TSC1 loss increases risk for tauopathy by inducing tau acetylation and preventing tau clearance via chaperone-mediated autophagy

Impaired degradation of PLCG1 by chaperone-mediated autophagy promotes cellular senescence and intervertebral disc degeneration

Defects in chaperone-mediated autophagy (CMA) are associated with cellular senescence, but the mechanism remains poorly understood. Here, we found that CMA inhibition induced cellular senescence in a calcium-dependent manner and identified its role in TNF-induced senescence of nucleus pulposus cells (NPC) and intervertebral disc degeneration. Based on structural and functional proteomic screens, PLCG1 (phospholipase C gamma 1) was predicted as a potential substrate for CMA deficiency to affect calcium homeostasis. We further confirmed that PLCG1 was a key mediator of CMA in the regulation of intracellular calcium flux. Aberrant accumulation of PLCG1 caused by CMA blockage resulted in calcium overload, thereby inducing NPC senescence. Immunoassays on human specimens showed that reduced LAMP2A, the rate-limiting protein of CMA, or increased PLCG1 was associated with disc senescence, and the TNF-induced disc degeneration in rats was inhibited by overexpression of Lamp2a or knockdown of Plcg1. Because CMA dysregulation, calcium overload, and cellular senescence are common features of disc degeneration and other age-related degenerative diseases, the discovery of actionable molecular targets that can link these perturbations may have therapeutic value.Abbreviation: ATRA: all-trans-retinoic acid; BrdU: bromodeoxyuridine; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; CDKN2A/p16-INK4A: cyclin dependent kinase inhibitor 2A; CMA: chaperone-mediated autophagy; DHI: disc height index; ER: endoplasmic reticulum; IP: immunoprecipitation; IP3: inositol 1,4,5-trisphosphate; ITPR/IP3R: inositol 1,4,5-trisphosphate receptor; IVD: intervertebral disc; IVDD: intervertebral disc degeneration; KD: knockdown; KO: knockout; Leu: leupeptin; MRI: magnetic resonance imaging; MS: mass spectrometry; N/L: NH4Cl and leupeptin; NP: nucleus pulposus; NPC: nucleus pulposus cells; PI: protease inhibitors; PLC: phospholipase C; PLCG1: phospholipase C gamma 1; ROS: reactive oxygen species; RT-qPCR: real-time quantitative reverse transcription PCR; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; SASP: senescence-associated secretory phenotype; STV: starvation; TMT: tandem mass tag; TNF: tumor necrosis factor; TP53: tumor protein p53; UPS: ubiquitin-proteasome system.

Tau in neurodegenerative diseases: molecular mechanisms, biomarkers, and therapeutic strategies

The deposition of abnormal tau protein is characteristic of Alzheimer's disease (AD) and a class of neurodegenerative diseases called tauopathies. Physiologically, tau maintains an intrinsically disordered structure and plays diverse roles in neurons. Pathologically, tau undergoes abnormal post-translational modifications and forms oligomers or fibrous aggregates in tauopathies. In this review, we briefly introduce several tauopathies and discuss the mechanisms mediating tau aggregation and propagation. We also describe the toxicity of tau pathology. Finally, we explore the early diagnostic biomarkers and treatments targeting tau. Although some encouraging results have been achieved in animal experiments and preclinical studies, there is still no cure for tauopathies. More in-depth basic and clinical research on the pathogenesis of tauopathies is necessary.

Interaction between resveratrol and SIRT1: role in neurodegenerative diseases

Neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, pose significant health challenges and economic burdens worldwide. Recent studies have emphasized the potential therapeutic value of activating silent information regulator-1 (SIRT1) in treating these conditions. Resveratrol, a compound known for its ability to potently activate SIRT1, has demonstrated promising neuroprotective effects by targeting the underlying mechanisms of neurodegeneration. In this review, we delve into the crucial role of resveratrol-mediated SIRT1 upregulation in improving neurodegenerative diseases. The role of the activation of SIRT1 by resveratrol was reviewed. Moreover, network pharmacology was used to elucidate the possible mechanisms of resveratrol in these diseases. Activation of SIRT1 by resveratrol had positive effects on neuronal function and survival and alleviated the hallmark features of these diseases, such as protein aggregation, oxidative stress, neuroinflammation, and mitochondrial dysfunction. In terms of network pharmacology, the signaling pathways by which resveratrol protects against different neurodegenerative diseases were slightly different. Although the precise mechanisms underlying the neuroprotective effects of resveratrol and SIRT1 activation remain under investigation, these findings offer valuable insights into potential therapeutic strategies for neurodegenerative diseases.

Complicated Role of Post-translational Modification and Protease-Cleaved Fragments of Tau in Alzheimer's Disease and Other Tauopathies

Tau, a microtubule-associated protein predominantly localized in neuronal axons, plays a crucial role in promoting microtubule assembly, stabilizing their structure, and participating in axonal transport. Perturbations in tau's structure and function are implicated in the pathogenesis of neurodegenerative diseases collectively known as tauopathies, the most common disorder of which is Alzheimer's disease (AD). In tauopathies, it has been found that tau has a variety of post-translational modification (PTM) abnormalities and/or tau is cleaved into a variety of fragments by some specific proteolytic enzymes; however, the precise contributions of these abnormal modifications and fragments to disease onset and progression remain incompletely understood. Herein, we provide an overview about the involvement of distinctive abnormal tau PTMs and different tau fragments in the pathogenesis of AD and other tauopathies and discuss the involvement of proteolytic enzymes such as caspases, calpains, and asparagine endopeptidase in mediating tau cleavage while also addressing the intercellular transmission role played by tau. We anticipate that further exploration into PTMs and fragmented forms of tau will yield valuable insights for diagnostic approaches and therapeutic interventions targeting AD and other related disorders.

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.

Near-infrared imaging for visualizing the synergistic relationship between autophagy and NFS1 protein during multidrug resistance using an ICT-TICT integrated platform

Drug resistance is a major challenge for cancer treatment, and its identification is crucial for medical research. However, since drug resistance is a multi-faceted phenomenon, it is important to simultaneously evaluate multiple target fluctuations. Recently developed fluorescence-based probes that can simultaneously respond to multiple targets offer many advantages for real-time and in situ monitoring of cellular metabolism, including ease of operation, rapid reporting, and their non-invasive nature. As such we developed a dual-response platform (Vis-H2S) with integrated ICT-TICT to image H2S and viscosity in mitochondria, which could simultaneously track fluctuations in cysteine desulfurase (NFS1 protein and H2S inducer) and autophagy during chemotherapy-induced multidrug resistance. This platform could monitor multiple endogenous metabolites and the synergistic relationship between autophagy and NFS1 protein during multidrug resistance induced by chemotherapy. The results indicated that chemotherapeutic drugs simultaneously up-regulate the levels of NFS1 protein and autophagy. It was also found that the NFS1 protein was linked with autophagy, which eventually led to multidrug resistance. As such, this platform could serve as an effective tool for the in-depth exploration of drug resistance mechanisms.

The mTOR pathway genes MTOR, Rheb, Depdc5, Pten, and Tsc1 have convergent and divergent impacts on cortical neuron development and function

Brain somatic mutations in various components of the mTOR complex 1 (mTORC1) pathway have emerged as major causes of focal malformations of cortical development and intractable epilepsy. While these distinct gene mutations converge on excessive mTORC1 signaling and lead to common clinical manifestations, it remains unclear whether they cause similar cellular and synaptic disruptions underlying cortical network hyperexcitability. Here, we show that in utero activation of the mTORC1 activator genes, Rheb or MTOR, or biallelic inactivation of the mTORC1 repressor genes, Depdc5, Tsc1, or Pten in the mouse medial prefrontal cortex leads to shared alterations in pyramidal neuron morphology, positioning, and membrane excitability but different changes in excitatory synaptic transmission. Our findings suggest that, despite converging on mTORC1 signaling, mutations in different mTORC1 pathway genes differentially impact cortical excitatory synaptic activity, which may confer gene-specific mechanisms of hyperexcitability and responses to therapeutic intervention.

The mTOR pathway genes mTOR, Rheb, Depdc5, Pten, and Tsc1 have convergent and divergent impacts on cortical neuron development and function

Brain somatic mutations in various components of the mTOR complex 1 (mTORC1) pathway have emerged as major causes of focal malformations of cortical development and intractable epilepsy. While these distinct gene mutations converge on excessive mTORC1 signaling and lead to common clinical manifestations, it remains unclear whether they cause similar cellular and synaptic disruptions underlying cortical network hyperexcitability. Here, we show that in utero activation of the mTORC1 activators, Rheb or mTOR, or biallelic inactivation of the mTORC1 repressors, Depdc5, Tsc1, or Pten in mouse medial prefrontal cortex leads to shared alterations in pyramidal neuron morphology, positioning, and membrane excitability but different changes in excitatory synaptic transmission. Our findings suggest that, despite converging on mTORC1 signaling, mutations in different mTORC1 pathway genes differentially impact cortical excitatory synaptic activity, which may confer gene-specific mechanisms of hyperexcitability and responses to therapeutic intervention.

Tau-targeting therapies for Alzheimer disease: current status and future directions

Alzheimer disease (AD) is the most common cause of dementia in older individuals. AD is characterized pathologically by amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the brain, with associated loss of synapses and neurons, which eventually results in dementia. Many of the early attempts to develop treatments for AD focused on Aβ, but a lack of efficacy of these treatments in terms of slowing disease progression led to a change of strategy towards targeting of tau pathology. Given that tau shows a stronger correlation with symptom severity than does Aβ, targeting of tau is more likely to be efficacious once cognitive decline begins. Anti-tau therapies initially focused on post-translational modifications, inhibition of tau aggregation and stabilization of microtubules. However, trials of many potential drugs were discontinued because of toxicity and/or lack of efficacy. Currently, the majority of tau-targeting agents in clinical trials are immunotherapies. In this Review, we provide an update on the results from the initial immunotherapy trials and an overview of new therapeutic candidates that are in clinical development, as well as considering future directions for tau-targeting therapies.

Chaperone-mediated autophagy in neurodegenerative diseases: mechanisms and therapy

Chaperone-mediated autophagy (CMA) is the selective degradation process of intracellular components by lysosomes, which is required for the degradation of aggregate-prone proteins and contributes to proteostasis maintenance. Proteostasis is essential for normal cell function and survival, and it is determined by the balance of protein synthesis and degradation. Because postmitotic neurons are highly susceptible to proteostasis disruption, CMA is vital for the nervous system. Since Parkinson's disease (PD) was first linked to CMA dysfunction, an increasing number of studies have shown that CMA loss, as seen during aging, occurs in the pathogenetic process of neurodegenerative diseases. Here, we review the molecular mechanisms of CMA, as well as the physiological function and regulation of this autophagy pathway. Following, we highlight its potential role in neurodegenerative diseases, and the latest advances and challenges in targeting CMA in therapy of neurodegenerative diseases.

Chaperone-mediated autophagy: Molecular mechanisms, biological functions, and diseases

Chaperone-mediated autophagy (CMA) is a lysosomal degradation pathway that eliminates substrate proteins through heat-shock cognate protein 70 recognition and lysosome-associated membrane protein type 2A-assisted translocation. It is distinct from macroautophagy and microautophagy. In recent years, the regulatory mechanisms of CMA have been gradually enriched, including the newly discovered NRF2 and p38-TFEB signaling, as positive and negative regulatory pathways of CMA, respectively. Normal CMA activity is involved in the regulation of metabolism, aging, immunity, cell cycle, and other physiological processes, while CMA dysfunction may be involved in the occurrence of neurodegenerative disorders, tumors, intestinal disorders, atherosclerosis, and so on, which provides potential targets for the treatment and prediction of related diseases. This article describes the general process of CMA and its role in physiological activities and summarizes the connection between CMA and macroautophagy. In addition, human diseases that concern the dysfunction or protective role of CMA are discussed. Our review deepens the understanding of the mechanisms and physiological functions of CMA and provides a summary of past CMA research and a vision of future directions.

Acetylation discriminates disease-specific tau deposition

Pathogenic aggregation of the protein tau is a hallmark of Alzheimer's disease and several other tauopathies. Tauopathies are characterized by the deposition of specific tau isoforms as disease-related tau filament structures. The molecular processes that determine isoform-specific deposition of tau are however enigmatic. Here we show that acetylation of tau discriminates its isoform-specific aggregation. We reveal that acetylation strongly attenuates aggregation of four-repeat tau protein, but promotes amyloid formation of three-repeat tau. We further identify acetylation of lysine 298 as a hot spot for isoform-specific tau aggregation. Solid-state NMR spectroscopy demonstrates that amyloid fibrils formed by unmodified and acetylated three-repeat tau differ in structure indicating that site-specific acetylation modulates tau structure. The results implicate acetylation as a critical regulator that guides the selective aggregation of three-repeat tau and the development of tau isoform-specific neurodegenerative diseases.

The Deficits of Insulin Signal in Alzheimer's Disease and the Mechanisms of Vanadium Compounds in Curing AD

Vanadium is a well-known essential trace element, which usually exists in oxidation states in the form of a vanadate cation intracellularly. The pharmacological study of vanadium began with the discovery of its unexpected inhibitory effect on ATPase. Thereafter, its protective effects on β cells and its ability in glucose metabolism regulation were observed from the vanadium compound, leading to the application of vanadium compounds in clinical trials for curing diabetes. Alzheimer's disease (AD) is the most common dementia disease in elderly people. However, there are still no efficient agents for treating AD safely to date. This is mainly because of the complexity of the pathology, which is characterized by senile plaques composed of the amyloid-beta (Aβ) protein in the parenchyma of the brain and the neurofibrillary tangles (NFTs), which are derived from the hyperphosphorylated tau protein in the neurocyte, along with mitochondrial damage, and eventually the central nervous system (CNS) atrophy. AD was also illustrated as type-3 diabetes because of the observations of insulin deficiency and the high level of glucose in cerebrospinal fluid (CSF), as well as the impaired insulin signaling in the brain. In this review, we summarize the advances in applicating the vanadium compound to AD treatment in experimental research and point out the limitations of the current study using vanadium compounds in AD treatment. We hope this will help future studies in this field.

Tau pathology in neurodegenerative disease: disease mechanisms and therapeutic avenues

Tauopathies are disorders associated with tau protein dysfunction and insoluble tau accumulation in the brain at autopsy. Multiple lines of evidence from human disease, as well as nonclinical translational models, suggest that tau has a central pathologic role in these disorders, historically thought to be primarily related to tau gain of toxic function. However, a number of tau-targeting therapies with various mechanisms of action have shown little promise in clinical trials in different tauopathies. We review what is known about tau biology, genetics, and therapeutic mechanisms that have been tested in clinical trials to date. We discuss possible reasons for failures of these therapies, such as use of imperfect nonclinical models that do not predict human effects for drug development; heterogeneity of human tau pathologies which may lead to variable responses to therapy; and ineffective therapeutic mechanisms, such as targeting of the wrong tau species or protein epitope. Innovative approaches to human clinical trials can help address some of the difficulties that have plagued our field's development of tau-targeting therapies thus far. Despite limited clinical success to date, as we continue to refine our understanding of tau's pathogenic mechanism(s) in different neurodegenerative diseases, we remain optimistic that tau-targeting therapies will eventually play a central role in the treatment of tauopathies.

Mutations in α-synuclein, TDP-43 and tau prolong protein half-life through diminished degradation by lysosomal proteases

BACKGROUND

Autosomal dominant mutations in α-synuclein, TDP-43 and tau are thought to predispose to neurodegeneration by enhancing protein aggregation. While a subset of α-synuclein, TDP-43 and tau mutations has been shown to increase the structural propensity of these proteins toward self-association, rates of aggregation are also highly dependent on protein steady state concentrations, which are in large part regulated by their rates of lysosomal degradation. Previous studies have shown that lysosomal proteases operate precisely and not indiscriminately, cleaving their substrates at very specific linear amino acid sequences. With this knowledge, we hypothesized that certain coding mutations in α-synuclein, TDP-43 and tau may lead to increased protein steady state concentrations and eventual aggregation by an alternative mechanism, that is, through disrupting lysosomal protease cleavage recognition motifs and subsequently conferring protease resistance to these proteins.

RESULTS

To test this possibility, we first generated comprehensive proteolysis maps containing all of the potential lysosomal protease cleavage sites for α-synuclein, TDP-43 and tau. In silico analyses of these maps indicated that certain mutations would diminish cathepsin cleavage, a prediction we confirmed utilizing in vitro protease assays. We then validated these findings in cell models and induced neurons, demonstrating that mutant forms of α-synuclein, TDP-43 and tau are degraded less efficiently than wild type despite being imported into lysosomes at similar rates.

CONCLUSIONS

Together, this study provides evidence that pathogenic mutations in the N-terminal domain of α-synuclein (G51D, A53T), low complexity domain of TDP-43 (A315T, Q331K, M337V) and R1 and R2 domains of tau (K257T, N279K, S305N) directly impair their own lysosomal degradation, altering protein homeostasis and increasing cellular protein concentrations by extending the degradation half-lives of these proteins. These results also point to novel, shared, alternative mechanism by which different forms of neurodegeneration, including synucleinopathies, TDP-43 proteinopathies and tauopathies, may arise. Importantly, they also provide a roadmap for how the upregulation of particular lysosomal proteases could be targeted as potential therapeutics for human neurodegenerative disease.

Microtubule Cytoskeletal Network Alterations in a Transgenic Model of Tuberous Sclerosis Complex: Relevance to Autism Spectrum Disorders

Tuberous sclerosis complex (TSC) is a rare genetic multisystem disorder caused by loss-of-function mutations in the tumour suppressors TSC1/TSC2, both of which are negative regulators of the mammalian target of rapamycin (mTOR) kinase. Importantly, mTOR hyperactivity seems to be linked with the pathobiology of autism spectrum disorders (ASD). Recent studies suggest the potential involvement of microtubule (MT) network dysfunction in the neuropathology of "mTORopathies", including ASD. Cytoskeletal reorganization could be responsible for neuroplasticity disturbances in ASD individuals. Thus, the aim of this work was to study the effect of Tsc2 haploinsufficiency on the cytoskeletal pathology and disturbances in the proteostasis of the key cytoskeletal proteins in the brain of a TSC mouse model of ASD. Western-blot analysis indicated significant brain-structure-dependent abnormalities in the microtubule-associated protein Tau (MAP-Tau), and reduced MAP1B and neurofilament light (NF-L) protein level in 2-month-old male B6;129S4-Tsc2tm1Djk/J mice. Alongside, pathological irregularities in the ultrastructure of both MT and neurofilament (NFL) networks as well as swelling of the nerve endings were demonstrated. These changes in the level of key cytoskeletal proteins in the brain of the autistic-like TSC mice suggest the possible molecular mechanisms responsible for neuroplasticity alterations in the ASD brain.

HMGCS2-Induced Autophagic Degradation of Tau Involves Ketone Body and ANKRD24

BACKGROUND

Accumulation of hyperphosphorylated Tau (pTau) contributes to the formation of neurofibrillary tangles in Alzheimer's disease (AD), and targeting Tau/pTau metabolism has emerged as a therapeutic approach. We have previously reported that mitochondrial 3-hydroxy-3-methylglutaryl-COA synthase 2 (HMGCS2) is involved in AD by promoting autophagic clearance of amyloid-β protein precursor via ketone body-associated mechanism, whether HMGCS2 may also regulate Tau metabolism remains elusive.

OBJECTIVE

The present study was to investigate the role of HMGCS2 in Tau/p degradation.

METHODS

The protein levels of Tau and pTau including pT217 and pT181, as well as autophagic markers LAMP1 and LC3-II were assessed by western blotting. The differentially regulated genes by HMGCS2 were analyzed by RNA sequencing. Autophagosomes were assessed by transmission electron microscopy.

RESULTS

HMGCS2 significantly decreased Tau/pTau levels, which was paralleled by enhanced formation of autophagic vacuoles and prevented by autophagic regulators chloroquine, bafilomycin A1, 3-methyladenine, and rapamycin. Moreover, HMGCS2-induced alterations of LAMP1/LC3-II and Tau/pTau levels were mimicked by ketone body acetoacetate or β-hydroxybutyrate. Further RNA-sequencing identified ankyrin repeat domain 24 (ANKRD24) as a target gene of HMGCS2, and silencing of ANKRD24 reduced LAMP1/LC3-II levels, which was accompanied by the altered formation of autophagic vacuoles, and diminished the effect of HMGCS2 on Tau/pTau.

CONCLUSION

HMGCS2 promoted autophagic clearance of Tau/pTau, in which ketone body and ANKRD24 played an important role.

Tuberous sclerosis complex is associated with a novel human tauopathy

Tuberous sclerosis complex (TSC) is a neurogenetic disorder leading to epilepsy, developmental delay, and neurobehavioral dysfunction. The syndrome is caused by pathogenic variants in TSC1 (coding for hamartin) or TSC2 (coding for tuberin). Recently, we reported a progressive frontotemporal dementia-like clinical syndrome in a patient with a mutation in TSC1, but the neuropathological changes seen in adults with TSC with or without dementia have yet to be systematically explored. Here, we examined neuropathological findings in adults with TSC (n = 11) aged 30-58 years and compared them to age-matched patients with epilepsy unrelated to TSC (n = 9) and non-neurological controls (n = 10). In 3 of 11 subjects with TSC, we observed a neurofibrillary tangle-predominant "TSC tauopathy" not seen in epilepsy or non-neurological controls. This tauopathy was observed in the absence of pathological amyloid beta, TDP-43, or alpha-synuclein deposition. The neurofibrillary tangles in TSC tauopathy showed a unique pattern of post-translational modifications, with apparent differences between TSC1 and TSC2 mutation carriers. Tau acetylation (K274, K343) was prominent in both TSC1 and TSC2, whereas tau phosphorylation at a common phospho-epitope (S202) was observed only in TSC2. TSC tauopathy was observed in selected neocortical, limbic, subcortical, and brainstem sites and showed a 3-repeat greater than 4-repeat tau isoform pattern in both TSC1 and TSC2 mutation carriers, but no tangles were immunolabeled with MC1 or p62 antibodies. The findings suggest that individuals with TSC are at risk for a unique tauopathy in mid-life and that tauopathy pathogenesis may involve TSC1, TSC2, and related molecular pathways.

Protein acylation: mechanisms, biological functions and therapeutic targets

Metabolic reprogramming is involved in the pathogenesis of not only cancers but also neurodegenerative diseases, cardiovascular diseases, and infectious diseases. With the progress of metabonomics and proteomics, metabolites have been found to affect protein acylations through providing acyl groups or changing the activities of acyltransferases or deacylases. Reciprocally, protein acylation is involved in key cellular processes relevant to physiology and diseases, such as protein stability, protein subcellular localization, enzyme activity, transcriptional activity, protein-protein interactions and protein-DNA interactions. Herein, we summarize the functional diversity and mechanisms of eight kinds of nonhistone protein acylations in the physiological processes and progression of several diseases. We also highlight the recent progress in the development of inhibitors for acyltransferase, deacylase, and acylation reader proteins for their potential applications in drug discovery.

Defective proteostasis in induced pluripotent stem cell models of frontotemporal lobar degeneration

Impaired proteostasis is associated with normal aging and is accelerated in neurodegeneration. This impairment may lead to the accumulation of protein, which can be toxic to cells and tissue. In a subset of frontotemporal lobar degeneration with tau pathology (FTLD-tau) cases, pathogenic mutations in the microtubule-associated protein tau (MAPT) gene are sufficient to cause tau accumulation and neurodegeneration. However, the pathogenic events triggered by the expression of the mutant tau protein remain poorly understood. Here, we show that molecular networks associated with lysosomal biogenesis and autophagic function are disrupted in brains from FTLD-tau patients carrying a MAPT p.R406W mutation. We then used human induced pluripotent stem cell (iPSC)-derived neurons and 3D cerebral organoids from patients carrying the MAPT p.R406W mutation and CRISPR/Cas9, corrected controls to evaluate proteostasis. MAPT p.R406W was sufficient to induce morphological and functional deficits in the lysosomal pathway in iPSC-neurons. These phenotypes were reversed upon correction of the mutant allele with CRISPR/Cas9. Treatment with mTOR inhibitors led to tau degradation specifically in MAPT p.R406W neurons. Together, our findings suggest that MAPT p.R406W is sufficient to cause impaired lysosomal function, which may contribute to disease pathogenesis and serve as a cellular phenotype for drug screening.

Shared mechanisms of neural circuit disruption in tuberous sclerosis across lifespan: Bridging neurodevelopmental and neurodegenerative pathology

Tuberous Sclerosis (TS) is a rare genetic disorder manifesting with multiple benign tumors impacting the function of vital organs. In TS patients, dominant negative mutations in TSC1 or TSC2 increase mTORC1 activity. Increased mTORC1 activity drives tumor formation, but also severely impacts central nervous system function, resulting in infantile seizures, intractable epilepsy, and TS-associated neuropsychiatric disorders, including autism, attention deficits, intellectual disability, and mood disorders. More recently, TS has also been linked with frontotemporal dementia. In addition to TS, accumulating evidence implicates increased mTORC1 activity in the pathology of other neurodevelopmental and neurodegenerative disorders. Thus, TS provides a unique disease model to address whether developmental neural circuit abnormalities promote age-related neurodegeneration, while also providing insight into the therapeutic potential of mTORC1 inhibitors for both developing and degenerating neural circuits. In the following review, we explore the ability of both mouse and human brain organoid models to capture TS pathology, elucidate disease mechanisms, and shed light on how neurodevelopmental alterations may later contribute to age-related neurodegeneration.

Oxidative Stress in Tauopathies: From Cause to Therapy

Oxidative stress (OS) is the result of an imbalance between the production of reactive oxygen species (ROS) and the antioxidant capacity of cells. Due to its high oxygen demand, the human brain is highly susceptible to OS and, thus, it is not a surprise that OS has emerged as an essential component of the pathophysiology of several neurodegenerative diseases, including tauopathies. Tauopathies are a heterogeneous group of age-related neurodegenerative disorders characterized by the deposition of abnormal tau protein in the affected neurons. With the worldwide population aging, the prevalence of tauopathies is increasing, but effective therapies have not yet been developed. Since OS seems to play a key role in tauopathies, it has been proposed that the use of antioxidants might be beneficial for tau-related neurodegenerative diseases. Although antioxidant therapies looked promising in preclinical studies performed in cellular and animal models, the antioxidant clinical trials performed in tauopathy patients have been disappointing. To develop effective antioxidant therapies, the molecular mechanisms underlying OS in tauopathies should be completely understood. Here, we review the link between OS and tauopathies, emphasizing the causes of OS in these diseases and the role of OS in tau pathogenesis. We also summarize the antioxidant therapies proposed as a potential treatment for tauopathies and discuss why they have not been completely translated to clinical trials. This review aims to provide an integrated perspective of the role of OS and antioxidant therapies in tauopathies. In doing so, we hope to enable a more comprehensive understanding of OS in tauopathies that will positively impact future studies.

Biological aging processes underlying cognitive decline and neurodegenerative disease

Alzheimer's disease and related dementias (ADRD) are among the top contributors to disability and mortality in later life. As with many chronic conditions, aging is the single most influential factor in the development of ADRD. Even among older adults who remain free of dementia throughout their lives, cognitive decline and neurodegenerative changes are appreciable with advancing age, suggesting shared pathophysiological mechanisms. In this Review, we provide an overview of changes in cognition, brain morphology, and neuropathological protein accumulation across the lifespan in humans, with complementary and mechanistic evidence from animal models. Next, we highlight selected aging processes that are differentially regulated in neurodegenerative disease, including aberrant autophagy, mitochondrial dysfunction, cellular senescence, epigenetic changes, cerebrovascular dysfunction, inflammation, and lipid dysregulation. We summarize research across clinical and translational studies to link biological aging processes to underlying ADRD pathogenesis. Targeting fundamental processes underlying biological aging may represent a yet relatively unexplored avenue to attenuate both age-related cognitive decline and ADRD. Collaboration across the fields of geroscience and neuroscience, coupled with the development of new translational animal models that more closely align with human disease processes, is necessary to advance novel therapeutic discovery in this realm.

Altered Cerebrospinal Fluid Exosomal microRNA Levels in Young-Onset Alzheimer's Disease and Frontotemporal Dementia

Background:

micro-RNAs (miRNAs) are stable, small, non-coding RNAs enriched in exosomes. Their variation in levels according to different disease etiologies have made them a promising diagnostic biomarker for neurodegenerative diseases such as Alzheimer’s disease (AD). Altered expression of miR-320a, miR-328-3p, and miR-204-5p have been reported in AD and frontotemporal dementia (FTD).

Objective:

To determine their reliability, we aimed to examine the expression of three exosomal miRNAs isolated from cerebrospinal fluid (CSF) of patients with young-onset AD and FTD (< 65 years), correlating with core AD biomarkers and cognitive scores.

Methods:

Exosomes were first isolated from CSF samples of 48 subjects (8 controls, 28 AD, and 12 FTD), followed by RNA extraction and quantitative PCR to measure the expression of miR-320a, miR-328-3p, and miR-204-5p.

Results:

Expression of all three markers (miR-320a (p = 0.005), miR-328-3p (p = 0.049), and miR-204-5p (p = 0.036)) were significantly lower in AD versus controls. miR-320a was reduced in FTD versus controls (p = 0.049) and miR-328-3p was lower in AD versus FTD (p = 0.054). Notably, lower miR-328-3p levels could differentiate AD from FTD and controls with an AUC of 0.702, 95% CI: 0.534– 0.870, and showed significant correlation with lower CSF Aβ₄₂ levels (r = 0.359, p = 0.029). Pathway enrichment analysis identified potential targets of miR-328-3p implicated in the AMPK signaling pathway linked to amyloid-β and tau metabolism in AD.

Conclusion:

Overall, we demonstrated miR-320a and miR-204-5p as reliable biomarkers for AD and FTD and report miR-328-3p as a novel AD biomarker.