Hepatitis C, a life threatening disease, caused by the hepatitis C virus (HCV) currently affects over 170-200 million people worldwide (~3% of global human population), more than five times the percentage of total HIV infections. HCV infection has been shown to be a major cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma and is the leading cause of liver transplantation in the U.S. HCV has escaped every therapeutic target to date by means of its error-prone RNA polymerase, which allows it to mutate prolifically. The current standard anti-HCV therapy, which is pegylated interferon a combined with ribavirin, is difficult to tolerate, and more than 50% of HCV patients are refractory to it. No protective vaccine or therapeutic antibody is available, making the need for the development of an efficacious immunoprophylactic and therapeutic agent imperative. HCV is an enveloped virus with a positive sense RNA genome of ~9.6 kilobases (kb), which carries a large open reading frame (ORF), flanked by 5'- and 3'- untranslated regions (UTRs). Interestingly, within the highly mutational HCV RNA, there are a limited number of 100% conserved and functionally vital motifs, located in the 5' UTR, coding region and in the 3' UTR. Within the HCV genome, these motifs have been proposed to be involved in multiple exclusive interactions with each other and furthermore, these interactions have been demonstrated to be essential for HCV replication and/or translation of the viral proteins. / Bayer School of Natural and Environmental Sciences; / Chemistry and Biochemistry / PhD; / Dissertation;

成人骨量的更新与维持通过骨重塑来实现。骨重塑包括骨吸收与骨形成两个偶联的过程，其中成骨细胞介导骨形成，破骨细胞介导骨吸收，当偶联的骨吸收超过骨吸收就会导致骨量丢失，进而导致发生骨质疏松症的发生。目前，临床治疗骨质疏松的药物如阿仑膦酸盐、雌激素受体调节剂、活性维生素D、雌激素替代治疗、降钙素、骨化三醇等都是基于针对破骨细胞的调控来抑制骨吸收，但是对于已经丢失的骨量无法恢复。唯一被美国FDA批准用来通过刺激新骨形成来恢复丢失的骨量的治疗药物就是甲状旁腺激素。然而，这种药物在刺激新骨形成的同时也刺激了骨吸收，即：在使用18个月后有明显促进骨吸收的副作用。 / 酪蛋白激酶相互作用蛋白-1（CKIP-1）基因是一个新发现的骨形成的负调控基因，CKIP-1基因敲除小鼠在骨发育和正常骨代谢过程中均未发现激活骨吸收。CKIP-1敲除导致小鼠胫骨近端骨量与胫骨皮质骨形成速率显著高于野生型，且这一差异随着小鼠的增龄而显著，而骨外器官没有发现异常表型，提示CKIP-1是潜在相对安全的治疗骨质疏松的靶向基因。特别是我们最近研发的一种天门冬氨酸－丝氨酸－丝氨酸重复三肽修饰的脂质体递送（(Asp-Ser-Ser)₆-liposome）系统能够实现靶向骨形成表面的小干扰核酸的递送，并明显减少了小干扰核酸在非骨组织的分布。因此，提出本课题的研究假设：特异性静默骨内CKIP-1可以促进骨形成而不刺激骨吸收，从而为骨质疏松的临床治疗提供安全有效的治疗手段。 / 为了确定CKIP-1基因表达在老年绝经后妇女骨骼中与骨形成内在联系，首先，我们通过对发生骨折的老年绝经后妇女的骨痂标本中CKIP-1 mRNA和蛋白表达的测定，发现CKIP-1基因mRNA和蛋白表达水平与骨形成能力负相关。并且，这种相关性在骨质疏松动物模型中进一步得到证实。其次，针对我们研究假设，从一组针对大鼠、小鼠、猴和人类的成骨样细胞的CKIP-1 mRNA的跨种属siRNA序列中筛选出体外静默效率最高CKIP-1小干扰核酸序列si-3。接着，体内外实验证实si-3序列在健康动物体内的静默效率和促进成骨的功能。同时，确定尾静脉注射（Asp-Ser-Ser）₆-liposome 包裹的CKIP-1小干扰核酸在 大鼠和小鼠为的最佳剂量分别为3.75mg/kg和7.5mg/kg以及注射周期为每两周一次。最后，为了检验CKIP-1 小干扰核酸是否可通过促进骨形成从而逆转绝经后骨质疏松症中的骨丢失，我们分别以绝经后骨质疏松大鼠和小鼠为实验动物模型，通过测定骨形态计量学参数、骨量和骨结构等来评价骨靶向递送系统（(Asp-Ser-Ser)₆-liposome）递送的CKIP-1 siRNA对老年绝经后骨质疏松症的治疗效果。动态活体CT分析结果表明，与0周未治疗的基础值相比，经6周治疗骨密度（BMD）, 相对骨体积分数（BV/TV）和骨小梁厚度（Tb.Th）在小干扰核酸治疗组显著增加。此外，在治疗6周后小干扰核酸治疗组骨密度，相对骨体积和骨小梁厚度显示较高于模型对照组。0周与其它检测时间点之间的对比分析较显示，小干扰核酸治疗组的新生骨显著高于模型组或假手术组。组织形态学分析结果表明在治疗6周后，无论是股骨远端或中段的矿化沉积率（MAR）、骨形成速率（BFR） 和组的骨形成表面（Ob.S/ BS）在OVX组和siRNA组均显著高于模型对照组，而模型对照组和小干扰核酸治疗组的骨吸收表面（Oc.S/ BS）之间无显著性差异。 / 结论：CKIP-1基因小核酸干扰治疗在老年绝经后骨质疏松中能够显著促进骨形成并不会加剧骨吸收，该药物具有显著逆转骨丢失的作用。 / Osteoporosis is characterized by an imbalance between bone formation and bone resorption. Therefore, promoting bone formation and inhibiting bone resorption are the two major therapeutic strategies in the treatment of osteoporosis. Currently, the only Food and Drug Administration (FDA)-approved anabolic agent capable of stimulating bone formation is parathyroid hormone (PTH). However, dominant bone resorption after 18-month treatment with PTH is a great concern (Rubin and Bilezikian 2003). Thus, development of alternative bone anabolic agents is highly desirable. / Casein kinase-2 interacting protein-1 (CKIP-1), which is encoded by Plekho1, and thus also known as Plekho1, is a newly discovered negative regulator of bone formation during bone development and subsequent bone maintenance that does not activate bone resorption (Lu, Yin et al. 2008). Specifically, CKIP-1 protein functions as the auxiliary factor of ubiquitin ligase Smad ubiquitylation regulatory factor 1 (Smurf1) to interrupt the bone anabolic BMP-signalling pathway, which has been demonstrated to be a specific suppressor of bone formation (Yamashita, Ying et al. 2005). In a previous study, we found that CKIP-1 expression in female rat bone increases with aging, whereas bone formation decreases with aging (Guo, Zhang et al. 2010). Systemic examination of the tissue distribution of CKIP-1 expression has revealed that is abundantly expressed in the musculoskeletal system but sparingly expressed in the liver, lungs, kidneys, pancreas, and other organs (Zhang, Tang et al. 2007). In addition, an abnormal tissue phenotype in heart, liver, spleen, lung, and kidney tissue has not been observed in CKIP-1 gene knockout mice (KO), even at an advanced age (Lu, Yin et al. 2008). Thus, CKIP-1 gene silencing might be a potential strategy for promoting bone anabolic action in reversing bone loss. / RNA interference (RNAi), a natural cellular process that regulates gene expression by a highly precise mechanism of sequence-directed gene silencing at the stage of translation by degrading specific messenger RNA and then blocking translation of the specific gene, has been employed for gene silencing in vivo (Frank-Kamenetsky, Grefhorst et al. 2008). Accordingly, RNAi should be an appropriate target for CKIP-1 gene silencing in vivo. / We raised the hypothesis that therapeutic RNAi targeting of CKIP-1 might promote bone formation for reversing postmenopausal bone loss. To test the hypothesis, we performed several studies to achieve the following specific aims: (1) To explore the relationship between CKIP-1 expression and bone formation in aged postmenopausal osteoporosis; (2) To Identify a cross-species CKIP-1 siRNA sequence with high knockdown efficiency; (3) To validate of the identified CKIP-1 siRNA in healthy rodents in vivo; (4) To examine the anabolic effect of the identified CKIP-1 siRNA on bone in osteoporotic animal models. / The relationship between CKIP-1 gene expression and bone formation in bone specimens from aged postmenopausal women: To explore the association between CKIP-1 gene expression and bone formation in bone specimens from aged postmenopausal women, the gene expression of CKIP-1 and ALP in the bone specimens from aged female patients were examined. We found the protein expression of CKIP-1 increased during aging and negatively correlate to bone formation as indicated by the mRNA expression of ALP (Guo., Zhang. et al. 2011). Further, we also found the decreased bone formation during aging was partly rescued in Ckip-1 KO mice during aging. / A cross-species CKIP-1 siRNA sequence: Recently, we identified a specific CKIP-1 siRNA sequence (CKIP-1 siRNA si-3) with high knockdown efficiency across rat, mouse, rhesus, and human osteoblast-like cells that does not induce immunostimulatory activity and promotes osteoblast differentiation across the species in vitro and bone formation in rats in vivo (Guo, Zheng et al. 2012). / Validation of the CKIP-1 siRNA si-3 capsulated by bone-targeted siRNA delivery system in healthy rodents in vivo: We developed a bone-targeting siRNA delivery system (tripeptide aspartate-serine-serine linked with liposome, i.e. (Asp-Ser-Ser)₆-liposome) that can remarkably reduce the exposure of non-bone tissue to CKIP-1 siRNA (Zhang, Guo et al. 2012). To validate the identified CKIP-1 siRNA in healthy rodents in vivo, the established continuous CKIP-1 gene silencing protocol is optimized in adult rats and mice in vivo by hydrodynamic tail vein injection of 3.75mg/kg for rats and 7.5 mg/kg for mice every 2 weeks (Guo, Zhang et al. 2010). The osteogenic effects of CKIP-1 siRNA in both rats and mice were further validated in vivo. / Anabolic effect of CKIP-1 siRNA si-3 on bone in aged postmenopausal osteoporosis: For evaluation of the anabolic effect of CKIP-1 siRNA si-3 on reversing bone loss due to osteoporosis in an animal model, we intravenously injected ovariectomized (OVX) rats and mice with CKIP-1 siRNA delivered by the (Asp-Ser-Ser)₆-liposome, a liposome linked with six repeated aspartate-serine-serine moiety, every 2 weeks for 6 weeks. In vivo and ex vivo microCT analysis demonstrated a change over time in the variables examined and different change patterns over time among the groups examined after administration. We found that the siRNA group had experienced a significant increase in bone mineral density (BMD), relative bone volume (BV/TV), and trabecular thickness (Tb.Th) between weeks 0 and 6; had a higher BMD, BV/TV, and Tb.Th compared to the OVX group at week 6; and had a similar Tb.Th to that of the SHAM group at week 6. Registration analysis between week 0 and other time points revealed that the siRNA had a greater number of newly formed bone than the OVX and SHAM groups. Histomorphometric analysis showed that the siRNA group had a significantly higher mineralization rate (MAR), a significantly higher bone-formation rate (BFR), a significantly larger osteoblast surface (Ob.S/BS) at both the distal and mid-shaft femur compared to the OVX group after 6 weeks of treatment but not a significantly different Oc.S/BS. / Significance: Confirmation of our hypothesis by our results helps establish CKIP-1’s role as a pivotal negative regulator of bone formation in the aging skeleton and provides evidence that inhibiting CKIP-1 is a novel anabolic treatment for osteoporosis, indicating great potential for the use of therapeutic RNAi in orthopaedics and traumatology. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Guo, Baosheng. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves [132-150]). / Abstract also in Chinese. / Declaration --- p.i / Acknowledgements --- p.ii / Abstract --- p.iii / 论文摘要 --- p.vii / Table of Content --- p.ix / Abbreviations --- p.xvii / List of Figures --- p.xix / List of Tables --- p.xxii / Chapter CHAPTER 1 --- Review of recent anabolic therapy for osteoporosis --- p.1 / Chapter 1.1. --- Epidemiology of postmenopausal osteoporosis --- p.1 / Chapter 1.1.1. --- Definition of osteoporosis --- p.1 / Chapter 1.1.2. --- Epidemiology and health challenge of postmenopausal osteoporosis --- p.2 / Chapter 1.2. --- General pathophysiological understanding of osteoporosis and current challenge for osteoporosis treatment --- p.3 / Chapter 1.2.1. --- Bone modeling and remodeling --- p.3 / Chapter 1.2.2. --- Pathophysiological process of osteoporosis --- p.4 / Chapter 1.2.3. --- Systemic risk factors in the pathophysiology of osteoporosis --- p.5 / Chapter 1.2.4. --- Local risk factors in the osteoporosis pathophysiology --- p.6 / Chapter 1.2.5. --- Two therapeutic strategies for osteoporosis treatment --- p.7 / Chapter 1.3. --- Current and potential anabolic agents for osteoporosis treatment --- p.8 / Chapter 1.3.1. --- PTH analogues --- p.8 / Chapter 1.3.2. --- Potential concerns regarding PTH administration --- p.9 / Chapter 1.3.3. --- Potential PTH alternatives --- p.10 / Chapter 1.3.4. --- Modulation of Wnt/β-cateinin pathway --- p.10 / Chapter 1.3.5. --- Aptamer-based technology in osteoporosis treatment --- p.14 / Chapter 1.4. --- CKIP-1: A novel negative regulator of bone formation --- p.15 / Chapter 1.4.1. --- TGF-β/BMP signaling pathways involved in regulating bone formation --- p.15 / Chapter 1.4.2. --- CKIP-1 interrupts BMP signaling pathway --- p.16 / Chapter 1.4.3. --- CKIP-1 negatively regulates bone formation without activating bone resorption --- p.17 / Chapter 1.5. --- RNA interference strategy in anabolic therapy of osteoporosis --- p.18 / Chapter 1.5.1. --- siRNA-mediated gene silencing in osteoporosis treatment --- p.18 / Chapter 1.5.2. --- MicroRNAs as potential therapeutic targets in the anabolic treatment of osteoporosis --- p.20 / Chapter 1.5.3. --- Bone targeted RNAi-based anabolic-agents delivery --- p.23 / Chapter 1.6. --- Summary --- p.24 / Chapter CHAPTER 2 --- The relationship between CKIP-1 expression and bone formation in aged postmenopausal osteoporosis --- p.26 / Chapter 2.1 --- Introduction --- p.26 / Chapter 2.2 --- Materials and methods --- p.28 / Chapter 2.2.1 --- Bone specimen collection from aged postmenopausal women --- p.28 / Chapter 2.2.2 --- Total RNA extraction, reverse transcription and quantitative real-time PCR --- p.28 / Chapter 2.2.3 --- Total protein extraction and western blot analysis --- p.30 / Chapter 2.2.4 --- CKIP-1 expression in bone and other tissues --- p.31 / Chapter 2.2.5 --- Relationship between CKIP-1 expression and bone formation in aged ovariectomized rats --- p.31 / Chapter 2.2.6 --- Role of CKIP-1 in regulating bone formation in aged ovariectomized mice --- p.32 / Chapter 2.2.7 --- Statistics --- p.32 / Chapter 2.3 --- Results --- p.33 / Chapter 2.3.1 --- Correlation analysis between CKIP-1 expression and bone formation-related gene expression in bone specimens from agedd postmenopausal women across age --- p.33 / Chapter 2.3.2 --- CKIP-1 gene expression pattern in bone and other tissues --- p.37 / Chapter 2.3.3 --- Correlation between CKIP-1 expression and bone formation in rat bone --- p.38 / Chapter 2.3.4 --- CKIP-1 negatively regulates bone formation in aged ovariectomized mice by using CKIP-1 knockout mice --- p.39 / Chapter 2.4 --- Summary --- p.41 / Chapter CHAPTER 3 --- Identification of a cross-species CKIP-1 siRNA sequence --- p.43 / Chapter 3.1 --- Introduction --- p.43 / Chapter 3.2 --- Materials and methods --- p.44 / Chapter 3.2.1 --- Design rationale and modification for cross-species CKIP-1 siRNA --- p.44 / Chapter 3.2.2 --- In vitro screening for cross-species CKIP-1 siRNA sequences --- p.45 / Chapter 3.2.3 --- Investigation of the effects of the identified CKIP-1 siRNA on the expression of osteoblast phenotype genes --- p.47 / Chapter 3.2.4 --- Total RNA extraction, reverse transcription and quantitative real-time PCR --- p.47 / Chapter 3.2.5 --- Western blot analysis --- p.51 / Chapter 3.2.6 --- Evaluation of calcium deposition --- p.51 / Chapter 3.2.7 --- BMP-2 reporter activity assay in MC3T3-E1 cells --- p.52 / Chapter 3.2.8 --- Isolation of the primary human blood monocytes and IFN-α and TNF-α measurement --- p.53 / Chapter 3.2.9 --- Statistics --- p.54 / Chapter 3.3 --- Results --- p.54 / Chapter 3.3.1 --- Bio-informatic analysis of the designed CKIP-1 siRNA sequences --- p.54 / Chapter 3.3.2 --- Identified the cross-species CKIP-1 siRNA sequences by In vitro screening --- p.56 / Chapter 3.3.3 --- Effects of the identified CKIP-1 siRNA on the expression of osteoblast phenotype genes --- p.60 / Chapter 3.3.4 --- Effects of the identified CKIP-1 siRNA on matrix mineralization --- p.65 / Chapter 3.3.5 --- Effect of the identified CKIP-1 siRNA on BMP signaling --- p.67 / Chapter 3.3.6 --- Effects of the identified CKIP-1 siRNA on the ratio of RANKL/OPG --- p.67 / Chapter 3.3.7 --- Effects of the identified CKIP-1 siRNA on immunostimulatory activity --- p.68 / Chapter 3.4 --- Summary --- p.71 / Chapter 3.4.1 --- CKIP-1 siRNA si-3 as the identified sequence --- p.71 / Chapter 3.4.2 --- CKIP-1 siRNA si-3 promoted osteoblast differentiation in vitro --- p.72 / Chapter CHAPTER 4 --- Validation of the identified CKIP-1 siRNA in healthy rodents in vivo --- p.74 / Chapter 4.1 --- Introduction --- p.74 / Chapter 4.2 --- Materials and methods --- p.74 / Chapter 4.2.1 --- Localization of intraosseous siRNA delivered by (Asp-Ser-Ser)₆-liposome --- p.75 / Chapter 4.2.2 --- Cell-selective delivery in vivo of CKIP-1 siRNA --- p.76 / Chapter 4.2.3 --- Dose-response study of CKIP-1 siRNA --- p.77 / Chapter 4.2.4 --- Time-course study of CKIP-1 siRNA --- p.77 / Chapter 4.2.5 --- Examination of the effect of the identified siRNA on the expression of osteoblast phenotype genes --- p.78 / Chapter 4.2.6 --- Measurement for serum PINP and urinary DPD --- p.80 / Chapter 4.2.7 --- 5’-RACE Analysis --- p.81 / Chapter 4.2.8 --- Laser captured micro-dissection (LCM) --- p.82 / Chapter 4.2.9 --- Evaluation the anabolic effect of the identified siRNA on healthy rat bone --- p.82 / Chapter 4.2.10 --- Evaluation the anabolic effect of the identified siRNA on healthy mouse bone --- p.84 / Chapter 4.2.11 --- Micro CT analysis --- p.84 / Chapter 4.2.12 --- Dynamic bone histomorphometric analysis --- p.85 / Chapter 4.2.13 --- Statistics --- p.86 / Chapter 4.3 --- Results --- p.87 / Chapter 4.3.1 --- Rationale of bone targeted delivery of CKIP-1 siRNA by (Asp-Ser-Ser)₆-liposome --- p.87 / Chapter 4.3.2 --- Intraosseous distribution of siRNA delivered by (Asp-Ser-Ser)₆-liposome --- p.89 / Chapter 4.3.3 --- Optimal dosage and duration for CKIP-1 siRNA administration in vivo --- p.92 / Chapter 4.3.4 --- Knockdown efficiency of CKIP-1 siRNA in osteoblasts by LCM in combination with Q-PCR --- p.94 / Chapter 4.3.5 --- Examination of the effect of the identified siRNA on the expression of osteoblast phenotype genes --- p.96 / Chapter 4.3.6 --- RNAi mechanism of CKIP-1 siRNA action in vivo --- p.99 / Chapter 4.3.7 --- Anabolic effect of the identified siRNA on healthy rat bone --- p.101 / Chapter 4.3.8 --- Anabolic effect of the identified siRNA on healthy mouse bone . --- p.104 / Chapter 4.4 --- Summary --- p.107 / Chapter 4.4.1 --- Intraosseous localization of CKIP-1 siRNA after systemic administration --- p.107 / Chapter 4.4.2 --- Evidence of RNAi in bone tissue from systemic administration of CKIP-I siRNA --- p.107 / Chapter 4.4.3 --- CKIP-1 siRNA si-3 promots bone formation in rats and mice in vivo --- p.108 / Chapter CHAPTER 5 --- Anabolic effect of the identified CKIP-1 siRNA on bone in postmenopausal osteoporostic animal models --- p.110 / Chapter 5.1. --- Introduction --- p.110 / Chapter 5.2. --- Materials and Methods --- p.110 / Chapter 5.2.1. --- Evaluation of anabolic effect of CKIP-1 siRNA on osteoporotic mouse bone --- p.111 / Chapter 5.2.2. --- Evaluation of anabolic effect of CKIP-1 siRNA on osteoporotic rat bone --- p.112 / Chapter 5.2.3. --- In vivo micro-CT analysis and registration of proximal tibia from osteoporotic rats --- p.112 / Chapter 5.2.4. --- Ex vivo micro-CT analysis of the distal femur and 5th lumbar vertebrae body of osteoporotic rats --- p.115 / Chapter 5.2.5. --- Ex vivo micro-CT analysis of distal femur from osteoporotic mice --- p.115 / Chapter 5.2.6. --- Bone histomorphometric analysis --- p.116 / Chapter 5.2.7. --- Mechanical testing --- p.117 / Chapter 5.2.8. --- Statistics --- p.118 / Chapter 5.3. --- Results --- p.116 / Chapter 5.3.1. --- Anabolic effect of CKIP-1 siRNA si-3 on osteoporotic mouse bone --- p.118 / Chapter 5.3.2. --- In vivo microCT data of proximal tibia from aged osteoporotic rats --- p.121 / Chapter 5.3.3. --- Ex vivo microCT data of distal femur from aged osteoporotic rats --- p.124 / Chapter 5.3.4. --- Ex vivo microCT data of 5th LV body from aged osteoporotic rats --- p.126 / Chapter 5.3.5. --- Bone histomorphometric analysis of aged osteoporotic rats --- p.129 / Chapter 5.3.6. --- Mechanical testing of the mid-shaft femur of aged osteoporotic rats --- p.132 / Chapter 5.4. --- Summary --- p.134 / Chapter CHAPTER 6 --- Discussions --- p.134 / Chapter 6.1 --- CKIP-1 siRNA design rationale and further modification --- p.135 / Chapter 6.1.1 --- Specificity design rationale of the CKIP-1 siRNA --- p.135 / Chapter 6.1.2 --- Stability enhancing modification of CKIP-1 siRNA --- p.136 / Chapter 6.1.3 --- Safety concerns with CKIP-1 siRNA therapy --- p.136 / Chapter 6.2 --- Development of bone-targeted siRNA delivery --- p.136 / Chapter 6.3 --- Prospects for and limitation of application of study findings to clinical therapeutics --- p.137 / References --- p.139 / Publications --- p.159

Indiana University-Purdue University Indianapolis (IUPUI) / Alzheimer disease (AD) results, in part, from the excess accumulation of the amyloid-β peptide (Aβ) as neuritic plaques in the brain. The short Aβ peptide is derived from a large transmembrane precursor protein, APP. Two different proteolytic enzymes, BACE1 and the gamma-secretase complex, are responsible for cleaving Aβ peptide from APP through an intricate processing pathway. Dysregulation of APP and BACE1 levels leading to excess Aβ deposition has been implicated in various forms of AD. Thus, a major goal in this dissertation was to discover novel regulatory pathways that control APP and BACE1 expression as a means to identify novel drug targets central to the Aβ-generating process. MicroRNAs (miRNA) are short, non-coding RNAs that act as post-transcriptional regulators of gene expression through specific interactions with target mRNAs. Global analyses predict that over sixty percent of human transcripts contain evolutionarily conserved miRNA target sites. Therefore, the specific hypothesis tested was that miRNA are relevant regulators of APP and BACE1 expression. In this work, several specific miRNA were identified that regulate APP protein expression (miR-101, miR-153 and miR-346) or BACE1 expression (miR-339-5p). These miRNAs mediated their post-transcriptional effects via interactions with specific target sites in the APP and BACE1 transcripts. Importantly, these miRNA also altered secretion of Aβ peptides in primary human fetal brain cultures. Surprisingly, miR-346 stimulated APP expression via target sites in the APP 5’-UTR. The mechanism of this effect appears to involve other RNA-binding proteins that bind to the APP 5’-UTR. Expression analyses demonstrated that these miRNAs are expressed to varying degrees in the human brain. Notably, miR-101, miR-153 and miR-339-5p are dysregulated in the AD brain at various stages of the disease. The work in this dissertation supports the hypothesis that miRNAs are important regulators of APP and BACE1 expression and are capable of altering Aβ homeostasis. Therefore, these miRNA may possibly serve as novel therapeutic targets for AD.