Fig 2: mGluR1 PAM treatment impacts active zone length.A Representative EM images show synaptic structures in WT mice treated with mGluR1 PAM Ro677467 together with Lanabecestat or Verubecestat. B, C Active zone lengths and their cumulative frequency histogram were quantified and compared among four treated groups and WT like above and show a relatively increase in size in the animals treated with BACE1 inhibitors alone or in combination with PAMs. D Number of docked vesicles (within 5 nm from presynaptic membrane) per active zone is also significantly decreased. E Synaptic vesicle distribution up to 200 nm distance from presynaptic membrane of active zone is also impacted in the groups with BACE1 inhibitor treatments (N = 60, ***P < 0.001, Student’s t test).

Fig 3: Model of the interactions between mGluR5, PrPC, and anti-PrP antibodies.(A) In untreated neurons, mGluR5-PrPC complexes are distributed within and outside spines. Upon exposure to prion-mimetic antibodies (B), mGluR5 translocates to the spine, where it may enhance neurotoxicity by contributing to a Ca2+ overload. (C) Exposure to POM2, in contrast, engages the N-terminal “flexible tail” of PrPC, thereby making it unavailable to mGluR5. Consequently, mGluR5-PrPC (and possibly also mGluR1-PrPC) complexes do not translocate to spines. As a result, POM2 affords functional neuroprotection similarly to mGluR5 antagonists. (D) We speculate that prion infection may trigger topological rearrangements similar to those observed after POM1 exposure.

Fig 4: mGluR1-positive allosteric modulator ameliorates defects in learning and memory in BACE1-null mice.A, B BACE1-null mice treated with Ro0711401 were first tested on the Y-maze task in comparison to mock-treated controls. Total numbers of arm entry were shown in A, and changes in percentage of spontaneous alternation were not obvious among three groups shown in B. BACE1-null mice exhibited high numbers of entry. This increase was reverted by Ro0711401 treatment. C–E BACE1-null mice with or without Ro0711401 were tested in an open field. Significant reversions in the total distance covered (C) and average speed (D) were observed in BACE1-null mice treated with Ro0711401 compared to mock treatment. E Heat maps showing that mice treated with Ro0711401 explored both the corners and the center of the open-field arena similar to WT, while BACE1-null mice spent more time in the corners. The anxiety seen in BACE1-null mice was mitigated by PAM treatment. F–J Mice were tested in the Morris water maze. In the habitation (F) and training (G), BACE1-null mice showed defects in learning, taking much longer time compared to WT and BACE1-null treated with Ro0711401. H On day 9 in the Morris water maze test, the number of entries made to the platform quadrant looking for the hidden platform were visibly increased when BACE1-null mice were treated with Ro0711401, and this is more obvious in the representative track plots (I). N = 12 each in WT and BACE1-/- group and 10 in BACE1-/- with Ro0711401 treatment; **P < 0.01; ***P < 0.01; Student’s t test. Values are expressed as mean ± SEM. J LTP was recorded on horizontal hippocampal slices from 16-month-old mice as described above after treatment with Ro0711401 for ~50 days. The LTP in the Ro0711401 treatment group was comparable to WT in this age group and both were significantly higher than BACE1-null mice at 16 months (N = 7 for BACE1-/-, and N = 10 for BACE1-/- + Ro0711401, N = 8 for WT; **P < 0.01, unpaired Student’s t test).

Fig 5: BACE1 deficiency causes reductions in synaptic proteins.A Hippocampal synaptosomes prepared from 15- and 25-month-old mice were examined on the blot using antibodies as indicated. While levels of most synaptic proteins were not significantly differed between wild type (WT) and BACE1-null samples, mGluR1 and PSD-95 were clearly reduced in BACE1-null samples. B Bar graphs showing a significant change in levels of mGluR1 and PSD-95 in aging mice (N = 3 independent experiments, *P < 0.05; Student’s t test). C Brain lysates from 12-month-old WT and BACE1-null mice were analyzed by antibodies as specified on the western blot. Reduction of complexin, VAMP, and synaptophysin was noted, while BACE1 substrate neuregulin-1 (Nrg1) was elevated due to abolished cleavage. D Bar graphs showed statistical significance (N = 4, **P < 0.01, *P < 0.05, Student’s t test).