Therapeutic and diagnostic challenges for frontotemporal dementia

Minimotifs dysfunction is pervasive in neurodegenerative disorders

Minimotifs are modular contiguous peptide sequences in proteins that are important for posttranslational modifications, binding to other molecules, and trafficking to specific subcellular compartments. Some molecular functions of proteins in cellular pathways can be predicted from minimotif consensus sequences identified through experimentation. While a role for minimotifs in regulating signal transduction and gene regulation during disease pathogenesis (such as infectious diseases and cancer) is established, the therapeutic use of minimotif mimetic drugs is limited. In this review, we discuss a general theme identifying a pervasive role of minimotifs in the pathomechanism of neurodegenerative diseases. Beyond their longstanding history in the genetics of familial neurodegeneration, minimotifs are also major players in neurotoxic protein aggregation, aberrant protein trafficking, and epigenetic regulation. Generalizing the importance of minimotifs in neurodegenerative diseases offers a new perspective for the future study of neurodegenerative mechanisms and the investigation of new therapeutics.

Antibody Therapeutics Targeting Aβ and Tau

The astonishing findings that active and passive immunization against amyloid-β (Aβ) in mouse models of Alzheimer's disease (AD) dramatically decreased amyloid burden led to a rapid initiation of human clinical trials with much enthusiasm. However, methodological issues and adverse effects relating to these clinical trials arose, challenging the effectiveness and safety of these reagents. Efforts are now underway to develop safer immunotherapeutic approaches toward Aβ and the treatment of individuals at risk for AD before or in the earliest stages of cognitive decline with new hopes. Furthermore, several studies have shown tau as a potential immunotherapeutic target for the treatment of tauopathy-related diseases including frontotemporal lobar dementia (FTLD). Both active and passive immunization targeting tau in mouse models of tauopathy effectively decreased tau pathology while improving cognitive performance. These preclinical studies have highlighted tau as an alternative target with much anticipation of clinical trials to be undertaken.

TDP-43 protein variants as biomarkers in amyotrophic lateral sclerosis

BACKGROUND

TDP-43 aggregates accumulate in individuals affected by amyotrophic lateral sclerosis (ALS) and other neurodegenerative diseases, representing potential diagnostic and therapeutic targets. Using an atomic force microscopy based biopanning protocol developed in our lab, we previously isolated 23 TDP-43 reactive antibody fragments with preference for human ALS brain tissue relative to frontotemporal dementia, a related neurodegeneration, and healthy samples from phage-displayed single chain antibody fragment (scFv) libraries. Here we further characterize the binding specificity of these different scFvs and identify which ones have promise for detecting ALS biomarkers in human brain tissue and plasma samples.

RESULTS

We developed a sensitive capture ELISA for detection of different disease related TDP-43 variants using the scFvs identified from the ALS biopanning. We show that a wide variety of disease selective TDP-43 variants are present in ALS as the scFvs show different reactivity profiles amongst the ALS cases. When assaying individual human brain tissue cases, three scFvs (ALS-TDP6, ALS-TDP10 and ALS-TDP14) reacted with all the ALS cases and 12 others reacted with the majority of the ALS cases, and none of the scFvs reacted with any control samples. When assaying individual human plasma samples, 9 different scFvs reacted with all the sporadic ALS samples and again none of them reacted with any control samples. These 9 different scFvs had different patterns of reactivity with plasma samples obtained from chromosome 9 open reading frame 72 (c9orf72) cases indicating that these familial ALS genetic variants may display different TDP-43 pathology than sporadic ALS cases.

CONCLUSIONS

These results indicated that a range of disease specific TDP-43 variants are generated in ALS patients with different variants being generated in sporadic and familial cases. We show that a small panel of scFvs recognizing different TDP-43 variants can generate a neuropathological and plasma biomarker profile with potential to distinguish different TDP-43 pathologies.

Behavioral Evolution of Progressive Semantic Aphasia in Comparison with Nonfluent Aphasia

BACKGROUND

Patients with primary progressive aphasia (PPA) usually develop significant behavioral disturbances with progression of the disease. We tested our clinical observation that development of disruptive agitation is more likely in semantic than in nonfluent PPA and examined which clinical variables could be associated with this behavior.

METHODS

We retrospectively analyzed neuropsychiatric scores and the need for behavioral treatments in semantic PPA (n = 41) and nonfluent PPA (n = 39) cases and compared first (1-3 years since the onset of symptoms) and last (5-13 years since the onset) evaluations. Clinical variables and laterality of temporal atrophy were associated with symptoms in semantic PPA cases.

RESULTS

The semantic PPA group developed more frequent (p = 0.03) and intense agitation (p = 0.0008) and had a greater need for antipsychotic drugs (p = 0.001) than the nonfluent PPA group. Presence of agitation was clearly associated with psychotic symptoms (delusions/hallucinations) but was not associated with gender, age at onset, duration of the disease, or laterality of temporal atrophy. In contrast, nonfluent PPA cases were more frequently depressed and treated with antidepressants (p = 0.0007). There were no differences in anxiety, irritability, apathy, perseverations, hyperorality, or abnormal motor behavior.

CONCLUSIONS

Semantic PPA in advanced disease is frequently associated with agitation and psychotic symptoms with fewer mood symptoms, while nonfluent PPA maintains a high prevalence of depression. This implies different treatment and care and support needs for each group.

PERK-opathies: An Endoplasmic Reticulum Stress Mechanism Underlying Neurodegeneration

The unfolded protein response (UPR) plays a vital role in maintaining cell homeostasis as a consequence of endoplasmic reticulum (ER) stress. However, prolonged UPR activity leads to cell death. This time-dependent dual functionality of the UPR represents the adaptive and cytotoxic pathways that result from ER stress. Chronic UPR activation in systemic and neurodegenerative diseases has been identified as an early sign of cellular dyshomeostasis. The Protein Kinase R-like ER Kinase (PERK) pathway is one of three major branches in the UPR, and it is the only one to modulate protein synthesis as an adaptive response. The specific identification of prolonged PERK activity has been correlated with the progression of disorders such as diabetes, Alzheimer's disease, and cancer, suggesting that PERK plays a role in the pathology of these disorders. For the first time, the term "PERK-opathies" is used to group these diseases in which PERK mediates detriment to the cell culminating in chronic disorders. This article reviews the literature documenting links between systemic disorders with the UPR, but with a specific emphasis on the PERK pathway. Then, articles reporting links between the UPR, and more specifically PERK, and neurodegenerative disorders are presented. Finally, a therapeutic perspective is discussed, where PERK interventions could be potential remedies for cellular dysfunction in chronic neurodegenerative disorders.