| dc.description.abstract | Manganese is an essential micronutrient, required for the activity of many enzymes. Our lab has established that cellular and mouse models of Huntington’s Disease (HD) exhibit reduced striatal Mn bioavailability. This deficiency manifests as defects in Mn-responsive arginase and ATM/p53 pathways. Here we posit that reduced Mn bioavailability may also incur defects in IGF signaling and autophagy- Mn-responsive processes which are perturbed in HD and have been therapeutically targeted in HD models. Utilizing STHdh, immortalized striatal neuroprogenitors and hiPSC-dervied striatal-like neuroprogenitors, we found that Mn-induced IGF signaling (p-IGFR/IR, p-AKT) and autophagy (LC3-II, p62) are dampened in HD cell models- the former of which is remedied via co-treatment with Mn and IGF. While previous studies have shown Mn can activate tyrosine kinases activity of p-IGFR/IR in biochemical or non-living systems, we have found that biologically relevant concentrations of Mn can increase p-IGFR/IR phosphorylation and maximal downstream phosphorylation of AKT in cells (higher than saturating concentrations of IGF or Mg alone). I have shown previously that the majority of Mn-induced AKT is dependent on PI3K, though it was still unknown which kinase upstream of PI3K was the initial site-of-action of Mn. Utilizing a panel of small molecules inhibitors, we determined that >80% of Mn-induced p-AKT is dependent on direct interactions with the IGFR/IR receptors as opposed to other, upstream activators. While glucose uptake, a downstream process mediated by AKT and perturbed in early HD pathology, is greatly reduced in HD STHdh cells, Mn treatment incurred a significant increase in glucose uptake. Using TEM, we found Mn treatment also ameliorated the previously reported autophagy-dependent cargo recognition failure in HD cells, reducing the number of empty autophagosomes to WT levels. Lastly, in HEK293 cells expressing 72Q-HTT-GFP, Mn treatment alone did not affect the number of mutant HTT aggregates. However, co-treatment with chloroquine, an autophagy inhibitor, and Mn increased the number of mutant HTT aggregates suggesting Mn may increase aggregate-autophagosome association. Together, these data suggest that striatal Mn-deficiency may contribute to defective IGF signaling and autophagy in HD. Additionally, these studies provide proof-of-principle support for increasing bioavailable Mn to restore HD phenotypes and pathology. | |
