Allan Z. Zhao

Bio: Allan Z. Zhao is an academic researcher from Guangdong University of Technology. The author has contributed to research in topics: Leptin & Cancer. The author has an hindex of 30, co-authored 67 publications receiving 3444 citations. Previous affiliations of Allan Z. Zhao include University of Pittsburgh & University of Washington.

Induction of leptin resistance through direct interaction of C-reactive protein with leptin.

Abstract: The mechanisms underlying leptin resistance are still being defined. We report here the presence in human blood of several serum leptin-interacting proteins (SLIPs), isolated by leptin-affinity chromatography and identified by mass spectrometry and immunochemical analysis. We confirmed that one of the major SLIPs is C-reactive protein (CRP). In vitro, human CRP directly inhibits the binding of leptin to its receptors and blocks its ability to signal in cultured cells. In vivo, infusion of human CRP into ob/ob mice blocked the effects of leptin upon satiety and weight reduction. In mice that express a transgene encoding human CRP, the actions of human leptin were completely blunted. We also found that physiological concentrations of leptin can stimulate expression of CRP in human primary hepatocytes. Recently, human CRP has been correlated with increased adiposity and plasma leptin. Thus, our results suggest a potential mechanism contributing to leptin resistance, by which circulating CRP binds to leptin and attenuates its physiological functions.

A subset of olfactory neurons that selectively express cGMP-stimulated phosphodiesterase (PDE2) and guanylyl cyclase-D define a unique olfactory signal transduction pathway

Abstract: Odorant information is encoded by a series of intracellular signal transduction events thought to be mediated primarily by the second messenger cAMP. We have found a subset of olfactory neurons that express the cGMP-stimulated phosphodiesterase (PDE2) and guanylyl cyclase-D (GC-D), suggesting that cGMP in these neurons also can have an important regulatory function in olfactory signaling. PDE2 and GC-D are both expressed in olfactory cilia where odorant signaling is initiated; however, only PDE2 is expressed in axons. In contrast to most other olfactory neurons, these neurons appear to project to a distinct group of glomeruli in the olfactory bulb that are similar to the subset that have been termed “necklace glomeruli.” Furthermore, this subset of neurons are unique in that they do not contain several of the previously identified components of olfactory signal transduction cascades involving cAMP and calcium, including a calcium/calmodulin-dependent PDE (PDE1C2), adenylyl cyclase III, and cAMP-specific PDE (PDE4A). Interestingly, these latter three proteins are expressed in the same neurons; however, their subcellular distribution is distinct. PDE1C2 and adenylyl cyclase III are expressed almost exclusively in the olfactory cilia whereas PDE4A is present only in the cell bodies and axons. These data strongly suggest that selective compartmentalization of different PDEs and cyclases is an important feature for the regulation of signal transduction in olfactory neurons and likely in other neurons as well. In addition, the data implies that an olfactory signal transduction pathway specifically modulated by cGMP is present in some neurons of the olfactory neuroepithelium.

A phosphatidylinositol 3-kinase phosphodiesterase 3B-cyclic AMP pathway in hypothalamic action of leptin on feeding.

Abstract: Using male Sprague-Dawley rats implanted with third intracerebroventricular (ICV) cannulae, we found that cilostamide, a phosphodiesterase 3 (PDE3) inhibitor, (i) reversed the established effects of leptin on food intake and body weight, (ii) blocked, at the hypothalamic level, the leptin-induced tyrosine phosphorylation of signal transducer and activator of transcription 3 (Stat3) and (iii) blocked the DNA binding of p-Stat3. Additionally, ICV administration of leptin increased hypothalamic phosphatidylinositol 3-kinase (PI3K) and PDE3B activities and decreased cyclic AMP (cAMP) concentration. These results indicate that a PI3K–PDE3B–cAMP pathway interacting with the Janus kinase 2 (Jak2)–Stat3 pathway constitutes a critical component of leptin signaling in the hypothalamus.

Leptin inhibits insulin secretion by activation of phosphodiesterase 3B.

Abstract: The molecular signaling events by which leptin exerts its functions in vivo are not well delineated. Here, we show a novel leptin signaling mechanism that requires phospho- inositide 3-kinase (PI 3-kinase)-dependent activation of cy- clic nucleotide phosphodiesterase 3B (PDE3B) and subse- quent suppression of cAMP levels. In pancreatic b cells, leptin causes the activation of PDE3B, which leads to marked inhibition of glucagon-like peptide-1-stimulated in- sulin secretion. The effect of leptin is abolished when insulin secretion is induced with cAMP analogues that cannot be hydrolyzed by PDE3B. Selective inhibitors of PDE3B and PI 3-kinase completely prevent the leptin effect on insulin secretion and cAMP accumulation. The results demonstrate that one of the physiological effects of leptin, suppression of insulin secretion, is mediated through activation of PDE3B and suggest PDE3B as a mediator of leptin action in other tissues. ( J. Clin. Invest. 1998. 102:869-873.) Key words: cAMPdiabetesphosphoinositide 3-kinaseb cellgluca- gon-like peptide-1

Cyclic Nucleotide Phosphodiesterases: Molecular Regulation to Clinical Use

Abstract: Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that regulate the cellular levels of the second messengers, cAMP and cGMP, by controlling their rates of degradation. There are 11 different PDE families, with each family typically having several different isoforms and splice variants. These unique PDEs differ in their three-dimensional structure, kinetic properties, modes of regulation, intracellular localization, cellular expression, and inhibitor sensitivities. Current data suggest that individual isozymes modulate distinct regulatory pathways in the cell. These properties therefore offer the opportunity for selectively targeting specific PDEs for treatment of specific disease states. The feasibility of these enzymes as drug targets is exemplified by the commercial and clinical successes of the erectile dysfunction drugs, sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra). PDE inhibitors are also currently available or in development for treatment of a variety of other pathological conditions. In this review the basic biochemical properties, cellular regulation, expression patterns, and physiological functions of the different PDE isoforms will be discussed. How these properties relate to the current and future development of PDE inhibitors as pharmacological agents is especially considered. PDEs hold great promise as drug targets and recent research advances make this an exciting time for the field of PDE research.

PAS Domains: Internal Sensors of Oxygen, Redox Potential, and Light

Abstract: PAS domains are newly recognized signaling domains that are widely distributed in proteins from members of the Archaea and Bacteria and from fungi, plants, insects, and vertebrates. They function as input modules in proteins that sense oxygen, redox potential, light, and some other stimuli. Specificity in sensing arises, in part, from different cofactors that may be associated with the PAS fold. Transduction of redox signals may be a common mechanistic theme in many different PAS domains. PAS proteins are always located intracellularly but may monitor the external as well as the internal environment. One way in which prokaryotic PAS proteins sense the environment is by detecting changes in the electron transport system. This serves as an early warning system for any reduction in cellular energy levels. Human PAS proteins include hypoxia-inducible factors and voltage-sensitive ion channels; other PAS proteins are integral components of circadian clocks. Although PAS domains were only recently identified, the signaling functions with which they are associated have long been recognized as fundamental properties of living cells.

AMP-kinase regulates food intake by responding to hormonal and nutrient signals in the hypothalamus

Abstract: AMP-kinase regulates food intake by responding to hormonal and nutrient signals in the hypothalamus