Atrophy of brown adipocytes in the adult mouse causes transformation into white adipocyte-like cells

Adipose tissue is an important endocrine regulator of glucose metabolism and energy homeostasis. Researches have focused on this tissue not only as a target for pharmacotherapy of obesity and insulin resistance but also as an endocrine tissue with leptin secretion and high insulin sensitivity. Brown adipose tissue (BAT) additionally plays a unique role in thermoregulation through the mitochondrial uncoupling protein 1 (UCP1), which uncouples oxidative phosphorylation. As a genetic tissue ablation model of BAT, we made transgenic mice expressing herpes simplex virus thymidine kinase (HSV-TK) driven by the brown adipocyte- specific UCP1 minimal regulatory element. The HSV-TK transgene was expressed specifically in BAT and more than 35% increase of apoptosis was induced by ganciclovir (GCV) treatment. Nevertheless, the expression level was not high enough to induce BAT ablation in GCV-treated adult mice. Importantly, however, we found that brown adipocytes in the periphery of interscapular BAT were transformed into white adipocyte-like unilocular cells. These cells express white adipocyte-specific leptin protein but are different in the ultrastructure of mitochondria from classical white adipocytes. Our data indicates that atrophy of BAT causes transformation into white adipocyte-like cells in the adult mouse and also suggests that further molecular understanding of adipocyte plasticity using our transgenic mouse model might be beneficial for the development of anti-obesity/anti-diabetic therapies.

Lipofilling of the lips: ultrastructural evaluation by transmission electron microscopy of injected adipose tissue

OBJECTIVE

To determine if facial autologous fat grafts preserve the morphologic features of adipocytes and guarantee a successful long-term outcome.

METHODS

In a previous study, we performed lipofilling in 99 patients between January 1, 1999, and December 31, 2001. In all patients, we performed 3 fat injections at 28-day intervals. We injected 0.4 mL of adipose tissue in the parafrenal area of the upper lip for each treatment. After 4 months, we obtained a biopsy specimen from the same area. We performed an ultrastructural evaluation on freshly harvested fat at the time of harvesting, on stored fat (-30 degrees C) at 8-week and 12-month intervals, and on the biopsy specimens obtained 4 months after treatment.

RESULTS

We observed good preservation of the ultrastructure in the harvested tissue. On histologic examination of the parafrenal area 4 months after grafting, some zones of the biopsy specimens showed putative adipocytes, fat cysts, and collagen fibers adequate for volume increase of the treated area. Ultrastructural images showed lipid droplets intermingled in the connective tissue, phagocytes with internal lipid droplets, and well-preserved adipocytes.

CONCLUSIONS

This study demonstrates that by using a less traumatic surgical technique, it is possible to increase the cell survival rate of transplanted fat, thereby maintaining a certain number of viable cells and creating a volume increase in the grafted area. The multiple-stage injection technique seems to be a good method, especially when performed with fat stored at -30 degrees C.

[Myocardial fatty dystrophy in patients with Fallot tetralogy]

Fatty degeneration (FD) was studied histochemically and ultrastructurally in surgical biopsies from 147 patients aged 22 days to 40 years with Fallot's tetralogy. FD was most pronounced in patients aged 3 to 6 years when the main part of cardiomyocytes completed the program of ontogenetical growth and started growing as hypertrophic mature cells. An increase of FD is considered as manifestation of an initial stage of hypertrophy of mature cardiomyocytes.

Electron microscopic study of the differentiation of rat white subcutaneous adipocytes in situ

In the present study we investigated the process of differentiation of rat subcutaneous white adipocytes in situ using electron microscopy.

MATERIAL AND METHODS

Rat fetuses (Wistar rat) at 15 - 21 days of pregnancy were used. Sections of the subcutaneous tissue of a hind leg were prepared for examination with transmission electron microscopy by routine techniques.

RESULTS

The electron microscopic study showed that the embryonal differentiation of rat subcutaneous white adipose cells in situ started on the 15 - 16th day of gestation and was expressed by lipid accumulation and concomitant changes in the cell organelles. We observed the following in the differentiating adipocytes: 1. abundant glycogen granules; 2. appearance and accumulation of lipid droplets with gradual formation of several lipid droplets or one large lipid drop which pushed the nucleus to the periphery and rounded the cell; 3. large elongated mitochondria with densely packed transverse cristae; disintegration of cristae, swelling and vacuolization occurring in some of the mitochondria; 4. well developed endoplasmic reticulum with elongated and dilated cisternae; the initial predominance of rough endoplasmatic reticulum being superseded by prevalence of smooth endoplasmatic reticulum. The ultrastructural analysis we did revealed the consecutive stages in the adipocyte differentiation and the formation of adipocyte phenotype during the embryonal development of the rat.

An alternative design of locked percutaneous device for skeletal extension through skin

A skeletal extension bar (SEB) through the skin may be involved with many treatments of orthopedic diseases. A new locked percutaneous device (LPD), LPD-III, was designed for the SEB not only to allow the skin to bind onto the SEB, similarly to the LPD, but also to allow the skin binding to shift up or down the SEB while the body changes weight. Two designs of LPD-III were tried. The LPD-III-F was made from a formation of nylon hooks, fixed directly onto the SEB surface. Soft tissue can lock and shift onto the hook formation naturally. The LPD-III-S was made by attaching a stainless steel spring as a single row of rings on a nylon sleeve. Tissue can lock through the spring rings and the nylon sleeve can be manually shifted on the SEB to follow the change of thickness of soft tissue. The SEB is a stainless steel bar implanted in the sheep ilium through the skin and buttock. Two sheep were employed, both implanted with a SEB with LPD-III-F in one ilium and another SEB with LPD-III-S in the other ilium. Our experiment demonstrates that: first, both designs, LPD-III-F and LPD-III-S, function well as a skin junction shifting device; second, the LPD-III-F has abilities to re-bind the skin that not only repair damaged binding junction but also shift the skin binding up to overcome skin downgrowth; and third, powerful evidence certifies again that the mechanical connection exists in LPD.

[Adipose tissue within peripheral nerves. Study of the human sciatic nerve]

AIM

To describe the distribution of intraneural adipose cells in relation to nerve fascicles in a portion of peripheral nerve usually involved in accomplishing an anesthetic blockade of a lower extremity.

METHOD

Using a scanning electron microscope, we studied sciatic nerve samples from the point of amputation of a lower limb of three patients. The samples were obtained at the upper angle of the popliteal fossa, 10-15 cm cephalad to the knee joint line.

RESULTS

During dissection of the sciatic nerve samples, we observed a solitary trunk, but examination of the cross-sections under the microscope revealed the components of two clearly separated branches joined by supporting tissue. The sciatic nerve had an oval form in the portion under study, measuring 6.5 to 7.5 mm by 3.6 to 3.9 mm. Between the fascicles, the adipose tissue varied in thickness from 0.5 mm in the central zones to 0.2 mm in the peripheral zones. The adipocytes, which were all similar in the size with diameters of 40 microns, were empty, as a result of elimination of the lipid vacuoles during fixation. The adipose tissue was distributed inside the epineurium to surround isolated fascicles or groups of fascicles.

CONCLUSIONS

The adipose tissue inside a nerve surrounded the fascicles to form adipose sheaths that separated the fascicles from one another. The thicknesses of these adipose sheaths varied from one fascicle to another. Cells join to make it possible to create a compact adipose sheet that can delay the diffusion of local anesthetic injected near a nerve and that can therefore interfere with the characteristics of an anesthetic blockade.

Giant membrane vesicles as a model to study cellular substrate uptake dissected from metabolism

In order to use giant vesicles for substrate uptake studies in metabolically important tissues, we characterized giant vesicles isolated from heart, liver, skeletal muscle and adipose tissue. We investigated which cell types and which plasma membrane regions are involved in giant vesicle formation and we examined the presence of transporters for metabolic substrates. Analysis of giant vesicles with markers specific for distinct cell types and distinct domains of the plasma membrane reveals that the plasma membrane of parenchymal cells, but not endothelial cells, are the source of the vesicle membranes. In addition, plasma membrane regions enriched in caveolae and involved in docking of recycling vesicles from the endosomal compartment are retained in giant vesicles, indicating that KCl-induced alterations in recycling processes are involved in giant vesicle formation. Giant vesicles contain vesicular lumen consisting of the soluble constituents of the cytoplasm including, fatty-acid binding proteins. Furthermore, giant vesicles isolated from heart, liver, skeletal muscle and adipose tissue are similar in size (10-15 microm) and shape and do not contain subcellular organelles, providing the advantage that substrate fluxes in the different organs can be studied independently of the surface/volume ratio but most importantly in the absence of intracellular metabolism.

Fat liquefaction: effect of low-level laser energy on adipose tissue

Low-level laser energy has been increasingly used in the treatment of a broad range of conditions and has improved wound healing, reduced edema, and relieved pain of various etiologies. This study examined whether 635-nm low-level lasers had an effect on adipose tissue in vivo and the procedural implementation of lipoplasty/liposuction techniques. The experiment investigated the effect of 635-nm, 10-mW diode laser radiation with exclusive energy dispersing optics. Total energy values of 1.2 J/cm(2), 2.4 J/cm(2), and 3.6 J/cm(2) were applied on human adipose tissue taken from lipectomy samples of 12 healthy women. The tissue samples were irradiated for 0, 2, 4, and 6 minutes with and without tumescent solution and were studied using the protocols of transmission electron microscopy and scanning electron microscopy. Nonirradiated tissue samples were taken for reference. More than 180 images were recorded and professionally evaluated. All microscopic results showed that without laser exposure the normal adipose tissue appeared as a grape-shaped node. After 4 minutes of laser exposure, 80 percent of the fat was released from the adipose cells; at 6 minutes of laser exposure, 99 percent of the fat was released from the adipocyte. The released fat was collected in the interstitial space. Transmission electron microscopic images of the adipose tissue taken at x60,000 showed a transitory pore and complete deflation of the adipocytes. The low-level laser energy affected the adipose cell by causing a transitory pore in the cell membrane to open, which permitted the fat content to go from inside to outside the cell. The cells in the interstitial space and the capillaries remained intact. Low-level laser-assisted lipoplasty has a significant impact on the procedural implementation of lipoplasty techniques.

Electron and immuno-electron microscopy of abdominal fat identifies and characterizes amyloid fibrils in suspected cardiac amyloidosis

We evaluated the role of electron microscopy and immuno-electron microscopy studies on abdominal fat fine-needle biopsy samples in diagnosis and characterization of cardiac amyloidosis. The series consists of 15 patients with echocardiographic evidence of "restrictive cardiomyopathy" suspected to be due to amyloidosis. Patients underwent: clinical examination, electrocardiography, 2-D and Doppler echocardiography, immunofixation of serum and urine for detection of monoclonal immunoglobulins, and abdominalfat biopsies that were investigated with polarized light (Congo red), electron and immuno-electron microscopy using specific antibodies to kappa and lambda light chains, apolipoprotein A1, serum amyloid A (SAA), and transthyretin (TTR). Ultrastructural study of abdominal fat samples identified amyloid deposits in 15/15 cases. Immuno-electron microscopy specifically stained amyloid fibrils with antibodies anti-lambda (n = 8), -kappa (n = 2), -apolipoprotein A1 (n = 2) and -TTR (n = 3). Immuno-electron microscopy revealed TTR immuno-labelling in 2 patients with accidental monoclonal components, and a A reaction in I patient without monoclonal components. TTR and apolipoprotein A1 positive cases carried missense mutations in the corresponding genes. Our results demonstrate that amyloid deposits are present in the abdominalfat of patients suspected to have cardiac amyloidosis and that immuno-electron microscopy was able to characterize the amyloid protein in all cases.

Altered tumor necrosis factor-alpha (TNF-alpha) processing in adipocytes and increased expression of transmembrane TNF-alpha in obesity

Tumor necrosis factor-alpha (TNF-alpha) is synthesized as a 26-kDa transmembrane protein (mTNF-alpha), which may present on the cell surface or be processed to release the 17-kDa soluble form (sTNF-alpha). Because regulation of this ectodomain shedding might be critical in the generation of systemic versus local cytokine responses, we examined the rate of mTNF-alpha processing in adipocytes and its regulation in obesity. Here, we demonstrate that the 26-kDa mTNF-alpha is present in adipose tissue and that its production is significantly increased in different rodent obesity models as well as in obese humans. There was no apparent deficiency in the level of the major TNF-alpha converting enzyme in adipose tissue to account for the excess amount of mTNF-alpha produced in obesity. However, experiments in cultured fat cells stably expressing TNF-alpha demonstrated a significantly decreased rate of TNF-alpha cleavage in differentiated adipocytes compared with preadipocytes. Thus, a decreased processing rate of mTNF-alpha in mature adipocytes combined with an increase in TNF-alpha production may be a potential mechanism resulting in elevated membrane-associated TNF-alpha in adipose tissue in obesity.

Biomechanics of the heel pad for type 2 diabetic patients

OBJECTIVES

To quantify the dynamic behavior of the heel pad in type 2 diabetic patients and age-matched healthy individuals using mathematical modeling.

BACKGROUND

No single parameter can fully describe the heel-pad biomechanical properties during the loading-unloading process.

DESIGN

A descriptive study using pseudoelastic modeling was conducted to simulate the heel-pad stress-strain relationship in the loaded and unloaded states. Transmission electron microscope was used to examine six heel specimens taken from amputated legs in diabetic and non-diabetic patients.

METHODS

Energy dissipation ratio, loading curvature, and unloading curvature were calculated from the stress-strain curve-fits. Differences in ultrastructure between the heel pad of healthy subjects and those with diabetes were described.

RESULTS

The diabetic patients had a significantly higher mean energy dissipation ratio (mean 36.1% (SD, 8.7%) vs mean 27.9% (SD, 6.1%); P<0.001) and mean unloaded curvatures (mean 11.8 (SD, 5.1) vs mean 8.46 (SD, 2.6); P<0.001) than those of the control group. The collagen fibrils in diabetic heel samples were ruptured with unclear striation and uneven distribution.

CONCLUSIONS

The curvature parameters may explain the poor rebound phenomenon resulting in the high impact energy in diabetic heel pads. Breakdown in collagen fibrils may be responsible for this observation.

RELEVANCE

These findings can be integrated into the fabrication of orthotics that dissipate excessive heel impact energy and protect against injury.

Caveolin-2-deficient mice show evidence of severe pulmonary dysfunction without disruption of caveolae

Caveolin-2 is a member of the caveolin gene family with no known function. Although caveolin-2 is coexpressed and heterooligomerizes with caveolin-1 in many cell types (most notably adipocytes and endothelial cells), caveolin-2 has traditionally been considered the dispensable structural partner of the widely studied caveolin-1. We now directly address the functional significance of caveolin-2 by genetically targeting the caveolin-2 locus (Cav-2) in mice. In the absence of caveolin-2 protein expression, caveolae still form and caveolin-1 maintains its localization in plasma membrane caveolae, although in certain tissues caveolin-1 is partially destabilized and shows modestly diminished protein levels. Despite an intact caveolar membrane system, the Cav-2-null lung parenchyma shows hypercellularity, with thickened alveolar septa and an increase in the number of endothelial cells. As a result of these pathological changes, these Cav-2-null mice are markedly exercise intolerant. Interestingly, these Cav-2-null phenotypes are identical to the ones we and others have recently reported for Cav-1-null mice. As caveolin-2 expression is also severely reduced in Cav-1-null mice, we conclude that caveolin-2 deficiency is the clear culprit in this lung disorder. Our analysis of several different phenotypes observed in caveolin-1-deficient mice (i.e., abnormal vascular responses and altered lipid homeostasis) reveals that Cav-2-null mice do not show any of these other phenotypes, indicating a selective role for caveolin-2 in lung function. Taken together, our data show for the first time a specific role for caveolin-2 in mammalian physiology independent of caveolin-1.

Balancing susceptibility to infection and autoimmunity: a role for leptin?

The immune responses to many infections have long been known to share features with autoimmune responses. In particular, both types of response are typified by the enhanced reactivity of T helper 1 cells - with high levels of interleukin-2, interferon gamma and tumor necrosis factor alpha - and are accompanied often by organ-specific and/or systemic damage and the production of IgG. Paradoxically, the geographical distributions of incidence of infectious diseases and autoimmunity are complementary, rather than coincident. In less-developed societies, an epidemiological association between susceptibility to infection and malnutrition has been observed, whereas in affluent countries, an increased incidence of autoimmune diseases has been described. We suggest that these observations can be explained partly by taking into consideration the immune effects of the adipocyte-derived hormone leptin, which has been shown recently to act as a link between nutritional status and the immune response.

The Cytoscan model E-II in intraoperative parathyroid gland identification in a rabbit model

BACKGROUND

Intraoperative parathyroid gland identification and preservation is often a challenge even in the hands of experienced surgeons as they could be indistinguishable from fat or thyroid tissue.

OBJECTIVE

The goal of this study was to demonstrate the use of the Cytoscan Model E-II, which uses orthogonal polarization spectral (OPS) imaging technology, as an intravital microscope in identifying parathyroid glands intraoperatively and differentiating the parathyroid glands from fat and thyroid tissue in a rabbit model.

METHODS

The necks of 4 New England white rabbits were explored with the animals under a general anesthesia. The Cytoscan was used to obtain images of the vasculature of tissue suspected to be parathyroid, fat, and thyroid tissue. These were confirmed by histologic evaluation.

RESULTS

All tissues were correctly identified by the Cytoscan and confirmed by histologic analysis. There was an obvious difference in the images obtained of fatty tissue as compared with parathyroid tissues. There was also an appreciable difference between parathyroid and thyroid tissue based on the difference in vascularity.

CONCLUSIONS

OPS imaging technology can be used in identifying parathyroid glands based on the difference in vascularity from fat and the pattern and density of vessels when compared with thyroid tissue in a rabbit model.

SIGNIFICANCE

The Cytoscan may play a future role in real time intraoperative identification of human parathyroid glands. Future investigation is warranted.

Angiogenesis in adipose tissues and skeletal muscles with rebound weight-gain after diet-restriction in rabbits

The mechanisms of excessive body weight gain after diet-restriction are still unclear. In this study, we investigated expression of angiogenic factors in adipose tissue and skeletal muscle of rabbits which had rebound weight gains; trying to make inquiries into the mechanisms of this rebound weight gain. Ten rabbits were divided into two groups. One group had free food intake (group C), and the other group had restricted food intake until day 40 of the experiments and then had free food intake (group DR). Specimens of adipose tissue and skeletal muscle were collected from each rabbit on days 20, 40, and 60 after the initial examination, and expressions of CD34, vascular endothelial growth factor (VEGF), and platelet-derived endothelial cell growth factor (PD-ECGF) were investigated. Expression of VEGF was significantly strong in the adipose tissue of group DR at the recovery period of body weight. In conclusion, rebound weight gain after a restricted-diet may be associated with angiogenesis in adipose tissue, and the angiogenesis may be induced by VEGF.

Comparison of expression of apoptosis regulatory proteins in the adipose tissue of tumor-bearing and diet-restricted rabbits

We investigated the expression of apoptosis regulatory proteins in the adipose tissue of tumor-bearing and diet-restricted rabbits, and analyzed the differences between the two groups. The apoptotic index in the tumor-bearing group was 25.1+/-12.4 on day 10 and increased to 27.2+/-14.4 by day 20. Thereafter, however, it gradually decreased, falling to 11.2+/-7.8 on day 30 and 0.67+/-0.88 on day 40. By contrast, no apoptotic cells were detected in the diet-restricted group at any of the times examined. Bcl-2 immunoreactivity was either not detected at all, or was only weakly observed in both groups. Bax expression, on the other hand, gradually increased after implantation in the tumor-bearing group. In 2 of the 5 tumor-bearing rabbits, Bax expression in adipocytes was moderate 10 days after tumor implantation, and strong by day 20, but steadily decreased thereafter. By contrast, hardly any Bax-immunopositive cells were detected in the diet-restricted group. These results suggested that loss of body weight in the tumor-bearing group was different from that in the diet-restricted group, and that it was related to adipocyte apoptosis.

FOXC2 is a winged helix gene that counteracts obesity, hypertriglyceridemia, and diet-induced insulin resistance

Obesity, hyperlipidemia, and insulin resistance are common forerunners of type 2 diabetes mellitus. We have identified the human winged helix/forkhead transcription factor gene FOXC2 as a key regulator of adipocyte metabolism. Increased FOXC2 expression, in adipocytes, has a pleiotropic effect on gene expression, which leads to a lean and insulin sensitive phenotype. FOXC2 affects adipocyte metabolism by increasing the sensitivity of the beta-adrenergic-cAMP-protein kinase A (PKA) signaling pathway through alteration of adipocyte PKA holoenzyme composition. Increased FOXC2 levels, induced by high fat diet, seem to counteract most of the symptoms associated with obesity, including hypertriglyceridemia and diet-induced insulin resistance--a likely consequence hereof would be protection against type 2 diabetes.

Properties of porcine white adipose tissue and liver mitochondrial subpopulations

Properties of porcine white adipose tissue heavy and light mitochondrial subpopulations were investigated so as to identify any functional heterogeneity. Liver mitochondrial subpopulations were concurrently evaluated since their properties have been studied in some detail. Mitochondrial subpopulations were isolated by means of differential centrifugation and the relative purity estimated using marker enzymes. Due to the greater contamination of the light mitochondrial fractions, mtDNA content, determined by PCR analysis, was used as a basis to demonstrate any mitochondrial heterogeneity. Enzymatic activity, electron microscopy, lipid analysis and Western blotting were used to characterise the different populations. With the exception of liver cytochrome c oxidase, the enzymatic capacity of adipose and liver heavy mitochondria ranged between approximately two- and threefold higher than the corresponding light fraction. The cardiolipin content and mean mitochondrial diameters paralleled these differences, suggesting an increased mitochondrial mass rather than a functional difference. However, the cytochrome c oxidase activity of the liver heavy mitochondria was 4.75-fold higher relative to the light fraction. A strong correlation between cytochrome c oxidase activity and the subunit I content was evident. Adipose tissue mitochondrial subpopulations would seem to possess a comparable oxidative capacity per gram mitochondrial protein, while liver heavy mitochondria possess an increased oxidative capacity and mass.

Tissue engineering strategies for adipose tissue repair

Tissue engineering is a relatively young field that combines engineering, clinical science, and life sciences to, in part, repair or regrow tissues. Adipose tissue has recently become a focus area for tissue engineering, encouraged by the large number of reconstructive, cosmetic, and correctional indications that could be addressed with clinically translatable adipose tissue engineering strategies. This review discusses the three aspects of an adipose construct, namely cell types, scaffold, and microenvironment, and presents current tissue engineering strategies under pursuit.

Biochemical properties of porcine white adipose tissue mitochondria and relevance to fatty acid oxidation

The capacity of white adipose tissue mitochondria to support a high beta-oxidative flux was investigated by comparison to liver mitochondria. Based on marker enzyme activities and electron microscopy, the relative purity of the isolated mitochondria was similar thus allowing a direct comparison on a protein basis. The results confirm the comparable capacity of adipose tissue and liver mitochondria for palmitoyl-carnitine oxidation. Relative to liver, both citrate synthase and alpha-ketoglutarate dehydrogenase were increased 7.87- and 10.38-fold, respectively. In contrast, adipose tissue NAD-isocitrate dehydrogenase was decreased (2.85-fold). Such modifications in the citric acid cycle are expected to severely restrict citrate oxidation in porcine adipose tissue. Except for cytochrome c oxidase, activities of the enzyme complexes comprising the electron transport chain were not significantly different. The decrease in adipose cytochrome c oxidase activity could partly be attributed to a decreased inner membrane as suggested by lipid and enzyme analysis. In addition, Western blotting indicated that adipose and liver mitochondria possess similar quantities of cytochrome c oxidase protein. Taken together these results indicate that not only is the white adipose tissue protoplasm relatively rich in mitochondria, but that these mitochondria contain comparable enzymatic machinery to support a relatively high beta-oxidative rate.

Comparison of adipose tissue changes following administration of rosiglitazone in the dog and rat

Rosiglitazone (BRL-49653-C), a thiazolidinedione, is a potent agonist for the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma). Thiazolidinediones have been reported to induce adipocyte differentiation in vitro and there is limited data on their effects in vivo. The objective of this study was to compare the effects of rosiglitazone on adipocyte differentiation between dogs and rats. Morphological (light and ultrastructural) and morphometric evaluations were conducted on perirenal adipose tissue from dogs that have been treated for 1 month with 0.4, 5, 60 mg/kg/day and rats treated for the same period with 80 mg/kg/day. There was a dose-related change in the phenotype of white adipose tissue in dogs, reflected by an increase in nuclear numerical density (up to threefold) and cytoplasmic area fraction (up to 2.1-fold). In addition, there was an enlargement of the nuclei and a reduction in the size of the white adipocyte lipid vacuoles. Ultrastructural changes included an increase in the number of mitochondria per adipocyte. In the rat, similar changes were seen in nuclear numerical density (1.5-fold increase) and cytoplasmic area fraction (2.2-fold increase). There were also increased numbers of mitochondria per cell in white adipocytes giving them similar numbers of mitochondria to brown adipocytes. In the brown adipocytes, there was a reduction in cytoplasmic area fraction with a corresponding increase in the size of the lipid filled vacuoles in other words there was a converging of the phenotypes of the white and brown adipose tissues.

Adipose tissue expression of gelatinases in mouse models of obesity

Following the observation by Brown et al. (Am J Physiol 1997; 272: C937-49) that primary rat adipocytes in culture secrete gelatinase A (MMP-2), we have evaluated gelatinase expression in adipose tissue with the use of mouse models of obesity. Wild-type mice were kept on a standard fat diet (SFD) or on a high fat diet (42% fat, HFD) and- genetically obese db/db mice were kept on SFD; gonadal and subcutaneous fat pads were removed and analysed ex vivo. These studies revealed that: 1) the HFD induced adipocyte hypertrophy; 2) after 32 weeks, significantly higher levels of 70 kDa (p <0.05) and 65 kDa proMMP-2 (p <0.01) were observed in extracts of gonadal fat pads of mice on HFD; 3) the contribution of active MMP-2 to the total level was comparable in SFD and HFD groups (20 to 30%); and 4) gelatinase B (MMP-9) was not consistently detected. These findings were confirmed by gelatin zymography and by mRNA determination using competitive RT-PCR. The presence of MMP-2 in the adipose tissue was confirmed immunologically and its localization in adipocytes revealed by immunogold electron microscopy. The potential functional role of MMP-2 in adipose tissue remains to be determined.

Lack of in vivo effect of vanadium on GLUT4 translocation in white adipose tissue of streptozotocin-diabetic rats

Vanadium treatment, in vivo, corrects the severe hyperglycemia observed in streptozotocin (STZ)-diabetic rats. A number of metabolic effects of vanadium have been demonstrated in vitro and might contribute importantly to normalization of glucose homeostasis. However, many in vitro effects of vanadium occur at concentrations substantially higher than those achieved in vivo. Effects of vanadium on white adipose tissue have been particularly well characterized in vitro. To examine the relationship between in vitro and in vivo actions of vanadium, we examined the effects of vanadium treatment on acute glucose tolerance and adipose tissue GLUT4 control in vivo. In agreement with previous studies, vanadium treatment of STZ-diabetic rats restored normoglycemia with no appreciable restoration of insulin secretion. GLUT4 expression in white adipose tissue was reduced by 22% in STZ-diabetic rats compared with controls. Vanadium treatment did not significantly alter GLUT4 expression in controls, but completely restored normal expression levels in STZ-diabetic rats. In overnight-fasted control animals, GLUT4 translocation to the plasma membrane (PM) was maximally elevated (by 50%) in adipose tissue within 5 to 10 minutes after an intravenous (IV) glucose challenge. No glucose-induced translocation of GLUT4 was detected in diabetic rats, and peak PM GLUT4 content was 40% lower than in controls. Vanadium treatment did not increase peak PM GLUT4 content in either control or diabetic animals in response to a glucose load. Finally, the suppression of whole-body acute glucose tolerance in diabetic animals was only partially normalized by vanadium treatment. We conclude: (1) that concentrations of vanadium effective for maintaining normoglycemia in vivo (typically below 30 micromol/L) promote normal GLUT4 expression, but do not influence the subcellular localization of GLUT4 in white adipose tissue and (2) that in vivo effects of vanadium may not necessarily reflect the actions observed in vitro at supraphysiologic concentrations.

Cellular Activities of 20K- and 22K-hGH Do Not Necessarily Correlate with Their Binding Affinities for Rat GH Receptor

Even though 20K human growth hormone (20K-hGH) has 3-10% binding affinity for the rat liver and adipose tissue microsomes as compared to 22K-hGH, it was also reported that 20K-hGH has the same potency as 22K-hGH in the hypophysectomized rat weight gain assay. In order to investigate the reason why such controversial data exist, we have studied 20K- and 22K-hGH using the rat GH receptor extracellular domain (rGHR-ECD) and full-length rGHR. When we examined the complex formation of rGHR-ECD with 20K- and 22K-hGH in gel filtration assay, 20K-hGH formed no complex while 22K-hGH formed a 1:1 complex. Next, rGHR cDNA was introduced into Ba/F3 cells and CHO-K1 cells, and stable transfectants (Ba/F3-rGHR and CHO-rGHR) were established. In the proliferation of Ba/F3-rGHR cells, 20K-hGH had 10-fold lower activity than 22K-hGH, which is consistent with their affinities for rGHR. But surprisingly, in the Spi2.1 gene promoter activation in CHO-rGHR cells, 20K- and 22K-hGH had the same activity, which was found not only in stable CHO-rGHR clones but also in CHO-K1 cells transiently expressing rGHR. In conclusion, these results indicate that cellular activities of 20K- and 22K-hGH do not necessarily correlate with their binding affinities for rGHR.

The structure of the bilaminar zone in the human temporomandibular joint: a light and scanning electron microscopy study in young and elderly subjects

The bilaminar zone (BZ) in the human temporomandibular joint (TMJ) of toothed adults (GI) and toothless, elderly humans (GII) were analysed using light and scanning electron microscopy (SEM). In both groups the BZ consists of an upper and a lower stratum of connective tissue separated by a vascularized middle region. The superior stratum contains bundles of collagen fibres disposed in different directions. The fibres are fairly thick and transversely oriented immediately posterior to the TMJ disc. The initial part of the inferior stratum contains curved bundles of collagen fibres oriented anterio-posteriorly. From the middle to the posterior part of the inferior stratum, the fibres are right-aligned in GI and clearly sinuous in nature in GII. In both groups, the middle and posterior portions of the middle region are distinguished by the presence of vessels and vascular spaces. Loosely arranged connective and adipose tissues are also evident. The vascular spaces are wider in GII than in GI. The predominance of type I collagen fibres is clear in all regions of the BZ in both groups. The elastic fibres lie parallel to the collagen fibres in both groups and they are thicker and more abundant in GI, apparently decreasing in GII.