Novel Majeed Syndrome–Causing LPIN2 Mutations Link Bone Inflammation to Inflammatory M2 Macrophages and Accelerated Osteoclastogenesis

Abstract

Objective. To identify novel heterozygous LPIN2 mutations in a patient with Majeed syndrome and characterize the pathomechanisms that lead to the development of sterile osteomyelitis.Methods. Targeted genetic analysis and functional studies assessing monocyte responses, macrophage differentiation, and osteoclastogenesis were conducted to compare the pathogenesis of Majeed syndrome to interleukin-1 (IL-1)-mediated diseases including neonatal-onset multisystem inflammatory disease (NOMID) and deficiency of the IL-1 receptor antagonist (DIRA).Results. A 4-year-old girl of mixed ethnic background presented with sterile osteomyelitis and elevated acute-phase reactants. She had a 17.8-kb deletion on the maternal LPIN2 allele and a splice site mutation, p.R517H, that variably spliced out exons 10 and 11 on the paternal LPIN2 allele. The patient achieved long-lasting remission receiving IL-1 blockade with canakinumab. Compared to controls, monocytes and monocyte-derived M1-like macrophages from the patient with Majeed syndrome and those with NOMID or DIRA had elevated caspase 1 activity and IL-1β secretion. In contrast, lipopolysaccharide-stimulated, monocyte-derived, M2-like macrophages from the patient with Majeed syndrome released higher levels of osteoclastogenic mediators (IL-8, IL-6, tumor necrosis factor, CCL2, macrophage inflammatory protein 1α/β, CXCL8, and CXCL1) compared to NOMID patients and healthy controls. Accelerated osteoclastogenesis in the patient with Majeed syndrome was associated with higher NFATc1 levels, enhanced JNK/MAPK, and reduced Src kinase activation, and partially responded to JNK inhibition and IL-1 (but not IL-6) blockade.Conclusion. We report 2 novel compound heterozygous disease-causing mutations in LPIN2 in an American patient with Majeed syndrome. LPIN2 deficiency drives differentiation of proinflammatory M2-like macrophages and enhances intrinsic osteoclastogenesis. This provides a model for the pathogenesis of sterile osteomyelitis which differentiates Majeed syndrome from other IL-1-mediated autoinflammatory diseases.ClinicalTrials.gov identifier: NCT02974595.

Majeed Syndrome: A Review of the Clinical, Genetic and Immunologic Features

“…As expected, monocytes and monocyte-derived M1-like macrophages from patients with Majeed syndrome as well as monocytes from individuals with another genetically driven NLRP3 inflammasomopathy Neonatal Onset Multisystem Inflammatory Disorder [NO-MID] had elevated caspase-1 activity and their cells secreted more IL-1β levels when compared to healthy controls [81]. Yet, only the cells from Majeed syndrome patients (versus NOMID or healthy controls) showed increased expression of osteoclastogenic mediators including IL-8, IL-6, TNF, CCL2, MIP1α, MIP-1β, CXCL8/IL-8 and CXCL1 in M2-like macrophages stimulated with LPS [81]. In addition, Majeed cells showed increased osteoclastogenesis in response to RANKL and M-CSF, associated with higher NFATc1 levels, showed enhanced JNK/MAP kinase activation and reduced Src kinase activation.…”

“…We and others have shown that the pro-inflammatory cytokine IL-1 drives the inflammatory bone disease and systemic inflammation in Majeed syndrome [64]. Therapeutically blocking the IL-1RI or IL-1β (n = 10), but not TNF (n = 4), results in prompt resolution of systemic inflammation and healing of the sterile osteomyelitis seen in Majeed syndrome patients (Table 2) [64,79,81,83,85,86]. There is additional evidence that dysregulated IL-1 mediated signaling is central to the pathogenesis of sterile osteomyelitis.…”

“…These come from 10 unrelated families (the reports by Al-Mosawi et al in 2007 and 2019 are from the same extended family). All patients reported to date have been homozygous with only two patients having a compound heterozygous genotype [81,82]. Most of the mutations are deleterious mutations predicted to lead to a truncated protein and loss of function.…”

“…Most recently macrophage polarization has been implicated in the sterile osteomyelitis that is a prominent feature of Majeed syndrome. Bhuyan et al report extensive investigations on cells obtained from the first Majeed syndrome patient who resides in the US who was found to be heterozygous for 2 novel LPIN2 mutations (Table 1, K1) [81]. As expected, monocytes and monocyte-derived M1-like macrophages from patients with Majeed syndrome as well as monocytes from individuals with another genetically driven NLRP3 inflammasomopathy Neonatal Onset Multisystem Inflammatory Disorder [NO-MID] had elevated caspase-1 activity and their cells secreted more IL-1β levels when compared to healthy controls [81].…”

“…Bhuyan et al report extensive investigations on cells obtained from the first Majeed syndrome patient who resides in the US who was found to be heterozygous for 2 novel LPIN2 mutations (Table 1, K1) [81]. As expected, monocytes and monocyte-derived M1-like macrophages from patients with Majeed syndrome as well as monocytes from individuals with another genetically driven NLRP3 inflammasomopathy Neonatal Onset Multisystem Inflammatory Disorder [NO-MID] had elevated caspase-1 activity and their cells secreted more IL-1β levels when compared to healthy controls [81]. Yet, only the cells from Majeed syndrome patients (versus NOMID or healthy controls) showed increased expression of osteoclastogenic mediators including IL-8, IL-6, TNF, CCL2, MIP1α, MIP-1β, CXCL8/IL-8 and CXCL1 in M2-like macrophages stimulated with LPS [81].…”