Differential expression of novel adiponectin receptor-1 transcripts in skeletal muscle of subjects with normal glucose tolerance and type 2 diabetes

ADIPOR1 is essential for vision and its RPE expression is lost in the Mfrprd6 mouse

The knockout (KO) of the adiponectin receptor 1 (AdipoR1) gene causes retinal degeneration. Here we report that ADIPOR1 protein is primarily found in the eye and brain with little expression in other tissues. Further analysis of AdipoR1 KO mice revealed that these animals exhibit early visual system abnormalities and are depleted of RHODOPSIN prior to pronounced photoreceptor death. A KO of AdipoR1 post-development either in photoreceptors or the retinal pigment epithelium (RPE) resulted in decreased expression of retinal proteins, establishing a role for ADIPOR1 in supporting vision in adulthood. Subsequent analysis of the Mfrprd6 mouse retina demonstrated that these mice are lacking ADIPOR1 in their RPE layer alone, suggesting that loss of ADIPOR1 drives retinal degeneration in this model. Moreover, we found elevated levels of IRBP in both the AdipoR1 KO and the Mfrprd6 models. The spatial distribution of IRBP was also abnormal. This dysregulation of IRBP hypothesizes a role for ADIPOR1 in retinoid metabolism.

Differentially expressed alternatively spliced genes in skeletal muscle from cancer patients with cachexia

BACKGROUND

Alternative splicing (AS) is a post-transcriptional gene regulatory mechanism that contributes to proteome diversity. Aberrant splicing mechanisms contribute to various cancers and muscle-related conditions such as Duchenne muscular dystrophy. However, dysregulation of AS in cancer cachexia (CC) remains unexplored. Our objectives were (i) to profile alternatively spliced genes (ASGs) on a genome-wide scale and (ii) to identify differentially expressed alternatively spliced genes (DASGs) associated with CC.

METHODS

Rectus abdominis muscle biopsies obtained from cancer patients were stratified into cachectic cases (n = 21, classified based on International consensus diagnostic framework for CC) and non-cachectic controls (n = 19, weight stable cancer patients). Human transcriptome array 2.0 was used for profiling ASGs using the total RNA isolated from muscle biopsies. Representative DASG signatures were validated using semi-quantitative RT-PCR.

RESULTS

We identified 8960 ASGs, of which 922 DASGs (772 up-regulated and 150 down-regulated) were identified at ≥1.4 fold-change and P < 0.05. Representative DASGs validated by semi-quantitative RT-PCR confirmed the primary findings from the human transcriptome arrays. Identified DASGs were associated with myogenesis, adipogenesis, protein ubiquitination, and inflammation. Up to 10% of the DASGs exhibited cassette exon (exon included or skipped) as a predominant form of AS event. We also observed other forms of AS events such as intron retention, alternate promoters.

CONCLUSIONS

Overall, we have, for the first time, conducted global profiling of muscle tissue to identify DASGs associated with CC. The mechanistic roles of the identified DASGs in CC pathophysiology using model systems is warranted, as well as replication of findings in independent cohorts.

Non-coding functions of alternative pre-mRNA splicing in development

A majority of messenger RNA precursors (pre-mRNAs) in the higher eukaryotes undergo alternative splicing to generate more than one mature product. By targeting the open reading frame region this process increases diversity of protein isoforms beyond the nominal coding capacity of the genome. However, alternative splicing also frequently controls output levels and spatiotemporal features of cellular and organismal gene expression programs. Here we discuss how these non-coding functions of alternative splicing contribute to development through regulation of mRNA stability, translational efficiency and cellular localization.

Orally active osteoanabolic agent GTDF binds to adiponectin receptors, with a preference for AdipoR1, induces adiponectin-associated signaling, and improves metabolic health in a rodent model of diabetes

Adiponectin is an adipocytokine that signals through plasma membrane-bound adiponectin receptors 1 and 2 (AdipoR1 and -2). Plasma adiponectin depletion is associated with type 2 diabetes, obesity, and cardiovascular diseases. Adiponectin therapy, however, is yet unavailable owing to its large size, complex multimerization, and functional differences of the multimers. We report discovery and characterization of 6-C-β-D-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'-tetrahydroxydihydroflavonol (GTDF) as an orally active adiponectin mimetic. GTDF interacted with both AdipoRs, with a preference for AdipoR1. It induced adiponectin-associated signaling and enhanced glucose uptake and fatty acid oxidation in vitro, which were augmented or abolished by AdipoR1 overexpression or silencing, respectively. GTDF improved metabolic health, characterized by elevated glucose clearance, β-cell survival, reduced steatohepatitis, browning of white adipose tissue, and improved lipid profile in an AdipoR1-expressing but not an AdipoR1-depleted strain of diabetic mice. The discovery of GTDF as an adiponectin mimetic provides a promising therapeutic tool for the treatment of metabolic diseases.

Effect of therapeutic dose of vitamin d on serum adiponectin and glycemia in vitamin d-insufficient or deficient type 2 diabetic patients

Background:

Lower vitamin D status has been reported in diabetic patients. Serum 25-hydroxyvitamin D and adiponectin were inversely associated with type 2 diabetes and insulin resistance. Vitamin D may involve in regulation of the adiponectin levels, which is directly related to insulin sensitivity.

Objectives:

The aim of this study was to investigate the effect of therapeutic dose of vitamin D on serum adiponectin and insulin resistance in vitamin D-insufficient or deficient type 2 diabetic patients.

Materials and Methods:

This double-blind, randomized, clinical trial was conducted on 81 type 2 diabetic patients with vitamin D level of 10-30 ng/mL. Intervention was 50000 IU vitamin D or placebo once a week for 8 weeks. At the beginning and end of the study, blood samples were collected after 12 hours of fasting and serum glucose, insulin, 25-hydroxyvitamin D, and adiponectin were measured. Insulin resistance was calculated by homeostasis model assessment (HOMA-IR).

Results:

After 8-week intervention, serum 25-hydroxyvitamin D significantly increased and reached the normal levels in patients receiving vitamin D (P < 0.001) and the levels of fasting serum glucose, insulin, and HOMA-IR were significantly decreased (P = 0.04, 0.02 and 0.007, respectively). No significant changes were observed in these levels in the placebo group. Significant differences were observed in mean changes in the above-mentioned variables between the two groups (P = 0.01, 0.04 and 0.006, respectively). No significant changes were found in serum adiponectin in the vitamin D and placebo groups (P = 0.83).

Conclusions:

Therapeutic dose of vitamin D can improve vitamin D status and glycemic indicators. But it seems that an 8-week intervention period was not sufficient to reveal the possible effects of vitamin D on serum adiponectin levels.

RNA-binding protein PTB and microRNA-221 coregulate AdipoR1 translation and adiponectin signaling

Adiponectin receptor 1 (AdipoR1) mediates adiponectin's pleiotropic effects in muscle and liver and plays an important role in the regulation of insulin resistance and diabetes. Here, we demonstrate a pivotal role for microRNA-221 (miR-221) and the RNA-binding protein polypyrimidine tract-binding protein (PTB) in posttranscriptional regulation of AdipoR1 during muscle differentiation and in obesity. RNA-immunoprecipitation and luciferase reporter assays illustrated that both PTB and miR-221 bind AdipoR1-3'UTR and cooperatively inhibit AdipoR1 translation. Depletion of PTB or miR-221 increased, while overexpression of these factors decreased, AdipoR1 protein synthesis in both muscle and liver cells. During myogenesis, downregulation of PTB and miR-221 robustly induced AdipoR1 translation, providing a mechanism for enhanced AdipoR1 protein expression and activation in differentiated muscle cells. In addition, since both PTB and miR-221 are upregulated in liver and muscle of genetic and dietary mouse models of obesity, this novel translational mechanism may be at least partly responsible for the reduction in AdipoR1 protein levels in obesity. These findings highlight the importance of translational control in regulating AdipoR1 protein expression and adiponectin signaling. Given that adiponectin is reduced in obesity, induction of AdipoR1 could potentially enhance adiponectin beneficial effects and ameliorate insulin resistance and diabetes.

uORFdb--a comprehensive literature database on eukaryotic uORF biology

Approximately half of all human transcripts contain at least one upstream translational initiation site that precedes the main coding sequence (CDS) and gives rise to an upstream open reading frame (uORF). We generated uORFdb, publicly available at http://cbdm.mdc-berlin.de/tools/uorfdb, to serve as a comprehensive literature database on eukaryotic uORF biology. Upstream ORFs affect downstream translation by interfering with the unrestrained progression of ribosomes across the transcript leader sequence. Although the first uORF-related translational activity was observed >30 years ago, and an increasing number of studies link defective uORF-mediated translational control to the development of human diseases, the features that determine uORF-mediated regulation of downstream translation are not well understood. The uORFdb was manually curated from all uORF-related literature listed at the PubMed database. It categorizes individual publications by a variety of denominators including taxon, gene and type of study. Furthermore, the database can be filtered for multiple structural and functional uORF-related properties to allow convenient and targeted access to the complex field of eukaryotic uORF biology.

Progress in understanding the relationship between adiponectin receptors R1&R2 and carcinomas

Adiponectin is a key hormone secreted by adipocytes. It is involved in glucose and lipid metabolism and insulin sensitization, and has anti-inflammatory, anti-arteriosclerosis and anti-carcinogenic effects. Many studies have found that adiponectin is related to coronary heart disease, type 2 diabetes mellitus, hypertension and cancer. Recently, adiponectin receptors R1 and R2 have been reported to be expressed in several malignancies, such as colorectal cancer, breast cancer, endometrial cancer, esophageal cancer, gastric cancer, prostate cancer and nephrocyte cancer.

Expression of adiponectin receptors R1 and R2 in colorectal carcinoma and colorectal adenoma

AIM: To investigate the relationship between expression of adiponectin receptors R1 and R2 and clinicopathological parameters in colorectal cancer and colorectal adenomas.

METHODS: Expression of adiponectin receptors R1 and R2 in surgical specimens of colorectal carcinoma (n = 51), colorectal adenomas (n = 42), and normal colorectal mucosa (n = 35) was detected by immunohistochemistry.

RESULTS: The expression of adiponectin receptors R1 and R2 was significantly higher in colorectal carcinoma than in colorectal adenomas (P = 0.047, 0.035), and in colorectal adenomas than in normal colorectal mucosa (P = 0.042, 0.046). Expression of adiponectin receptors was significantly correlated with histological differentiation, lymph node metastasis, and TNM stages (all P < 0.05), but not with other clinicopathological features including sex, age, tumor size.

CONCLUSION: Adiponectin receptors R1 and R2 are expressed in both colorectal carcinoma and normal colorectal mucosa. Expression of adiponectin receptors R1 and R2 is enhanced in colorectal cancer and adenomas. Adiponectin receptor expression closely correlates with tumor differentiation, lymph node metastasis and TNM stage in patients with colorectal cancer. Adiponectin receptors may become new targets for colorectal cancer treatment.