Overexpressed p32 localized in the endoplasmic reticulum and mitochondria negatively regulates calcium‑dependent endothelial nitric oxide synthase activit

Complement C1q Binding Protein (C1QBP): Physiological Functions, Mutation-Associated Mitochondrial Cardiomyopathy and Current Disease Models

Complement C1q binding protein (C1QBP, p32) is primarily localized in mitochondrial matrix and associated with mitochondrial oxidative phosphorylative function. C1QBP deficiency presents as a mitochondrial disorder involving multiple organ systems. Recently, disease associated C1QBP mutations have been identified in patients with a combined oxidative phosphorylation deficiency taking an autosomal recessive inherited pattern. The clinical spectrum ranges from intrauterine growth restriction to childhood (cardio) myopathy and late-onset progressive external ophthalmoplegia. This review summarizes the physiological functions of C1QBP, its mutation-associated mitochondrial cardiomyopathy shown in the reported available patients and current experimental disease platforms modeling these conditions.

Identification of mitofusin 1 and complement component 1q subcomponent-binding protein as mitochondrial targets in systemic lupus erythematosus

OBJECTIVE

Mitochondria are organelles that possess several bacterial features such as a double-stranded genome with hypomethylated CpG islets, formylated proteins, and cardiolipin-containing membranes. In systemic lupus erythematosus (SLE), mitochondria and their inner components are released into the extracellular space, potentially eliciting a pro-inflammatory response by the immune system. While cardiolipin and mitochondrial DNA and RNA are confirmed targets of autoantibodies, other antigenic mitochondrial proteins in SLE remain to be identified. Herein, we aim to characterize the protein repertoire recognized by anti-mitochondrial antibodies (AMA) in SLE patients.

METHODS

Using shotgun proteomic profiling, we identified 1345 proteins, 431 of which were associated with the mitochondrial proteome. Immunoreactivities to several of these candidates were assessed by direct ELISA in serum samples from a local cohort (healthy: n=30, SLE: n=87) and associated with demographic and disease characteristics.

RESULTS

We determined that IgGs to the C1q-binding protein (C1qBP) are significantly elevated in SLE patients included in our cohort (p=0.049) and are associated with positivity for lupus anticoagulant (p=0.049). IgG against the mitochondrial protein mitofusin 1 (Mfn1) displayed promising performances in the prediction of SLE diagnoses (aOR: 2.99, 95%CI: 1.39-6.43, p=0.0044) in our cohort. Moreover, anti-Mfn1 were associated with positivity to anti-phospholipids (p=0.011) and anti-dsDNA (p=0.0005).

CONCLUSION

This study presents the mitochondrial repertoire targeted in SLE, indicating that autoantibodies can recognize secreted and/or surface proteins of mitochondrial origin. Profiling of the AMA repertoire in large prospective cohorts may improve our knowledge on mitochondrial biomarkers and their usefulness for patient stratification.