The heat shock proteins A4 (HSPA4) ameliorates pathological myocardial remodeling through improving protein homeostasis

蛋白质质量控制（PQC）依赖于主要由分子伴侣进行的正确蛋白质折叠与由泛素-蛋白酶体（UPS）系统和自噬介导的靶向蛋白质水解之间的协作。蛋白质病是由蛋白质错误折叠引起的疾病，其特征在于异常蛋白质聚集。有丝分裂后的细胞如心肌细胞不能简单地通过细胞分裂或再生避免蛋白质错误折叠。因此，心脏中错误折叠蛋白质的负荷增加可能导致心肌功能障碍的进展。通过药物干预改善PQC的措施代表了治疗人类蛋白质病并由此治疗心力衰竭的新的治疗潜力。作为分子伴侣，热休克蛋白（HSP）有助于维持细胞内适当的PQC。HSPA 4是HSP 70家族的成员，在应激条件下的细胞存活中起作用。我们已经证明，HSPA 4蛋白水平在病理重塑的心脏中增加。有趣的是，经典的Hspa 4基因敲除（Hspa 4-/-）小鼠显示出与聚泛素化蛋白聚集相关的显著增加的病理性重塑。迄今为止，我们的数据表明，泛素聚集体在Hspa 4-/-心脏中的积累不是由蛋白酶体的缺陷引起的：1）。在Hspa 4-/-心脏中，在洗涤剂不溶性部分中检测到更多的泛素化蛋白聚集，所述洗涤剂不溶性部分优先通过自噬降解。2.）的情况。在Hspa 4 +/+和Hspa 4-/-心脏中，蛋白酶体活性和p53蛋白水平（蛋白酶体的典型底物）均未受到差异影响。3.）第三章在Hspa 4-/-心脏中观察到自噬体的积累。因此，我们希望深入研究自噬作为蛋白聚集体积累的可能机制，这可能是导致病理性重塑大大增加的原因。为此，我们建立了体外HSPA 4过表达使用腺病毒，以及HSPA 4敲低使用siRNA。此外，我们目前正在使用腺相关病毒（AAV 9）在体内产生心肌细胞特异性HSPA 4过表达。使用获得和丧失功能的方法，我们想探讨的假设，HSPA 4蛋白抑制病理性心肌重塑和延迟进展到心力衰竭，可能通过改善自噬介导的降解有毒，错误折叠的蛋白质。此外，我们希望确定控制Hspa 4表达的转录因子。

Protein quality control (PQC) depends on the collaboration between proper protein folding, which is mainly performed by molecular chaperones, and targeted proteolysis mediated by the ubiquitin-proteasome (UPS) system and autophagy. Proteinopathies are diseases caused by protein misfolding and characterized by abnormal protein aggregation. Post-mitotic cells such as cardiomyocytes cannot simply avoid protein misfolding by cell division or regeneration. An increased load of misfolded proteins in the heart may therefore contribute to a progression of myocardial dysfunction. Measures to improve PQC by pharmacological intervention represent a novel therapeutic potential to treat human proteopathies and thereby heart failure. As molecular chaperones, the heat shock proteins (HSPs) help to maintain the proper PQC in the cells. HSPA4 is a member of the HSP70 family that plays a role in cell survival under stress conditions. We have already shown that HSPA4 protein levels increase in pathologically-remodeled hearts. Interestingly, classical Hspa4 knockout (Hspa4-/-) mice show markedly increased pathological remodeling associated with the aggregation of polyubiquitinated proteins. Our data to date indicate that the accumulation of ubiquitin aggregates in Hspa4-/- hearts was not caused by a defect in the proteasome: 1.) More aggregation of ubiquitinated proteins were detected in In Hspa4-/- hearts in the detergent-insoluble fraction that is preferentially degraded by autophagy. 2.) Neither proteasome activity nor p53 protein level, a typical substrate of the proteasome, was differentially affected in Hspa4+/+ and Hspa4-/- hearts. 3.) An accumulation of autophagosomes was observed in Hspa4-/- hearts. Therefore, we want to deeply investigate the autophagy as a possible mechanism for the accumulation of protein aggregates, which may be responsible for the greatly increased pathological remodeling. For this purpose, we established in vitro HSPA4 overexpression using adenovirus, as well as HSPA4 knockdown using siRNA. Moreover, we are currently generating in vivo cardiomyocyte-specific HSPA4 overexpression using adeno-associated virus (AAV9). Using gain and loss-of-function approaches, we would like to explore the hypothesis that HSPA4 protein suppresses pathologic myocardial remodeling and delays the progression to heart failure, possibly by improving autophagy-mediated degradation of toxic, misfolded proteins. Moreover, we want to identify the transcription factors controlling Hspa4 expression.