AbstractAgeing and Alzheimer’s disease (AD) can affect glial and neuronal stiffness and the extracellular brain environment, including the extracellular matrix. The presence of mechanoreceptors such as Piezo1 in neurons and glia makes these cells highly mechanosensitive, with the amount of Piezo1 expressed increasing in age and in close proximity to amyloid plaques.Therefore, age-related and pathological alterations of the mechanical properties in the hippocampus may contribute to altered mechanical signalling which is seen in Alzheimer’s disease.
This work characterises the mechanical properties of young (3 month) and aged (18 month) wild-type C57Bl/6 mouse hippocampus, in ex vivo brain slices, at a high resolution of 30µm. In addition, the stiffness of aged (17 month) APPNL-G-F mouse hippocampus was also measured in order to investigate the effect of amyloid pathology on hippocampal mechanobiology.
In the APPNL-G-F mice there is a significant softening of the CA1 stratum oriens and CA1 stratum pyramidale compared to young and aged wild-type mice. In APPNL-G-F mice the the CA1 stratum radiatum is also softer compared to aged wild-type mice. We also observe a stiffening of the hilus in aged wild-type mice compared to young wild-type mice. The dentate gyrus granule cell layer also becomes significantly stiffer in aged wild-type mice compared to in young wild-type mice, and interestingly this stiffening effect is absent in the aged APPNL-G-F mice.
In this work we also developed a method of gathering reliable and consistent mechanical data from ex vivo tissue using atomic force microscopy. We also discovered that the stiffness of the mouse hippocampus varies along the dorsal-ventral axis of the hippocampus, with dorsal CA1 displaying increased stiffness compared to ventral.
The effect of AB42 on primary mouse microglia was also investigated using atomic force microscopy imaging and force-spectroscopy, and live-cell microscopy. We find that there is no significant effect on the appearance of the microglial membrane surface nor measured stiffness of microglia that have internalised AB42. The BV2 microglial cell line does display a significantly reduced cell velocity when exposed to AB42, and this decrease is restored by mechanoreceptor antagonist GsMTx4. GsMTx4 also enhances microglial phagocytosis.
In conclusion, our results show that tissue stiffness in hippocampi of a mouse model of Alzheimer’s disease is significantly reduced compared to healthy wild-types. This work also shows regional stiffening of the dentate gyrus with healthy ageing. This work also shows that GsMTx4 is able to modulate microglial activity.
|Date of Award||2021|
|Supervisor||Graham Sheridan (Supervisor), Mark Yeoman (Supervisor), Marcus Allen (Supervisor), Greg Scutt (Supervisor) & Andrei Lukashkin (Supervisor)|