CD43 is a cell-surface sialoglycoprotein of uncertain physiologic function expressed to various degrees by most leukocytes. We tested whether or not CD43 participates in intercellular adhesion by comparing the binding of human T lymphocytes to transfected HeLa cells stably expressing CD43 and sham-transfected HeLa cells (CD43-negative). Significantly fewer T lymphocytes adhered to the CD43-positive HeLa cells than to the CD43-negative HeLa cells. Diminished T-cell adherence to the CD43-positive HeLa cells was seen for all T lymphocytes tested, irrespective of their source or derivation. Antibody-blocking experiments revealed that CD43 interference with T-cell adhesion largely represented interference with T-cell leukocyte function-associated antigen 1 binding to HeLa cell intercellular adhesion molecule 1. The CD43 anti-adhesion effect was not overcome by treating cells with phorbol 12-myristate 13-acetate, a chemical that increases the binding avidity of leukocyte function-associated antigen 1 for intercellular adhesion molecule 1. However, neuraminidase treatment of the HeLa cell transfectants diminished the CD43 antiadhesion effect. These data indicate that CD43 expression by opposing cells can interfere with cell-cell adhesion. The data also suggest that CD43 might regulate T-cell adhesion by interfering with leukocyte function-associated 1 binding to intercellular adhesion molecule 1, a major activation-induced adhesion pathway among lymphocytes.

Targeted disruption of RIIβ-protein kinase A (PKA) in mice leads to a lean phenotype, increased nocturnal locomotor activity, and activation of brown adipose tissue. Because RIIβ is abundantly expressed in both white and brown adipose tissue as well as the brain, the contribution of neuronal vs. peripheral PKA to these phenotypes was investigated. We used a Cre-Lox strategy to reexpress RIIβ in a tissue-specific manner in either adipocytes or neurons. Mice with adipocyte-specific RIIβ reexpression remained hyperactive and lean, but pan-neuronal RIIβ reexpression reversed both phenotypes. Selective RIIβ reexpression in all striatal medium spiny neurons with Darpp32-Cre corrected the hyperlocomotor phenotype, but the mice remained lean. Further analysis revealed that RIIβ reexpression in D2 dopamine receptor-expressing medium spiny neurons corrected the hyperlocomotor phenotype, which demonstrated that the lean phenotype in RIIβ-PKA-deficient mice does not develop because of increased locomotor activity. To identify the neurons responsible for the lean phenotype, we used specific Cre-driver mice to reexpress RIIβ in agouti-related peptide (AgRP)-, proopiomelanocortin (POMC)-, single-minded 1 (Sim1)-, or steroidogenic factor 1 (SF1)-expressing neurons in the hypothalamus, but observed no rescue of the lean phenotype. However, when RIIβ was reexpressed in multiple regions of the hypothalamus and striatum driven by Rip2-Cre, or specifically in GABAergic neurons driven by Vgat-ires-Cre, both the hyperactive and lean phenotypes were completely corrected. Bilateral injection of adeno-associated virus1 (AAV1)-Cre directly into the hypothalamus caused reexpression of RIIβ and partially reversed the lean phenotype. These data demonstrate that RIIβ-PKA deficiency in a subset of hypothalamic GABAergic neurons leads to the lean phenotype.mouse genetics | obesity | exercise | cAMP W e reported previously that mice lacking the protein kinase A (PKA) regulatory subunit RΙΙβ (RΙΙβ KO) exhibit a 50% reduction in white adipose tissue (WAT) and are resistant to dietinduced obesity (DIO) and diabetes (1, 2). These mice have an extended lifespan and show diminished age-related metabolic dysfunctions such as fatty liver and insulin resistance (3). Compared with their WT littermates, RIIβ KO mice have normal to slightly increased food intake, a twofold increase in nocturnal physical activity, and a basal metabolic rate (VO 2 consumption) that is higher than WT if calculated based on total body weight (4-6). RIIβ is highly expressed in the mouse CNS, brown adipose tissue (BAT), and WAT with limited expression elsewhere (1, 7-9). At the molecular level, RIIβ deficiency is accompanied by a compensatory increase in the PKA regulatory subunit RIα, which results in increased basal PKA activity and decreased total C subunit activity in brain, BAT, and WAT (1). These changes in PKA subunit composition may also alter PKA holoenzyme localization to specific signaling complexes because RIIβ has a much higher affinity for anchoring proteins (AKAPs)...

Agouti lethal yellow (A y ) mice express agouti ectopically because of a genetic rearrangement at the agouti locus. The agouti peptide is a potent antagonist of the melanocortin 4 receptor (MC4R) expressed in neurons, and this leads to hyperphagia, hypoactivity, and increased fat mass. The MC4R signals through Gs and is thought to stimulate the production of cAMP and activation of downstream cAMP effector molecules such as PKA. Disruption of the RII␤ regulatory subunit gene of PKA results in release of the active catalytic subunit and an increase in basal PKA activity in cells where RII␤ is highly expressed. Because RII␤ is expressed in neurons including those in the hypothalamic nuclei where MC4R is prominent we tested the possibility that the RII␤ knockout might rescue the body weight phenotypes of the A y mice. Disruption of the RII␤ PKA regulatory subunit gene in mice leads to a 50% reduction in white adipose tissue and resistance to dietinduced obesity and hyperglycemia. The RII␤ mutation rescued the elevated body weight, hyperphagia, and obesity of A y mice. Partial rescue of the A y phenotypes was even observed on an RII␤ heterozygote background. These results suggest that the RII␤ gene mutation alters adiposity and locomotor activity by modifying PKA signaling pathways downstream of the agouti antagonism of MC4R in the hypothalamus.adiposity ͉ cAMP ͉ hypothalamus T he rapid increase in obesity in the human population and the associated increased risk for ailments such as diabetes and cardiovascular disease has driven an intense effort to understand the physiological pathways that regulate body weight. Both induced and spontaneous mutations in the mouse genome have been instrumental in identifying the genes and cell types that play a role in energy balance in mammals. We have previously determined that mice lacking the RII␤ regulatory subunit of PKA exhibit a 10% reduction in body weight and a 50% decrease in white adipose tissue (WAT) and are resistant to diet-induced obesity and hyperglycemia (1, 2). RII␤ knockout (KO) mice have a 2-fold increase in their nocturnal locomotor activity and an increase in resting metabolic rate as measured by oxygen consumption (1, 3, 4). These studies have established that signaling through the RII␤-PKA pathway can have dramatic effects on both body weight and energy expenditure in mice. The RII␤ subunit of PKA is highly expressed in WAT, brown adipose tissue (BAT), and brain (1, 5), but significant expression is also seen in several other tissues including thyroid, testis, and ovary (6-8). The contribution of each of these tissues to the overall RII␤ KO phenotype has not yet been resolved.The arcuate nucleus region (ARC) of the hypothalamus serves as a center to integrate signals that control feeding and energy expenditure. Two anatomically distinct populations of leptinresponsive neurons exist in the ARC; those that express neuropeptide Y (NPY) and agouti-related protein (AgRP) and those that express proopiomelanocortin (POMC) (9, 10). The NPY/AgRP and POMC neurons proj...

Mice lacking the RII beta regulatory subunit of protein kinase A exhibit a 50% reduction in white adipose tissue stores compared with wild-type littermates and are resistant to diet-induced obesity. RII beta(-/-) mice also have an increase in resting oxygen consumption along with a 4-fold increase in the brown adipose-specific mitochondrial uncoupling protein 1 (UCP1). In this study, we examined the basis for UCP1 induction and tested the hypothesis that the induced levels of UCP1 in RII beta null mice are essential for the lean phenotype. The induction of UCP1 occurred at the protein but not the mRNA level and correlated with an increase in mitochondria in brown adipose tissue. Mice lacking both RII beta and UCP1 (RII beta(-/-)/Ucp1(-/-)) were created, and the key parameters of metabolism and body composition were studied. We discovered that RII beta(-/-) mice exhibit nocturnal hyperactivity in addition to the increased oxygen consumption at rest. Disruption of UCP1 in RII beta(-/-) mice reduced basal oxygen consumption but did not prevent the nocturnal hyperactivity. The double knockout animals also retained the lean phenotype of the RII beta null mice, demonstrating that induction of UCP1 and increased resting oxygen consumption is not the cause of leanness in the RII beta mutant mice.