Miller, W. T. | Search bioRxiv

bioRxiv2024

A microglia clonal inflammatory disorder in Alzheimer's Disease

Somatic genetic heterogeneity resulting from post-zygotic DNA mutations is widespread in human tissues and can cause diseases, however few studies have investigated its role in neurodegenerative processes such as Alzheimers Disease (AD). Here we report the selective enrichment of microglia clones carrying pathogenic variants, that are not present in neuronal, glia/stromal cells, or blood, from patients with AD in comparison to age-matched controls. Notably, microglia-specific AD-associated variants preferentially target the MAPK pathway, including recurrent CBL ring-domain mutations. These variants activate ERK and drive a microglia transcriptional program characterized by a strong neuro-inflammatory response, both in vitro and in patients. Although the natural history of AD-associated microglial clones is difficult to establish in human, microglial expression of a MAPK pathway activating variant was previously shown to cause neurodegeneration in mice, suggesting that AD-associated neuroinflammatory microglial clones may contribute to the neurodegenerative process in patients. One-Sentence SummaryA subset of Alzheimer Disease patients carry mutant microglia somatic clones which promote neuro-inflammation.

neuroscience↗

bioRxiv2021

Phospholipid exchange shows insulin receptor activity is supported by both the propensity to form wide bilayers and ordered domains (rafts)

Using efficient methyl-alpha-cyclodextrin mediated lipid exchange, we studied the effect of altering plasma membrane outer leaflet phospholipid composition upon the activity of insulin receptor (IR) in mammalian cells. After substitution of endogenous lipids with lipids having an ability to form liquid ordered (Lo) domains (sphingomyelins) or liquid disordered (Ld) domains (unsaturated phosphatidylcholines (PCs)), we found that the propensity of lipids to form ordered domains is required for high IR activity. Additional substitution experiments using a series of saturated PCs showed that IR activity increased substantially with increasing acyl chain length. Increasing acyl chain length increases both bilayer width and the propensity to form ordered domains. To distinguish the effects of membrane width and domain formation, we incorporated purified IR into alkyl maltoside micelles with increasing hydrocarbon lengths. IR activity increases with increased chain length, but more modestly than by increasing lipid acyl chain length in cells. This suggests that the ability to form Lo domains as well as wide bilayer width contributes to increased IR activity. Inhibition of phosphatases with sodium orthovanadate showed that some of the lipid dependence of IR activity upon lipid structure reflected protection from phosphatases by lipids that support Lo domain formation. The results are consistent with a model in which a combination of bilayer width and ordered domain formation modulate IR activity via effects upon IR conformation and accessibility to phosphatases. SignificanceThis study shows how methyl--cyclodextrin mediated lipid exchange can be used to probe the influence of lipid structure upon the functioning of a transmembrane receptor. Plasma membranes having a propensity to form Lo domains are required to support a high level of IR activity. The studies indicate this may reflect an effect of lipid environment upon IR domain localization, which in turn alters its conformation and vulnerability to phosphatases. Alterations in lipid composition could conceivably regulate IR activity in vivo.

cell biology↗