The calcium-sensing receptor (CaSR) was cloned over 20 years ago and functionally demonstrated to regulate circulating levels of parathyroid hormone by maintaining physiological serum ionized calcium concentration ([Ca(2+)]). The receptor is highly expressed in the kidney; however, intrarenal and intraspecies distribution remains controversial. Recently, additional functions of the CaSR receptor in the kidney have emerged, including parathyroid hormone-independent effects. It is therefore critical to establish unequivocally the localization of the CaSR in the kidney to relate this to its proposed physiological roles. In this study, we determined CaSR expression in mouse, rat, and human kidneys using in situ hybridization, immunohistochemistry (using 8 different commercially available and custom-made antibodies), and proximity ligation assays. Negative results in mice with kidney-specific CaSR ablation confirmed the specificity of the immunohistochemistry signal. Both in situ hybridization and immunohistochemistry showed CaSR expression in the thick ascending limb, distal tubule, and collecting duct of all species, with the thick ascending limb showing the highest levels. Within the collecting ducts, there was significant heterogeneity of expression between cell types. In the proximal tubule, lower levels of immunoreactivity were detected by immunohistochemistry and proximity ligation assays. Proximity ligation assays were the only technique to demonstrate expression within glomeruli. This study demonstrated CaSR expression throughout the kidney with minimal discrepancy between species but with significant variation in the levels of expression between cell and tubule types. These findings clarify the intrarenal distribution of the CaSR and enable elucidation of the full physiological roles of the receptor within this organ.

Atopic dermatitis (AD) is an inflammatory skin disease characterized by infiltration of skin homing lymphocytes into the dermis. Most of these lymphocytes express the chemokine receptor CCR4, and the frequency of blood CCR4(+) lymphocytes correlates with AD disease severity. Canine AD is a pruritic inflammatory condition that shows many features of the human disease, including CCR4 overexpression. Therefore, we tested a potent selective CCR4 antagonist in an allergen challenge model of canine AD, both clinically and histologically, to investigate whether this chemokine pathway plays a role in the inflammatory response. Using a four-period randomized cross-over study design, 14 beagles were challenged with allergen and clinically monitored. Biopsy samples were taken before and after allergen challenge. A clear reduction of clinical scores was observed with oral prednisolone (P < 0.0001) but not for the CCR4 inhibitor. A subset of the dogs (5/13) showed partial inhibition (30-49%) of the clinical signs with CCR4 inhibitor treatment, and this finding was supported by the results of histopathologic analysis of skin biopsy samples. This partial response is consistent with redundancy in chemokine pathways and highlights the need for therapies blocking multiple pathways. This study shows the utility of this canine model of AD for testing new therapeutic agents.

Ulcerative colitis is a chronic inflammatory disease affecting the colon and is characterized by epithelial damage and barrier dysfunction. Upregulation of the tight junction protein claudin-2 by cytokines is hypothesized to contribute to the dysregulation of the epithelial barrier. New therapeutic agents which block the action of cytokines are being investigated in patients with ulcerative colitis. In order to understand the potential of these therapies, it is important to have reliable assays that can assess downstream endpoints that reflect drug mechanism of action. The aim of the current study was therefore to establish & validate an assay to reproducibly assess the expression and distribution of claudin-2 in human colon biopsy samples. Initially, the potential to measure claudin-2 protein by immunohistochemistry (IHC) was investigated. To identify suitable reagents to develop an IHC assay, pre-established criteria were used to screen five commercial antibodies by Western blotting, immunofluorescence and immunohistochemistry on claudin-2 positive and negative cells and healthy and ulcerative colitis colon tissue. Despite some of these antibodies specifically detecting claudin-2 using some of these techniques, none of the antibodies showed the expected specific staining pattern in formalin fixed human colon samples. As an alternative method to detect claudin-2 expression and distribution in formalin fixed biopsy sections, an in situ hybridization assay was developed. This assay underwent a novel tiered approach of validation to establish that it was fit-for-purpose, and suitable for clinical deployment. In addition, to understand the possible relationship of claudin-2 in the context of disease severity, expression was compared to the Geboes score. Overall, the microscopical Geboes score correlated with the claudin-2 biomarker score for samples that retained crypt morphology; samples with the highest Geboes score were not specifically distinguished, probably due to crypt destruction. In summary, we have applied a strategy for identifying target-specific antibodies in formalin fixed biopsy samples and highlighted that (published) antibodies may not correctly identify the intended antigen in tissues fixed using this method. Furthermore, we have developed and, for the first time, validated an in situ hybridization assay for detection of claudin-2 mRNA, suitable for use as a supportative method in clinical trials. Using our validated assay, we have demonstrated that increased claudin-2 expression correlates with the severity of ulcerative colitis, where crypt destruction is not seen.

Antagonism of the effects of glucagon as an adjunct therapy with other glucose-lowering drugs in the chronic treatment of diabetes has been suggested to aggressively control blood glucose levels. Antagonism of glucagon effects, by targeting glucagon secretion or disabling the glucagon receptor, is associated with α-cell hyperplasia. We evaluated the influence of total glucagon withdrawal on islets of Langerhans using prohormone convertase-2 knockout mice (PC2-ko), in which α-cell hyperplasia is present from a young age and persists throughout life, in order to understand whether or not sustained glucagon deficit would lead to islet tumorigenesis. PC2-ko and wild-type (WT) mice were maintained drug-free, and cohorts of these groups sampled at 3, 12 and 18 months for plasma biochemical and morphological (histological, immunohistochemical, electron microscopical and image analytical) assessments. WT mice showed no islet tumours up to termination of the study, but PC2-ko animals displayed marked changes in islet morphology from α-cell hypertrophy/hyperplasia/atypical hyperplasia, to adenomas and carcinomas, these latter being first encountered at 6-8 months. Islet hyperplasias and tumours primarily consisted of α-cells associated to varying degrees with other islet endocrine cell types. In addition to substantial increases in islet neoplasia, increased α-cell neogenesis associated primarily with pancreatic duct(ule)s was present. We conclude that absolute blockade of the glucagon signal results in tumorigenesis and that the PC2-ko mouse represents a valuable model for investigation of islet tumours and pancreatic ductal neogenesis.

The growth plate, ovary, adrenal gland, and rodent incisor tooth are sentinel organs for antiangiogenic effects since they respond reliably, quantitatively, and sensitively to inhibition of the vascular endothelial growth factor receptor (VEGFR). Here we report that treatment of rats with platelet-derived growth factor receptor beta (PDGFRb) inhibitors that target pericytes results in severe ovarian hemorrhage with degeneration and eventual rupture of the corpus luteum. Evaluation of the growth plate, adrenal gland, and incisor tooth that are typical target organs for antiangiogenic treatment in the rodent revealed no abnormalities. Histologically, the changes in the ovary were characterized by sinusoidal dilatation, increased vessel fragility, and hemorrhage into the corpus luteum. Immunocytochemical staining of vessels with alpha smooth muscle actin and CD31 that recognize pericytes and vascular endothelium, respectively, demonstrated that this effect was due to selective pericyte deficiency within corpora lutea. Further experiments in which rats were treated concurrently with both PDGFRb and VEGFR inhibitors ablated the hemorrhagic response, resulting instead in corpus luteum necrosis. These changes are consistent with the notion that selective pericyte loss in the primitive capillary network resulted in increased vessel fragility and hemorrhage, whereas concomitant VEGFR inhibition resulted in vessel regression and reduced vascular perfusion that restricted development of the hemorrhagic vessels. These results also highlight the utility of the rodent ovary to respond differentially to VEGFR and PDGFR inhibitors, which may provide useful information during routine safety assessment for determining target organ toxicity.