is a result of endothelial and adipocyte apoptosis combined, rather than any of functional components alone.

Morphological characteristics of abdominal adipose tissue in normal-weight and obese women of different metabolic profiles.

BACKGROUND AND AIMS: Morphological changes in adipose tissue reflect functional disorders that correlate with cardiometabolic complications of obesity. The metabolic risks vary among the obese individuals. Furthermore, normal-weight individuals are not necessarily metabolically healthy. Therefore, the aim of this study was to analyze morphological characteristics of the abdominal adipose tissue in normal-weight and obese individuals in regards to metabolic risks. METHODS AND RESULTS: The study group consisted of 30 overweight or obese and 20 normal-weight women undergoing elective surgery. Women of each group were divided into metabolically healthy and metabolically obese, based on the homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride, total-, LDL- and HDL-cholesterol levels. The size and numerical density of adipocytes, as well as volume density of blood vessels in subcutaneous and visceral adipose tissue were compared among subgroups. The results showed hypertrophy of adipocytes of visceral adipose tissue in metabolically obese normal-weight women. At the same time, metabolically healthy obese women had smaller adipocytes in both depots in comparison with "at risk" obese women. The lowest volume density of blood vessels correlated with the largest diameter of adipocytes in "at risk" obese women indicating hypoxic changes in visceral adipose tissue. The observed differences of the adipose tissue morphology did not correlate with considerable phenotypic differences within either the normal-weight or obese women group. CONCLUSION: Changes in adipocyte size, cellular and vascular density of adipose tissue in relation with metabolic disorders, regardless of nutritional level, suggest limited capacity of fat deposition and adipose tissue response to hypoxia.