Hypothalamic leptin gene therapy reduces body weight without accelerating age-related bone loss

Long-duration leptin transgene expression in dorsal vagal complex does not alter bone parameters in female Sprague Dawley rats

The hypothalamus and dorsal vagal complex (DVC) are both important for integration of signals that regulate energy balance. Increased leptin transgene expression in either the hypothalamus or DVC of female rats was shown to decrease white adipose tissue and circulating levels of leptin and adiponectin. However, in contrast to hypothalamus, leptin transgene expression in the DVC had no effect on food intake, circulating insulin, ghrelin and glucose, nor on thermogenic energy expenditure. These findings imply different roles for hypothalamus and DVC in leptin signaling. Leptin signaling is required for normal bone accrual and turnover. Leptin transgene expression in the hypothalamus normalized the skeletal phenotype of leptin-deficient ob/ob mice but had no long-duration (≥10 weeks) effects on the skeleton of leptin-replete rats. The goal of this investigation was to determine the long-duration effects of leptin transgene expression in the DVC on the skeleton of leptin-replete rats. To accomplish this goal, we analyzed bone from three-month-old female rats that were microinjected with recombinant adeno-associated virus encoding either rat leptin (rAAV-Leptin, n = 6) or green fluorescent protein (rAAV-GFP, control, n = 5) gene. Representative bones from the appendicular (femur) and axial (3rd lumbar vertebra) skeleton were evaluated following 10 weeks of treatment. Selectively increasing leptin transgene expression in the DVC had no effect on femur cortical or cancellous bone microarchitecture. Additionally, increasing leptin transgene expression had no effect on vertebral osteoblast-lined or osteoclast-lined bone perimeter or marrow adiposity. Taken together, the findings suggest that activation of leptin receptors in the DVC has minimal specific effects on the skeleton of leptin-replete female rats.

Endospanin Is a Candidate for Regulating Leptin Sensitivity

The hypothesis advanced is that endospanin, a highly conserved vesicle traffic protein in vertebrates, regulates leptin sensitivity in bone signaling. The effects of leptin on bones are well-studied but without consensus on whether the increases in leptin signaling stimulate bone gain or loss. The bone response may depend on leptin sensitivity, and endospanin is an established modulator of leptin sensitivity. An argument is advanced to develop zebrafish models for specific leptin signaling pathways. Zebrafish have well-developed molecular tools (e.g., CRISPR) and the advantage of non-destructive sampling of bones in the form of scales. Using these tools, experiments are described to substantiate the role of endospanin in zebrafish bone dynamics.

Evaluation of the Central Effects of Systemic Lentiviral-Mediated Leptin Delivery in Streptozotocin-Induced Diabetic Rats

Type 1 diabetes (T1D) is characterized by hyperphagia, hyperglycemia and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We have reported previously that daily leptin injections help to alleviate these symptoms. Therefore, we hypothesized that leptin gene therapy could help to normalize the neuroendocrine dysfunction seen in T1D. Adult male Sprague Dawley rats were injected i.v. with a lentiviral vector containing the leptin gene or green fluorescent protein. Ten days later, they were injected with the vehicle or streptozotocin (STZ). HPA function was assessed by measuring norepinephrine (NE) levels in the paraventricular nucleus (PVN) and serum corticosterone (CS). Treatment with the leptin lentiviral vector (Lepvv) increased leptin and insulin levels in non-diabetic rats, but not in diabetic animals. There was a significant reduction in blood glucose levels in diabetic rats due to Lepvv treatment. Both NE levels in the PVN and serum CS were reduced in diabetic rats treated with Lepvv. Results from this study provide evidence that leptin gene therapy in STZ-induced diabetic rats was able to partially normalize some of the neuroendocrine abnormalities, but studies with higher doses of the Lepvv are needed to develop this into a viable option for treating T1D.

Caloric Restriction and Hypothalamic Leptin Gene Therapy Have Differential Effects on Energy Partitioning in Adult Female Rats

Dieting is a common but often ineffective long-term strategy for preventing weight gain. Similar to humans, adult rats exhibit progressive weight gain. The adipokine leptin regulates appetite and energy expenditure but hyperleptinemia is associated with leptin resistance. Here, we compared the effects of increasing leptin levels in the hypothalamus using gene therapy with conventional caloric restriction on weight gain, food consumption, serum leptin and adiponectin levels, white adipose tissue, marrow adipose tissue, and bone in nine-month-old female Sprague-Dawley rats. Rats (n = 16) were implanted with a cannula in the 3rd ventricle of the hypothalamus and injected with a recombinant adeno-associated virus, encoding the rat gene for leptin (rAAV-Lep), and maintained on standard rat chow for 18 weeks. A second group (n = 15) was calorically-restricted to match the weight of the rAAV-Lep group. Both approaches prevented weight gain, and no differences in bone were detected. However, calorically-restricted rats consumed 15% less food and had lower brown adipose tissue Ucp-1 mRNA expression than rAAV-Lep rats. Additionally, calorically-restricted rats had higher abdominal white adipose tissue mass, higher serum leptin and adiponectin levels, and higher marrow adiposity. Caloric restriction and hypothalamic leptin gene therapy, while equally effective in preventing weight gain, differ in their effects on energy intake, energy expenditure, adipokine levels, and body composition.

Remodeling adipose tissue inflammasome for type 2 diabetes mellitus treatment: Current perspective and translational strategies

Obesity-associated type 2 diabetes mellitus (T2DM) is characterized by low-grade chronic systemic inflammation that arises primarily from the white adipose tissue. The interplay between various adipose tissue-derived chemokines drives insulin resistance in T2DM and has therefore become a subject of rigorous investigation. The adipocytokines strongly associated with glucose homeostasis include tumor necrosis factor-α, various interleukins, monocyte chemoattractant protein-1, adiponectin, and leptin, among others. Remodeling the adipose tissue inflammasome in obesity-associated T2DM is likely to treat the underlying cause of the disease and bring significant therapeutic benefit. Various strategies have been adopted or are being investigated to modulate the serum/tissue levels of pro- and anti-inflammatory adipocytokines to improve glucose homeostasis in T2DM. These include use of small molecule agonists/inhibitors, mimetics, antibodies, gene therapy, and other novel formulations. Here, we discuss adipocytokines that are strongly associated with insulin activity and therapies that are under investigation for modulation of their levels in the treatment of T2DM.

Adipocyte alterations in endometriosis: reduced numbers of stem cells and microRNA induced alterations in adipocyte metabolic gene expression

BACKGROUND

Endometriosis is an estrogen dependent, inflammatory disorder occurring in 5-10% of reproductive-aged women. Women with endometriosis have a lower body mass index (BMI) and decreased body fat compared to those without the disease, yet few studies have focused on the metabolic abnormalities in adipose tissue in women with endometriosis. Previously, we identified microRNAs that are differentially expressed in endometriosis and altered in the serum of women with the disease. Here we explore the effect of endometriosis on fat tissue and identified a role for endometriosis-related microRNAs in fat metabolism and a reduction in adipocyte stem cell number.

METHODS

Primary adipocyte cells cultured from 20 patients with and without endometriosis were transfected with mimics and inhibitors of microRNAs 342-3p or Let 7b-5p to model the status of these microRNAs in endometriosis. RNA was extracted for gene expression analysis by qRT-PCR. PCNA expression was used as a marker of adipocyte proliferation. Endometriosis was induced experimentally in 9-week old female C57BL/6 mice and after 10 months fat tissue was harvested from both the subcutaneous (inguinal) and visceral (mesenteric) tissue. Adipose-derived mesenchymal stem cells in fat tissue were characterized in both endometriosis and non-endometriosis mice by FACS analysis.

RESULTS

Gene expression analysis showed that endometriosis altered the expression of Cebpa, Cebpb, Ppar-γ, leptin, adiponectin, IL-6, and HSL, which are involved in driving brown adipocyte differentiation, appetite, insulin sensitivity and fat metabolism. Each gene was regulated by an alteration in microRNA expression known to occur in endometriosis. Analysis of the stem cell content of adipose tissue in a mouse model of endometriosis demonstrated a reduced number of adipocyte stem cells.

CONCLUSIONS

We demonstrate that microRNAs Let-7b and miR-342-3p affected metabolic gene expression significantly in adipocytes of women with endometriosis. Similarly, there is a reduction in the adipose stem cell population in a mouse model of endometriosis. Taken together these data suggest that endometriosis alters BMI in part through an effect on adipocytes and fat metabolism.

Effects of hypothalamic leptin gene therapy on osteopetrosis in leptin-deficient mice

Impaired resorption of cartilage matrix deposited during endochondral ossification is a defining feature of juvenile osteopetrosis. Growing, leptin-deficient ob/ob mice exhibit a mild form of osteopetrosis. However, the extent to which the disease is (1) self-limiting and (2) reversible by leptin treatment is unknown. We addressed the first question by performing histomorphometric analysis of femurs in rapidly growing (2-month-old), slowly growing (4-month-old) and skeletally mature (6-month-old) wild-type (WT) and ob/ob male mice. Absent by 6 months of age in WT mice, cartilage matrix persisted to varying extents in distal femur epiphysis, metaphysis and diaphysis in ob/ob mice, suggesting that the osteopetrotic phenotype is not entirely self-limiting. To address the second question, we employed hypothalamic recombinant adeno-associated virus (rAAV) gene therapy to restore leptin signaling in ob/ob mice. Two-month-old mice were randomized to one of the three groups: (1) untreated control, (2) rAAV-Leptin or (3) control vector rAAV-green fluorescent protein and vectors injected intracerebroventricularly. Seven months later, rAAV-leptin-treated mice exhibited no cartilage in the metaphysis and greatly reduced cartilage in the epiphysis and diaphysis. At the cellular level, the reduction in cartilage was associated with increased bone turnover. These findings (1) support the concept that leptin is important for normal replacement of cartilage by bone, and (2) demonstrate that osteopetrosis in ob/ob mice is bone-compartment-specific and reversible by leptin at skeletal sites capable of undergoing robust bone turnover.

Dexamethasone Down-regulates Osteocalcin in Bone Cells through Leptin Pathway

Glucocorticoid therapy, especially at higher doses, is associated with significant adverse side effects including osteoporosis. Leptin, secreted from adipose tissue, has diverse effects on bone tissue regulation. As glucocorticoids stimulate leptin synthesis and secretion directly in adipose tissue we hypothesised that dexamethasone (DEX) induced osteoporosis may, in part, be mediated by an osteoblast dependent leptin-leptin receptor pathway. Human bone cells expressed leptin and leptin receptors (Ob-Ra and Ob-Rb). DEX increased leptin, Ob-Ra and Ob-Rb expression in a dose-dependent manner while decreasing expression of osteocalcin. In the presence of leptin, Cbfa1 and osteonectin expression showed no significant change, whereas osteocalcin expression was decreased. Recombinant human quadruple antagonist leptin suppressed DEX-induced osteocalcin downregulation. The signaling pathway involved up-regulation of JAK2. In conclusion, upregulation of leptin and Ob-Rb in human bone cells by DEX is associated with down-regulation of osteocalcin expression. The down regulation of osteocalcin by DEX was partially through a leptin autocrine/paracrine loop. Adverse effects of DEX on the skeleton may be modified by targeting leptin signaling pathways.

Role of estrogen receptor signaling in skeletal response to leptin in female ob/ob mice

Leptin, critical in regulation of energy metabolism, is also important for normal bone growth, maturation and turnover. Compared to wild type (WT) mice, bone mass is lower in leptin-deficient ob/ob mice. Osteopenia in growing ob/ob mice is due to decreased bone accrual, and is associated with reduced longitudinal bone growth, impaired cancellous bone maturation and increased marrow adipose tissue (MAT). However, leptin deficiency also results in gonadal dysfunction, disrupting production of gonadal hormones which regulate bone growth and turnover. The present study evaluated the role of increased estrogen in mediating the effects of leptin on bone in ob/ob mice. Three-month-old female ob/ob mice were randomized into one of the 3 groups: (1) ob/ob + vehicle (veh), (2) ob/ob + leptin (leptin) or (3) ob/ob + leptin and the potent estrogen receptor antagonist ICI 182,780 (leptin + ICI). Age-matched WT mice received vehicle. Leptin (40 µg/mouse, daily) and ICI (10 µg/mouse, 2×/week) were administered by subcutaneous injection for 1 month and bone analyzed by X-ray absorptiometry, microcomputed tomography and static and dynamic histomorphometry. Uterine weight did not differ between ob/ob mice and ob/ob mice receiving leptin + ICI, indicating that ICI successfully blocked the uterine response to leptin-induced increases in estrogen levels. Compared to leptin-treated ob/ob mice, ob/ob mice receiving leptin + ICI had lower uterine weight; did not differ in weight loss, MAT or bone formation rate; and had higher longitudinal bone growth rate and cancellous bone volume fraction. We conclude that increased estrogen signaling following leptin treatment is dispensable for the positive actions of leptin on bone and may attenuate leptin-induced bone growth.

Low Body Mass Index in Endometriosis Is Promoted by Hepatic Metabolic Gene Dysregulation in Mice

The gynecological disease endometriosis is characterized by the deposition and proliferation of endometrial cells outside the uterus and clinically is linked to low body mass index (BMI). Gene expression in the liver of these women has not been reported. We hypothesized that endometriosis may impact hepatic gene expression, promoting a low BMI. To determine the effect of endometriosis on liver gene expression, we induced endometriosis in female mice by suturing donor mouse endometrium into the peritoneal cavity and measuring the weight of these mice. Dual-energy X-ray absorptiometry (DEXA) scanning of these mice showed lower body weight and lower total body fat than controls. Microarray analysis identified 26 genes differentially regulated in the livers of mice with endometriosis. Six of 26 genes were involved in metabolism. Four of six genes were upregulated and were related to weight loss, whereas two genes were downregulated and linked to obesity. Expression levels of Cyp2r1, Fabp4, Mrc1, and Rock2 were increased, whereas Igfbp1 and Mmd2 expression levels were decreased. Lep and Pparg, key metabolic genes in the pathways of the six genes identified from the microarray, were also upregulated. This dysregulation was specific to metabolic pathways. Here we demonstrate that endometriosis causes reduced body weight and body fat and disrupts expression of liver genes. We suggest that altered metabolism mediated by the liver contributes to the clinically observed low BMI that is characteristic of women with endometriosis. These findings reveal the systemic and multiorgan nature of endometriosis.

Age-related changes in acute central leptin effects on energy balance are promoted by obesity

Leptin is a key catabolic regulator of food intake (FI) and energy expenditure. Both aging and obesity have been shown to induce leptin-resistance. The present study aimed to analyze age-related changes in the anorexigenic and hypermetabolic responsiveness to acute intracerebroventricular leptin administration in different age-groups of normally fed male Wistar rats (adult and old rats from 3 to 24months of age, NF3 to NF24, respectively). The expressions of the long form of the leptin receptor (Ob-Rb) and inhibitory SOCS3 genes were also assessed by quantitative RT-PCR in the arcuate nucleus (ARC). The influence of high-fat diet-induced obesity (HF) on the anorexigenic leptin effects were also tested in younger and older middle-aged groups (HF6 and HF12). Leptin-induced anorexia varied with age: leptin suppressed re-feeding FI (following 48-h fasting) strongly in young adult (NF3), but not in younger or older middle-aged (NF6 or NF12) or in aging (NF18) rats. However, anorexigenic leptin effects reached statistical significance again in old NF24 rats. Leptin-induced hypermetabolism, on the other hand, showed monotonous age-related decline and disappeared by old age. Ob-Rb expression declined until 12months of age followed by a partial recovery in NF18 and NF24 groups. On the other hand, SOCS3 expression was high in NF6 and NF18 and to some extent in NF24 rats. Age-related alterations of Ob-Rb and SOCS3 expression in the ARC may partly contribute to the explanation of age-related variations in anorexigenic but not hypermetabolic leptin effects. High-fat diet-induced obesity was associated with resistance to leptin-induced anorexia in HF6, similar to that seen in NF6. However, instead of the expected leptin-resistance in HF12, a strong leptin-induced suppression of re-feeding was detected in these obese middle-aged rats. Our results suggest that acute central effects of leptin on anorexia and hypermetabolism change in disparate ways during aging, implying separate mechanisms (e.g. signal transduction pathways) of different leptin actions. The age-related pattern shown by leptin-induced anorexia may contribute to the explanation of middle-aged obesity, and partly to that of aging anorexia. Our findings concerning obese rats are in accord with previous observations on anorexigenic effects of peripherally administered cholecystokinin: diet-induced obesity appeared to accelerate the development of age-related regulatory alterations. Similarly, our present data also raise the possibility that chronic diet-induced obesity promotes responsiveness to centrally applied leptin at least concerning anorexigenic effects.

Leptin Production by Encapsulated Adipocytes Increases Brown Fat, Decreases Resistin, and Improves Glucose Intolerance in Obese Mice

The neuroendocrine effects of leptin on metabolism hold promise to be translated into a complementary therapy to traditional insulin therapy for diabetes and obesity. However, injections of leptin can provoke inflammation. We tested the effects of leptin, produced in the physiological adipocyte location, on metabolism in mouse models of genetic and dietary obesity. We generated 3T3-L1 adipocytes constitutively secreting leptin and encapsulated them in a poly-L-lysine membrane, which protects the cells from immune rejection. Ob/ob mice (OB) were injected with capsules containing no cells (empty, OB^[Emp]), adipocytes (OB^[3T3]), or adipocytes overexpressing leptin (OB^[Lep]) into both visceral fat depots. Leptin was found in the plasma of OB^[Lep], but not OB^[Emp] and OB^[3T3] mice at the end of treatment (72 days). The OB^[Lep] and OB^[3T3] mice have transiently suppressed appetite and weight loss compared to OB^[Emp]. Only OB^[Lep] mice have greater brown fat mass, metabolic rate, and reduced resistin plasma levels compared to OB^[Emp]. Glucose tolerance was markedly better in OB^[Lep]vs. OB^[Emp] and OB^[3T3] mice as well as in wild type mice with high-fat diet-induced obesity and insulin resistance treated with encapsulated leptin-producing adipocytes. Our proof-of-principle study provides evidence of long-term improvement of glucose tolerance with encapsulated adipocytes producing leptin.