NovelDNM1Lvariants impair mitochondrial dynamics through divergent mechanisms

Abstract

Imbalances in mitochondrial and peroxisomal dynamics are associated with a spectrum of human neurological disorders. Mitochondrial and peroxisomal fission both involve dynamin-related protein 1 (DRP1) oligomerisation and membrane constriction, although the precise biophysical mechanisms by which distinct DRP1 variants affect the assembly and activity of different DRP1 domains remains largely unexplored. We analysed four unreported de novo heterozygous variants in the dynamin-1-like gene DNM1L, affecting different highly conserved DRP1 domains, leading to developmental delay, seizures, hypotonia, and/or rare cardiac complications in infancy. Single-nucleotide DRP1 stalk domain variants were found to correlate with more severe clinical phenotypes, with in vitro recombinant human DRP1 mutants demonstrating greater impairments in protein oligomerisation, DRP1-peroxisomal recruitment, and both mitochondrial and peroxisomal hyperfusion compared to GTPase or GTPase-effector domain variants. Importantly, we identified a novel mechanism of pathogenesis, where a p.Arg710Gly variant uncouples DRP1 assembly from assembly-stimulated GTP hydrolysis, providing mechanistic insight into how assembly-state information is transmitted to the GTPase domain. Together, these data reveal that discrete, pathological DNM1L variants impair mitochondrial network maintenance by divergent mechanisms.

Human Fis1 directly interacts with Drp1 in an evolutionarily conserved manner to promote mitochondrial fission

“…2 A and S2 C ), consistent with prior results ( 33 ). In the absence of Fis1ΔN, Drp1 thermally unfolds in two transitions with midpoints at 48.7 ± 0.2 °C and 76.8 ± 0.2 °C corresponding to the GTPase and stalk domains, respectively, as described previously ( 50 , 51 ). Upon addition of increasing Fis1ΔN, only the second transition was altered and decreased in a concentration-dependent manner ( Figs.…”

“…Recombinant Drp1 isoform 1 was expressed and purified as previously described ( 50 ). Briefly, harvested cells were lysed using an EmlusiFlex C3 homogenizer (Avestin) at 15,000 p.s.i.…”

Mitochondrial signalling and homeostasis: from cell biology to neurological disease

“…OPEN ACCESS division is DNM1L, encoding a cytosolic dynamin GTPase DRP1 which is recruited to the OMM by adaptor proteins mitochondrial fission 1, mitochondrial fission factor, and mitochondrial dynamics proteins (MID49 and MID51). Pathogenic DNM1L variants within each of the DRP1 protein domains have been identified, primarily causing mitochondrial network hyperfusion and variable neurological phenotypes [73,74]. Mitochondrial fusion is largely regulated by the outer mitochondrial membrane (OMM) mitofusin proteins MFN1 and MFN2, and IMM protein optic atrophy 1 (OPA1).…”

Broadening horizons: the contribution of mitochondria-associated endoplasmic reticulum membrane (MAM) dysfunction in diabetic kidney disease

“…The mitochondrial fusion process is divided into OMM fusion and IMM fusion 82 . The OMM proteins MFN1 and MFN2, as well as the OMM protein optic atrophy 1 (OPA1), play major roles in mitochondrial fusion 51 . Whereas MFN2 on the surface of the ER regulates mitochondrial connections to maintain the whole mitochondrial network, MFN1 on the surface of mitochondria plays a critical role in mitochondrial docking and fusion.…”