The Motor Neuron Disease Mouse Model Hsod1-G93a Presents a Non-Canonical Profile of Senescence Biomarkers in the Spinal Cord

Recent evidence demonstrates a pathological role for senescent cells in Alzheimer’s and Parkinson’s diseases. The present study aimed to show senescence mechanisms including senescence-associated secretory phenotype (SASP) in the familial amyotrophic lateral sclerosis (ALS) transgenic mouse model hSOD1-G93A. We evaluated, as senescence biomarkers, the expression of p16 and p21 with reverse-transcriptase quantitative PCR (RT-qPCR), immunofluorescence (IF), and immunohistochemistry (IHC), as well as the senescence-associated b galactosidase (SA-b-gal) activity in the lumbar spinal cords (LSC) of this model. As SASP markers, we quantified the mRNA levels of Il1a, Il6, Ifna, and Ifnb. Furthermore, we explored if an alteration of alternative splicing is associated with senescence phenomena in this model. Thus, we quantified the Adipor2 cryptic exon inclusion levels, a specific splicing variant repressed by TAR-DNA binding of 43 kDa (TDP-43), using RT-qPCR. Our results show an atypical senescence-profile in LSC from transgenic mice, increasing p16 and p21 mRNA and protein levels in glial cells with a mostly cytoplasmic pattern, without the canonical increase in SA-beta-gal activity in these cells. Consistent with enhanced SASP, there is an increase in Il1a and Il6 expression. Also, TDP-43 splicing activity is compromised in this ALS model, in a direct relationship with the increase in p16 expression. However, senolytic drug Navitoclax -with reported benefits in Alzheimer and Parkinson disease mouse models - does not alter the present model’s disease progression. Navitoclax neither eliminates cells expressing senescence and nor represses the expression of SASP related genes. Globally, our findings support the existence of a non-canonical profile of senescence biomarkers in the LSC of the ALS model hSOD1-G93A.