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Abstract-We have previously shown that connexin 43 (Cx43) is present in mitochondria, that its genetic depletion abolishes the protection of ischemia-and diazoxide-induced preconditioning, and that it is involved in reactive oxygen species (ROS) formation in response to diazoxide. Here we investigated the intramitochondrial localization of Cx43, the mechanism of Cx43 translocation to mitochondria and the effect of inhibiting translocation on the protection of preconditioning. Confocal microscopy of mitochondria devoid of the outer membrane and Western blotting on fractionated mitochondria showed that Cx43 is located at the inner mitochondrial membrane, and coimmunoprecipitation of Cx43 with Tom20 (Translocase of the outer membrane 20) and with heat shock protein 90 (Hsp90) indicated that it interacts with the regular mitochondrial protein import machinery. In isolated rat hearts, geldanamycin, a blocker of Hsp90-dependent translocation of proteins to the inner mitochondrial membrane through the TOM pathway, rapidly (15 minutes) reduced mitochondrial Cx43 content by approximately one-third in the absence or presence of diazoxide. Geldanamycin alone had no effect on infarct size, but it ablated the protection against infarction afforded by diazoxide. Geldanamycin abolished the 2-fold increase in mitochondrial Cx43 induced by 2 preconditioning cycles of ischemia/reperfusion, but this effect was not associated with reduced protection. These results demonstrate that Cx43 is transported to the inner mitochondrial membrane through translocation via the TOM complex and that a normal mitochondrial Cx43 content is important for the diazoxide-related pathway of preconditioning. Key Words: mitochondria Ⅲ heat shock protein Ⅲ geldanamycin Ⅲ connexin 43 Ⅲ TOM (Translocase of the Outer Membrane) complex C ardiomyocyte death during acute coronary syndromes determines survival and quality of life of patients with coronary artery disease. 1 In the majority of these patients, cardiomyocyte death is the consequence of transient, prolonged ischemia, and there is strong evidence that a substantial part of cell death occurs at the time of reperfusion. 2,3 Preconditioning, a state of increased resistance against cell death induced by ischemia-reperfusion, is elicited by brief ischemia/reperfusion episodes or by certain pharmacological stimuli and has received particular attention. 4 A wealth of information has been collected on the molecular mechanisms involved in preconditioning, but many aspects of the signaling pathways and of the end effectors of the protection remain unknown. 4,5 An intriguing and unresolved aspect is the involvement of connexin 43 (Cx43), the protein forming gap junctions connecting adjacent ventricular cardiomyocytes, 6,7 in the genesis of preconditioning. 8,9 The protection of preconditioning is abolished in Cx43-deficient mice 10 but also in isolated cardiomyocytes from Cx43-deficient hearts, 11 indicating that it cannot be explained by effects of preconditioning on gap junction-mediated cell-to-cell c...

Connexin 43 (Cx43) is the predominant protein forming gap junctions and non-junctional hemichannels in ventricular myocardium, but Cx43 is also localized at the inner membrane of cardiomyocyte mitochondria. In cardiomyocytes, Cx43 is involved in the formation of reactive oxygen species, which are central to the signal transduction cascade of ischemic preconditioning's protection. Accordingly, genetically-induced or age-related loss of Cx43 abolishes infarct size reduction by ischemic preconditioning. Similarly, mitochondrial import inhibition of Cx43 completely blocks infarct size reduction by pharmacological preconditioning with diazoxide. In contrast to its importance for preconditioning-induced cardioprotection, Cx43 is not important for infarct size reduction by ischemic postconditioning. In summary, Cx43--especially Cx43 localized in mitochondria--appears to be one key element of the signal transduction cascade of the protection by preconditioning.

Nusinersen is the first approved drug for the treatment of spinal muscular atrophy (SMA). Treatment of SMA with nusinersen is based on a fixed dosing regimen. For other motoneuron diseases, such as amyotrophic lateral sclerosis (ALS), biomarkers are available for clinical diagnostics; however, no such biomarkers have yet been found for SMA. Serum and cerebrospinal fluid (CSF) samples of 11 patients with adult SMA type 3 were prospectively collected and analyzed during loading with nusinersen. Neurofilament heavy chain, tau protein, S100B protein, and neuron-specific enolase were investigated as potential biomarkers of motor neuron destruction. No significant pathological alterations in levels of neurofilament heavy chain, tau protein, or S100B protein were detected in the CSF or blood samples under baseline conditions or during loading with nusinersen. Neuron-specific enolase was marginally elevated in CSF and blood samples without significant alteration during treatment. In a mixed cohort of adult patients with SMA type 3, neurofilament heavy chain, tau protein, S100B protein, and neuron-specific enolase do not serve as potential biomarkers during the loading phase of nusinersen. The slow progression rate of SMA type 3 may not lead to detectable elevation of levels of these common markers of axonal degradation.

Background:Nusinersen is an intrathecally administered antisense oligonucleotide (ASO) and the first approved drug for the treatment of spinal muscular atrophy (SMA). However, progressive neuromyopathic scoliosis and the presence of spondylodesis can impede lumbar punctures in SMA patients. Our aim was to assess the feasibility and safety of the treatment in adults with SMA.Methods:For the intrathecal administration of nusinersen, we performed conventional, fluoroscopy-assisted and computer tomography (CT)-guided lumbar punctures in adult patients with type 2 and type 3 SMA. We documented any reported adverse events and performed blood tests.Results:We treated a total of 28 adult SMA patients (9 patients with SMA type 2 and 19 patients with SMA type 3) aged between 18–61 years with nusinersen. The mean Revised Upper Limb Module (RULM) score at baseline in SMA type 2 and SMA type 3 patients was 9.9 ± 4.6 and 29.5 ± 8.5, respectively. The mean Hammersmith Functional Motor Scale Expanded (HFMSE) score at baseline was 3.1 ± 2.5 and 31.2 ± 18.1, respectively. Half of the SMA type 3 patients were ambulatory at treatment onset. In total, we performed 122 lumbar punctures with 120 successful intrathecal administrations of nusinersen. Lumbar punctures were well tolerated, and no serious adverse events occurred.Conclusions:Our data demonstrate the feasibility and tolerability of intrathecal treatment with nusinersen in adults with SMA type 2 and type 3. However, treatment can be medically and logistically challenging, particularly in patients with SMA type 2 and in patients with spondylodesis.