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Increased calcium intake regulates colonic CaSR expression and inhibits induced colitis and Wnt/β-catenin signaling

Fri, 21 Dec 2012 05:00:00 GMT

Title: Increased calcium intake regulates colonic CaSR expression and inhibits induced colitis and Wnt/β-catenin signaling Authors: Turki, Razan Abstract: One of the major complications in patients with long standing inflammatory bowel disease (IBD) is colitis-associated colon cancer. The signaling pathways that promote the transformation of colitis to colorectal cancer (CRC) are unknown but one candidate is the prolonged interaction between tumor necrosis factor alpha (TNF-α) and its receptor, TNFR1. This interaction may stimulate a defective Wnt signaling pathway to evoke epithelial cells to hyperproliferate. This crypt hyperproliferation can lead to the development CRC. Activation of Extracellular Calcium-sensing receptor (CaSR) a G-protein coupled receptor, on sub-epithelial myfibroblasts has been found to stimulate the expression of Wnt5a, a member of Wnt family, while CaSR activation on the epithelial cells stimulates Wnt5a receptor, Ror2, a member of receptor tyrosine kinase family. Wnt5a/Ror2 (non canonical signaling) interaction has been suggested to decrease TNFR1 expression and inhibit Wnt/β-catenin signaling to regulate cellular growth. The aims of this thesis were to determine whether increased dietary calcium will increase colonic CaSR expression, characterize the colons of “rescued” CaSR/PTH double homozygous knockout and their response to an acute model of colitis, and assess whether CaSR activation influenced the status of Low-density lipoprotein receptor-related protein 6 (pLRP6), co-receptor for Wnt, in cell culture models. Our results demonstrated that CaSR expression is higher in the colon of the NIH-Swiss Webster mice after feeding them 2% calcium alone or in conjunction with vitamin D for four weeks compared to two weeks, suggesting that dietary calcium alone or together with vitamin D can regulate colonic CaSR expression. We found the CaSR-/PTH- colons had a significant reduction in the non canonical signaling and enhanced Wnt/β-catenin signaling and the amount of inflammation was increased, suggesting that CaSR can inhibit Wnt/β-catenin signaling in the colonic crypt and acts as an anti-inflammatory signal. Our results demonstrated that CaSR activation alone in CaSR-HEK and RKO cells reduced Wnt-stimulated LRP6 phosphorylation suggesting a crucial role of CaSR in the inhibition of LRP6 phosphorylation. The observations seen in this study strongly suggest a role for CaSR in inhibiting the defective Wnt/β-catenin signaling pathway, induced colitis, and LRP6 phosphorylation to regulate cellular growth. Description: Thesis (Master, Physiology) -- Queen's University, 2012-12-21 13:18:12.874

THE SUBFORNICAL ORGAN AND AREA POSTREMA MEDIATE THE CENTRAL EFFECTS OF CIRCULATING LEPTIN

Mon, 15 Oct 2012 04:00:00 GMT

Title: THE SUBFORNICAL ORGAN AND AREA POSTREMA MEDIATE THE CENTRAL EFFECTS OF CIRCULATING LEPTIN Authors: Smith, Pauline Abstract: Leptin is an adipokine that acts centrally to regulate feeding behaviour, energy expenditure and autonomic function via activation of its receptor (ObRb) in nuclei in the central nervous system (CNS). This thesis investigates the involvement of two sensory circumventricular organs (CVOs), the subfornical organ (SFO) and area postrema (AP), in mediating the central effects of leptin using a variety of experimental approaches. We first show that acute electrical stimulation of the SFO elicits feeding in satiated rats, supporting a role for this specialized CNS structure in the control of food intake. We then demonstrate, using RT-PCR, the presence of ObRb mRNA in SFO and, using whole cell current clamp electrophysiology, reveal that leptin influences the excitability of individual SFO neurons, causing both excitatory and inhibitory responses. Furthermore, we find that leptin activates the same SFO neurons activated by amylin. Given the association between obesity and hypertension and the well-established role of the SFO in cardiovascular regulation, we show that leptin microinjection into the SFO decreases blood pressure in young rats, effects that are abolished in leptin-resistant, diet induced obese rats, suggesting that leptin-insensitivity in the SFO of obese, leptin-resistant, individuals may contribute to obesity-related hypertension. Our studies also show that the medullary AP expresses ObRb and that leptin influences the excitability of AP neurons. Furthermore, we show that leptin and amylin act on the same subpopulation of neurons in the AP. Finally, our preliminary AP/SFO lesion studies reveal that animals with these lesions exhibit a profound decrease in body weight and food intake and no longer exhibit decreases in body weight in response to peripheral leptin administration. In summary, the data presented in this thesis suggest the SFO and AP to be important in body weight homeostasis and in mediating the central effects of leptin. In addition, these areas appear to be important in the integration of multiple signals derived from peripheral sources. Furthermore, the fact that the SFO appears to be involved in leptin effects on both energy balance and cardiovascular regulation attest to the integrative nature of the SFO in the control of diverse physiological functions. Description: Thesis (Ph.D, Physiology) -- Queen's University, 2012-10-15 14:57:15.387

EXERCISE LIMITATION IN MILD COPD: THE ROLE OF RESPIRATORY MECHANICAL FACTORS

Fri, 28 Sep 2012 04:00:00 GMT

Title: EXERCISE LIMITATION IN MILD COPD: THE ROLE OF RESPIRATORY MECHANICAL FACTORS Authors: Chin, Roberto Carlos Abstract: The majority of patients with chronic obstructive pulmonary disease (COPD) have milder airway obstruction and are not diagnosed in a timely fashion. Nevertheless, these patients are largely under-studied; this, despite new evidence of increased morbidity and mortality in this sub-population. Recent studies have highlighted the increased ventilatory requirements and abnormalities in respiratory mechanics as important features to explain the relatively reduced exercise tolerance and greater exertional dyspnea in these patients. However, it remains uncertain whether such abnormal mechanical factors actually limit exercise capacity in mild COPD. Accordingly, the objective of this study was to determine whether ventilatory constraints represent a primary factor in exercise limitation and increased dyspnea in this patient group. To determine the role of mechanical factors in exercise limitation in mild COPD, we selectively loaded the respiratory system by adding dead space (DS) to the breathing circuit. We compared ventilation, breathing pattern, operating lung volumes, and dyspnea intensity during incremental cycle exercise in 20 patients with GOLD stage I COPD (post-bronchodilator FEV1/FVC=61±5%, and FEV1=95±11% predicted; mean±SD) and 20 healthy age-, sex- and BMI-matched subjects under two conditions, in randomized order: unloaded control (CTRL) or ventilatory stimulation by 600mL of an added DS. Compared to the CTRL condition, both healthy and COPD participants had small decreases in peak work rate and no significant increase in peak ventilation with the added DS. At the highest equivalent work rate of 60 watts, DS caused a smaller increase in tidal volume (VT) in COPD compared with healthy subjects (+0.26±0.29 vs. +0.56±0.22 L respectively, p<0.01) with a correspondingly greater increase in dyspnea intensity (+1.8±1.8 vs. +0.2±0.6 Borg units, respectively, p<0.0001). At peak exercise, COPD patients failed to significantly increase VT, reflecting the fact that end-inspiratory lung volume (EILV) could not increase with DS vs. CTRL (5.25±0.91 vs. 5.16±0.84 L, respectively, p=0.41). This contrasts the results in health where EILV increased with DS vs. CTRL (5.40±1.01 vs. 5.13±0.90 L, respectively, p<0.05). We conclude that the lower exercise performance in mild COPD, compared with health, is explained by critical respiratory mechanical constraints which limit further increases in ventilation to support a higher metabolic load. Description: Thesis (Master, Physiology) -- Queen's University, 2012-09-28 12:04:50.507

A Study of Pro- and Anti-Nociceptive Factors In A Model of Colitis-Associated Visceral Pain

Sat, 08 Sep 2012 04:00:00 GMT

Title: A Study of Pro- and Anti-Nociceptive Factors In A Model of Colitis-Associated Visceral Pain Authors: Benson, JESSICA Abstract: Chronic abdominal pain is a major cause of patient morbidity in inflammatory bowel diseases (IBD). A balance of pro- and anti-nociceptive factors regulating colonic dorsal root ganglion (DRG) neurons, which synapse onto second order dorsal horn neurons, are known to regulate chronic pain but the mechanisms are poorly understood. This thesis examined whether neuroanatomical remodeling of DRG central nerve terminals underlies pro-nociceptive signaling and whether subsets of immune cells source the anti-nociceptive factor, β-endorphin. To examine pro-nociceptive mechanisms, acute and chronic dextran sulfate sodium (DSS) mouse models of colitis were established and substance P (SP; marker of nociceptor terminals) immunohistochemistry used to investigate changes in immunoreactivity of DRG terminals in the thoracic dorsal horn (segments T9-T13). SP immunoreactivity was increased in the dorsal horn (4 fold; P < 0.001) and central canal (P < 0.001) following chronic colitis. In contrast, SP immunoreactivity was unchanged in acute colitis. However, five weeks later SP immunoreactivity was increased both in the dorsal horn (4 fold; P < 0.01) and central canal (P < 0.001). In the cervical spinal cord, SP immunoreactivity was not increased following colitis, suggesting that changes seen in the thoracic level were specific to signaling from colonic DRG neurons. Immunoreactivity for the SP NK1 receptor on second order neurons was also examined and a significant increase in immunoreactivity was observed on post-synaptic second order cell bodies following chronic DSS. This could provide an additional mechanism for enhanced SP neurotransmission centrally. ii The source of the anti-nociceptive mediator, β-endorphin, during chronic DSS colitis was investigated using magnetic cell sorting and flow cytometry. The number of β- endorphin expressing CD4+ (2.4 fold; P < 0.05) and CD11b+ (2.6 fold; P < 0.05) cells in mice increased following chronic colitis. These findings suggest that during colitis there is a time-dependent increase of SP immunoreactivity in thoracic DRG central terminals, which could play a role in pro- nociceptive signaling in chronic inflammation. These actions may be balanced by anti- nociceptive factors such as β-endorphin which are found in subsets of immune cells. Description: Thesis (Master, Physiology) -- Queen's University, 2012-08-29 16:28:41.166