Kajsa Lindell

The size of body fat stores is known to influence fertility, indicating a link between adipose tissue and the reproductive system. Studies in mice have identified the adipocyte-derived hormone, leptin (Ob protein), as a possible mediator of this effect. The aim of this study was to investigate the possibility that leptin may have direct effects on the human ovary. To probe this hypothesis we first analyzed the expression of leptin receptors in the human ovary. Transcripts encoding both the long and short isoforms of the leptin receptor were present in human granulosa cells and thecal cells; however, the short isoforms were expressed at much higher levels. Immunoreactive leptin was present in follicular fluid at levels similar to those found in serum. ob gene expression, however, was undetectable in the ovary, as determined by reverse transcription-PCR, whereas it was easily detected in adipose tissue. To determine whether leptin could induce a biological response in ovarian cells, we examined the effect of leptin on estradiol production in cultured granulosa cells. Leptin (100 ng/mL) inhibited LH (0.1 ng/mL)-stimulated estradiol production. In contrast, leptin had no effect on estradiol production in the absence of LH. In conclusion, this study has demonstrated that the leptin receptor is expressed in the human ovary, that leptin is present in follicular fluid, and that leptin can induce a biological response in ovarian cells. These results suggest that leptin may have a direct effect on the human ovary.

Angiotensin II regulates blood pressure and may affect adipogenesis and adipocyte metabolism. Angiotensin II is produced by cleavage of angiotensinogen by renin and angiotensin-converting enzyme in the circulation. In addition, angiotensin II may be produced in various tissues by enzymes of the renin-angiotensin system (RAS) or the nonrenin-angiotensin system (NRAS). We have analyzed the expression of angiotensinogen and enzymes required for its conversion to angiotensin II in human adipose tissue. Northern blot demonstrated angiotensinogen expression in adipose tissue from nine obese subjects. Western blot revealed a distinct band of expected size of the angiotensinogen protein (61 kDa) in isolated adipocytes. RT-PCR, followed by Southern blot, demonstrated renin expression in human adipose tissue. Angiotensin-converting enzyme messenger RNA was detected by RT-PCR, and the identity of the PCR products was verified by restriction enzyme cleavage. Transcripts for cathepsin D and cathepsin G, components of the NRAS, were detected by RT-PCR, verified by restriction enzyme cleavage. We conclude that human adipose tissue expresses angiotensinogen and enzymes of RAS and NRAS. This opens the possibility that angiotensinogen-derived peptides, produced in adipose tissue itself, may affect adipogenesis and play a role in the pathogenesis of obesity.

OBJECTIVE: Abdominal obesity has a key role in the pathogenesis of prevalent and serious diseases and has been shown to be associated with an altered hypothalamic-pituitary-adrenal (HPA) axis function, which is regulated by endocrine feedback mediated via hippocampal glucocorticoid receptors (GR). RESEARCH METHODS AND PROCEDURES: We examined the HPA axis function by repeated salivary samples for the assessment of cortisol, as well as other endocrine, anthropometric, metabolic, and circulatory variables in middle-aged Swedish men (n = 284). With the restriction enzyme BclI, variants of the GR gene (GRL) locus were identified and two alleles with fragment lengths of 4.5 and 2.3 kilobases (kb) were detected. RESULTS: The observed frequencies were 40.1% for the 2.3- and 2.3-kb, 46.2% for the 4.5- and 2.3-kb, and 13.7% for the 4.5- and 4.5-kb genotypes. The larger allele (4.5 and 4.5 kb) was associated with elevated body mass index (BMI; p < 0.001), waist-to-hip circumference ratio (p = 0.015), abdominal sagittal diameter (p = 0.002), leptin (p < 0.001), and systolic blood pressure (borderline, p = 0.058). The 4.5- and 4.5-kb allele was associated with leptin after adjustment for BMI. Moreover, salivary cortisol values, particularly after stimulation by a standardized lunch (p = 0.040 to 0.086), were elevated in the men with the larger allele. DISCUSSION: These results indicate that there is an association between a deficient GR function, defined as a poor feedback regulation of the HPA axis activity, and a polymorphic restriction site at the GR gene locus. An abnormal control of HPA axis function due to genetic alterations may contribute to the pathogenesis of abdominal obesity.

Leptin affects body weight and reproduction mainly via receptors in the central nervous system. Different isoforms of the leptin receptor (leptin-R) exist, including a long isoform (leptin-RL) with signalling capacity and short isoforms (leptin-RS) with unknown function. The aim of this study was to examine leptin-R gene expression in different regions of the brain under conditions with altered body weight, in the female rat, including ovariectomy (OVX), oestradiol (E2) treatment, fasting and a genetic model of obesity (Zucker fa/fa). Leptin-R gene expression was analysed by in situ hybridization using probes recognizing all receptor isoforms (leptin-R) or specifically leptin-RL. Transcripts recognized by the leptin-R probe were abundant in the choroid plexus (CP), arcuate nucleus (ARC), ventromedial nucleus (VMN), thalamus (TH) and piriform cortex (PC). Leptin-RL transcripts were detected in the ARC, VMN, TH and PC but not in the CP. Although no sex difference was observed, leptin-R gene expression was reduced by E2 administration and increased by OVX. Administration of E2 reduced leptin-RL gene expression in the ARC and VMN but did not alter the expression in the TH or PC. OVX had no effect on the expression of leptin-RL mRNA. Fasting also caused a differential regulation of leptin-R mRNAs, with an increase in abundance of leptin-RL transcripts in the TH despite a decrease in leptin-R in this area. Obese Zucker rats had a similar pattern of expression with an increased expression of leptin-RL transcripts in all brain areas analysed and a decrease in leptin-R gene expression. These results demonstrate a differential regulation of leptin-RL and leptin-RS which could provide a mechanism for regulating access to, and sensitivity of, discrete regions of the brain for circulating leptin. We suggest that fasting and E2 alter the balance between leptin-RL and leptin-RS and that this could increase tissue sensitivity to leptin.

Recent animal studies indicate that leptin is involved in the regulation of blood pressure through the leptin receptor. Therefore, 51-yr-old men (N = 284) were selected; and anthropometric, endocrine, metabolic, and hemodynamic variables were examined in relation to polymorphisms of the leptin receptor gene (LEPR), by restriction fragment length polymorphism technique. Three polymorphisms were examined: Lys109Arg in exon 4, Gln223Arg in exon 6, and Lys656Asn in exon 14. In comparison with Lys109 homozygotes, Arg109 homozygotes (9%) showed lower body mass index (BMI) and abdominal sagittal diameter, as well as lower systolic (10.0 mm Hg) and diastolic (7.8 mm Hg) blood pressure. Additionally, Arg223 homozygotes (26.8%) showed lower blood pressure (7.6/5.7 mm Hg) than Gln223 homozygotes. These lower blood pressure levels were independent of other variables. No differences were found with the Lys656Asn polymorphism. Measurements of body fat mass correlated with leptin concentration in Lys109 homozygotes and in Lys109 heterozygotes but not in Arg109 homozygotes. Blood pressure correlated with leptin only in men carrying the wild-type allele Lys109. With both elevated BMI and leptin, Lys109 homozygotes had higher blood pressure than the Arg109 homozygous men (12.4/6.9 mm Hg). Men with blood pressure > or = 140/90 mm Hg had, in comparison with normotensive men, increased BMI and leptin levels, and Lys109 homozygotes were significantly more prevalent. These results suggest that leptin is associated with blood pressure regulation in men through the leptin receptor. When BMI and leptin are elevated, increased blood pressure is found only with the most prevalent LEPR genotype at codons 109 and 223, whereas variants of this receptor seem to protect from hypertension. This might explain why not all obese men are hypertensive.