title: Hypothalamic leptin resistance is associated with impaired leptin signal transduction in aged obese rats.
abstract: Leptin contributes to the regulation of both food intake and energy expenditure. We previously demonstrated that the F344xBN rat, a rodent model for late-onset obesity, is leptin-resistant and that leptin signal transduction following peripheral administration of leptin is impaired in these aged, overweight rats. To determine if leptin signal transduction is impaired in response to central administration of leptin and whether reduced hypothalamic leptin receptors may be contributing to the impaired signal transduction, we examined the in vivo dose-response leptin-induced STAT3 activation (phosphorylation and binding activity to the SIE M67 oligonucleotide) in response to i.c.v. administration of leptin along with the level of hypothalamic leptin receptor protein in young and older, late-onset obese rats. The leptin-induced maximum phosphorylation of STAT3 was 41% greater in young compared with older obese rats, but the dose required for half-maximal phosphorylation of STAT3 was similar in both the young (41 ng) and old-obese (47 ng) rats. There were no changes in total STAT3 protein with leptin or age, and leptin did not increase phosphorylation of STAT1. Leptin increased phosphorylation of STAT3 transcription factor binding eight-fold in the young but only four-fold in the aged-obese rats, and leptin receptor protein was 50% greater in the young compared with aged rats. These data indicate that aged-overweight rats demonstrate reduced signal transduction in response to centrally administered leptin that may be the result of the diminished leptin receptor protein observed in the aged-obese rats. The diminished leptin receptors and impaired leptin signal transduction may explain the diminished physiological responses observed following leptin administration in older rats. This impaired leptin signal transduction may be due either to the elevated obesity with age or to age itself, or to both.
authors.affiliation: Geriatric Research, Education and Clinical Center, Malcom Randall Veterans Affairs Medical Center, Gainesville, FL 32608-1197, USA. scarpace@ufl.edu
authors.forename: P J
authors.initials: PJ
authors.lastname: Scarpace
authors.forename: M
authors.initials: M
authors.lastname: Matheny
authors.forename: N
authors.initials: N
authors.lastname: Tümer
mesh_terms: D000375:Aging / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D020738:Leptin / Q000097:blood* / Q000494:pharmacology*; D008297:Male; D009765:Obesity / Q000097:blood* / Q000235:genetics / Q000503:physiopathology; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344 / Q000097:blood*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D020738:Leptin; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; C494081:Stat1 protein, rat; C494088:Stat3 protein, rat; D015534:Trans-Activators