Enzymatic regulation of CCL2 bioactivity in neuroinflammation

目前的建议侧重于调节由C-C基序趋化因子CCL2介导的神经炎症效应。我们假设CCL2的生物活性是通过酶催化的翻译后修饰来调节的。一方面，二肽基肽酶IV/CD26 （DP4）截断CCL2的n端，启动进一步的蛋白水解降解，并消除其生物活性。另一方面，由谷氨酰环化酶QC和/或isoQC催化的n端焦谷氨酸修饰保护CCL2免受蛋白水解降解并提高其生物活性。因此，我们认为QC/isoQC和DP4酶的串联作为神经炎症的促炎和抗炎分子检查点，因为它们可以特异性地调节体内神经炎症条件下CCL2的活性和功能结果。我们建议通过专门研究(i) QC/isoQC和DP4的表达和酶活性的调节，大脑中稳定/降解的CCL2变异的产生，以及炎症性中风小鼠模型中局部小胶质细胞和浸润性外周单核细胞的激活，（ii） QC/isoQC的后果，来举例说明这些调节的酶作用在脑部疾病中的作用。DP4和CCL2消融对上述标志物和缺血模型中梗死面积和神经运动缺陷等功能结果的影响；（iii） CCL2修饰变体募集小胶质细胞和单核细胞的机制和动力学。这包括CCL2与其主要受体CCR2结合的分析，CCR2位于单核细胞和巨噬细胞上，细胞内ERK1/2信号级联的激活和趋化性。因此，该建议针对的是与酶处理途径内源性解决炎症相关的一个重要方面，这可能与许多脑部疾病有关。此外，该结果为在神经炎症条件下使用临床相关的酶抑制剂提供了启示。

The present proposal focuses on the regulation of neuroinflammatory effects mediated by the C-C motif chemokine CCL2. We hypothesize that the biological activity of CCL2 is tuned by enzyme-catalyzed post-translational modification. On the one hand, N-terminal CCL2 truncation by dipeptidyl peptidase IV/CD26 (DP4) initiates further proteolytical degradation and abolishes its biological activity. On the other hand, N-terminal pyroglutamate modification catalyzed by the glutaminyl cyclases QC and/or isoQC protects CCL2 from proteolytical degradation and increases its biological activity. Thus, we consider the tandem of the QC/isoQC and DP4 enzymes as pro- and anti-inflammatory molecular check-points in neuroinflammation, as they may specifically modulate CCL2 activity and the functional outcome in neuroinflammatory conditions in vivo.We propose to exemplify these regulated enzymatic actions in brain disease by specifically investigating (i) the regulation of expression and enzyme activity of QC/isoQC and DP4 and generation of stabilized/degraded CCL2 variants in brain as well as the activation of local microglia and infiltrating peripheral monocytes in an inflammatory stroke mouse model, (ii) the consequences of QC/isoQC, DP4 and CCL2 ablation in knock-out mice on the above markers and on the functional outcome such as infarct size and neurological motor deficits in the ischemia model, (iii) the mechanisms and kinetics of microglia and monocyte recruitment by modified CCL2 variants. This includes the analysis of CCL2 binding to its primary receptor CCR2, which is located on monocytes and macrophages, the activation of intracellular ERK1/2 signaling cascade and chemotaxis. Thus, the proposal targets an important aspect related to the endogenous resolution of inflammation by enzyme processing pathways, which might be associated with a number of brain diseases. Furthermore, the results provide implications for the use of clinically relevant enzyme inhibitors in neuroinflammatory conditions.