Year: 2015
Type: letter
Abstract: Potential conflict of interest: Nothing to report. Reply: We appreciate the letter of Schneider and colleagues, which adds to the conversation on the role of necroptosis and receptor interacting protein kinase‐1 (RIPK1) in acetaminophen toxicity. We both agree that necroptosis does not contribute to acetaminophen toxicity. We have shown that RIPK3 and mixed lineage kinase domain‐like knockout mice are not protected from acetaminophen, but we showed that two very different short‐term approaches to inhibit RIPK1 did protect through a mechanism upstream of c‐Jun N‐terminal kinase.1 Furthermore, both approaches, RIPK1 kinase inhibitors and highly specific antisense, still protected the RIPK3 knockouts, explaining why so many investigators have seen protection with necrostatin‐1, which is clearly independent of necroptosis. Schneider et al. developed a conditional liver‐specific long‐term knockout using alfp‐Cre, leading to deletion of RIPK1 in utero. They view this approach as the gold standard to understand the contribution of a gene to disease pathogenesis. However, all scientific methods have inherent limitations, and interpretation of experimental data is complicated by unforeseen complexities, especially when comparing different experimental approaches. As noted, two very different approaches were used, one with a lifetime without RIPK1 and one with a very brief period of inhibition or knockdown. One could argue that the approaches we employed to inhibit RIPK1, necrostatin‐1 and methoxy‐ethyl antisense oligonucleotide, may have fortuitously similar off‐target effects. On the other hand, the mouse model employed by Schneider et al. may have its own pitfalls as gene deletion early in life may elicit various unforeseen adaptive responses. An inducible liver‐specific deletion in adult animals would better address this concern. The authors raise the interesting possibility that the really important target of our RIPK1 inhibitory approaches may be RIPK1 in the nonparenchymal compartment. We consider this a less likely explanation as we confirmed that exposure to necrostatin in isolated primary mouse hepatocytes in vitro protected against acetaminophen‐induced necrosis. This indicates a hepatocyte autonomous effect. However, it remains possible that the in vivo antisense oligonucleotide treatment, which concentrates mainly in liver, may knock down RIPK1 in both parenchymal and nonparenchymal cells, the latter contributing to its protective effect. In summary, we look forward to full details on their work and thank them for sharing their findings. Because very different approaches have been used, it may be premature to conclude that RIPK1 has no role; and we believe our findings support a necroptosis‐independent role for RIPK1. The conversation will continue, which is how progress is made.
Source: Hepatology
DOI: 10.1002/hep.28221
Authors: Lily Dara, Neil Kaplowitz
Institution: University of Southern California
Language: English
Subfield: Pharmacology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W4236020325