Methods for detection of the Ob receptor and the diagnosis of body weight disorders, including obesity and cachexia

#The present invention relates to the discovery, identification and characterization of nucleotides that encode Ob receptor (ObR), a receptor protein that participates in mammalian body weight regulation. The invention encompasses obR nucleotides, host cell expression systems, ObR proteins, fusion proteins, polypeptides and peptides, antibodies to the receptor, transgenic animals that express an obR transgene, or recombinant knock-out animals that do not express the ObR, antagonists and agonists of the receptor, and other compounds that modulate obR gene expression or ObR activity that can be used for diagnosis, drug screening, clinical trial monitoring, and/or the treatment of body weight disorders, including but not limited to obesity, cachexia and anorexia.

#Obesity represents the most prevalent of body weight disorders, and it is the most important nutritional disorder in the western world, with estimates of its prevalence ranging from 30% to 50% within the middle-aged population. Other body weight disorders, such as anorexia nervosa and bulimia nervosa which together affect approximately 0.2% of the female population of the western world, also pose serious health threats. Further, such disorders as anorexia and cachexia (wasting) are also prominent features of other diseases such as cancer, cystic fibrosis, and AIDS.

#Obesity, defined as an excess of body fat relative to lean body mass, also contributes to other diseases. For example, this disorder is responsible for increased incidences of diseases such as coronary artery disease, stroke, and diabetes. (See, e.g., Nishina, P. M. et al., 1994, Metab. 43:554-558.) Obesity is not merely a behavioral problem, i.e., the result of voluntary hyperphagia. Rather, the differential body composition observed between obese and normal subjects results from differences in both metabolism and neurologic/metabolic interactions. These differences seem to be, to some extent, due to differences in gene expression, and/or level of gene products or activity (Friedman, J. M. et al., 1991, Mammalian Gene 1:130-144).

#FIGS. 1A-1D. Nucleotide sequence (SEQ ID NO:1) and deduced amino acid sequence (SEQ ID NO:2) of murine obR (short form) cDNA encoding murine short form ObR protein (894 amino acids). The domains of short form murine ObR are: signal sequence (amino acid residue 1 to about amino acid residue 22), extracellular domain (from about amino acid residue 23 to about amino acid residue 837), transmembrane domain (from about amino acid residue 838 to about amino acid residue 860), and cytoplasmic domain (from about amino acid residue 861 to about amino acid residue 894). Potential N-linked glycosylation sites in the extracellular domain are indicated by asterisks above the first amino acid of the N-X-S and N-X-T motifs. Underscores indicate motifs conserved in the class I cytokine receptor family.

#FIG. 2A. COS-7 cells transfected with the ObR cDNA were treated with various AP or AP-Ob fusion proteins at 1 nM (diluted in DMEM+10% FBS). Columns show the average of two binding determinations and error bars show the difference between the two. 1) Unfused AP, 2) AP-Ob (mouse), 3) AP-Ob (mouse)+100 nM mouse Ob, 4) AP-Ob (mouse)+100 nM human Ob, 5) AP-Ob (human), 6) Ob-AP (mouse), 7) AP-Ob (mouse) incubated with mock transfected (vector- no insert) COS-7 cells.

#FIG. 2B. Binding isotherm and Scatchard analysis of the interaction of AP-Ob and ObR. COS-7 cells transfected with the obR cDNA were incubated with various concentrations of the AP-Ob (mouse) fusion protein. Scatchard transformation is shown as an inset.

#ObR, described for the first time herein, is a novel receptor protein that participates in body weight regulation. ObR is a transmembrane protein that spans the membrane once and belongs to the Class I family of cytokine receptors, and is most closely related to the gp130 signal transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. Signal transduction is triggered by the binding of Ob to the receptor. Neutralization of Ob, removal of Ob, or interference with its binding to ObR results in weight gain. ObR mRNA is detected in the choroid plexus, and other tissues, including the hypothalamus.

#The invention encompasses the use of obR nucleotides, ObR proteins and peptides, as well as antibodies to the ObR (which can, for example, act as ObR agonists or antagonists), antagonists that inhibit receptor activity or expression, or agonists that activate receptor activity or increase its expression in the diagnosis and treatment of body weight disorders, including, but not limited to obesity, cachexia and anorexia in animals, including humans. The diagnosis of an ObR abnormality in a patient, or an abnormality in the ObR signal transduction pathway, will assist in devising a proper treatment or therapeutic regimen. In addition, obR nucleotides and ObR proteins are useful for the identification of compounds effective in the treatment of body weight disorders regulated by the ObR.

#In particular, the invention described in the subsections below encompasses ObR, polypeptides or peptides corresponding to functional domains of the ObR (e.g., ECD, TM or CD), mutated, truncated or deleted ObRs (e.g. an ObR with one or more functional domains or portions thereof deleted, such as ΔTM and/or ΔCD), ObR fusion proteins (e.g. an ObR or a functional domain of ObR, such as the ECD, fused to an unrelated protein or peptide such as an immunoglobulin constant region, i.e., IgFc), nucleotide sequences encoding such products, and host cell expression systems that can produce such ObR products.