Noristani Harun N, Boukhaddaoui Hassan, Saint-Martin Guillaume, Auzer Pauline, Sidiboulenouar Rahima, Lonjon Nicolas, Alibert Eric, Tricaud Nicolas, Goze-Bac Christophe, Coillot Christophe, Perrin Florence E
Institut National de la Santé et de la Recherche Médicale, U1051Montpellier, France.
University of Montpellier, Montpellier; Institut National de la Santé et de la Recherche Médicale, U1198, Montpellier; École Pratique des Hautes ÉtudesParis, France.
Front Aging Neurosci. 2017 Jul 19;9:230. doi: 10.3389/fnagi.2017.00230. eCollection 2017.
Central nervous system (CNS) injury has been observed to lead to microglia activation and monocytes infiltration at the lesion site. diffusion magnetic resonance imaging (diffusion MRI or DWI) allows detailed examination of CNS tissues, and recent advances in clearing procedures allow detailed imaging of fluorescent-labeled cells at high resolution. No study has yet combined diffusion MRI and clearing procedures to establish a possible link between microglia/monocytes response and diffusion coefficient in the context of spinal cord injury (SCI). We carried out MRI of the spinal cord at different time-points after spinal cord transection followed by tetrahydrofuran based clearing and examined the density and morphology of microglia/monocytes using two-photon microscopy. Quantitative analysis revealed an early marked increase in microglial/monocytes density that is associated with an increase in the extension of the lesion measured using diffusion MRI. Morphological examination of microglia/monocytes somata at the lesion site revealed a significant increase in their surface area and volume as early as 72 hours post-injury. Time-course analysis showed differential microglial/monocytes response rostral and caudal to the lesion site. Microglia/monocytes showed a decrease in reactivity over time caudal to the lesion site, but an increase was observed rostrally. Direct comparison of microgliamonocytes morphology, obtained through multiphoton, and the longitudinal apparent diffusion coefficient (ADC), measured with diffusion MRI, highlighted that axonal integrity does not correlate with the density of microglia/monocytes or their somata morphology. We emphasize that differential microglial/monocytes reactivity rostral and caudal to the lesion site may thus coincide, at least partially, with reported temporal differences in debris clearance. Our study demonstrates that the combination of diffusion MRI and two-photon microscopy may be used to follow structural tissue alteration. Lesion extension coincides with microglia/monocytes density; however, a direct relationship between ADC and microglia/monocytes density and morphology was not observed. We highlighted a differential rostro-caudal microglia/monocytes reactivity that may correspond to a temporal difference in debris clearance and axonal integrity. Thus, potential therapeutic strategies targeting microglia/monocytes after SCI may need to be adjusted not only with the time after injury but also relative to the location to the lesion site.
已观察到中枢神经系统（CNS）损伤会导致损伤部位的小胶质细胞活化和单核细胞浸润。扩散磁共振成像（扩散MRI或DWI）能够对中枢神经系统组织进行详细检查，并且近年来在清除程序方面的进展使得能够对荧光标记细胞进行高分辨率的详细成像。尚未有研究将扩散MRI与清除程序相结合，以在脊髓损伤（SCI）的背景下建立小胶质细胞/单核细胞反应与扩散系数之间的可能联系。我们在脊髓横断后的不同时间点对脊髓进行MRI检查，随后采用基于四氢呋喃的清除方法，并使用双光子显微镜检查小胶质细胞/单核细胞的密度和形态。定量分析显示，小胶质细胞/单核细胞密度早期显著增加，这与使用扩散MRI测量的损伤范围扩大有关。对损伤部位小胶质细胞/单核细胞胞体的形态学检查显示，早在损伤后72小时，其表面积和体积就显著增加。时间进程分析显示，损伤部位头端和尾端的小胶质细胞/单核细胞反应存在差异。损伤部位尾端的小胶质细胞/单核细胞反应性随时间降低，但在头端观察到增加。通过多光子获得的小胶质细胞/单核细胞形态与通过扩散MRI测量的纵向表观扩散系数（ADC）的直接比较突出表明，轴突完整性与小胶质细胞/单核细胞的密度或其胞体形态无关。我们强调，损伤部位头端和尾端小胶质细胞/单核细胞反应性的差异可能因此至少部分与报道的碎片清除时间差异一致。我们的研究表明，扩散MRI和双光子显微镜的结合可用于跟踪组织结构改变。损伤范围与小胶质细胞/单核细胞密度一致；然而，未观察到ADC与小胶质细胞/单核细胞密度及形态之间的直接关系。我们突出了头-尾小胶质细胞/单核细胞反应性的差异，这可能与碎片清除和轴突完整性的时间差异相对应。因此，脊髓损伤后针对小胶质细胞/单核细胞的潜在治疗策略可能不仅需要根据损伤后的时间进行调整，还需要根据与损伤部位的位置关系进行调整。
