Haploinsufficiency of tau decreases survival of the mouse model of Niemann-Pick disease type C1 but does not alter tau phosphorylation

Genetic forms of tauopathies: inherited causes and implications of Alzheimer's disease-like TAU pathology in primary and secondary tauopathies

Tauopathies are a heterogeneous group of neurologic diseases characterized by pathological axodendritic distribution, ectopic expression, and/or phosphorylation and aggregation of the microtubule-associated protein TAU, encoded by the gene MAPT. Neuronal dysfunction, dementia, and neurodegeneration are common features of these often detrimental diseases. A neurodegenerative disease is considered a primary tauopathy when MAPT mutations/haplotypes are its primary cause and/or TAU is the main pathological feature. In case TAU pathology is observed but superimposed by another pathological hallmark, the condition is classified as a secondary tauopathy. In some tauopathies (e.g. MAPT-associated frontotemporal dementia (FTD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD)) TAU is recognized as a significant pathogenic driver of the disease. In many secondary tauopathies, including Parkinson's disease (PD) and Huntington's disease (HD), TAU is suggested to contribute to the development of dementia, but in others (e.g. Niemann-Pick disease (NPC)) TAU may only be a bystander. The genetic and pathological mechanisms underlying TAU pathology are often not fully understood. In this review, the genetic predispositions and variants associated with both primary and secondary tauopathies are examined in detail, assessing evidence for the role of TAU in these conditions. We highlight less common genetic forms of tauopathies to increase awareness for these disorders and the involvement of TAU in their pathology. This approach not only contributes to a deeper understanding of these conditions but may also lay the groundwork for potential TAU-based therapeutic interventions for various tauopathies.

Genetic and sporadic forms of tauopathies-TAU as a disease driver for the majority of patients but the minority of tauopathies

Ageing-associated tauopathies like frontotemporal dementia (FTD), variants thereof (like progressive supranuclear palsy (PSP), pick diseases (PiD), corticobasal degeneration (CBD)), and of course the most prevalent form of dementia, Alzheimer Disease (AD), are widely recognized forms of tauopathies. The list of tauopathies is expanding. We now include: (i) tauopathies where the disease cause or trigger is clearly either physical, such as in Traumatic Brain Injury (TBI) or Chronic Traumatic Encephalopathy (CTE), and (ii) genetic diseases that result in tauopathy but have pathogenic genetic variants in genes not related to TAU. Examples of the latter are myotonic dystrophy Type 1 and Type 2 (DM1, DM2, due to pathogenic genetic variants in the genes DMPK and CNBP, respectively), Niemann-Pick Disease Type C (NPD, due to mutations in NPC1 or NPC2), Kufs Disease (CLN6), Christianson Syndrome (SLC9A6), familial forms of Parkinson Disease (PD), and many others. In terms of affected brain regions and cell types, intracellular distribution of TAU pathology/aggregates, age of disease onset, velocity of disease progression and spreading of TAU pathology, there is, however, little in common in most of these disease entities. Here, I reason that TAU/MAPT is causative for the minority of tauopathies (e.g., MAPT-related FTD/PSP and Vacuolar Tauopathy (VCP)) and a critical mediator for others, like shown by overwhelming evidence for AD. However, TAU may also be a mere bystander or even protective in other settings. Improved understanding of rare tauopathies is necessary to develop specific treatments, but also to improve our understanding of the pathomechanistic role of TAU and to identify diseases that may profit from TAU-based therapies.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

Understanding and Treating Niemann-Pick Type C Disease: Models Matter

Biomedical research aims to understand the molecular mechanisms causing human diseases and to develop curative therapies. So far, these goals have been achieved for a small fraction of diseases, limiting factors being the availability, validity, and use of experimental models. Niemann–Pick type C (NPC) is a prime example for a disease that lacks a curative therapy despite substantial breakthroughs. This rare, fatal, and autosomal-recessive disorder is caused by defects in NPC1 or NPC2. These ubiquitously expressed proteins help cholesterol exit from the endosomal–lysosomal system. The dysfunction of either causes an aberrant accumulation of lipids with patients presenting a large range of disease onset, neurovisceral symptoms, and life span. Here, we note general aspects of experimental models, we describe the line-up used for NPC-related research and therapy development, and we provide an outlook on future topics.