VGF-Derived Peptide TLQP-21: Biology and Pathophysiology
The Vgf gene is a member of the extended granin family of peptides . VGF encodes a 615 amino acid protein (617 in rodents) that is stored in dense core granules and processed to yield several bioactive peptides, released through the regulated pathway. At least 7 peptides have been shown to possess non redundant biological functions in rodents while VGF fragments are increasingly recognized as useful biomarkers for human disease . We have recently identified and functionally characterized the C-terminal internal fragment designated TLQP-21 . TLQP-21 is a multifunctional peptide active in the regulation of energy balance, glucose homeostasis, gastric function, nociception, reproduction and stress . Intracerebroventricular infusion of TLQP-21 increases energy expenditure and prevents obesity without activating central hypothalamic neuropeptides or feeding . In periphery, TLQP-21  is co-stored with norepinephrine-synthesizing enzyme tyrosine hydroxylase in sympathetic nerves innervating the adipose organ; increases lipolysis downstream of β-adrenergic receptor signaling pathway; increases sympathetic innervation to adipose fat pads and decreases adipocytes diameters without exerting negative cardiovascular effects or activating energy expenditure . TLQP-21 is active at the C3aR1 receptor [4,5] (a second putative receptor has also been described ). We demonstrated that TLQP-21 activates C3aR1 with a folding upon binding mechanism and that the C-terminal amonoacids are required for TLQP-21 biological activity . Interestingly the murine sequence is more active than the human sequence on both the murine and human C3aR1 .
We are currently investigating the molecular mechanism of TLQP-21 induced pro-lipolysis effects and its biological role in humans.
The long term goal is to use molecular and physiological knowledge to develop innovative drugs for the treatment of obesity and type 2 diabetes.
Supported by NIH/NIDDK DK102496 and Minnesota Partnership for Biotechnology and Medical Genomics, Decade of Discovery in Diabetes Grant.
A mouse model of Chronic Psychosocial Stress: Energetics, Obesity, Psychpathologies and Aging
Epidemiological evidence demonstrates that psychiatric and metabolic diseases are rising exponentially to pandemic level. A substantial number of obese individuals show eating disorders, psychiatric conditions, stressful life events, more medical complaints and poorer quality of life. Unfortunately, current animal models largely fail to recapitulate the vast array of symptoms which are observed in the obese human population.
We developed a unique mouse model of chronic psychosocial stress [1,2].
Briefly stable resident/intruder pairs of adult male mice are established after a baseline period. In the stress phase resident/intruder pairs live in the same cage separated by a perforated partition, which allows sensory but not physical contact and are allowed a brief daily physical interaction which lasted a maximum of 10 min. Subordinate and dominant mice are identified by direct observation.
We demonstrated that subordinate mice (mice having low social rank) manifest a complex syndrome characterized by a depression-like behavior, increased anxiety, neuroimmune and neuroendocrine abnormalities.
Role of brown adipose tissue in obesity and Type 2 diabetes: We are investigating the molecular mechanism of subordination stress induced obesity and T2D [3,4]. We recently established that the level of adaptive thermogenesis and the functional status of the brown adipose tissue determine the resilience or the vulnerability to stress-induced vulnerability to diet-induced obesity in mice in spite of similar level of hyperphagia . Specifically, under physiological conditions promoting low adaptive thermogenesis and BAT activity (e.g. housing at mouse thermoneutrality, i.e. 28-30°C or genetic deletion of the βARs), exposure to CSS acts as a stimulus for BAT activation and thermogenesis, resulting in resistance to diet-induced obesity despite the presence of hyperphagia. Conversely, in wt mice acclimatized to room temperature and therefore characterized by sustained BAT function, exposure to CSS increased vulnerability to obesity. Mechanistically we demonstrated that βARs are dispensable for subordination stress-induced BAT browning and identified a stress-inducible sympathetic/brown adipocyte purinergic pathway of browning in mice and showed that it is conserved in humans.
Aging: We are investigating if stress, hyperphagia and nutrients partitioning will differentially affect ageing and result in accelerated mortality in dominant or subordinate mice. Supported by NIH Transformative Award R01. 1R01AG043972-01. Energetics, Disparities, & Lifespan: a unified hypothesis.
Binge Eating Disorder: We demonstrated that subordinate mice manifest spontaneous and persistent binge eating-like episodes associated with weight gain and vulnerability to obesity . We are currently investigating the underlying central nervous system pathways regulating stress-induced binging.