Myosin Isoforms in Urinary Bladder Function

描述（由申请人提供）：我们研究的长期目标是研究平滑肌肌球蛋白重链（SMHC）亚型在膀胱平滑肌（SM）生理学和病理学中的作用。我们以前已经表明，一个单一的SMHC基因的氨基端（SM-A和SM-B）和羧基端（SM 1和SM 2）的选择性剪接产生四种不同的SMHC亚型：SM 1A，SM 1B，SM 2A和SM 2B。膀胱平滑肌主要表达SM 1B和SM 2B肌球蛋白亚型。我们的实验室最近证明，氨基末端亚型SM-B亚型是膀胱平滑肌收缩动力学的重要决定因素。然而，C-末端亚型SM 1和SM 2的功能相关性尚未完全理解。为了理解SM 1与SM 2亚型的功能意义，我们最近建立了一个SM 2肌球蛋白缺陷的小鼠模型。雌性纯合子小鼠在出生后不久死亡，而SM 2雄性无效小鼠存活长达一个月，但死于肾衰竭，并且还表现出严重的膀胱膨胀和肾积水。我们的假设是，SM 1/SM 2亚型在膀胱体和尿道中的调节表达对于泌尿系统的功能成熟至关重要。基于初步数据，我们还假设SM 2：SM 1比例的转换将影响肌球蛋白丝组装并导致膀胱功能障碍。因此，当前提案的主要目标是研究SM 2肌球蛋白的丢失如何影响1）雄性和雌性小鼠的膀胱平滑肌发育和成熟，2）膀胱体和尿道内的肌球蛋白丝结构和分布，以及3）SM 2空膀胱的收缩特性及其对激动剂介导的刺激的反应。这些研究是确定C-末端亚型SM 1和SM 2在膀胱平滑肌生理学中的作用的重要一步，并将使我们能够了解开关SM 1/SM 2比率如何有助于膀胱平滑肌的病理生理学。公共卫生相关性：本研究计划的主要目的是了解平滑肌中表达的肌球蛋白（负责产生力的收缩蛋白）亚型的功能作用。本研究计划将使用不含SM 2肌球蛋白亚型的小鼠模型，研究该蛋白亚型在膀胱发育和功能中的作用。

DESCRIPTION (provided by applicant): The long term goal of our research is to investigate the role of smooth muscle myosin heavy chain (SMHC) isoforms in urinary bladder smooth muscle (SM) physiology and pathology. We have shown previously that alternative splicing of a single SMHC gene both at the amino terminus (SM-A and SM-B) and carboxyl-terminus (SM1 and SM2) generate four different SMHC isoforms: SM1A, SM1B, SM2A and SM2B. Urinary bladder smooth muscle expresses predominantly SM1B and SM2B myosin isoforms. Our laboratory recently demonstrated that the NH2-terminal isoform SM-B isoform is an important determinant of the kinetics of urinary bladder smooth muscle contraction. However, the functional relevance of C-terminal isoforms SM1 and SM2 has not been completely understood. To understand the functional significance of the SM1 vs. SM2 isoforms we have recently generated a mouse model that is deficient in SM2 myosin. The female homozygous mice die soon after birth, whereas SM2 male null mice survive up to one month, but die of renal failure and also exhibit severe urinary bladder distension and hydronephrosis. Our hypothesis is that regulated expression of SM1/SM2 isoforms in the bladder body and urethra is critical for the functional maturation of urinary system. Based on the preliminary data, we additionally hypothesize that a switch in SM2:SM1 ratio will affect myosin filament assembly and contribute to bladder dysfunction. Therefore, the major goals of the current proposal are to study how loss of SM2 myosin affects 1) urinary bladder smooth muscle development and maturation in male and female mice, 2) myosin filament structure and distribution within the bladder body and urethra and, 3) the contractile properties of the SM2 null bladder and its response to agonist mediated stimulation. These studies are a major step towards defining the roles of C-terminal isoforms SM1 and SM2 in bladder smooth muscle physiology and will allow us to understand how a switch SM1/SM2 ratio could contribute to pathophysiology of the bladder smooth muscle. PUBLIC HEALTH RELEVANCE: A major goal of this research proposal is to understand the functional role of myosin (contractile protein responsible for force generation) isoforms expressed in smooth muscle .This proposal will examine the role of SM2 myosin isoform in bladder development and function using a mouse model which does not contain this protein.