A pair of kinases, RIPK1 and RIPK3, as well as the RIPK3 substrate MLKL cause a form of programmed necrotic cell death in mammals termed necroptosis. We report here that male reproductive organs of both Ripk3- and Mlkl-knockout mice retain ‘youthful’ morphology and function into advanced age, while those of age-matched wild-type mice deteriorate. The RIPK3 phosphorylation of MLKL, the activation marker of necroptosis, is detected in spermatogonial stem cells in the testes of old but not in young wild-type mice. When the testes of young wild-type mice are given a local necroptotic stimulus, their reproductive organs showed accelerated aging. Feeding of wild-type mice with an RIPK1 inhibitor prior to the normal onset of age-related changes in their reproductive organs blocked the appearance of signs of aging. Thus, necroptosis in testes promotes the aging-associated deterioration of the male reproductive system in mice.DOI: http://dx.doi.org/10.7554/eLife.27692.001

On the basis of its essential role in driving inflammation and disease pathology, cell necrosis has gradually been verified as a promising therapeutic target for treating atherosclerosis, systemic inflammatory response syndrome (SIRS), and ischemia injury, among other diseases. Most necrosis inhibitors targeting receptor-interacting protein 1 (RIP1) still require further optimization because of weak potency or poor metabolic stability. We conducted a phenotypic screen and identified a micromolar hit with novel amide structure. Medicinal chemistry efforts yielded a highly potent, selective, and metabolically stable drug candidate, compound 56 (RIPA-56). Biochemical studies and molecular docking revealed that RIP1 is the direct target of this new series of type III kinase inhibitors. In the SIRS mice disease model, 56 efficiently reduced tumor necrosis factor alpha (TNFα)-induced mortality and multiorgan damage. Compared to known RIP1 inhibitors, 56 is potent in both human and murine cells, is much more stable in vivo, and is efficacious in animal model studies.

Demyelination in the central nervous system (CNS) underlies many human diseases, including multiple sclerosis (MS). We report here the findings of our study of the CNS demyelination process using immune-induced [experimental autoimmune encephalomyelitis (EAE)] and chemical-induced [cuprizone (CPZ)] mouse models of demyelination. We found that necroptosis, a receptor-interacting protein 3 (RIP3) kinase and its substrate mixed lineage kinase domainlike protein (MLKL)-dependent cell death program, played no role in the demyelination process, whereas the MLKL-dependent, RIP3independent function of MLKL in the demyelination process initially discovered in the peripheral nervous system in response to nerve injury, also functions in demyelination in the CNS in these models. Moreover, a receptor-interacting protein 1 (RIP1) kinase inhibitor, RIPA-56, blocked disease progression in the EAE-induced model but showed no effect in the CPZ-induced model. It does so most likely at a step of monocyte elevation downstream of T cell activation and myelin-specific antibody generation, although upstream of breakdown of the blood-brain barrier. RIP1-kinase dead knock-in mice shared a similar result as mice treated with the RIP1 inhibitor. These results indicate that RIP1 kinase inhibitor is a potential therapeutic agent for immune-mediated demyelination diseases that works by prevention of monocyte elevation, a function previously unknown for RIP1 kinase.RIP1 kinase | myelin | demyelination | multiple sclerosis | MLKL M yelin is a lipid-rich (fatty) substance formed by glial cells called oligodendrocytes in the central nervous system (CNS) and by Schwann cells in the peripheral nervous system (PNS) that protects and nourishes neuron axons by wrapping the axons (1). Physiologically, the myelin structure speeds the transmission of electrical impulses called action potentials along myelinated axons by insulating the axon and reducing axonal membrane capacitance (2). The demyelination process occurs during nerve injury and happens in many human diseases, including, for example, in the PNS, Charcot-Marie-Tooth disease (3) and abdominal numbness brought about by diabetes (4), and in the CNS, multiple sclerosis (MS), during which the insulating covers of nerve cells in the brain and spinal cord are damaged by infiltrated immune cells, such as T cells and monocytes (5,6). Patients with MS are paralyzed gradually from the lower body to the upper body and eventually die; most of these patients are young adults ranging in age from their 20s-40s (7).The molecular mechanisms that underlie these demyelination diseases are largely unknown. A recent study indicated that preventing oligodendrocytes from necroptosis, a regulated form of necrotic cell death induced by ligands of the tumor necrosis factor (TNF) receptor family or Toll-like receptors, as well as certain viral infections, could decrease disease symptoms in MS disease models of experimental autoimmune encephalomyelitis (EAE) and a cuprizone (CPZ)-induced demyelination model (8). The TNF re...

We designed and synthesized All-in-One (AIO) reactive azide reagents for bioorthogonal reactions with highly efficient Cu(I) ligand moieties, an azido group, and functional tags for imaging or purification. The AIO reagents displayed fast and efficient click ligation and can be applied in a wide range of in vivo systems.