Mitochondrial intermediate peptidase is a novel regulator of sirtuin-3 activation by caloric restriction.

Sirtuin-3 (SIRT3) regulates mitochondrial quality and is involved in the anti-ageing and pro-longevity actions of caloric restriction (CR). Here, we show that CR upregulates the mature form of SIRT3 and mitochondrial intermediate peptidase (MIPEP), a mitochondrial signal peptidase (MtSPase), in white adipose tissue. We also demonstrate that upregulation of mature SIRT3 is dependent on MIPEP in 3T3-L1 cells, suggesting that MIPEP may contribute to the maintenance of mitochondrial quality during CRvia activation of SIRT3. This novel mechanism of SIRT3 activation through MIPEP facilitates the elucidation of additional molecular pathways of CR.

Sterol regulatory element-binding protein-1c orchestrates metabolic remodeling of white adipose tissue by caloric restriction.

Caloric restriction (CR) can delay onset of several age-related pathophysiologies and extend lifespan in various species, including rodents. CR also induces metabolic remodeling involved in activation of lipid metabolism, enhancement of mitochondrial biogenesis, and reduction of oxidative stress in white adipose tissue (WAT). In studies using genetically modified mice with extended lifespans, WAT characteristics influenced mammalian lifespans. However, molecular mechanisms underlying CR-associated metabolic remodeling of WAT remain unclear. Sterol regulatory element-binding protein-1c (Srebp-1c), a master transcription factor of fatty acid (FA) biosynthesis, is responsible for the pathogenesis of fatty liver (steatosis). Our study showed that, under CR conditions, Srebp-1c enhanced mitochondrial biogenesis via increased expression of peroxisome proliferator-activated receptor gamma coactivator-1α (Pgc-1α) and upregulated expression of proteins involved in FA biosynthesis within WAT. However, via Srebp-1c, most of these CR-associated metabolic alterations were not observed in other tissues, including the liver. Moreover, our data indicated that Srebp-1c may be an important factor both for CR-associated suppression of oxidative stress, through increased synthesis of glutathione in WAT, and for the prolongevity action of CR. Our results strongly suggested that Srebp-1c, the primary FA biosynthesis-promoting transcriptional factor implicated in fatty liver disease, is also the food shortage-responsive factor in WAT. This indicated that Srebp-1c is a key regulator of metabolic remodeling leading to the beneficial effects of CR.

Clinical characteristics of perinatal lethal hypophosphatasia: a report of 6 cases.

Hypophosphatasia is a rare inherited disorder caused by deficient tissue-nonspecific alkaline phosphatase activity. It is classified into 6 subtypes, and the perinatal lethal form of hypophosphatasia is the most severe. Patients with this form suffer from various symptoms, including respiratory failure, premature craniosynostosis, rachitic changes in the metaphyses, convulsions and hypercalcemia. This report presents 6 cases of the perinatal lethal form of hypophosphatasia. All of the patients showed shortening of the long bones in utero in ultrasonographic examinations. Two of the six patients died at birth because they could not establish spontaneous breathing. Three of the remaining four patients also died before 1 yr of age. The major cause of death was respiratory failure due to hypoplastic lung. All of the patients, except for the two who died at birth, experienced convulsions in their clinical courses. Vitamin B6 therapy effectively reduced the frequency and severity of convulsions. However, it could not always make the patients convulsion free. Three patients underwent a genetic analysis. The 1559delT mutation, which abolishes Alkaline Phosphatase (ALP) activity, was a hot spot. A homozygous 1559delT mutation was observed in two patients. However, they differed in severity of symptoms. Although a good genotype-phenotype correlation has been reported in hypophosphatasia, the genotype alone does not always predict the life span of the patients. These cases therefore suggested the importance of genetic counseling.