The DNA and RNA processing protein TDP-43 undergoes both functional and pathogenic aggregation. Functional TDP-43 aggregates form reversible, transient species such as nuclear bodies, stress ...granules, and myo-granules. Pathogenic, irreversible TDP-43 aggregates form in amyotrophic lateral sclerosis and other neurodegenerative conditions. Here we find the features of TDP-43 fibrils that confer both reversibility and irreversibility by determining structures of two segments reported to be the pathogenic cores of human TDP-43 aggregation: SegA (residues 311-360), which forms three polymorphs, all with dagger-shaped folds; and SegB A315E (residues 286-331 containing the amyotrophic lateral sclerosis hereditary mutation A315E), which forms R-shaped folds. Energetic analysis suggests that the dagger-shaped polymorphs represent irreversible fibril structures, whereas the SegB polymorph may participate in both reversible and irreversible fibrils. Our structures reveal the polymorphic nature of TDP-43 and suggest how the A315E mutation converts the R-shaped polymorph to an irreversible form that enhances pathology.
A head-to-head comparison was performed between vascular endothelial growth factor blockade and laser for treatment of diabetic macular edema (DME).
Two similarly designed, double-masked, randomized, ...phase 3 trials, VISTA(DME) and VIVID(DME).
We included 872 patients (eyes) with type 1 or 2 diabetes mellitus who presented with DME with central involvement.
Eyes received either intravitreal aflibercept injection (IAI) 2 mg every 4 weeks (2q4), IAI 2 mg every 8 weeks after 5 initial monthly doses (2q8), or macular laser photocoagulation.
The primary efficacy endpoint was the change from baseline in best-corrected visual acuity (BCVA) in Early Treatment Diabetic Retinopathy Study (ETDRS) letters at week 52. Secondary efficacy endpoints at week 52 included the proportion of eyes that gained ≥ 15 letters from baseline and the mean change from baseline in central retinal thickness as determined by optical coherence tomography.
Mean BCVA gains from baseline to week 52 in the IAI 2q4 and 2q8 groups versus the laser group were 12.5 and 10.7 versus 0.2 letters (P < 0.0001) in VISTA, and 10.5 and 10.7 versus 1.2 letters (P < 0.0001) in VIVID. The corresponding proportions of eyes gaining ≥ 15 letters were 41.6% and 31.1% versus 7.8% (P < 0.0001) in VISTA, and 32.4% and 33.3% versus 9.1% (P < 0.0001) in VIVID. Similarly, mean reductions in central retinal thickness were 185.9 and 183.1 versus 73.3 μm (P < 0.0001) in VISTA, and 195.0 and 192.4 versus 66.2 μm (P < 0.0001) in VIVID. Overall incidences of ocular and nonocular adverse events and serious adverse events, including the Anti-Platelet Trialists' Collaboration-defined arterial thromboembolic events and vascular deaths, were similar across treatment groups.
At week 52, IAI demonstrated significant superiority in functional and anatomic endpoints over laser, with similar efficacy in the 2q4 and 2q8 groups despite the extended dosing interval in the 2q8 group. In general, IAI was well-tolerated.
α-Synuclein (aSyn) fibrillar polymorphs have distinct in vitro and in vivo seeding activities, contributing differently to synucleinopathies. Despite numerous prior attempts, how polymorphic aSyn ...fibrils differ in atomic structure remains elusive. Here, we present fibril polymorphs from the full-length recombinant human aSyn and their seeding capacity and cytotoxicity in vitro. By cryo-electron microscopy helical reconstruction, we determine the structures of the two predominant species, a rod and a twister, both at 3.7 Å resolution. Our atomic models reveal that both polymorphs share a kernel structure of a bent β-arch, but differ in their inter-protofilament interfaces. Thus, different packing of the same kernel structure gives rise to distinct fibril polymorphs. Analyses of disease-related familial mutations suggest their potential contribution to the pathogenesis of synucleinopathies by altering population distribution of the fibril polymorphs. Drug design targeting amyloid fibrils in neurodegenerative diseases should consider the formation and distribution of concurrent fibril polymorphs.
Deposits of amyloid fibrils of α-synuclein are the histological hallmarks of Parkinson's disease, dementia with Lewy bodies and multiple system atrophy, with hereditary mutations in α-synuclein ...linked to the first two of these conditions. Seeing the changes to the structures of amyloid fibrils bearing these mutations may help to understand these diseases. To this end, we determined the cryo-EM structures of α-synuclein fibrils containing the H50Q hereditary mutation. We find that the H50Q mutation results in two previously unobserved polymorphs of α-synuclein: narrow and wide fibrils, formed from either one or two protofilaments, respectively. These structures recapitulate conserved features of the wild-type fold but reveal new structural elements, including a previously unobserved hydrogen-bond network and surprising new protofilament arrangements. The structures of the H50Q polymorphs help to rationalize the faster aggregation kinetics, higher seeding capacity in biosensor cells and greater cytotoxicity that we observe for H50Q compared to wild-type α-synuclein.
To assess long-term outcomes 7 to 8 years after initiation of intensive ranibizumab therapy in exudative age-related macular degeneration (AMD) patients.
Multicenter, noninterventional cohort study.
...Sixty-five AMD patients originally treated with ranibizumab in the phase 3 Anti-VEGF Antibody for the Treatment of Predominantly Classic Choroidal Neovascularization in AMD (ANCHOR) trial, Minimally Classic/Occult Trial of the Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular AMD (MARINA) trial, and Open-Label Extension Trial of Ranibizumab for Choroidal Neovascularization Secondary to Age-Related Macular Degeneration (HORIZON).
Fourteen clinical trial sites recruited their original subjects for a return evaluation. Individual subject comparisons were obtained from the ANCHOR, MARINA, and HORIZON databases.
The primary end point was percentage with best-corrected visual acuity (BCVA) of 20/70 or better; secondary outcomes included mean change in letter score compared with previous time points and anatomic results on fluorescein angiography, spectral-domain ocular coherence tomography (OCT), and fundus autofluorescence (FAF).
At a mean of 7.3 years (range, 6.3-8.5 years) after entry into ANCHOR or MARINA, 37% of study eyes met the primary end point of 20/70 or better BCVA, with 23% achieving a BCVA of 20/40 or better. Thirty-seven percent of study eyes had BCVA of 20/200 or worse. Forty-three percent of study eyes had a stable or improved letter score (≥0-letter gain) compared with ANCHOR or MARINA baseline measurements, whereas 34% declined by 15 letters or more, with overall a mean decline of 8.6 letters (P<0.005). Since exit from the HORIZON study, study eyes had received a mean of 6.8 anti-vascular endothelial growth factor (VEGF) injections during the mean 3.4-year interval; a subgroup of patients who received 11 or more anti-VEGF injections had a significantly better mean gain in letter score since HORIZON exit (P<0.05). Active exudative disease was detected by spectral-domain OCT in 68% of study eyes, and 46% were receiving ongoing ocular anti-VEGF treatments. Macular atrophy was detected by FAF in 98% of eyes, with a mean area of 9.4 mm(2); the area of atrophy correlated significantly with poor visual outcome (P<0.0001).
Approximately 7 years after ranibizumab therapy in the ANCHOR or MARINA trials, one third of patients demonstrated good visual outcomes, whereas another third had poor outcomes. Compared with baseline, almost half of eyes were stable, whereas one third declined by 15 letters or more. Even at this late stage in the therapeutic course, exudative AMD patients remain at risk for substantial visual decline.
Human islet amyloid polypeptide (hIAPP) functions as a glucose-regulating hormone but deposits as amyloid fibrils in more than 90% of patients with type II diabetes (T2D). Here we report the cryo-EM ...structure of recombinant full-length hIAPP fibrils. The fibril is composed of two symmetrically related protofilaments with ordered residues 14-37. Our hIAPP fibril structure (i) supports the previous hypothesis that residues 20-29 constitute the core of the hIAPP amyloid; (ii) suggests a molecular mechanism for the action of the hIAPP hereditary mutation S20G; (iii) explains why the six residue substitutions in rodent IAPP prevent aggregation; and (iv) suggests regions responsible for the observed hIAPP cross-seeding with β-amyloid. Furthermore, we performed structure-based inhibitor design to generate potential hIAPP aggregation inhibitors. Four of the designed peptides delay hIAPP aggregation in vitro, providing a starting point for the development of T2D therapeutics and proof of concept that the capping strategy can be used on full-length cryo-EM fibril structures.
To evaluate the safety and efficacy of dexamethasone intravitreal implant (Ozurdex, DEX implant) 0.7 and 0.35 mg in the treatment of patients with diabetic macular edema (DME).
Two randomized, ...multicenter, masked, sham-controlled, phase III clinical trials with identical protocols were conducted. Data were pooled for analysis.
Patients (n = 1048) with DME, best-corrected visual acuity (BCVA) of 20/50 to 20/200 Snellen equivalent, and central retinal thickness (CRT) of ≥300 μm by optical coherence tomography.
Patients were randomized in a 1:1:1 ratio to study treatment with DEX implant 0.7 mg, DEX implant 0.35 mg, or sham procedure and followed for 3 years (or 39 months for patients treated at month 36) at ≤40 scheduled visits. Patients who met retreatment eligibility criteria could be retreated no more often than every 6 months.
The predefined primary efficacy endpoint for the United States Food and Drug Administration was achievement of ≥15-letter improvement in BCVA from baseline at study end. Safety measures included adverse events and intraocular pressure (IOP).
Mean number of treatments received over 3 years was 4.1, 4.4, and 3.3 with DEX implant 0.7 mg, DEX implant 0.35 mg, and sham, respectively. The percentage of patients with ≥15-letter improvement in BCVA from baseline at study end was greater with DEX implant 0.7 mg (22.2%) and DEX implant 0.35 mg (18.4%) than sham (12.0%; P ≤ 0.018). Mean average reduction in CRT from baseline was greater with DEX implant 0.7 mg (−111.6 μm) and DEX implant 0.35 mg (−107.9 μm) than sham (−41.9 μm; P < 0.001). Rates of cataract-related adverse events in phakic eyes were 67.9%, 64.1%, and 20.4% in the DEX implant 0.7 mg, DEX implant 0.35 mg, and sham groups, respectively. Increases in IOP were usually controlled with medication or no therapy; only 2 patients (0.6%) in the DEX implant 0.7 mg group and 1 (0.3%) in the DEX implant 0.35 mg group required trabeculectomy.
The DEX implant 0.7 mg and 0.35 mg met the primary efficacy endpoint for improvement in BCVA. The safety profile was acceptable and consistent with previous reports.
hnRNPA2 is a human ribonucleoprotein (RNP) involved in RNA metabolism. It forms fibrils both under cellular stress and in mutated form in neurodegenerative conditions. Previous work established that ...the C-terminal low-complexity domain (LCD) of hnRNPA2 fibrillizes under stress, and missense mutations in this domain are found in the disease multisystem proteinopathy (MSP). However, little is known at the atomic level about the hnRNPA2 LCD structure that is involved in those processes and how disease mutations cause structural change. Here we present the cryo-electron microscopy (cryoEM) structure of the hnRNPA2 LCD fibril core and demonstrate its capability to form a reversible hydrogel in vitro containing amyloid-like fibrils. Whereas these fibrils, like pathogenic amyloid, are formed from protein chains stacked into β-sheets by backbone hydrogen bonds, they display distinct structural differences: the chains are kinked, enabling non-covalent cross-linking of fibrils and disfavoring formation of pathogenic steric zippers. Both reversibility and energetic calculations suggest these fibrils are less stable than pathogenic amyloid. Moreover, the crystal structure of the disease-mutation-containing segment (D290V) of hnRNPA2 suggests that the replacement fundamentally alters the fibril structure to a more stable energetic state. These findings illuminate how molecular interactions promote protein fibril networks and how mutation can transform fibril structure from functional to a pathogenic form.
Alzheimer's disease (AD) is the consequence of neuronal death and brain atrophy associated with the aggregation of protein tau into fibrils. Thus disaggregation of tau fibrils could be a therapeutic ...approach to AD. The small molecule EGCG, abundant in green tea, has long been known to disaggregate tau and other amyloid fibrils, but EGCG has poor drug-like properties, failing to fully penetrate the brain. Here we have cryogenically trapped an intermediate of brain-extracted tau fibrils on the kinetic pathway to EGCG-induced disaggregation and have determined its cryoEM structure. The structure reveals that EGCG molecules stack in polar clefts between the paired helical protofilaments that pathologically define AD. Treating the EGCG binding position as a pharmacophore, we computationally screened thousands of drug-like compounds for compatibility for the pharmacophore, discovering several that experimentally disaggregate brain-derived tau fibrils in vitro. This work suggests the potential of structure-based, small-molecule drug discovery for amyloid diseases.
Aggregation of α-synuclein is a defining molecular feature of Parkinson’s disease, Lewy body dementia, and multiple systems atrophy. Hereditary mutations in α-synuclein are linked to both Parkinson’s ...disease and Lewy body dementia; in particular, patients bearing the E46K disease mutation manifest a clinical picture of parkinsonism and Lewy body dementia, and E46K creates more pathogenic fibrils in vitro. Understanding the effect of these hereditary mutations on α-synuclein fibril structure is fundamental to α-synuclein biology. We therefore determined the cryo-electron microscopy (cryo-EM) structure of α-synuclein fibrils containing the hereditary E46K mutation. The 2.5-Å structure reveals a symmetric double protofilament in which the molecules adopt a vastly rearranged, lower energy fold compared to wild-type fibrils. We propose that the E46K misfolding pathway avoids electrostatic repulsion between K46 and K80, a residue pair which form the E46-K80 salt bridge in the wild-type fibril structure. We hypothesize that, under our conditions, the wild-type fold does not reach this deeper energy well of the E46K fold because the E46-K80 salt bridge diverts α-synuclein into a kinetic trap—a shallower, more accessible energy minimum. The E46K mutation apparently unlocks a more stable and pathogenic fibril structure.
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