Functional Consequences of Perturbed CXCL12 Signal Processing: Analyses of Immature Hematopoiesis in GRK6-Deficient Mice
Functional Consequences of Perturbed CXCL12 Signal Processing: Analyses of Immature Hematopoiesis in GRK6-Deficient Mice
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DOI：
10.1089/scd.2014.0284
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发表时间：
2015-03-15
影响因子：
4
通讯作者：
Boenig, Halvard
中科院分区：
文献类型：
--
作者：
Chudziak, Doreen;Spohn, Gabriele;Boenig, Halvard
造血干细胞和祖细胞(HSPC)位于一个富含CXCL12的环境中，CXCL12是CXCR4的配体，在BM的所有未成熟的造血细胞上都有结构性的表达。这种配体-受体对关键地控制了HSPC在骨髓中的保留和(相对)静止。有趣的是，在趋化因子丰富的环境中，BM-HSPC的CXCR4表面表达和CXCL12敏感性持续保持。BM-HSPC这种特殊的G蛋白信号整合模式背后的机制尚不清楚。G蛋白受体激酶(G-Protein Receptor Kinase，GRKs)通过配体诱导的细胞内结构域磷酸化来控制受体的功能，导致受体内部化和一过性不稳定。因此，使用GRK6缺陷(GRK6(-/-))小鼠，我们试图解决扰动配体诱导的CXCR4(In)激活如何在体外和体内影响HSPC行为。在体外，GRK6(-/-)HSPC表现出对CXCL12的高反应性，这与预期不谋而合。在体内，GRK6(-/-)未成熟造血的特征是脾内未成熟造血显著扩张，在连续竞争性移植中有轻微的再生性缺陷。粒细胞集落刺激因子(G-CSF)和AMD3100的强制动员是正常的，非竞争性移植或药物性骨髓抑制后的造血再生也是正常的。这些观察表明，GRK介导的对配体结合后CXCR4信号输入的限制在很大程度上是BM驻留的HSPC所必需的，这可能解释了BM-HSPC如何保持连续的CXCL12反应。
Hematopoietic stem and progenitor cells (HSPCs) reside in bone marrow (BM) in an environment rich in CXCL12, the ligand for CXCR4, which is constitutively expressed on all immature hematopoietic cells in BM. This ligand-receptor pair critically controls HSPC retention and (relative) quiescence in BM. Interestingly, in a chemokine-abundant environment, CXCR4 surface expression and CXCL12 sensitivity of BM-residing HSPCs are continuously maintained. The mechanisms underlying this peculiar pattern of G-protein signal integration by BM-HSPCs are unknown. G-protein receptor kinases (GRKs) control receptor function by phosphorylating the intracellular domains upon ligand-induced activation, which results in receptor internalization and transient refractoriness. Using, therefore, a GRK6-deficient (GRK6(-/-)) mouse, we sought to address how perturbed ligand-induced CXCR4 (in)activation affects HSPC behavior in vitro and in vivo. In vitro, GRK6(-/-) HSPCs were characterized by hyper-responsiveness to CXCL12, as expected. In vivo, GRK6(-/-) immature hematopoiesis was characterized by a marked expansion of immature hematopoiesis in spleens and a modest repopulation defect in serial competitive transplantation. Enforced mobilization with granulocyte colony-stimulating factor (G-CSF) and AMD3100 was normal, as was hematopoietic regeneration after noncompetitive transplantation or pharmacological myelosuppression. These observations illustrate that GRK-mediated restriction of CXCR4 signal input after ligand engagement is largely dispensable for BM-resident HSPCs, which may explain how continuous CXCL12 responsiveness of BM-HSPCs can be maintained.