Biallelic mutations in the death domain of PIDD1 impair caspase-2 activation and are associated with intellectual disability

Abstract

PIDD1 encodes p53-Induced Death Domain protein 1, which acts as a sensor surveilling centrosome numbers and p53 activity in mammalian cells. Early results also suggest a role in DNA damage response where PIDD1 may act as a cell-fate switch, through interaction with RIP1 and NEMO/IKKg, activating NF-κB signaling for survival, or as an apoptosis-inducing protein by activating caspase-2. Biallelic truncating mutations in CRADD—the protein bridging PIDD1 and caspase-2—have been reported in intellectual disability (ID), and in a form of lissencephaly. Here, we identified five families with ID from Iran, Pakistan, and India, with four different biallelic mutations in PIDD1, all disrupting the Death Domain (DD), through which PIDD1 interacts with CRADD or RIP1. Nonsense mutations Gln863* and Arg637* directly disrupt the DD, as does a missense mutation, Arg815Trp. A homozygous splice mutation in the fifth family is predicted to disrupt splicing upstream of the DD, as confirmed using an exon trap. In HEK293 cells, we show that both Gln863* and Arg815Trp mutants fail to co-localize with CRADD, leading to its aggregation and mis-localization, and fail to co-precipitate CRADD. Using genome-edited cell lines, we show that these three PIDD1 mutations all cause loss of PIDDosome function. Pidd1 null mice show decreased anxiety, but no motor abnormalities. Together this indicates that PIDD1 mutations in humans may cause ID (and possibly lissencephaly) either through gain of function or secondarily, due to altered scaffolding properties, while complete loss of PIDD1, as modeled in mice, may be well tolerated or is compensated for.

Do Autophagy Enhancers/ROS Scavengers Alleviate Consequences of Mild Mitochondrial Dysfunction Induced in Neuronal-Derived Cells?

“…з Rot. for 72 and 96 h vs. control, p < 0.05 as previously described [ 23 ] and confirmed now. Lithium: A .…”

“…As we reported earlier [ 23 ], the predominant effect of 10 pM, rotenone for 72 and 96 h on SH-SY5Y cells was on mitochondrial respiration parameters. We, therefore, now assessed the effect of the autophagy enhancers and the ROS scavengers added for the last 24/48 h of the exposure to rotenone for 72/96 h, respectively, on mitochondrial and nonmitochondrial respiration (OCR parameters) ( Figure 2 ; Table 2 ).…”

“…As already recently described by Damri et al [ 23 ], among the five mitochondrial respiration complexes, rotenone significantly affected only CoI and CoIV protein levels. Specifically, exposure to rotenone significantly enhanced/decreased CoI activity following 72/96 h, respectively.…”

“…We have recently modeled very mild mitochondrial dysfunction by exposing SH-SY5Y cells to very low rotenone doses in vitro and by chronically injecting (in vivo) mice with very low rotenone doses [ 23 ]. In the present study, we examined in the SH-SY5Y cells (in vitro) whether any of the autophagy enhancers trehalose [ 33 ], rapamycin [ 34 ], and lithium [ 35 ], or the ROS scavengers NAC [ 36 ] and Mn-Tbap [ 37 ], or resveratrol, both an autophagy enhancer and a ROS scavenger [ 38 ], reverse the consequences of mild mitochondrial dysfunction.…”

“…Here we recapitulated our recently reported model of mild mitochondrial dysfunction [ 23 ] in the human neuron-derived cell line, SH-SY5Y, induced by low rotenone (a mitochondrial complex I inhibitor) concentrations never used before, to examine whether autophagy enhancers or ROS scavengers which are either generally accepted as safe (GRAS) compounds or approved drugs (mood stabilizers) can amend neuronal mild mitochondrial dysfunction. The rationale for using ROS scavengers was that higher rotenone doses, regularly used to model Parkinson’s disease (PD) [ 24 ], have been reported to raise mitochondrial ROS production, a crucial player in apoptosis [ 25 ].…”