Medical Research Council Functional Genomics Unit, and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, United Kingdom.
J Neurosci. 2009 Dec 9;29(49):15366-74. doi: 10.1523/JNEUROSCI.5188-09.2009.
Deregulation of the insulin-like growth factor 1 (IGF-1) signaling pathway is a recurrent finding in mouse models and human patients with cerebellar ataxia and thus represents a common pathological cascade in neuronal cell death that may be targeted for therapy. We have previously identified a point mutation in AF4, a transcription cofactor of RNA polymerase II elongation and chromatin remodeling, that causes progressive and highly specific Purkinje cell (PC) death in the ataxic mouse mutant robotic, leading to the accumulation of AF4 in PCs. Here we confirm that the spatiotemporal pattern of PC degeneration in the robotic cerebellum correlates with the specific profile of AF4 upregulation. To identify the underlying molecular pathways, we performed microarray gene expression analysis of PCs obtained by laser capture microdissection (LCM) at the onset of degeneration. Igf-1 was significantly downregulated in robotic PCs compared with wild-type controls before and throughout the degenerative process. Consistently, we observed a decrease in the activation of downstream signaling molecules including type 1 IGF receptor (IGF-1R) and the extracellular signal-regulated kinase (ERK) 1 and ERK2. Chromatin immunoprecipitation confirmed that Igf-1 is a direct and the first validated target of the AF4 transcriptional regulatory complex, and treatment of presymptomatic robotic mice with IGF-1 indeed markedly delayed the progression of PC death. This study demonstrates that small changes in the levels of a single transcriptional cofactor can deleteriously affect normal cerebellum function and opens new avenues of research for the manipulation of the IGF-1 pathway in the treatment of cerebellar ataxia in humans.
胰岛素样生长因子 1（IGF-1）信号通路的失调是小脑共济失调的小鼠模型和人类患者中反复出现的发现，因此代表了神经元细胞死亡的常见病理级联，可能成为治疗的靶点。我们之前已经鉴定出 AF4 的一个点突变，AF4 是 RNA 聚合酶 II 延伸和染色质重塑的转录共因子，它导致共济失调小鼠突变体 robotic 中浦肯野细胞（PC）进行性和高度特异性死亡，导致 AF4 在 PCs 中的积累。在这里，我们确认 robotic 小脑 PC 退化的时空模式与 AF4 上调的特定模式相关。为了确定潜在的分子途径，我们对激光捕获显微解剖（LCM）获得的 PC 进行了微阵列基因表达分析。与野生型对照相比，在退化开始时，robotic PCs 中的 Igf-1 明显下调，在退化过程中一直如此。一致地，我们观察到下游信号分子（包括 1 型 IGF 受体（IGF-1R）和细胞外信号调节激酶（ERK）1 和 ERK2）的激活减少。染色质免疫沉淀证实 Igf-1 是 AF4 转录调节复合物的直接和第一个验证的靶标，并且 IGF-1 对有症状前 robotic 小鼠的治疗确实显著延迟了 PC 死亡的进展。这项研究表明，单个转录共因子水平的微小变化可能会对正常小脑功能产生有害影响，并为在人类小脑共济失调治疗中操纵 IGF-1 途径开辟了新的研究途径。
