Frontotemporal Dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS) are neurodegenerative diseases characterized by abnormal accumulation of TDP-43, an ubiquitous protein critically involved in RNA metabolism. These diseases caused by proteostatic perturbations commonly trigger the Unfolded Protein Response (UPR). This study investigates the relationship between the key UPR component ATF4 and TDP-43 in physiological and pathological contexts, using immunocytochemistry in SH-SY5Y and N2a neuroblastoma cells. Activation of the PERK UPR pathway leads to increased ATF4 translation. Single-cell SH-SY5Y analysis revealed a statistically significant positive correlation between the endogenous nuclear TDP-43 and ATF4 levels. The slope is twice as steep in cells treated with the ER stress inducer tunicamycin (Tn) compared to controls. Nuclear ATF4 showed significant colocalization with TDP-43 (Manders coefficient, M = 0.66), and Tn treatment significantly increased this colocalization (M = 0.72). These findings suggest a potential link between TDP-43 levels and activation of the ATF4-mediated stress response. We also overexpressed wild-type (WT) nuclear TDP-43 or a cytoplasmic form of TDP-43 (ΔNLS) to recapitulate key ALS/FTD features in N2a cells. Both variants led to a significant increase in endogenous ATF4 levels (WT = 1.6 fold; ΔNLS = 2.0 fold), indicating activation of the ATF4/PERK UPR branch. Overall, these results help understand the role of UPR activation in ALS/FTD.