Graduate Program of Neuroscience, The University of Western Ontario, Canada; Robarts Research Institute, The University of Western Ontario, Canada.
Robarts Research Institute, The University of Western Ontario, Canada.
Nitric Oxide. 2020 Jan 1;94:125-134. doi: 10.1016/j.niox.2019.11.005. Epub 2019 Nov 21.
Microglia population is primarily determined by a finely-regulated proliferation process during early development of the central nervous system (CNS). Nitric oxide (NO) is known to inhibit proliferation in numerous cell types. However, how NO signaling regulates microglia proliferation remains elusive. Using wildtype (WT) and inducible nitric oxide synthase knockout (iNOS) mice, this study investigated the role and underlying mechanisms of iNOS/NO signaling in microglia proliferation. Here we reported that iNOS mice displayed significantly more BrdU-labeled proliferating microglia in the cortex than that in WT mice at postnatal day 10. Compared to microglia isolated from WT mouse cortex, significantly more iNOS microglia displayed the specific cell-cycle markers Ki67 and phospho-histone H3 (pH3) in their nuclei. In addition, treating WT microglia with the NOS inhibitor LNAME drastically increased the percentage of cells expressing Ki67 and pH3, whereas treating iNOS microglia with NOC18, a slow-release NO-donor, significantly decreased the percentage of microglia expressing the two cell-cycle markers. Moreover, inhibition of protein kinase-G (PKG) in WT microglia increased the proportion of microglia expressing Ki67 and pH3, whereas activation of PKG signaling using 8Br-cGMP in iNOS microglia significantly decreased the fraction of microglia displaying Ki67 and pH3. Interestingly, in the presence of a PKG inhibitor, NOC18 increased the quantity of iNOS microglia expressing Ki67 and pH3. Together, these results indicate that basal activity of iNOS/NO signaling impedes microglial cell-cycle progression and attenuates proliferation through activation of the cGMP-PKG pathway. However, NO increases microglia cell-cycle progression in the absence of cGMP-PKG signaling.
小胶质细胞群体主要由中枢神经系统（CNS）早期发育过程中精细调节的增殖过程决定。一氧化氮（NO）已知可抑制多种细胞类型的增殖。然而，NO 信号如何调节小胶质细胞增殖仍不清楚。本研究使用野生型（WT）和诱导型一氧化氮合酶敲除（iNOS）小鼠，研究了 iNOS/NO 信号在小胶质细胞增殖中的作用和潜在机制。我们报道，与 WT 小鼠相比，iNOS 小鼠在出生后第 10 天大脑皮质中 BrdU 标记的增殖小胶质细胞明显更多。与从 WT 小鼠大脑皮质分离的小胶质细胞相比，iNOS 小胶质细胞的细胞核中明显有更多的特异性细胞周期标志物 Ki67 和磷酸化组蛋白 H3（pH3）。此外，用 NOS 抑制剂 LNAME 处理 WT 小胶质细胞可大大增加表达 Ki67 和 pH3 的细胞比例，而用 NOC18（一种缓慢释放的 NO 供体）处理 iNOS 小胶质细胞可显著降低表达这两种细胞周期标志物的小胶质细胞比例。此外，在 WT 小胶质细胞中抑制蛋白激酶-G（PKG）可增加表达 Ki67 和 pH3 的小胶质细胞比例，而在用 8Br-cGMP 激活 iNOS 小胶质细胞中的 PKG 信号后，显著降低了显示 Ki67 和 pH3 的小胶质细胞分数。有趣的是，在存在 PKG 抑制剂的情况下，NOC18 增加了表达 Ki67 和 pH3 的 iNOS 小胶质细胞数量。综上所述，这些结果表明，iNOS/NO 信号的基础活性通过激活 cGMP-PKG 途径阻碍小胶质细胞细胞周期进程并减弱增殖。然而，在没有 cGMP-PKG 信号的情况下，NO 会增加小胶质细胞的细胞周期进程。
