The Impact of RIPK1 Kinase Inhibition on Atherogenesis: A Genetic and a Pharmacological Approach.

RIPK1 (receptor-interacting serine/threonine-protein kinase 1) enzymatic activity drives both apoptosis and necroptosis, a regulated form of necrosis. Because necroptosis is involved in necrotic core development in atherosclerotic plaques, we investigated the effects of a RIPK1 ^S25D/S25D mutation, which prevents activation of RIPK1 kinase, on atherogenesis in ApoE ^-/- mice. After 16 weeks of western-type diet (WD), atherosclerotic plaques from ApoE ^-/- RIPK1 ^S25D/S25D mice were significantly larger compared to ApoE ^-/- RIPK1 ^+/+ mice (167 ± 34 vs. 78 ± 18 × 10 ³ µm ² , p = 0.01). Cell numbers (350 ± 34 vs. 154 ± 33 nuclei) and deposition of glycosaminoglycans (Alcian blue: 31 ± 6 vs. 14 ± 4%, p = 0.023) were increased in plaques from ApoE ^-/- RIPK1 ^S25D/S25D mice while macrophage content (Mac3: 2.3 ± 0.4 vs. 9.8 ± 2.4%, p = 0.012) was decreased. Plaque apoptosis was not different between both groups. In contrast, pharmacological inhibition of RIPK1 kinase with GSK'547 (10 mg/kg BW/day) in ApoE ^-/- Fbn1 ^C1039G+/- mice, a model of advanced atherosclerosis, did not alter plaque size after 20 weeks WD, but induced apoptosis (TUNEL: 136 ± 20 vs. 62 ± 9 cells/mm ² , p = 0.004). In conclusion, inhibition of RIPK1 kinase activity accelerated plaque progression in ApoE ^-/- RIPK1 ^S25D/S25D mice and induced apoptosis in GSK'547-treated ApoE ^-/- Fbn1 ^C1039G+/- mice. Thus, without directly comparing the genetic and pharmacological studies, it can be concluded that targeting RIPK1 kinase activity does not limit atherogenesis.