Expression analysis of protein homeostasis pathways in the peripheral blood mononuclear cells of sporadic amyotrophic lateral sclerosis patients

Misfolded protein aggregates are the hallmark of Amyotrophic Lateral Sclerosis (ALS) which suggests involvement of protein homeostasis pathways in etiology of ALS. However, status of protein homeostasis in peripheral blood of ALS is not well established. We analyzed expression levels of key genes of proteostasis pathways in peripheral blood mononuclear cells (PBMCs) of sporadic ALS (sALS) patients and healthy controls. Increased protein carbonylation was observed in patients reflecting oxidative damage in PBMCs. We observed increased transcript and protein levels of GRP78 suggesting Endoplasmic reticulum (ER) insult to cells. Further, significant upregulation of spliced XBP1 and two stress sensors: IRE1α/ERN1 and ATF6 indicated induction of unfolded protein response (UPR). Genes involved in autophagosome initiation (ULK1, ULK2, ATG13); nucleation and elongation (BECLIN1, ATG7, ATG16L1, ATG5, ATG10) and vesicular trafficking genes were significantly increased in patients. Increased lipidation of LC3 validated induction of autophagy. Accumulation of low molecular weight ubiquitinated proteins in patients suggested deregulation of proteasome (UPS) pathway. In addition, cytosolic chaperones (HSP70 and HSP27) and HSF1 were elevated in patients. Increased TDP43 indicated role of TDP43 in disease pathology. Our findings suggest that there is oxidative insult and upregulation of UPR, vesicular trafficking and autophagy in PBMCs of sALS patients.