Leptin action in the brain: How (and when) it makes fat burn

Identification of ALK in Thinness

There is considerable inter-individual variability in susceptibility to weight gain despite an equally obesogenic environment in large parts of the world. Whereas many studies have focused on identifying the genetic susceptibility to obesity, we performed a GWAS on metabolically healthy thin individuals (lowest 6th percentile of the population-wide BMI spectrum) in a uniquely phenotyped Estonian cohort. We discovered anaplastic lymphoma kinase (ALK) as a candidate thinness gene. In Drosophila, RNAi mediated knockdown of Alk led to decreased triglyceride levels. In mice, genetic deletion of Alk resulted in thin animals with marked resistance to diet- and leptin-mutation-induced obesity. Mechanistically, we found that ALK expression in hypothalamic neurons controls energy expenditure via sympathetic control of adipose tissue lipolysis. Our genetic and mechanistic experiments identify ALK as a thinness gene, which is involved in the resistance to weight gain.

The Effects of Leptin on Glial Cells in Neurological Diseases

It is known that various endocrine modulators, including leptin and ghrelin, have neuroprotective roles in neurological diseases. Leptin is a hormone produced by adipocytes and was originally identified as a gene related to obesity in mice. The leptin receptors in the hypothalamus are the main target for the homeostatic regulation of body weight. Recent studies have demonstrated that leptin receptors are also expressed in other regions of the central nervous system (CNS), such as the hippocampus, cerebral cortex, and spinal cord. Accordingly, these studies identified the involvement of leptin in the regulation of neuronal survival and neural development. Furthermore, leptin has been shown to have neuroprotective functions in animal models of neurological diseases and demyelination. These observations also suggest that dysregulation of leptin signaling may be involved in the association between neurodegeneration and obesity. In this review, we summarize novel functions of leptin in animal models of neurodegenerative diseases. Specifically, we focus on the emerging evidence for the role of leptin in non-neuronal cells in the CNS, including astrocytes, microglia, and oligodendrocytes. Understanding leptin-mediated neuroprotective signals and molecular mechanisms underlying remyelination will be helpful to establish therapeutic strategies against neurological diseases.

Daily cycle in hepatic lipid metabolism in obese mice, Neotomodon alstoni: Sex differences

Disruption of circadian rhythms influences the pathogenesis of obesity, particularly with the basic regulation of food intake and metabolism. A link between metabolism and the circadian clock is the peroxisome proliferator-activated receptors (PPARs). The Neotomodon alstoni mouse, known as the "Mexican volcano mouse," may develop obesity if fed a normo-caloric diet. This manuscript documents the changes in part of the hepatic lipid homeostasis in both sexes of lean and obese N. alstoni mice, comparing the daily changes in the BMAL1 clock protein, in regulators of lipid metabolism (PGC-1α, PPARα-γ, SREBP-1c, and CPT-1α) and in free fatty acid (FFA) and hepatic triacylglyceride (TAG) metabolites in light-dark cycles. Hepatic tissue and blood were collected at 5, 10, 15, 19, and 24 h. Samples were analyzed by western blotting to determine the relative presence of protein. The results indicate that obesity affects daily changes in lipid metabolism and the BMAL1 profile in females considerably more than in males. These results suggest that the impact of obesity on lipid metabolism has important differences according to sex.

Secret talk between adipose tissue and central nervous system via secreted factors-an emerging frontier in the neurodegenerative research

First seen as a storage organ, the white adipose tissue (WAT) is now considered as an endocrine organ. WAT can produce an array of bioactive factors known as adipokines acting at physiological level and playing a vital role in energy metabolism as well as in immune response. The global effect of adipokines in metabolic activities is well established, but their impact on the physiology and the pathophysiology of the central nervous system (CNS) remains poorly defined. Adipokines are not only produced by the WAT but can also be expressed in the CNS where receptors for these factors are present. When produced in periphery and to affect the CNS, these factors may either cross the blood brain barrier (BBB) or modify the BBB physiology by acting on cells forming the BBB. Adipokines could regulate neuroinflammation and oxidative stress which are two major physiological processes involved in neurodegeneration and are associated with many chronic neurodegenerative diseases. In this review, we focus on four important adipokines (leptin, resistin, adiponectin, and TNFα) and one lipokine (lysophosphatidic acid-LPA) associated with autotaxin, its producing enzyme. Their potential effects on neurodegeneration and brain repair (neurogenesis) will be discussed. Understanding and regulating these adipokines could be an interesting lead to novel therapeutic strategy in order to counteract neurodegenerative disorders and/or promote brain repair.

Immunohistochemical evidence of leptin and its receptor in the carpal glands of domestic pigs and wild boar

BACKGROUND

In recent years, the protein hormone leptin has been the subject of numerous studies designed to clarify and interpret its functional significance; it has been speculated that this goes well beyond the control of appetite and energy metabolism. In particular, the presence of leptin and its receptor has been observed in various glands anatomically and functionally related to the reproductive apparatus. This has led to the hypothesis that leptin may act directly in the functional control of these glands and, in general, the control of reproductive function.

HYPOTHESIS/OBJECTIVES

The presence and distribution of leptin and its receptor in the carpal glands of domestic pigs and wild boar are examined, using immunohistochemical techniques.

ANIMALS

Tissue samples were collected from five domestic pigs and five wild boar, following slaughter.

RESULTS

The presence of leptin and its receptor was demonstrated in the glands, localized in the dark cells of the glandular secretory epithelium. In addition, no difference was observed between wild boar and domestic pigs.

CONCLUSIONS AND CLINICAL IMPORTANCE

We hypothesize that leptin may be produced by the carpal gland and may act on the gland's secretory epithelial cells with an autocrine/paracrine mechanism, thus affecting the secretory activity of the gland itself.