Loss of Miro1-directed mitochondrial movement results in a novel murine model for neuron disease

Defective mitochondrial distribution in neurons is proposed to cause ATP depletion and calcium-buffering deficiencies that compromise cell function. However, it is unclear whether aberrant mitochondrial motility and distribution alone are sufficient to cause neurological disease. Calcium-binding mitochondrial Rho (Miro) GTPases attach mitochondria to motor proteins for anterograde and retrograde transport in neurons. Using two new KO mouse models, we demonstrate that Miro1 is essential for development of cranial motor nuclei required for respiratory control and maintenance of upper motor neurons required for ambulation. Neuron-specific loss of Miro1 causes depletion of mitochondria from corticospinal tract axons and progressive neurological deficits mirroring human upper motor neuron disease. Although Miro1-deficient neurons exhibit defects in retrograde axonal mitochondrial transport, mitochondrial respiratory function continues. Moreover, Miro1 is not essential for calcium-mediated inhibition of mitochondrial movement or mitochondrial calcium buffering. Our findings indicate that defects in mitochondrial motility and distribution are sufficient to cause neurological disease.Motor neuron diseases (MNDs), including ALS and spastic paraplegia (SP), are characterized by the progressive, length-dependent degeneration of motor neurons, leading to muscle atrophy, paralysis, and, in some cases, premature death. There are both inherited and sporadic forms of MNDs, which can affect upper motor neurons, lower motor neurons, or both. Although the molecular and cellular causes of most MNDs are unknown, many are associated with defects in axonal transport of cellular components required for neuron function and maintenance (1–6).A subset of MNDs is associated with impaired mitochondrial respiration and mitochondrial distribution. This observation has led to the hypothesis that neurodegeneration results from defects in mitochondrial motility and distribution, which, in turn, cause subcellular ATP depletion and interfere with mitochondrial calcium ([Ca²⁺]_m) buffering at sites of high synaptic activity (reviewed in ref. 7). It is not known, however, whether mitochondrial motility defects are a primary cause or a secondary consequence of MND progression. In addition, it has been difficult to isolate the primary effect of mitochondrial motility defects in MNDs because most mutations that impair mitochondrial motility in neurons also affect transport of other organelles and vesicles (1, 8–11).In mammals, the movement of neuronal mitochondria between the cell body and the synapse is controlled by adaptors called trafficking kinesin proteins (Trak1 and Trak2) and molecular motors (kinesin heavy chain and dynein), which transport the organelle in the anterograde or retrograde direction along axonal microtubule tracks (7, 12–24). Mitochondrial Rho (Miro) GTPase proteins are critical for transport because they are the only known surface receptors that attach mitochondria to these adaptors and motors (12–15, 18, 25, 26). Miro proteins are tail-anchored in the outer mitochondrial membrane with two GTPase domains and two predicted calcium-binding embryonic fibroblast (EF) hand motifs facing the cytoplasm (12, 13, 25, 27, 28). A recent Miro structure revealed two additional EF hands that were not predicted from the primary sequence (29). Studies in cultured cells suggest that Miro proteins also function as calcium sensors (via their EF hands) to regulate kinesin-mediated mitochondrial “stopping” in axons (15, 16, 26). Miro-mediated movement appears to be inhibited when cytoplasmic calcium is elevated in active synapses, effectively recruiting mitochondria to regions where calcium buffering and energy are needed. Despite this progress, the physiological relevance of these findings has not yet been tested in a mammalian animal model. In addition, mammals ubiquitously express two Miro orthologs, Miro1 and Miro2, which are 60% identical (12, 13). However, the individual roles of Miro1 and Miro2 in neuronal development, maintenance, and survival have no been evaluated.We describe two new mouse models that establish the importance of Miro1-mediated mitochondrial motility and distribution in mammalian neuronal function and maintenance. We show that Miro1 is essential for development/maintenance of specific cranial neurons, function of postmitotic motor neurons, and retrograde mitochondrial motility in axons. Loss of Miro1-directed retrograde mitochondrial transport is sufficient to cause MND phenotypes in mice without abrogating mitochondrial respiratory function. Furthermore, Miro1 is not essential for calcium-mediated inhibition of mitochondrial movement or [Ca²⁺]_m buffering. These findings have an impact on current models for Miro1 function and introduce a specific and rapidly progressing mouse model for MND.     

New Insight Into Thermodynamical Stability of Carbamazepine

Carbamazepine (CBZ)—an antiepileptic drug—belongs to Biopharmaceutics Classification System II Class. It has low solubility and consequently limited bioavailability. One of the ways to improve drugs solubility is amorphization of their structure. Herein, cooling CBZ—at different cooling rates—was investigated as a way to obtain glassy, better soluble form. During preliminary differential scanning calorimetry experiments, some peculiar behavior of the examined material, different from those stated in the literature, was observed. Further investigations using differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscope revealed that decomposition temperature of CBZ is about 30°C lower than previously assumed. Moreover, high-resolution thermogravimetric measurements indicate that some decomposition processes could start even below the temperature reported as the melting point of the form I of CBZ.     

Is Parenteral Phosphate Replacement in the Intensive Care Unit Safe?

Hypophosphatemia is well recognized in the intensive care setting, associated with refeeding and continuous forms of renal replacement therapy (CCRT). However, it is unclear as to when and how to administer intravenous phosphate supplementation in the general intensive care setting. There have been recent concerns regarding phosphate administration and development of acute kidney injury. We therefore audited our practice of parenteral phosphate administration. We prospectively audited parenteral phosphate administration (20 mmol) in 58 adult patients in a general intensive care unit in a University tertiary referral center. Fifty‐eight patients were audited; mean age 57.2 ± 2.0 years, 70.7% male. The median duration of the infusion was 310 min (228–417), and 50% of the patients were on CRRT. 63.8% of patients were hypophosphatemic (<0.87 mmol/L) prior to the phosphate infusion, and serum phosphate increased from 0.79 ± 0.02 to 1.07 ± 0.03 mmol/L, P < 0.001. Two patients became hyperphosphatemic (>1.45 mmol/L). There was no correlation between the change in serum phosphate and the pre‐infusion phosphate. Although there were no significant changes in serum urea, creatinine or other electrolytes, arterial ionized calcium fell from 1.15 ± 0.01 to 1.13 ± 0.01 mmol/L, P < 0.01. Although infusion of 20 mmol phosphate did not appear to adversely affect renal function and corrected hypophosphatemia in 67.7% of cases, we found that around 33% of patients who were given parenteral phosphate were not hypophosphatemic, and that the fall in ionized calcium raises the possibility of the formation of calcium‐phosphate complexes and potential for soft tissue calcium deposition.     

Mitochondrial ROMK Channel Is a Molecular Component of MitoKATP

Rationale: Activation of the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) has been implicated in the mechanism of cardiac ischemic preconditioning, yet its molecular composition is unknown. Objective: To use an unbiased proteomic analysis of the mitochondrial inner membrane to identify the mitochondrial K(+) channel underlying mitoK(ATP). Methods and Results: Mass spectrometric analysis was used to identify KCNJ1(ROMK) in purified bovine heart mitochondrial inner membrane and ROMK mRNA was confirmed to be present in neonatal rat ventricular myocytes and adult hearts. ROMK2, a short form of the channel, is shown to contain an N-terminal mitochondrial targeting signal, and a full-length epitope-tagged ROMK2 colocalizes with mitochondrial ATP synthase β. The high-affinity ROMK toxin, tertiapin Q, inhibits mitoK(ATP) activity in isolated mitochondria and in digitonin-permeabilized cells. Moreover, short hairpin RNA-mediated knockdown of ROMK inhibits the ATP-sensitive, diazoxide-activated component of mitochondrial thallium uptake. Finally, the heart-derived cell line, H9C2, is protected from cell death stimuli by stable ROMK2 overexpression, whereas knockdown of the native ROMK exacerbates cell death. Conclusions: The findings support ROMK as the pore-forming subunit of the cytoprotective mitoK(ATP) channel.     

Serum albumin as a determinant of cortisol release in patients with acute ischemic stroke

ObjectiveAnimal studies demonstrated that protein malnutrition increases pituitary-adrenorcortical activity and leads to excessive cortisol release. The aim of our study was to determine the association between serum albumin and cortisol level in patients with acute ischemic stroke.MethodsFifty-nine patients with first-ever ischemic stroke were included. Serum albumin level was measured within 36 h after stroke symptoms onset. Serum cortisol was measured between 36 and 72 h after stroke onset at 6 a.m., 10 a.m., 6 p.m. and 10 p.m.ResultsThe patients in upper tertile of serum albumin had significantly lower cortisol level measured at 6 a.m. (median with interquartiles: 549.0 [430.4–667.7] nmol/L vs 590.4 [482.8–918.7] nmol/L, P = 0.047) and 10 a.m. (402.8 [344.9–510.4] nmol/L vs 634.6 [482.8–827.7] nmol/L, P < 0.01) than patients in lower and middle tertiles. On logistic regression analysis adjusted for age and stroke severity, patients in lower and middle tertile of serum albumin had about 7-times higher risk of hypercortisolemia than patients in upper tertile (P < 0.01).ConclusionsLow serum albumin level in patients with ischemic stroke is associated with higher serum cortisol level and predisposes to hypercortisolemia.     

Error-prone mammalian female meiosis from silencing the spindle assembly checkpoint without normal interkinetochore tension

It is well established that chromosome segregation in female meiosis I (MI) is error-prone. The acentrosomal meiotic spindle poles do not have centrioles and are not anchored to the cortex via astral microtubules. By Cre recombinase-mediated removal in oocytes of the microtubule binding site of nuclear mitotic apparatus protein (NuMA), which is implicated in anchoring microtubules at poles, we determine that without functional NuMA, microtubules lose connection to MI spindle poles, resulting in highly disorganized early spindle assembly. Subsequently, very long spindles form with hyperfocused poles. The kinetochores of homologs make attachments to microtubules in these spindles but with reduced tension between them and accompanied by alignment defects. Despite this, the spindle assembly checkpoint is normally silenced and the advance to anaphase I and first polar body extrusion takes place without delay. Females without functional NuMA in oocytes are sterile, producing aneuploid eggs with altered chromosome number. These findings establish that in mammalian MI, the spindle assembly checkpoint is unable to sustain meiotic arrest in the presence of one or few misaligned and/or misattached kinetochores with reduced interkinetochore tension, thereby offering an explanation for why MI in mammals is so error-prone.     

Influence of L-arginine on expression of HSP70 and p-53 proteins – early biomarkers of cellular danger in renal tubular cells. Immunohistochemical assessment

Introduction

The aim of the present study was to investigate expression of HSP70 and p-53 proteins as mechanisms of protection of the renal tubular epithelial cells from l-arginine that induces cellular stress.

Material and methods

The study material consisted of 16 white Wistar female rats. The rats were divided into 2 equal groups. The rats in the experimental group received L-arginine 40 mg/kg body weight per capita every other day for 2 weeks and were decapitated after 3 weeks of the experiment. After decapitation, specimens from the kidney were collected, fixed in 10% formalin, and then embedded in paraffin blocks. Proteins HSP70 and p-53 on slides were detected using the standard three-step immunohistochemical method.

Results

The quantitative evaluation of HSP70 and p-53 expression showed that the area occupied with positive HSP70 and p-53 reaction in the rat renal tubular cells of the experimental group (p-53: 2835.44 ±254.72 µm²; HSP70: 24111.42 ±4290.88 µm²) was more statistically significant than the control group (p-53: 1882.05 ±466.43 µm²; HSP70: 11388.63 ±1455.24 µm²). In the present study, the dose of L-arginine was similar to the one that was used in the gestosis treatment of pregnant women.

Conclusions

The renal epithelial cells responded to L-arginine therapy, increasing expression of HSP70 and p-53 proteins. The study showed that L-arginine as a donor of exogenous nitric oxide has a disruptive effect on the renal tubular cells of rat kidneys. Thus it is going to be a subject of the author''s future investigations.