KRIT1 loss-of-function induces a chronic Nrf2-mediated adaptive homeostasis that sensitizes cells to oxidative stress: Implication for Cerebral Cavernous Malformation disease

Abstract

KRIT1 (CCM1) is a disease gene responsible for Cerebral Cavernous Malformations (CCM), a major cerebrovascular disease of proven genetic origin affecting 0.3–0.5% of the population.Previously, we demonstrated that KRIT1 loss-of-function is associated with altered redox homeostasis and abnormal activation of the redox-sensitive transcription factor c-Jun, which collectively result in pro-oxidative, pro-inflammatory and pro-angiogenic effects, suggesting a novel pathogenic mechanism for CCM disease and raising the possibility that KRIT1 loss-of-function exerts pleiotropic effects on multiple redox-sensitive mechanisms.To address this possibility, we investigated major redox-sensitive pathways and enzymatic systems that play critical roles in fundamental cytoprotective mechanisms of adaptive responses to oxidative stress, including the master Nrf2 antioxidant defense pathway and its downstream target Glyoxalase 1 (Glo1), a pivotal stress-responsive defense enzyme involved in cellular protection against glycative and oxidative stress through the metabolism of methylglyoxal (MG). This is a potent post-translational protein modifier that may either contribute to increased oxidative molecular damage and cellular susceptibility to apoptosis, or enhance the activity of major apoptosis-protective proteins, including heat shock proteins (Hsps), promoting cell survival.Experimental outcomes showed that KRIT1 loss-of-function induces a redox-sensitive sustained upregulation of Nrf2 and Glo1, and a drop in intracellular levels of MG-modified Hsp70 and Hsp27 proteins, leading to a chronic adaptive redox homeostasis that counteracts intrinsic oxidative stress but increases susceptibility to oxidative DNA damage and apoptosis, sensitizing cells to further oxidative challenges. While supporting and extending the pleiotropic functions of KRIT1, these findings shed new light on the mechanistic relationship between KRIT1 loss-of-function and enhanced cell predisposition to oxidative damage, thus providing valuable new insights into CCM pathogenesis and novel options for the development of preventive and therapeutic strategies.

Systems-wide analysis unravels the new roles of CCM signal complex (CSC)

“…Heat shock proteins (HSPs), mainly functioning as chaperones, whose altered expression levels can result in misfolded proteins and lead to degradation. Up-regulation of both HSPA4 and HSPB1 was observed in CCM2 deficient HBMVEC lines, contradicting to previous report that CCM1 deficient cells have decreased levels of heat shock proteins (HSP, Hsp70 and Hsp27), which have a protective role in handling cellular stress 170 . DDB1, perturbed in all three CCMs-KD HBMVEC cells, is a part of the DDB1-CUL4 ubiquitin ligase complex, a key factor in autophagy.…”

VEGF signalling enhances lesion burden in KRIT1 deficient mice

“…These discrepancies may be due to experimental differences (ie knockdown level, activation/inactivation of specific tyrosines on VEGFR2) and remain to be reconciled. Alternatively, recent reports have demonstrated a role for inflammatory signalling and oxidative stress in CCM lesion development, including the up‐regulation of the oxidative stress‐responsive transcription factor Nrf2, which indirectly promotes VEGF expression . Furthermore, Tang et al noted that activation of Toll‐like receptor‐4 (TLR4) signalling by blood‐borne gram‐negative bacteria led to greater CCM lesion burden in a mouse model of CCM .…”

“…23 These discrepancies may be due to experimental differences (ie knockdown level, activation/inactivation of specific tyrosines on VEGFR2) and remain to be reconciled. Alternatively, recent reports have demonstrated a role for inflammatory signalling and oxidative stress in CCM lesion development, including the up-regulation of the oxidative stress-responsive transcription factor Nrf2, 24 F I G U R E 5 Loss of CCM protein family members increases VEGFR2 tyrosine phosphorylation. A, Tyrosine phosphorylation of VEGFR2 in HPAEC transfected with negative control (NC), anti-KRIT1, anti-CCM2 and anti-CCM3 siRNA.…”

Vitamin D Deficiency and the Risk of Cerebrovascular Disease

“…Genetic studies in CCM patient cohorts have led to the identification of three disease genes, CCM1/KRIT1, CCM2, and CCM3, which have been implicated in all major mechanisms of vascular integrity maintenance and endothelial barrier function, including the coordination of redox signaling and autophagy governing cell homeostasis and stress responses [43,[171][172][173][174][175][176][177][178][179][180]. Consistent with such pleiotropic functions, accumulated evidence from animal models and patient cohorts has demonstrated that loss-of-function mutations of CCM genes only predispose to the development of CCM disease.…”