Physiology and Pharmacology of BRS-3 (Bombesin-Like Receptor 3)

2016财年的进展包括： 为了研究BRS-3作用的特定细胞、部位、组织和递质，我们产生了BRS-3小鼠。用牙线标记的小鼠可以确定特定细胞中Brs3的必要性。我们正在使用这种小鼠，通过培育生殖系cre表达的小鼠。这些允许在由其cre驱动程序表达模式定义的细胞中敲除Brs3。 同样，我们也培育出了loxTB-Brs3小鼠。LoxTB-Brs3小鼠可以确定特定细胞中Brs3的充分性。我们正在用生殖系Cre表达的小鼠培育这只小鼠。这些允许在由其cre驱动程序表达模式定义的细胞中敲除Brs3。 最后，我们产生了Brs3-T2A-CreERT2小鼠，在其中，cre作为与内源性Brs3 mRNA融合的mRNA表达。这些小鼠以他莫昔芬依赖的方式和已报道的Brs3的分布模式表达cre。这只小鼠被用来利用化学遗传学和光遗传学选择性地激活Brs3神经元。 我们研究了BRS-3基因缺失和激活对小鼠血压和心率的影响(2)。在自由生活、遥测Brs3缺失的小鼠中，静息心率比野生型对照组低10%，而静息平均动脉压没有变化。在体力活动期间，Brs3基因缺失的小鼠的心率和血压增加得更多，达到了与对照组小鼠相似的心率和更高的平均动脉压。静脉注射BRS-3激动剂MK-5046增加了野生型小鼠的平均动脉压和心率，但对Brs3基因缺失的小鼠没有影响，这种增加可以被中枢交感神经降解剂可乐定预先阻断。综上所述，这些数据表明，BRS-3有助于静息心脏交感神经张力，但不是活动诱导的心率和血压增加所必需的。数据表明，BRS-3的激活通过中枢交感机制增加心率和血压。 到目前为止，还没有鉴定出高亲和力的内源性配体。为了检测循环中的内源性BRS-3配体，我们成功地在Brs3-/y小鼠和野生型(WT)小鼠之间或WT对照小鼠之间建立了共生小鼠对。Brs3-/y-WT和WT-WT配对在手术后立即减轻了相似的体重，在接受高脂肪饮食9周后，Brs3-/y-WT配对的体重超过了WT-WT配对。在Brs3/y-WT配对中，Brs3/y小鼠的肥胖率高于WT小鼠，但瘦肉和肝脏重量相当。与WT-WT配对的WT小鼠相比，Brs3-/y和WT配对的Brs3-/y和WT小鼠的瘦体重都更大，Brs3-/y小鼠的肥胖率也更高。这些结果与瘦素受体缺失(db/db)和WT小鼠的共生配对的报告形成对比，后者db/db小鼠中的高瘦素水平导致WT共生配对的体重减轻。我们的数据表明，循环中的内源性BRS-3配体，如果存在，不足以减少Brs3-/y小鼠异源共生伙伴的肥胖。 我们还发表了一篇关于Brs3(3)的简短评论。

Progress in FY2016 includes the following: In order to study the specific cells, sites, tissues, and transmitters by which BRS-3 acts, we have generated floxed Brs3 mouse. The floxed mice allow determination of necessity of Brs3 in the particular cells. We are in the process of using this mouse by breeding with germline cre-expressing mice. These allow knockout of Brs3 in cells defined by their cre driver expression pattern. Similarly, we have generated loxTB-Brs3 mice. The loxTB-Brs3 mice allow determination of sufficiency of Brs3 in the particular cells. We are in the process of breeding this mouse with germline cre-expressing mice. These allow knockout of Brs3 in cells defined by their cre driver expression pattern. Finally we have generated Brs3-T2A-CreERT2 mice, in which cre is expressed as a fusion mRNA with the endogenous Brs3 mRNA. These mice express cre in a tamoxifen-dependent manner and in the reported distribution pattern of Brs3. This mouse is being used to selectively activate Brs3 neurons using chemogenetics and optogenetics. We examined the effects of BRS-3 deletion and activation on blood pressure and heart rate in mice (2). In free-living, telemetered Brs3 null mice the resting heart rate was 10% lower than wild-type controls, while the resting mean arterial pressure was unchanged. During physical activity, the heart rate and blood pressure increased more in Brs3 null mice, reaching a similar heart rate and higher mean arterial pressure than control mice. Intravenous infusion of the BRS-3 agonist MK-5046 increased mean arterial pressure and heart rate in wild-type but not in Brs3 null mice, and this increase was blocked by pretreatment with clonidine, a central sympatholytic. Taken together, the data demonstrate that BRS-3 contributes to resting cardiac sympathetic tone, but is not required for activity-induced increases in heart rate and blood pressure. The data suggest that BRS-3 activation increases heart rate and blood pressure via a central sympathetic mechanism. To date, no high affinity endogenous ligand has been identified. In an effort to detect a circulating endogenous BRS-3 ligand, we successfully generated parabiotic pairs of mice between Brs3-/y and wild type (WT) mice or between WT controls (2). The Brs3-/y-WT and WT-WT pairs lost similar weight immediately after surgery and after 9 weeks on a high fat diet, the Brs3-/y-WT pairs weighed more than the WT-WT pairs. Within the Brs3-/y-WT pairs, the Brs3-/y mice had greater adiposity than the WT mice, but comparable lean and liver weights. Compared to WT mice in WT-WT pairs, Brs3-/y and WT mice in Brs3-/y-WT pairs each had greater lean mass, and the Brs3-/y mice also had greater adiposity. These results contrast to those reported for parabiotic pairs of leptin receptor null (db/db) and WT mice, where high leptin levels in the db/db mice cause the WT parabiotic partners to lose weight. Our data demonstrate that a circulating endogenous BRS-3 ligand, if present, is not sufficient to reduce adiposity in parabiotic partners of Brs3-/y mice. We also published a short review on Brs3 (3).