A Novel Interaction between MFN2/Marf and MARK4/PAR-1 Is Implicated in Synaptic Defects and Mitochondrial Dysfunction.

As cellular energy powerhouses, mitochondria undergo constant fission and fusion to maintain functional homeostasis. The conserved dynamin-like GTPase, Mitofusin2 (MFN2)/mitochondrial assembly regulatory factor (Marf), plays a role in mitochondrial fusion, mutations of which are implicated in age-related human diseases, including several neurodegenerative disorders. However, the regulation of MFN2/Marf-mediated mitochondrial fusion, as well as the pathologic mechanism of neurodegeneration, is not clearly understood. Here, we identified a novel interaction between MFN2/Marf and microtubule affinity-regulating kinase 4 (MARK4)/PAR-1. In the Drosophila larval neuromuscular junction, muscle-specific overexpression of MFN2/Marf decreased the number of synaptic boutons, and the loss of MARK4/PAR-1 alleviated the synaptic defects of MFN2/Marf overexpression. Downregulation of MARK4/PAR-1 rescued the mitochondrial hyperfusion phenotype caused by MFN2/Marf overexpression in the Drosophila muscles as well as in the cultured cells. In addition, knockdown of MARK4/PAR-1 rescued the respiratory dysfunction of mitochondria induced by MFN2/Marf overexpression in mammalian cells. Together, our results indicate that the interaction between MFN2/Marf and MARK4/PAR-1 is fine-tuned to maintain synaptic integrity and mitochondrial homeostasis, and its dysregulation may be implicated in neurologic pathogenesis.

Inter-organ regulation by the brain in Drosophila development and physiology.

The brain plays an essential role in regulating physiological homeostasis by communicating with other organs. Neuronal cells either directly innervate target tissues and transmit signals or secrete systemic factors into the hemolymph to regulate bodily functions, including physiology, development, metabolism, and immunity. In this review, we discuss the systemic functions of inter-organ communication mediated by the brain in four distinct categories: (1) nutrient sensing and feeding, (2) gastrointestinal activity and metabolism, (3) development and metamorphosis, and (4) immunity and hematopoiesis. First, we describe how chemosensory signals are sensed and transmitted to the brain in Drosophila and how the brain stimulates or modifies feeding behavior. Second, we summarize the brain-organ axis that regulates appetite activities and neuroendocrine pathways that maintain metabolic homeostasis. Third, we discuss how overall development in Drosophila is achieved by insulin and how it affects ecdysone signaling to initiate pupariation. Finally, we discuss how the central or peripheral nervous system controls hematopoiesis and innate immunity in Drosophila larvae. Given the functional parallels between Drosophila and humans, homologous pathways are likely to be conserved in human development and disease models, and the fly model system will continue to provide mechanistic insights into understanding complex interactions.

Detection of intracellular monosodium urate crystals in gout synovial fluid using optical diffraction tomography.

Optical diffraction tomography (ODT) enables imaging of unlabeled intracellular components by measuring the three-dimensional (3D) refractive index (RI). We aimed to detect intracellular monosodium urate (MSU) crystals in synovial leukocytes derived from gout patients using ODT. The 3D RI values of the synthetic MSU crystals, measured by ODT, ranged between 1.383 and 1.440. After adding synthetic MSU crystals to a macrophage, RI tomograms were reconstructed using ODT, and the reconstructed RI tomograms discerned intracellular and extracellular MSU crystals. We observed unlabeled synthetic MSU crystal entry into the cytoplasm of a macrophage through time-lapse imaging. Furthermore, using gout patient-derived synovial leukocytes, we successfully obtained RI tomogram images of intracellular MSU crystals. The 3D RI identification of MSU crystals was verified with birefringence through polarization-sensitive ODT measurements. Together, our results provide evidence that this novel ODT can identify birefringent MSU crystals in synovial leukocytes of patients with gout.

Actin-microtubule crosslinker Pod-1 tunes PAR-1 signaling to control synaptic development and tau-mediated synaptic toxicity.

Partitioning-defective 1 (PAR-1), a conserved cell polarity regulator, plays an important role in synaptic development, and its mutation affects the formation of synaptic boutons and localization of postsynaptic density protein Discs large (Dlg) at the neuromuscular junction (NMJ) in Drosophila. Drosophila PAR-1 and its human homolog, Microtubule affinity-regulating kinases (MARK), are also known to be implicated in Alzheimer's disease (AD) by controlling tau-mediated Aß toxicity. However, the molecular mechanisms of PAR-1 function remain incompletely understood. Here we identified Pod-1, an actin-microtubule crosslinker, which functionally and physically interacts with PAR-1 in Drosophila. Pod-1 prominently co-localizes with PAR-1 in the postsynaptic region and regulates PAR-1 activity at the NMJ. Synaptic defects, including the reduction of boutons and delocalization of Dlg caused by PAR-1 overexpression, were rescued by Pod-1 knockdown. Conversely, the reduction of synaptic boutons in PAR-1 overexpressed NMJ was synergistically enhanced by the overexpression of Pod-1. Furthermore, Pod-1 increases the PAR-1 dependent S262 phosphorylation of tau, which is known to contribute to tau-mediated Aß toxicity. In line with the change of tau phosphorylation, Pod-1 knockdown rescued tau-mediated synaptic toxicity at the NMJ. Our results suggest that Pod-1 may act as a modulator of PAR-1 in synaptic development and tau-mediated toxicity.

Systemic control of immune cell development by integrated carbon dioxide and hypoxia chemosensation in Drosophila.

Drosophila hemocytes are akin to mammalian myeloid blood cells that function in stress and innate immune-related responses. A multi-potent progenitor population responds to local signals and to systemic stress by expanding the number of functional blood cells. Here we show mechanisms that demonstrate an integration of environmental carbon dioxide (CO2) and oxygen (O2) inputs that initiate a cascade of signaling events, involving multiple organs, as a stress response when the levels of these two important respiratory gases fall below a threshold. The CO2 and hypoxia-sensing neurons interact at the synaptic level in the brain sending a systemic signal via the fat body to modulate differentiation of a specific class of immune cells. Our findings establish a link between environmental gas sensation and myeloid cell development in Drosophila. A similar relationship exists in humans, but the underlying mechanisms remain to be established.

Iron Homeostasis Controls Myeloid Blood Cell Differentiation in Drosophila.

Iron is an essential divalent ion for aerobic life. Life has evolved to maintain iron homeostasis for normal cellular and physiological functions and therefore imbalances in iron levels exert a wide range of consequences. Responses to iron dysregulation in blood development, however, remain elusive. Here, we found that iron homeostasis is critical for differentiation of Drosophila blood cells in the larval hematopoietic organ, called the lymph gland. Supplementation of an iron chelator, bathophenanthroline disulfate (BPS) results in an excessive differentiation of the crystal cell in the lymph gland. This phenotype is recapitulated by loss of Fer1HCH in the intestine, indicating that reduced levels of systemic iron enhances crystal cell differentiation. Detailed analysis of Fer1HCH-tagged-GFP revealed that Fer1HCH is also expressed in the hematopoietic systems. Lastly, blocking Fer1HCH expression in the mature blood cells showed marked increase in the blood differentiation of both crystal cells and plasmatocytes. Thus, our work suggests a relevance of systemic and local iron homeostasis in blood differentiation, prompting further investigation of molecular mechanisms underlying iron regulation and cell fate determination in the hematopoietic system.

Long-term percutaneous coronary intervention rates and associated independent predictors for progression of nonintervened nonculprit coronary lesions.

After successful percutaneous coronary intervention (PCI), unpredictable coronary events occur that are caused by in-stent restenosis and the progression of preexisting nonculprit coronary lesions. However, little is known about the long-term clinically driven PCI rates for the progression of nonculprit coronary lesions discovered during culprit-lesion PCI or its independent predictors, including several biomarkers. In this study, the clinical and angiographic data of 1,395 PCI patients treated from January 2004 to May 2007 were retrospectively analyzed. Of these patients, 507 were eligible for this study. After baseline PCI (i.e., culprit-lesion PCI), 81 patients (16%) underwent additional clinically driven PCI to treat preexisting nonculprit coronary lesions during the study period. The cumulative rates of clinically driven PCI for nonculprit coronary lesions were 7.7% (n = 39) at 1 year, 14% (n = 70) at 2 years, and 16% (n = 81) at 3 years. The independent predictors of clinically driven PCI included a larger number of significant coronary lesions (odds ratio [OR] 2.29, 95% confidence interval [CI] 1.5 to 3.5, p <0.001), low high-density lipoprotein (<40 mg/dl; OR 2.01, 95% CI 1.01 to 3.98, p = 0.046), hypercholesterolemia (total cholesterol >200 mg/dl; OR 1.46, 95% CI 1.22 to 1.97, p = 0.04), history of PCI (OR 1.24, 95% CI 1.09 to 1.60, p = 0.003), and increased triglyceride levels (OR 1.003, 95% CI 1.001 to 1.007, p = 0.038) at the time of baseline PCI. In conclusion, PCI patients with nonculprit coronary lesions underwent additional clinically driven PCI at rates of 7.7% at 1 year, 14% at 2 years, and 16% at 3 years because of the progression of preexisting nonculprit coronary lesions. Overall coronary artery disease burden and poor lipid profiles at baseline PCI confer significant risks for clinically driven PCI.

Comparison of Left Ventricular Hypertrophy, Fibrosis and Dysfunction According to Various Disease Mechanisms such as Hypertension, Diabetes Mellitus and Chronic Renal Failure.

BACKGROUND: Left ventricular hypertrophy (LVH) has been known as an important predictor of prognosis of cardiovascular disease. Carboxy-terminal propeptide of procollagen type I (PIP) is related with myocardial fibrosis. We sought to analyze the differences in the characteristics of LVH, myocardial fibrosis, and LV functions among hypertension (HBP), diabetes mellitus (DM) and chronic renal failure (CRF). METHODS: We enrolled consecutive patients with LVH. Patients were grouped as HBP (n=50), DM (n=41), CRF (n=31). Age and sex-matched normal control was also enrolled (n=32). Echocardiography and blood sampling for serum PIP level measuring was performedin all participants. RESULTS: There were no differences in baseline characteristics except systolic blood pressure among four groups. In three patients groups, their LV mass indices were significantly increased than control. Serum PIP level in CRF was much higher than others (CRF 1505.5 vs. HBP 868.7 vs. DM 687.5 vs. control 826.4, p<0.0001). LV diastolic and systolic function evaluated by E', E/E, S' and midwall fractional shortening was significantly decreased in three patients groups. However, LAVi was significantly elevated and LV ejection fraction was significantly decreased in CRF compared to others. In correlation analysis, indices of diastolic function were weakly, but statistically correlated with PIP (E': r=0.234, p=0.006; LAVi: r=0.231, p=0.006). CONCLUSION: In CRF, LV function was more deteriorated and serum PIP was more elevated when compared to HBP or DM. Therefore, myocardial fibrosis may play an important role to LV dysfunction as well as LV hypertrophy in CRF in some degree.