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）生理和病理中的作用。我们之前已经证明，单个SMHC基因在氨基端（SM-A和SM-B）和羧基端（SM1和SM2）的选择性剪接产生四种不同的SMHC亚型：SM1A， SM1B， SM2A和SM2B。膀胱平滑肌主要表达SM1B和SM2B肌球蛋白亚型。我们的实验室最近证明了nh2末端异构体SM-B异构体是膀胱平滑肌收缩动力学的重要决定因素。然而，c端同种异构体SM1和SM2的功能相关性尚未完全了解。为了了解SM1和SM2亚型的功能意义，我们最近建立了一个SM2肌球蛋白缺乏的小鼠模型。雌性纯合子小鼠出生后很快死亡，而SM2雄性无合子小鼠可存活1个月，但死于肾功能衰竭，并表现出严重的膀胱膨胀和肾积水。我们的假设是，膀胱体和尿道中SM1/SM2亚型的调控表达对泌尿系统功能成熟至关重要。根据初步数据，我们进一步假设SM2:SM1比例的改变会影响肌球蛋白丝的组装并导致膀胱功能障碍。因此，本研究的主要目标是研究SM2肌球蛋白的缺失对1)雄性和雌性小鼠膀胱平滑肌发育和成熟的影响；2)肌球蛋白丝在膀胱体和尿道内的结构和分布；3)SM2空膀胱的收缩特性及其对激动剂介导的刺激的反应。这些研究是定义c端同种异构体SM1和SM2在膀胱平滑肌生理中的作用的重要一步，并将使我们了解SM1/SM2比率的开关如何有助于膀胱平滑肌的病理生理。公共卫生相关性：本研究计划的一个主要目标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。本研究将使用不含SM2肌球蛋白的小鼠模型来研究SM2肌球蛋白异构体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.