Loss of MBNL1-mediated retrograde BDNF signaling in the myotonic dystrophy brain.

Reduced brain volume including atrophy in grey and white matter is commonly seen in myotonic dystrophy type 1 (DM1). DM1 is caused by an expansion of CTG trinucleotide repeats in the 3' untranslated region (UTR) of the Dystrophia Myotonica Protein Kinase (DMPK) gene. Mutant DMPK mRNA containing expanded CUG RNA (DMPK-CUGexp) sequesters cytoplasmic MBNL1, resulting in morphological impairment. How DMPK-CUGexp and loss of MBNL1 cause histopathological phenotypes in the DM1 brain remains elusive. Here, we show that BDNF-TrkB retrograde transport is impaired in neurons expressing DMPK-CUGexp due to loss of cytoplasmic MBNL1 function. We reveal that mature BDNF protein levels are reduced in the brain of the DM1 mouse model EpA960/CaMKII-Cre. Exogenous BDNF treatment did not rescue impaired neurite outgrowth in neurons expressing DMPK-CUGexp, whereas overexpression of the cytoplasmic MBNL1 isoform in DMPK-CUGexp-expressing neurons improved their responsiveness to exogenous BDNF. We identify dynein light chain LC8-type 2, DYNLL2, as an MBNL1-interacting protein and demonstrate that their interaction is RNA-independent. Using time-lapse imaging, we show that overexpressed MBNL1 and DYNLL2 move along axonal processes together and that MBNL1-knockdown impairs the motility of mCherry-tagged DYNLL2, resulting in a reduced percentage of retrograde DYNLL2 movement. Examination of the distribution of DYNLL2 and activated phospho-TrkB (pTrkB) receptor in EpA960/CaMKII-Cre brains revealed an increase in the postsynaptic membrane fraction (LP1), indicating impaired retrograde transport. Finally, our neuropathological analysis of postmortem DM1 tissue reveals that reduced cytoplasmic MBNL1 expression is associated with an increase in DYNLL2 and activated pTrkB receptor levels in the synaptosomal fraction. Together, our results support that impaired MBNL1-mediated retrograde BDNF-TrkB signaling may contribute to the histopathological phenotypes of DM1.

Time-varying serum albumin levels and all-cause mortality in prevalent peritoneal dialysis patients: a 5-year observational study.

BACKGROUND: In this study, we investigated the association of time-varying serum albumin levels with mortality over a 5-year period in one cohort of patients undergoing long-term peritoneal dialysis (PD) therapy. METHODS: The participants in this study enrolled 302 patients who underwent long-term PD at a single PD center in Taiwan. We reviewed medical records from 2011 to 2015 retrospectively. Time-averaged albumin level and serum albumin reach rate (defined as the percentage of serum albumin measurements that reached ≥3.5 g/dL) were applied as the predictor variables in the first 2 years (2011-2012). All-cause mortality was used as the outcome variable in the subsequent 3 years (2013-2015). Hazard function of all-cause mortality in the study participants was examined by using Cox proportional hazard regression models . RESULTS: Patients with different albumin reach rates (75-< 100%, 50-< 75%, 1-< 50%) did not exhibit a significantly increased risk for all-cause mortality. Patients with a 0% albumin reach rate exhibited a significantly increased risk for all-cause mortality (hazard ratio [HR] 7.59, 95% confidence interval [CI], 2.38-24.21) by fully adjusted analysis. Patients with time-averaged albumin levels of < 3.5 g/dL (HR 15.49, 95% CI 1.74-137.72) exhibited a higher risk for all-cause mortality than those with serum albumin levels ≥4.0 g/dL. CONCLUSIONS: This study demonstrated that higher serum albumin reach rates and higher time-averaged serum albumin levels are associated with a lower mortality rate over a 5-year period among patients undergoing long-term PD.

Ubiquitination of MBNL1 Is Required for Its Cytoplasmic Localization and Function in Promoting Neurite Outgrowth.

The Muscleblind-like protein family (MBNL) plays an important role in regulating the transition between differentiation and pluripotency and in the pathogenesis of myotonic dystrophy type 1 (DM1), a CTG expansion disorder. How different MBNL isoforms contribute to the differentiation and are affected in DM1 has not been investigated. Here, we show that the MBNL1 cytoplasmic, but not nuclear, isoform promotes neurite morphogenesis and reverses the morphological defects caused by expanded CUG RNA. Cytoplasmic MBNL1 is polyubiquitinated by lysine 63 (K63). Reduced cytoplasmic MBNL1 in the DM1 mouse brain is consistent with the reduced extent of K63 ubiquitination. Expanded CUG RNA induced the deubiqutination of cytoplasmic MBNL1, which resulted in nuclear translocation and morphological impairment that could be ameliorated by inhibiting K63-linked polyubiquitin chain degradation. Our results suggest that K63-linked ubiquitination of MBNL1 is required for its cytoplasmic localization and that deubiquitination of cytoplasmic MBNL1 is pathogenic in the DM1 brain.

Reduced cytoplasmic MBNL1 is an early event in a brain-specific mouse model of myotonic dystrophy.

Myotonic dystrophy type 1 (DM1) is caused by an expansion of CTG repeats in the 3' untranslated region (UTR) of the dystrophia myotonia protein kinase (DMPK) gene. Cognitive impairment associated with structural change in the brain is prevalent in DM1. How this histopathological abnormality during disease progression develops remains elusive. Nuclear accumulation of mutant DMPK mRNA containing expanded CUG RNA disrupting the cytoplasmic and nuclear activities of muscleblind-like (MBNL) protein has been implicated in DM1 neural pathogenesis. The association between MBNL dysfunction and morphological changes has not been investigated. We generated a mouse model for postnatal expression of expanded CUG RNA in the brain that recapitulates the features of the DM1 brain, including the formation of nuclear RNA and MBNL foci, learning disability, brain atrophy and misregulated alternative splicing. Characterization of the pathological abnormalities by a time-course study revealed that hippocampus-related learning and synaptic potentiation were impaired before structural changes in the brain, followed by brain atrophy associated with progressive reduction of axon and dendrite integrity. Moreover, cytoplasmic MBNL1 distribution on dendrites decreased before dendrite degeneration, whereas reduced MBNL2 expression and altered MBNL-regulated alternative splicing was evident after degeneration. These results suggest that the expression of expanded CUG RNA in the DM1 brain results in neurodegenerative processes, with reduced cytoplasmic MBNL1 as an early event response to expanded CUG RNA.

Implication of cerebral dopamine-beta hydroxylase for cardiovascular and mood regulation in rats.

The essentiality of the role of norepinephrine (NE) in the central nervous system has recently been reconsidered. NE exerts many effects and mediates a number of functions in living organisms. Dopamine-beta-hydroxylase (DBH) is the crucial enzyme for NE and epinephrine biosynthesis. Removal of this enzyme causes deficient NE at sympathetic terminals characterized by orthostatic hypotension in humans. The hypothesis tested in this study was that NE deficiency in the central nervous system caused autonomic failure in cardiovascular regulation. The immunotoxin anti-DBH-saporin (DSAP) was used to examine the putative role of cerebral NE. Male Sprague-Dawley rats were injected, intracerebroventricularly (icv), with DSAP and cardiovascular reactivity, as well as behavioral variables in the open-field locomotion test (OLT), sucrose intake test (SIT) and forced swim test (FST), were monitored for changes. The results indicated that treatment with DSAP caused significant reductions in spontaneous blood pressure (BP) and heart rate (HR), and a decrease in the rearing position on the OLT, in the same group of rats. In addition, a significant increase in mobility with low concurrent immobility frequencies was observed on the FST. However, there was no variation on the SIT. In conclusion, a deficiency in the cerebral DBH might dysregulate the autonomic outflows and, thus, leads to lower BP and HR. However, there was no mood change such as despair or anhedonia observed in the experiments.

[Testicular microlithiasis: ultrasonic diagnosis and correlation with male infertility].

OBJECTIVE: To study the sonographic appearance of testicular microlithiasis (TM) and its correlation with male infertility. METHODS: We conducted high-resolution 2D ultrasound examination for 1 198 patients with scrotal diseases, including 379 with infertility and 819 with other testicular diseases. RESULTS: TM was found in 21 of the infertile men (5.54%) and 12 of the other 819 fertile patients (1.47%). TM was correlated with male infertility (r = 0. 115, P < 0.01), with a higher incidence in the infertile patients than in patients with other testicular diseases (P < 0.05). Sonography of TM showed high-echo dots in the testicular parenchyma, sparse, sporadic or converted, about 1 mm in diameter and without shadow. CONCLUSION: The sonographic appearance of TM, with its obvious features, is conducive to the definite diagnosis of the disease. TM is correlated with male infertility.