Mutation-free baby born from a mitochondrial encephalopathy, lactic acidosis and stroke-like syndrome carrier after blastocyst trophectoderm preimplantation genetic diagnosis.

To investigate the applicability of preimplantation genetic diagnosis (PGD), we used trophectoderm (TE) biopsy to determine the mutation load in a 35-year-old female with mitochondrial encephalopathy, lactic acidosis and stroke-like syndrome (MELAS). Transfer of a mutation-free blastocyst gave birth to a healthy boy with undetectable mutation in any of the analyzed tissues. We found strong correlation among TE cells (r=0.90) within blastocysts and also between cytoplasmic fragments and TE (r=0.95). This is the first case of mutation-free baby born from a MELAS patient after TE biopsy and supports the applicability of blastocyst PGD for patients with mtDNA disorders to establish healthy offspring.

Humanins, the neuroprotective and cytoprotective peptides with antiapoptotic and anti-inflammatory properties.

Humanin (HN) is a newly discovered 24-amino acid peptide, which may suppress neuronal cell death. HN cDNA includes an open reading frame (HN-ORF) of 75 bases located 950 bases downstream of the 5' end of the HN cDNA. It has been demonstrated that HN cDNA is 99% identical to the mitochondrial DNA (mtDNA) sequence. HN homologs have been identified as expressed sequence tags (ESTs) in both rats and nematodes. Certain regions that are homologous to the HN cDNA exist on human chromosomes. HN forms homodimers and multimers and this action seems to be essential for peptide function. HN acts as a ligand for formyl peptide receptor-like 1 (FPRL1) and 2 (FPRL2). It has been demonstrated that HN plays a protective role through its antiapoptotic activity that interferes with Bax activation, which suppresses Bax-dependent apoptosis. HN has also been shown to suppress the c-Jun N-terminal kinase (JNK) and ASK/JNK-mediated neuronal cell death. Several studies have also confirmed that HN could be important in the prevention of angiopathy-associated Alzheimer's disease dementia, diseases related to mitochondrial dysfunction (MELAS), and other types of ß-amyloid accumulation-associated neurodegeneration. Avery recent study demonstrated a pluripotent cytoprotective effect and mechanisms of HNs in cells not from the CNS, such as germ cells or pancreatic ß-cells, and the potent physiological consequences that result from HN interaction with IGFBP3 and STAT3. In vivo studies suggest that HN may also protect against cognitive impairment due to ischemia/reperfusion injury.

Acquisition of the wobble modification in mitochondrial tRNALeu(CUN) bearing the G12300A mutation suppresses the MELAS molecular defect.

The A3243G mutation in the mitochondrial gene for human mitochondrial (mt) tRNA(Leu(UUR)), responsible for decoding of UUR codons, is associated with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). We previously demonstrated that this mutation causes defects in 5-taurinomethyluridine (taum(5)U) modification at the anticodon first (wobble) position of the mutant mt tRNA(Leu(UUR)), leading to a UUG decoding deficiency and entraining severe respiratory defects. In addition, we previously identified a heteroplasmic mutation, G12300A, in the other mt leucine tRNA gene, mt tRNA(Leu(CUN)), which functions as a suppressor of the A3243G respiratory defect in cybrid cells containing A3243G mutant mtDNA. Although the G12300A mutation converts the anticodon sequence of mt tRNA(Leu(CUN)) from UAG to UAA, this tRNA carrying an unmodified wobble uridine still cannot decode the UUG codon. Mass spectrometric analysis of the suppressor mt tRNA(Leu(CUN)) carrying the G12300A mutation from the phenotypically revertant cells revealed that the wobble uridine acquires de novo taum(5)U modification. In vitro translation confirmed the functionality of the suppressor tRNA for decoding UUG codons. These results demonstrate that the acquisition of the wobble modification in another isoacceptor tRNA is critical for suppressing the MELAS mutation, and they highlight the primary role of the UUG decoding deficiency in the molecular pathogenesis of MELAS syndrome.