Transcriptomic Analysis in the Hippocampus and Retina of Tg2576 AD Mice Reveals Defective Mitochondrial Oxidative Phosphorylation and Recovery by Tau 12A12mAb Treatment

Increasing evidence implicates decreased energy metabolism and mitochondrial dysfunctions among the earliest pathogenic events of Alzheimer's disease (AD). However, the molecular mechanisms underlying bioenergetic dysfunctions in AD remain, to date, largely unknown. In this work, we analyzed transcriptomic changes occurring in the hippocampus and retina of a Tg2576 AD mouse model and wild-type controls, evaluating their functional implications by gene set enrichment analysis. The results revealed that oxidative phosphorylation and mitochondrial-related pathways are significantly down-regulated in both tissues of Tg2576 mice, supporting the role of these processes in the pathogenesis of AD. In addition, we also analyzed transcriptomic changes occurring in Tg2576 mice treated with the 12A12 monoclonal antibody that neutralizes an AD-relevant tau-derived neurotoxic peptide in vivo. Our analysis showed that the mitochondrial alterations observed in AD mice were significantly reverted by treatment with 12A12mAb, supporting bioenergetic pathways as key mediators of its in vivo neuroprotective and anti-amyloidogenic effects. This study provides, for the first time, a comprehensive characterization of molecular events underlying the disrupted mitochondrial bioenergetics in AD pathology, laying the foundation for the future development of diagnostic and therapeutic tools.

The Cleavage-Specific Tau 12A12mAb Exerts an Anti-Amyloidogenic Action by Modulating the Endocytic and Bioenergetic Pathways in Alzheimer's Disease Mouse Model

Beyond deficits in hippocampal-dependent episodic memory, Alzheimer's Disease (AD) features sensory impairment in visual cognition consistent with extensive neuropathology in the retina. 12A12 is a monoclonal cleavage specific antibody (mAb) that in vivo selectively neutralizes the AD-relevant, harmful N-terminal 20-22 kDa tau fragment(s) (i.e., NH₂htau) without affecting the full-length normal protein. When systemically injected into the Tg2576 mouse model overexpressing a mutant form of Amyloid Precursor Protein (APP), APPK670/671L linked to early onset familial AD, this conformation-specific tau mAb successfully reduces the NH₂htau accumulating both in their brain and retina and, thus, markedly alleviates the phenotype-associated signs. By means of a combined biochemical and metabolic experimental approach, we report that 12A12mAb downregulates the steady state expression levels of APP and Beta-Secretase 1 (BACE-1) and, thus, limits the Amyloid beta (Aβ) production both in the hippocampus and retina from this AD animal model. The local, antibody-mediated anti-amyloidogenic action is paralleled in vivo by coordinated modulation of the endocytic (BIN1, RIN3) and bioenergetic (glycolysis and L-Lactate) pathways. These findings indicate for the first time that similar molecular and metabolic retino-cerebral pathways are modulated in a coordinated fashion in response to 12A12mAb treatment to tackle the neurosensorial Aβ accumulation in AD neurodegeneration.

Targeting Tau to Treat Clinical Features of Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by severe motor, cognitive and psychiatric impairments. While motor deficits often confirm diagnosis, cognitive dysfunctions usually manifest early in the disease process and are consistently ranked among the leading factors that impact the patients' quality of life. The genetic component of HD, a mutation in the huntingtin (HTT) gene, is traditionally presented as the main contributor to disease pathology. However, accumulating evidence suggests the implication of the microtubule-associated tau protein to the pathogenesis and therefore, proposes an alternative conceptual framework where tau and mutant huntingtin (mHTT) act conjointly to drive neurodegeneration and cognitive dysfunction. This perspective on disease etiology offers new avenues to design therapeutic interventions and could leverage decades of research on Alzheimer's disease (AD) and other tauopathies to rapidly advance drug discovery. In this mini review, we examine the breadth of tau-targeting treatments currently tested in the preclinical and clinical settings for AD and other tauopathies, and discuss the potential application of these strategies to HD.

Alzheimer's disease: phenotypic approaches using disease models and the targeting of tau protein

Introduction: Hyperphosphorylated and aggregated tau protein is the main hallmark of a class of neurodegenerative disorders known as tauopathies. Tau is a microtubule-binding protein which is important for microtubule assembly and stabilization, for proper axonal transport and overall neuronal integrity. However, in tauopathies, tau undergoes aberrant post-translational modifications that fundamentally affect its normal function. The etiology of these devastating diseases is unclear and there is no treatment for these disorders.Areas covered: This review examines the neurobiology of tau, tau post-translational modifications, and tau pathophysiology. Progress regarding the effort to identify and assess novel tau-targeted therapeutic strategies in preclinical studies is also discussed. We performed a search on PubMed of the relevant literature published between 1995 and 2020.Expert opinion: Tau diversity and the lack of clinically available test to diagnose and identify tauopathies are major obstacles; they represent a possible reason for the lack of success of clinical trials. However, given the encouraging advances in PET tau imaging and tau neurobiology, we believe that a more personalized approach could be on the horizon and that this will be key to addressing the heterogeneity of tau pathology.

Advances in the therapy of Alzheimer's disease: targeting amyloid beta and tau and perspectives for the future

Worldwide multidisciplinary translational research has led to a growing knowledge of the genetics and molecular pathogenesis of Alzheimer's disease (AD) indicating that pathophysiological brain alterations occur decades before clinical signs and symptoms of cognitive decline can be diagnosed. Consequently, therapeutic concepts and targets have been increasingly focused on early-stage illness before the onset of dementia; and distinct classes of compounds are now being tested in clinical trials. At present, there is a growing consensus that therapeutic progress in AD delaying disease progression would significantly decrease the expanding global burden. The evolving hypothesis- and evidence-based generation of new diagnostic research criteria for early-stage AD has positively impacted the development of clinical trial designs and the characterization of earlier and more specific target populations for trials in prodromal as well as in pre- and asymptomatic at-risk stages of AD.

Cis phosphorylated tau as the earliest detectable pathogenic conformation in Alzheimer disease, offering novel diagnostic and therapeutic strategies

After protein phosphorylation on certain serine or threonine residues preceding a proline (pSer/Thr-Pro), the function of certain phosphorylated protein is further regulated by cis-trans conformational change. Due to the lack of any tool to detect such two conformations in cells, however, it is not even known whether any cis or trans conformation exists in vivo, not to mention their conformation-specific functions or regulation. We developed a novel peptide chemistry technology to generate the first pair of antibodies that can distinguish cis from trans pThr231-Pro tau. Cis, but not trans, pThr231-tau appears early in mild cognitive impairment (MCI) neurons and further accumulates in only degenerating neurons as Alzheimer disease (AD) progresses, localizing to dystrophic neurites, which are known to correlate well with memory loss. Unlike trans p-tau, the cis cannot promote microtubule assembly, and is more resistant to dephosphorylation and degradation and more prone to aggregation. Pin1 accelerates cis to trans isomerization to prevent tau pathology in AD. Thus, during MCI and AD development, cis pThr231-Pro tau is the earliest detectable pathogenic tau conformation and antibodies and vaccines against the pathogenic cis p-tau may be used for the early diagnosis and treatment of AD. These findings offer in vivo approach to study conformational regulation of Pro-directed phosphorylation signaling.