吡格列酮对大鼠创份性脑损伤后炎症因子抑制作用的研究

目的 探讨过氧化物酶体增殖物激活受体-γ(PPAR-γ)及其激活剂噻唑烷二酮类药物--吡格列酮对创伤性脑损伤(TBI)大鼠模型脑组织中正常T细胞活化后表达和分泌的调节蛋白(RANTES)、巨噬细胞移动抑制因子(MIF)表达的影响. 方法成年SD大鼠按照随机数字表法分为正常对照组(10只)、假手术组(10只)、TBI模型组(12只)及吡格列酮治疗组(12只).后两组采用改进的Feeney自由落体脑损伤装置制作TBI大鼠模型.伤后18 h分别给予生理盐水及20mg/(kg·d)吡格列酮治疗:假手术组不进行自由落体致伤,其余步骤同上,术后给与生理盐水治疗;正常对照组不进行任何处理.7 d后收集各组大鼠脑组织,计算脑组织含水量,并采用RT-PCR及Westernblot法检测各组PPAR-γ、RANTES及MIF的mRNA、蛋白表达差异. 结果与对照组及假手术组相比,TBI损伤组大鼠脑组织含水量明显增加,且PPAR-γmRNA表达明显增强,同时RANTES、MIF mRNA及蛋白表达也明显上调;而吡格列酮治疗组大鼠脑组织PPAR-γ的表达进一步增加,RANTES及MIF表达则有所下降. 结论吡格列酮对减轻创伤性脑损伤后持续存在的炎症反应及脑水肿具有一定作用,其机制可能与降低脑组织中RANTES及MIF等炎性细胞因子含量有关.     

吡格列酮对糖尿病大鼠中枢神经系统PPAR-γ表达的影响

目的 研究吡格列酮对糖尿病大鼠海马、下丘脑处PPAR-γ表达的影响及与大鼠认知功能的关系.方法 雄性SD大鼠随机分为对照组(C组)、糖尿病组(D组)、糖尿病+吡格列酮组(DP组),每组10只.8周后行Morris水迷宫评价大鼠的空间学习记忆能力,Western Blot方法检测大鼠海马、下丘脑处PPAR-γ表达水平.结果 Morris水迷宫中,D组大鼠逃避潜伏期较C组和DP组延长差异均有统计学意义(P<0.05).大鼠海马和下丘脑处,PPAR-γ的表达D组较C组减少,DP组较D组增多,差异均有统计学意义(P<0.05).结论 吡格列酮能够增加糖尿病大鼠海马、下丘脑组织局部PPAR-γ表达水平,并且这种表达的增加可能是吡格列酮改善糖尿病大鼠空间学习记忆能力的机制之一.     

吡格列酮对大鼠脑出血后脑组织细胞凋亡及自由基水平的影响

目的:探讨吡格列酮对大鼠脑出血的保护作用及可能作用机制。方法:雄性SD大鼠分为6组,干预组1造模前6 h给药(吡格列酮15 mg.kg-1.d-1,灌胃),造模后维持原剂量;干预组2造模前6 h给药,造模后停用;干预组3造模前不给药,造模后给药;干预组4造模前后均不给药;另设假手术组和正常大鼠组。各组大鼠术后72 h处死,检测脑组织中超氧化物歧化酶(SOD)及丙二醛(MDA)浓度,Western blot测定过氧化小体增殖剂激活型受体γ(PPARγ)及半胱氨酸蛋白-3(caspase-3)表达;苏木精-伊红染色及TUNEL染色观察脑水肿及细胞凋亡。结果:吡格列酮能显著减轻脑出血大鼠72 h后的脑组织水肿程度,减少凋亡细胞数量,增加SOD活性和PPARγ蛋白表达,抑制MDA水平及caspase-3蛋白表达,且脑出血前预防性给药的效果较出血后治疗的效果好。结论:吡格列酮可减轻大鼠脑出血性脑损伤,可能作用机制是增加脑组织中PPARγ蛋白表达及SOD活性,抑制自由基水平和细胞凋亡。     

吡格列酮治疗血管性痴呆的实验研究

目的 探讨过氧化物酶体增殖物激活受体(PPARγ)激动剂吡格列酮对血管性痴呆(VD)的治疗作用.方法 将SD大鼠随机分为假手术组、VD组、吡格列酮高剂量[20 mg/(kg·d)]组及低剂量[5 mg/(kg·d)]组,采用Pulsinelli改良四血管结扎法建立VD模型;各组予以相应的药物干预7 d;检测各组大鼠Morris水迷宫定航试验潜伏期;应用免疫组化法观察脑组织PPARγ阳性神经元数及PPARγ的表达.结果 与VD组相比,吡格列酮高、低剂量组大鼠定航试验潜伏期明显缩短(均P<0.01);皮质区PPARγ阳性神经元数量及PPARγ表达量明显增加(均P<0.01);高剂量组的改变更明显.结论 吡格列酮可有效改善VD大鼠的认知功能,其神经保护作用可能与增加神经元PPARγ表达有关,并且呈剂量依赖性.     

Epac在生长激素分泌性垂体腺瘤细胞中过表达并促进其对奥曲肽耐药的分子机制研究

目的 探索生长激素分泌性垂体腺瘤(GHPAs)对奥曲肽耐药的分子机制。方法 收集临床GHPAs患者肿瘤及旁侧正常组织标本各10例。采用qPCR法、Western blot法和免疫组织化学(IHC)法检测上述各10例标本中cAMP直接激活的交换蛋白(Epac)的表达情况。在大鼠垂体腺瘤GH3细胞中过表达Epac。CCK-8法测定过表达Epac前后及给予奥曲肽处理前后细胞增殖能力的变化;ELISA测定细胞分泌生长激素(GH)情况的变化;qPCR法和Western blot法测定细胞中SSTR2和ZAC1表达水平的变化。慢病毒转染GH3细胞过表达Epac并进行BALB/c裸鼠荷瘤实验,测定过表达Epac前后及给予奥曲肽治疗前后,裸鼠荷瘤增殖能力的变化;Western blot测定促肿瘤增殖关键通路蛋白Ras-1和ERK1/2的表达情况变化。结果 针对临床标本的研究,相较于旁侧正常组织,GHPAs组织中Epac mRNA和蛋白质表达水平均明显升高(P<0.05)。体外(in vitro)细胞水平实验,与pcDNA3.1组GH3细胞相比,pcDNA3.1+octreotide组GH3细胞增...     

半乳糖凝集素-3对垂体腺瘤细胞增殖和凋亡的影响

目的观察半乳糖凝集素-3(Gal-3)对垂体腺瘤细胞生长的影响并探讨其可能的作用机制。方法采用RNA干扰(RNAi)抑制Gal-3基因的表达,应用Western blot分别检测Gal-3蛋白和细胞凋亡相关基因Bcl-2、Bax蛋白的表达情况,然后应用3-(4,5-二甲基噻唑-2)-2,5-二苯基四氮唑(MTT)法和流式细胞仪(FCM)检测大鼠垂体腺瘤细胞系GH3细胞增殖和细胞凋亡的情况。结果①RNAi后24 h、48 h,Gal-3均明显下调(P0.05),至72 h后较48 h略有回升(P0.05),同时伴有Bcl-2表达水平的明显下调(P0.05),而Bax蛋白表达无明显变化(P0.05);②RNAi下调Gal-3表达水平后,在不同时间点(24 h、48 h、72 h)GH3细胞的增殖能力均受到显著抑制(P0.05);③RNAi后GH3细胞的凋亡细胞比例明显增加,由处理前的5.2%上升至21.7%。结论下调Gal-3的表达导致促凋亡基因Bcl-2的表达下调,而抑凋亡基因Bax的表达水平不变,同时导致GH3细胞增殖受抑,细胞凋亡增加,提示Gal-3在垂体腺瘤细胞的增殖和进展中发挥重要作用,有望为垂体腺瘤的防治提供一个新的分子靶点。     

罗格列酮抑制垂体腺瘤GH3细胞及促凋亡作用的研究

目的探讨罗格列酮对GH3细胞增殖的影响及其促细胞凋亡的机制。方法不同浓度罗格列酮作用GH3细胞后,流式细胞仪检测细胞周期和细胞凋亡,Elisa法分析罗格列酮对生长激素合成的影响,Western blot法分析GH3细胞Cyclin D3、bcl-2和bax的变化。结果罗格列酮作用GH3细胞48 h后,以浓度效应关系抑制GH3细胞增殖、并使细胞增殖周期中G0-G1期阻滞,S期和G2-M期百分率降低;Western blot法示罗格列酮作用GH3细胞提高了Cyclin D3和bax的表达,而bcl-2的表达降低。结论罗格列酮促GH3细胞凋亡并抑制GH分泌,可能成为垂体生长激素腺瘤病人新的治疗方法。     

过氧化物酶体增殖物激活受体γ在垂体腺瘤中的表达

目的 通过检测过氧化物酶体增殖物激活受体γ(PPARγ)在人垂体腺瘤组织中的表达,探讨其在垂体腺瘤中的相关机制.方法 通过免疫组化法确定经手术切除的83例垂体腺瘤组织细胞来源;采用RT-PCR、适时定量PCR检测研究83例垂体腺瘤组织及6例正常垂体组织PPARγ的mRNA表达量,采用Western blot法检测组织PPARγ蛋白质表达水平,分析不同类型垂体腺瘤组织之间核酸及蛋白水平表达量的差异.结果 GH腺瘤17例、PRL腺瘤15例、ACTH腺瘤18例、多激素腺瘤(MCPAs)17例、无功能腺瘤(NFAs)16例及正常对照组6例;mRNA水平检测显示所有垂体腺瘤组织的表达量均高于正常对照组,其中GH腺瘤的表达量最高,与其他组比较P＜0.05;蛋白水平检测显示GH腺瘤、PRL腺瘤、ACTH腺瘤及MCPAs的表达量均高于正常对照组(P＜0.05),GH腺瘤的表达量最高,NFAs的表达量与正常对照组差异无统计学意义(P＞0.05).结论 PPARγ转录及蛋白表达水平在人GH、PRL、ACTH及MCPAs垂体腺瘤组织中高表达,该基因与垂体腺瘤有一定的相关性,而无功能垂体腺瘤在核酸水平的表达量增高,蛋白水平的表达量不高,可能与激素的分泌水平有关;在GH腺瘤中的表达量最高,且与其他组相比,差异有统计学意义(P＜0.05),说明该类肿瘤与PPARγ的关系最为密切,可能与生长激素能刺激PPARγ的表达有关.     

过氧化物酶体增殖物激活受体-γ在人侵袭性垂体腺瘤中的分布与表达

目的研究过氧化物酶体增殖物激活受体-γ(PPAR-γ)在人侵袭性垂体腺瘤组织中的分布情况和表达水平。方法30例垂体腺瘤组织依据影像学Knosp分级及术中所见分为侵袭组与非侵袭组。免疫组织化学染色分析PPAR-γ在垂体腺瘤组织中的分布情况,W estern B lot分析PPAR-γ在垂体腺瘤中的表达水平,比较PPAR-γ在侵袭性组与非侵袭组之间、各种内分泌类型腺瘤的侵袭组与非侵袭组之间分布与表达差异。结果侵袭组PPAR-γ表达水平明显高于非侵袭性组(P<0.05),侵袭性泌乳素腺瘤、侵袭性无功能腺瘤中PPAR-γ的表达水平显著高于相应的非侵袭组(P<0.05),而在生长激素腺瘤中,侵袭组与非侵袭组间PPAR-γ表达水平无明显差异(P>0.1)。结论PPAR-γ可能在人垂体腺瘤侵袭性方面发挥重要作用,并有可能成为侵袭性垂体腺瘤治疗的新靶点。     

白黎芦醇对垂体腺瘤GH3细胞的抑制作用

目的 探讨选择性雌激素受体调节剂白黎芦醇对垂体腺瘤GH3细胞中电压依赖性K^ 电流(IK(V))和细胞增殖的影响。方法 不同浓度白黎芦醇作用GH3细胞，应用MTT比色法测定细胞增殖，流式细胞仪检测细胞周期分布，运用全细胞膜片钳技术记录和分析白黎芦醇对GH3细胞中IK(V)的作用。结果 白黎芦醇作用GH3细胞3d后，以浓度效应关系抑制GH3细胞增殖，并使细胞增殖周期中G0／G1期阻滞，S期和G2／M期百分率降低。全细胞膜片钳结果显示，白黎芦醇以浓度和时间效应抑制IK(V)。结论 白黎芦醇抑制GH3细胞增殖可能是通过阻断电压依赖性K^ 通道起作用。提示可应用选择性抗雌激素药物治疗垂体腺瘤。     

土木香内酯对人胶质瘤U251细胞增殖、凋亡的影响

目的 探讨土木香内酯对人胶质瘤U251细胞增殖、凋亡的影响及其作用机制。方法 体外培养人胶质瘤U251细胞,取对数期生长的U251细胞分为空白对照组和土木香内酯（浓度分别为2.5、5.0、10.0 μmol/L）组,每组各10个复孔。使用MTT法检测U251细胞的增殖抑制率,采用流式细胞术检测U251细胞的凋亡率,免疫印迹法检测PDK1/Akt/GSK3β蛋白表达,使用RT-PCR检测c-Myc, Cyclin D1 mRNA的表达水平。结果 随土木香内酯浓度增加,U251细胞增殖抑制率明显增高（P<0.05）,细胞调亡率明显增高（P<0.05）。与空白对照组相比,木香内酯组U251细胞PDK1、Akt和GSK3β蛋白表达水平均无明显差异（P>0.05）,但PDK1、Akt和GSK3β蛋白的磷酸化水平均显著降低（P<0.05）。随着土木香内酯浓度的增加,U251细胞c-Myc、CyclinD1 mRNA的表达水平明显降低（P<0.05）。结论 土木香内酯抑制人胶质瘤U251细胞的增殖并促进其凋亡,其作用机制可能是通过调节PDK1/Akt/GSK3β信号通路有关,且在一定范围内呈浓度依赖性。     

Stage‐specific requirement for cyclin D1 in glial progenitor cells of the cerebral cortex

Despite the vast abundance of glial progenitor cells in the mouse brain parenchyma, little is known about the molecular mechanisms driving their proliferation in the adult. Here we unravel a critical role of the G1 cell cycle regulator cyclin D1 in controlling cell division of glial cells in the cortical grey matter. We detect cyclin D1 expression in Olig2‐immunopositive (Olig2+) oligodendrocyte progenitor cells, as well as in Iba1+ microglia and S100β+ astrocytes in cortices of 3‐month‐old mice. Analysis of cyclin D1‐deficient mice reveals a cell and stage‐specific molecular control of cell cycle progression in the various glial lineages. While proliferation of fast dividing Olig2+ cells at early postnatal stages becomes gradually dependent on cyclin D1, this particular G1 regulator is strictly required for the slow divisions of Olig2+/NG2+ oligodendrocyte progenitors in the adult cerebral cortex. Further, we find that the population of mature oligodendrocytes is markedly reduced in the absence of cyclin D1, leading to a significant decrease in the number of myelinated axons in both the prefrontal cortex and the corpus callosum of 8‐month‐old mutant mice. In contrast, the pool of Iba1+ cells is diminished already at postnatal day 3 in the absence of cyclin D1, while the number of S100β+ astrocytes remains unchanged in the mutant. GLIA 2014;62:829–839     

体外共培养大鼠骨髓间充质干细胞对肝星状细胞增殖的影响：Cyclin D1与P27表达调控****

背景：在肝纤维化发生发展过程中,肝星状细胞起着关键作用。研究证实骨髓间充质干细胞移植可作为治疗肝纤维化的方法,但其逆转肝纤维化的机制不明。 目的：探讨体外共培养条件下,大鼠骨髓间充质干细胞对肝星状细胞增殖的调控机制。 方法：实验组在半透膜上接种大鼠骨髓间充质干细胞,在6孔塑料培养板上接种肝星状细胞,建立上下双层细胞共培养体系;对照组将大鼠骨髓间充质干细胞更换为成纤维细胞;空白组仅行肝星状细胞单独培养。WST-8法检测肝星状细胞生长抑制率,流式细胞仪分析细胞周期,RT-PCR检测肝星状细胞CyclinD1和P27 mRNA的表达,Western blot检测肝星状细胞CyclinD1和P27蛋白的表达。 结果与结论：与空白组、对照组比较,实验组共培养24,48,72 h肝星状细胞生长抑制率均显著升高(P < 0.01);共培养72 h G0/G1期细胞显著增加(P < 0.01),S期细胞显著减少(P < 0.01),可阻滞肝星状细胞由G0/G1期向S期转换。共培养24 h,实验组CyclinD1 mRNA及蛋白表达开始下调,至72 h时表达量显著低于对照组、空白组(P < 0.01);共培养全过程中各组p27 mRNA的表达无明显差异(P > 0.05),共培养24 h时实验组p27蛋白表达较对照组、空白组均显著上调(P < 0.01)。结果证实大鼠骨髓间充质干细胞能够抑制肝星状细胞的增殖,其机制可能是通过下调CyclinD1表达、上调P27蛋白表达,使细胞周期停滞于G0/G1期实现的。     

Rhombomere-specific analysis reveals the repertoire of genetic cues expressed across the developing hindbrain

Background

Maintaining the correct balance of proliferation versus differentiation in retinal progenitor cells (RPCs) is essential for proper development of the retina. The cell cycle regulator cyclin D1 is expressed in RPCs, and mice with a targeted null allele at the cyclin D1 locus (Ccnd1 ^-/-) have microphthalmia and hypocellular retinas, the latter phenotype attributed to reduced RPC proliferation and increased photoreceptor cell death during the postnatal period. How cyclin D1 influences RPC behavior, especially during the embryonic period, is unclear.

Results

In this study, we show that embryonic RPCs lacking cyclin D1 progress through the cell cycle at a slower rate and exit the cell cycle at a faster rate. Consistent with enhanced cell cycle exit, the relative proportions of cell types born in the embryonic period, such as retinal ganglion cells and photoreceptor cells, are increased. Unexpectedly, cyclin D1 deficiency decreases the proportions of other early born retinal neurons, namely horizontal cells and specific amacrine cell types. We also found that the laminar positioning of horizontal cells and other cell types is altered in the absence of cyclin D1. Genetically replacing cyclin D1 with cyclin D2 is not efficient at correcting the phenotypes due to the cyclin D1 deficiency, which suggests the D-cyclins are not fully redundant. Replacement with cyclin E or inactivation of cyclin-dependent kinase inhibitor p27Kip1 restores the balance of RPCs and retinal cell types to more normal distributions, which suggests that regulation of the retinoblastoma pathway is an important function for cyclin D1 during embryonic retinal development.

Conclusion

Our findings show that cyclin D1 has important roles in RPC cell cycle regulation and retinal histogenesis. The reduction in the RPC population due to a longer cell cycle time and to an enhanced rate of cell cycle exit are likely to be the primary factors driving retinal hypocellularity and altered output of precursor populations in the embryonic Ccnd1 ^-/- retina.     

Increased cyclin D1 in vulnerable neurons in the hippocampus after ischaemia and epilepsy: a modulator of in vivo programmed cell death?

Several observations suggest that delayed neuronal death in ischaemia, epilepsy and other brain disorders includes an apoptotic component, involving programmed cell death (PCD). PCD is hypothesized to result, in part, from aberrant control of the cell cycle. Because they are instrumental in mitosis, cyclins D are key markers to evaluate whether neurons indeed progress into the cell cycle in situations of pathology. Therefore, we investigated in rat brains, the expression of cyclins D in the delayed neuronal death that occurs following transient global ischaemia and kainate-induced seizures. Following a four-vessel occlusion insult, quantitative in situ hybridization revealed a highly significant and persistent 100% increase of cyclin D1 mRNA in the vulnerable pyramidal neurons of the CA1 hippocampal region. Ischaemia also induced a smaller and transient cyclin D1 mRNA increase in the resistant CA3 area and dentate gyrus. In contrast, the cyclin D2 and D3 mRNAs, expressed constitutively in the adult rat hippocampus, were not upregulated. Following kainate-induced seizures, cyclin D1 mRNA was induced in the vulnerable CA3 region, and to a lesser extent, in non-vulnerable regions. Cyclin D1 immunohistochemistry revealed increased protein levels in the cytoplasm and nucleus of neurons commited to die after ischaemia. Double labelling experiments indicate that cyclin D1 is also expressed in reactive astrocytes but not in microglial cells. Finally, we report that in neurons, cyclin D1 expression peaks before nuclear condensation and the appearance of DNA fragmentation. We propose that cyclin D1, when expressed at high levels in lesioned neurons, may act as a modulator of apoptosis.     

Differential gene expression in human brain pericytes induced by amyloid-beta protein

Cerebral amyloid angiopathy is one of the characteristics of Alzheimer's disease (AD) and this accumulation of fibrillar amyloid-beta (Alphabeta) in the vascular wall is accompanied by marked vascular damage. In vitro, Abeta1-40 carrying the 'Dutch' mutation (DAbeta1-40) induces degeneration of cultured human brain pericytes (HBP). To identify possible intracellular mediators of Abeta-induced cell death, a comparative cDNA expression array was performed to detect differential gene expression of Abeta-treated vs. untreated HBP. Messenger RNA expression of cyclin D1, integrin beta4, defender against cell death-1, neuroleukin, thymosin beta10, and integrin alpha5 were increased in DAbeta1-40-treated HBP, whereas insulin-like growth factor binding protein-2 mRNA expression was decreased. Corresponding protein expression was investigated in AD and control brains to explore a potential role for these proteins in pathological lesions of the AD brain. Cyclin D1 expression was increased in cerebral amyloid angiopathy and cells in a perivascular position, suggesting that the cell cycle may be disturbed during Abeta-mediated degeneration of cerebrovascular cells. Moreover, cyclin D1 expression, but also that of integrin beta4, defender against cell death-1, neuroleukin and thymosin beta10 was found in a subset of senile plaques, suggesting a role for these proteins in the pathogenesis of senile plaques.     

Voltage-activated K+ channels and membrane depolarization regulate accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in glial progenitor cells.

Neural cell development is regulated by membrane ion channel activity. We have previously demonstrated that cell membrane depolarization with veratridine or blockage of K+ channels with tetraethylammonium (TEA) inhibit oligodendrocyte progenitor (OP) proliferation and differentiation (); however the molecular events involved are largely unknown. Here we show that forskolin (FSK) and its derivative dideoxyforskolin (DFSK) block K+ channels in OPs and inhibit cell proliferation. The antiproliferative effects of TEA, FSK, DFSK, and veratridine were attributable to OP cell cycle arrest in G1 phase. In fact, (1) cyclin D accumulation in synchronized OP cells was not affected by K+ channel blockers or veratridine; (2) these agents prevented OP cell proliferation only if present during G1 phase; and (3) G1 blockers, such as rapamycin and deferoxamine, mimicked the anti-proliferative effects of K+ channel blockers. DFSK also prevented OP differentiation, whereas FSK had no effect. Blockage of K+ channels and membrane depolarization also caused accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in OP cells. The antiproliferative effects of K+ channel blockers and veratridine were still present in OP cells isolated from INK4a-/- mice, lacking the cyclin-dependent kinase inhibitors p16(INK4a) and p19(ARF). Our results demonstrate that blockage of K+ channels and cell depolarization induce G1 arrest in the OP cell cycle through a mechanism that may involve p27(Kip1) and p21(CIP1) and further support the conclusion that OP cell cycle arrest and differentiation are two uncoupled events.     

Alterations in cyclin A,B, and D1 in mouse dentate gyrus following TMT-induced hippocampal damage

The interactions of glia and neurons during injury and subsequent neurodegeneration are a subject of interest both in disease and chemical-induced brain injury. One such model is the prototypical hippocampal toxicant trimethyltin (TMT). An acute injection of TMT (2.0 mg/kg, i.p.) to postnatal day 21 CD-1 male mice produced neuronal necrosis and loss of dentate granule cells, astrocyte hypertrophy, and microglia activation in the hippocampus within 24 h. Neuronal necrosis and microglia differentiation to a phagocytic phenotype is temporally correlated with peak elevations in TNF-α, cyclin A2, cyclin B1 and cyclin D1 at 72 h post-TMT. TNF-α mRNA levels were significantly elevated in the hippocampus by 12 h and remained elevated for 72 h. mRNA levels for cyclin A2 and cyclin B1 were elevated by approximately 2-fold at 72 h. Immunohistochemistry suggested a cellular localization of cyclin A to microglia in the region of neuronal necrosis in the dentate, cyclin B in glial cells in juxtaposition to neurons in the hilus of the hippocampus and cyclin D1 to non-glial cells in the dentate. mRNA levels for cyclin D1 were elevated approximately 1.5-fold by 72 h as determined by RNase protection assay. No changes were seen in mRNA levels for cyclins E, F, G1, G2, H or I nor cyclin dependent kinases. These elevations are not associated with proliferation of microglia as determined by BrdU incorporation and Ki-67 immunohistochemistry. Upregulation of cell cycle genes was associated with cellular processes other than proliferation and may contribute to the differentiation of microglia to a phagocytic phenotype. These data suggest an integrated role for cell cycle regulation of neural cells in the manifestation of hippocampal pathophysiology.     

Potassium-induced apoptosis in rat cerebellar granule cells involves cell-cycle blockade at the G1/S transition

The role of regulators controlling the G1/S transition of the cell cycle was analyzed during neuronal apoptosis in post-mitotic cerebellar granule cells in an attempt to identify common mechanisms of control with transformed cells. Cyclin D1 and its associated kinase activity CDK4 (cyclin-dependent kinase 4) are major regulators of the G1/S transition. Whereas cyclin D1 is the regulatory subunit of the complex, CDK4 represents the catalytic domain that, once activated, will phosphorylate downstream targets such as the retinoblastoma protein, allowing cell-cycle progression. Apoptosis was induced in rat cerebellar granule cells by depleting potassium in presence of serum. Western-blot analyses were performed and protein kinase activities were measured. As apoptosis proceeded, loss in cell viability was coincident with a significant increase in cyclin D1 protein levels, whereas CDK4 expression remained essentially constant. Synchronized to cyclin D1 accumulation, cyclin-dependent kinase inhibitor p27Kip1 drastically dropped to 20% normal values. Cyclin D1/CDK4-dependent kinase activity increased early during apoptosis, reaching a maximum at 9-12 h and decreasing to very low levels by 48 h. Cyclin E, a major downstream target of cyclin D1, decreased concomitantly to the reduction in cyclin D1/CDK4-dependent kinase activity. We suggest that neuronal apoptosis takes place through functional alteration of proteins involved in the control of the G1/S transition of the cell cycle. Thus, apoptosis in post-mitotic neurons could result from a failed attempt to re-enter cell cycle in response to extracellular conditions affecting cell viability and it could involve mechanisms similar to those that promote proliferation in transformed cells.