Distinct subcellular localization of three isoforms of insulinoma-associated protein 2β in neuroendocrine tissues

Insulin granule morphology and crinosome formation in mice lacking the pancreatic β cell-specific phogrin (PTPRN2) gene

We recently reported that phogrin, also known as IA-2β or PTPRN2, forms a complex with the insulin receptor in pancreatic β cells upon glucose stimulation and stabilizes insulin receptor substrate 2. In β cells of systemic phogrin gene knockout (IA-2β-/-) mice, impaired glucose-induced insulin secretion, decreased insulin granule density, and an increase in the number and size of lysosomes have been reported. Since phogrin is expressed not only in β cells but also in various neuroendocrine cells, the precise impact of phogrin expressed in β cells on these cells remains unclear. In this study, we performed a comprehensive analysis of morphological changes in RIP-Cre+/-Phogrinflox/flox (βKO) mice with β cell-specific phogrin gene knockout. Compared to control RIP-Cre+/- Phogrin+/+ (Ctrl) mice, aged βKO mice exhibited a decreased density of insulin granules, which can be categorized into three subtypes. While no differences were observed in the density and size of lysosomes and crinosomes, organelles involved in insulin granule reduction, significant alterations in the regions of lysosomes responding positively to carbohydrate labeling were evident in young βKO mice. These alterations differed from those in Ctrl mice and continued to change with age. These electron microscopic findings suggest that phogrin expression in pancreatic β cells plays a role in insulin granule homeostasis and crinophagy during aging, potentially through insulin autocrine signaling and other mechanisms.

Knockdown of Ptprn-2 delays the onset of puberty in female rats

In the present study, we evaluated how Ptprn-2 (encoding tyrosine phosphatase, receptor type, N2 polypeptide protein) affects the onset of puberty in female rats. We evaluated the expression of Ptprn-2 mRNA and protein in the hypothalamus-pituitary-ovary axis of female rats using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunofluorescence at infancy, prepuberty, puberty, peripuberty, and adulthood. We evaluated the effects of Ptprn-2 gene knockdown on different aspects of reproduction-related biology in female rats, including the expression levels of puberty-related genes in vivo and in vitro, the time to onset of puberty, the concentration of serum reproductive hormones, the morphology of ovaries, and the ultrastructure of pituitary gonadotropin cells. Our results demonstrated that PTPRN-2 was primarily distributed in the arcuate nucleus (ARC), periventricular nucleus (PeN), adenohypophysis, and the ovarian follicular theca, stroma, and granulosa cells of female rats at various stages. Ptprn-2 mRNA levels significantly varied between peripuberty and puberty (P < 0.05) in the hypothalamus and pituitary gland. In hypothalamic cells, Ptprn-2 knockdown decreased the expression of Ptprn-2 and Rfrp-3 mRNA (P < 0.05) and increased the levels of Gnrh and Kiss-1 mRNA (P < 0.05). Ptprn-2 knockdown in the hypothalamus resulted in delayed vaginal opening compared to the control group (n = 12, P < 0.01), and Ptprn-2, Gnrh, and Kiss-1 mRNA levels (P < 0.05) all decreased, while the expression of Igf-1 (P < 0.05) and Rfrp-3 mRNA (P < 0.01) increased. The concentrations of FSH and P₄ in the serum of Ptprn-2 knockdown rats were lower than in control animals (P < 0.05). Large transverse perimeters and longitudinal perimeters (P < 0.05) were found in the ovaries of Ptprn-2 knockdown rats. There were fewer large secretory particles from gonadotropin cells in adenohypophysis tissue of the Ptprn-2 knockdown group compared to the control group. This indicates that Ptprn-2 knockdown can regulate levels of Gnrh, Kiss-1, and Rfrp-3 mRNA in the hypothalamus, regulate the concentration of serum FSH and P₄, and alter the morphology of ovarian and gonadotropin cells, delaying the onset of puberty in female rats.

Developmental Transcriptome Analysis and Identification of Genes Involved in Larval Metamorphosis of the Razor Clam, Sinonovacula constricta

The razor clam Sinonovacula constricta is an important commercial species. The deficiency of developmental transcriptomic data is becoming the bottleneck of further researches on the mechanisms underlying settlement and metamorphosis in early development. In this study, de novo transcriptome sequencing was performed for S. constricta at different early developmental stages by using Illumina HiSeq 2000 paired-end (PE) sequencing technology. A total of 112,209,077 PE clean reads were generated. De novo assembly generated 249,795 contigs with an average length of 585 bp. Gene annotation resulted in the identification of 22,870 unigene hits against the NCBI database. Eight unique sequences related to metamorphosis were identified and analyzed using real-time PCR. The razor clam reference transcriptome would provide useful information on early developmental and metamorphosis mechanisms and could be used in the genetic breeding of shellfish.

Human fibrocytes express multiple antigens associated with autoimmune endocrine diseases

CONTEXT

Factors common to multiple autoimmune diseases have been sought vigorously. Graves' disease (GD) and type 1 diabetes mellitus (T1DM) involve end-organ remodeling. Fibrocytes participate in inflammatory diseases and were recently shown to express thyroid-specific proteins such as the thyrotropin receptor and thyroglobulin.

OBJECTIVE

The objective of the study was to determine whether a broader repertoire of autoantigen expression, such as proteins associated with T1DM, can be ascribed to fibrocytes.

DESIGN, SETTING, AND PARTICIPANTS

Fibrocytes and fibroblasts were collected and analyzed from healthy individuals and those with autoimmune diseases in an academic clinical practice.

MAIN OUTCOME MEASURES

Real-time PCR, Western blot analysis, gene promoter analysis, cell transfections, and flow cytometric cell sorting were performed.

RESULTS

Islet cell antigen ICA512 (IA-2) and islet cell autoantigen of 69 kDa (ICA69), two islet-specific proteins implicated in T1DM, are expressed by fibrocytes from healthy donors and those with T1DM, GD, and multiple sclerosis. Both transcripts are detected by PCR, the proteins are resolved on Western blots, and both gene promoters are active in fibrocytes. Levels of ICA69 are substantially higher than those of IA-2 in fibrocytes. ICA69 localizes to CD34(+) GD orbital fibroblasts putatively derived from fibrocytes, whereas higher levels of IA-2 are found in CD34(-) fibroblasts.

CONCLUSIONS

In addition to autoantigens implicated in thyroid autoimmunity, fibrocytes and derivative fibroblasts express multiple autoantigens associated with T1DM. This expression results from active gene promoters and abundant steady-state mRNA encoding ICA69 and IA-2. These latest findings demonstrate that fibrocytes express antigens relevant to multiple forms of endocrine autoimmunity. They suggest the potential for these cells playing a direct role in immune reactivity directed at the thyroid and pancreatic islets.

Immunohistochemical analysis of IA-2 family of protein tyrosine phosphatases in rat gastrointestinal endocrine cells

Islet-associated protein-2 (IA-2) and IA-2β (also known as phogrin) are unique neuroendocrine-specific protein tyrosine phosphatases (PTPs). The IA-2 family of PTPs was originally identified from insulinoma cells and discovered to be major autoantigens in type 1 diabetes. Despite its expression in the neural and canonical endocrine tissues, data on expression of the IA-2 family of PTPs in gastrointestinal endocrine cells (GECs) are limited. Therefore, we immunohistochemically investigated the expression of the IA-2 family of PTPs in the rat gastrointestinal tract. In the stomach, IA-2 and IA-2β were expressed in GECs that secrete serotonin, somatostatin, and cholecystokinin/gastrin-1. In addition to these hormones, secretin, gastric inhibitory polypeptide (also known as the glucose-dependent insulinotropic peptide), glucagon-like peptide-1, and glucagon, but not ghrelin were coexpressed with IA-2 or IA-2β in duodenal GECs. Pancreatic islet cells that secrete gut hormones expressed the IA-2 family of PTPs. The expression patterns of IA-2 and IA-2β were comparable. These results reveal that the IA-2 family of PTPs is expressed in a cell type-specific manner in rat GECs. The extensive expression of the IA-2 family of PTPs in pancreo-gastrointestinal endocrine cells and in the enteric plexus suggests their systemic contribution to nutritional control through a neuroendocrine signaling network.