New splicing variants of mitochondrial Rho GTPase-1 (Miro1) transport peroxisomes.

Microtubule-dependent long-distance movement of peroxisomes occurs in mammalian cells. However, its molecular mechanisms remain undefined. In this study, we identified three distinct splicing variants of human mitochondrial Rho GTPase-1 (Miro1), each containing amino acid sequence insertions 1 (named Miro1-var2), 2 (Miro1-var3), and both 1 and 2 (Miro1-var4), respectively, at upstream of the transmembrane domain. Miro1-var4 and Miro1-var2 are localized to peroxisomes in a manner dependent on the insertion 1 that is recognized by the cytosolic receptor Pex19p. Exogenous expression of Miro1-var4 induces accumulation of peroxisomes at the cell periphery and augments long-range movement of peroxisomes along microtubules. Depletion of all Miro1 variants by knocking down MIRO1 suppresses the long-distance movement of peroxisomes. Such abrogated movement is restored by reexpression of peroxisomal Miro1 variants. Collectively, our findings identify for the first time peroxisome-localized Miro1 variants as adapter proteins that link peroxisomes to the microtubule-dependent transport complexes including TRAK2 in the intracellular translocation of peroxisomes in mammalian cells.

Mild reduction of plasmalogens causes rhizomelic chondrodysplasia punctata: functional characterization of a novel mutation.

Rhizomelic chondrodysplasia punctata (RCDP) is an autosomal recessive disorder due to the deficiency in ether lipid synthesis. RCDP type 1, the most prominent type, is caused by the dysfunction of the receptor of peroxisome targeting signal type 2, Pex7 (peroxisomal biogenesis factor 7), and the rest of the patients, RCDP types 2 and 3, have defects in peroxisomal enzymes catalyzing the initial two steps of alkyl-phospholipid synthesis, glyceronephosphate O-acyltransferase and alkylglycerone phosphate synthase (Agps). We herein investigated defects of two patients with RCDP type 3. Patient 1 had a novel missense mutation, T1533G, resulting in the I511M substitution in Agps. The plasmalogen level was mildly reduced, whereas the protein level and peroxisomal localization of Agps-I511M in fibroblasts were normal as in the control fibroblasts. Structure prediction analysis suggested that the mutated residue was located in the helix α15 on the surface of V-shaped active site tunnel in Agps, likely accounting for the mild defects of plasmalogen synthesis. These results strongly suggest that an individual with mildly affected level of plasmalogen synthesis develops RCDP. In fibroblasts from patient 2, the expression of AGPS mRNA and Agps protein was severely affected, thereby giving rise to the strong reduction of plasmalogen synthesis.

Impaired regulation of gonadotropins leads to the atrophy of the female reproductive system in klotho-deficient mice.

klotho-Deficient mice exhibit a syndrome resembling human premature ageing, with multiple pathological phenotypes in tissues including reproductive organs. It was proposed that Klotho might possess the hormonal effects on many organs. In this study, the female reproductive system of klotho mice was examined to reveal the mechanism that brought the female sterility by histological and molecular approaches. We observed cessation of ovarian follicular maturation at the preantral stage and the presence of numerous atretic ovarian follicles and atrophic uteri. In situ hybridization analysis revealed that LH receptor and aromatase P450 were not expressed in the ovaries. These results suggest the impairment of gonadal development during the antral transition process. We next addressed the responsible organs for the failure of antral transition. Transplantation of klotho ovaries to wild-type mice resulted in the ability to bear offspring. Administration of FSH or GnRH induced advanced maturation of ovaries and uteri in klotho mice. These results indicate that the female reproductive organs in klotho mice are potentially functional and that klotho gene deficiency leads to the atrophy of reproductive organs via impairment of the hypothalamic-pituitary axis. Absence of the estrus cycle and constant low trends of both FSH and LH levels were found in female klotho mice. Immunohistochemical analysis revealed that the production of both FSH and LH were decreased in pituitary gland. Taken together, our findings suggest the involvement of klotho in the regulatory control of pituitary hormones.