MicroRNA regulation of central glial cell line-derived neurotrophic factor (GDNF) signalling in depression

Although multiple studies have reported that peripheral glial cell line-derived neurotrophic factor (GDNF) is reduced in depression, cerebral GDNF signalling has yet to be examined in this condition. Here, we report an isoform-specific decrease in GDNF family receptor alpha 1 (GFRA1) mRNA expression, resulting in lowered GFRα1a protein levels in basolateral amygdala (BLA) samples from depressed subjects. Downregulation of GFRα1a was associated with increased expression of microRNAs, including miR-511, predicted to bind to long 3' untranslated region (3'-UTR)-containing transcripts (GFRA1-L) coding for GFRα1a. Transfection of human neural progenitor cells (NPCs) with a miR-511 mimic was sufficient to repress GFRA1-L/GFRα1a without altering GFRα1b, and resulted in pathway-specific changes in immediate early gene activity. Unexpectedly, GFRα1a knockdown did not reduce NPC responses to GDNF. Rather, it greatly enhanced mitogen-activated protein kinase signalling. This effect appeared to be mediated by GDNF/soluble GFRα1/neural cell adhesion molecule binding, and substituting the soluble GFRα1a/GFRα1b content of miR-511-transfected NPCs with that of controls rescued signalling. In light of previous reports suggesting that GFRα1b can inhibit GFRα1a-induced neuroplasticity, we also assessed the association between GFRα1 and doublecortin (DCX; a hyperplastic marker) in human BLA. Although controls displayed coordinated expression of GFRα1a and b isoforms and these correlated positively with DCX, the only significant association observed among depressed subjects was a strongly negative correlation between GFRα1b and DCX. Taken together, these results suggest that microRNA-mediated reductions of GFRα1a in depression change the quality, rather than the quantity, of GDNF signalling. They also suggest that central GDNF signalling may represent a novel target for antidepressant treatment.

Immunohistochemical and biochemical assessment of caspase-3 activation and DNA fragmentation following transient focal ischemia in the rat

In the present study, we evaluated the time-course of caspase-3 activation, and the evolution of cell death following focal cerebral ischemia produced by transient middle cerebral artery occlusion in rats. Ischemia-induced active caspase-3 immunoreactivity in the striatum but not the cortex at 3 and 6 h time points post-reperfusion. Furthermore, using a novel approach to visualize enzymatic activity, deltaC-APP, a C-terminal cleavage product of APP generated by caspase-3, was found to immunolocalize to the same areas as active caspase-3. Double-labeling studies demonstrated co-localization of these two proteins at the cellular level. Further double-labeling experiments revealed that active caspase-3 was confined to neuronal cells which were still viable and thus immunoreactive for NeuN. DNA fragmentation, assessed histologically by terminal dUTP nick-end labeling (TUNEL), was observed in a small number of cells in the striatum as early as 3 h, but only began to appear in the cortex by 6 h. DNA fragmentation was progressive, and by 24 h post-reperfusion, large portions of both the striatum and cortex showed TUNEL positive cells. However, double-labeling of active caspase-3 with TUNEL showed only minimal co-localization at all time-points. Thus, caspase-3 activation is an event that appears to occur prior to DNA fragmentation. As a confirmation of the histological TUNEL data, 24 h ischemia also induced the generation of nucleosome fragments, evidenced by cell death enzyme-linked immunosorbent assay. Using a novel ischemia-induced substrate cleavage biochemical approach, spectrin P120 fragment, a caspase-specific cleavage product of alpha II spectrin, a cytoskeletal protein, was shown to be elevated by western blotting. Brain concentrations of both nucleosomes and spectrin P120 correlate with the degree of injury previously assessed by triphenyltetrazolium chloride staining and infarct volume calculation. Together, our findings suggest a possible association between caspase-3 activation and ischemic cell death following middle cerebral artery occlusion brain injury.

Caspase 3 deficiency rescues peripheral nervous system defect in retinoblastoma nullizygous mice

The retinoblastoma tumor suppressor protein, pRb, is a key regulator of cell cycle and has been implicated in the terminal differentiation of neuronal cells. Mice nullizygous for pRb die by embryonic day 14.5 from hematopoietic and neurological defects attributed to failed differentiation (Clarke et al., 1992; Jacks et al., 1992; Lee et al., 1992). Previous studies by MacLeod et al. (1996) have demonstrated that the loss of p53 protects Rb-deficient CNS neurons but not peripheral nervous system (PNS) neurons from cell death. Thus, the mechanisms by which PNS neurons undergo apoptosis in response to Rb deficiency remain unknown. In view of the pivotal role of caspase 3 in the regulation of neuronal apoptosis during development, we examined its function in the execution of the wide-spread neuronal cell death induced by Rb deficiency. Our results support a number of conclusions. First, we show that caspase 3 becomes activated in all neuronal populations undergoing apoptosis. Second, caspase 3 deficiency does not extend the life span of Rb null embryos, because double null mutants exhibit high rates of liver apoptosis resulting in erythropoietic failure. Third, Rb/caspase 3 double-mutant neurons of the CNS exhibit widespread apoptosis similar to that seen in Rb mutants alone; thus caspase 3 deficiency does not protect this population from apoptosis. Finally, in contrast to the CNS, neurons of the PNS including those comprising the trigeminal ganglia and the dorsal root ganglia are protected from apoptosis in Rb/caspase 3 double-mutant embryos. Examination of the mechanistic differences between these two cell types suggest that CNS neurons may invoke other caspases to facilitate apoptosis in the absence of caspase 3. These findings suggest that PNS neurons are dependent on caspase 3 for the execution of apoptosis and that caspase 3 may serve as a key therapeutic target for neuroprotection after injury of this cell type.

Enzymes active in the areas undergoing cartilage resorption during the development of the secondary ossification center in the tibiae of rats aged 0-21 days: II. Two proteinases, gelatinase B and collagenase-3, are implicated in the lysis of collagen fibrils

In the transformation of the cartilaginous epiphysis into bone, the first indication of change in the surfaces destined for resorption is the cleavage of aggrecan core protein by unidentified matrix metalloproteinases (MMPs) (Lee et al., this issue). In cartilage areas undergoing resorption, the cleavage leaves as superficial, 6-microm-thick band of matrix, referred to as "pre-resorptive layer." This layer harbors G1-fragments of the aggrecan core protein within a framework of collagen-rich fibrils exhibiting various stages of degeneration. Investigation of this layer in every resorption area by gelatin histozymography and TIMP-2 histochemistry demonstrates the presence of an MMP whose histozymographic activity is inhibited by such a low dose of the inhibitor CT1746 as to identify it as gelatinase A or B. Attempts at blocking the histozymographic reactions with neutralizing antibodies capable of inhibiting either gelatinase A or B reveals that only those against gelatinase B do so. Immunostaining of sections with anti-gelatinase B IgG confirms the presence of gelatinase B in every pre-resorptive layer, that is, at the blind end of excavated canals (stage I; 6-day-old rats), at sites along the walls of the forming marrow space (stage II; 7days), at sites within the walls of this space as it becomes the ossification center (stage III; 9 days) and along the wall of the maturing center (stage IV; 10-21 days). We also report the presence of collagenase-3 in precisely the same sites, possibly as active enzyme, but this remains to be proven. Because the results reveal that collagenase-3 is present beside gelatinase B in every pre-resorptive layer and, because these sites exhibit various signs of degradation including fibrillar debris, reduction in fibril number, or overt loss, we propose that gelatinase B and collagenase-3 mediate the lysis of this pre-resorptive layer-most likely through a cooperative attack leading to the disintegration of the collagen fibril framework.

Enzymes active in the areas undergoing cartilage resorption during the development of the secondary ossification center in the tibiae of rats ages 0-21 days: I. Two groups of proteinases cleave the core protein of aggrecan

The formation of a secondary ossification center in the cartilaginous epiphysis of long bones requires the excavation of canals and marrow space and, therefore, the resorption of cartilage. On the assumption that its resorption requires the lysis of the major cartilage component aggrecan, it was noted that the core protein may be cleaved in vitro by proteinases from two subfamilies: matrix metalloproteinases (MMPs) and aggrecanases. Such cleavage results in aggrecan being replaced by a fragment of itself referred to as a "G1-fragment." To find out if this cleavage occurs in the developing epiphysis of the rat tibia, the approach has been to localize the G1 fragments. For this purpose two neoepitope antisera were applied, one capable of recognizing the MMP-generated G1-fragment that bears the C-terminus ...FVDIPEN341 and the other capable of recognizing the aggrecanase-generated G1-fragment that carries the C-terminus ...NITEGE373. With the aid of these antisera, we report here that aggrecan cleavage is localized to newly developed sites of erosion. Thus, at 6 days of age, canals allowing the entry of capillaries are dug out from the surface of the epiphysis in a radial direction (stage I), whereas immunostaining indicative of aggrecan cleavage by MMPs appears at the blind end of each canal. The next day, the canal blind ends fuse to create a marrow space in the epiphysis (stage II), whereas immunostaining produced by MMPs occurs along the walls of this space. By 9 days, clusters of hypertrophic chondrocytes are scattered along the marrow space wall to initiate the formation of the secondary ossification center (stage III), where the resorption sites are unreactive to either antiserum. From the 9th to the 21st day, the center keeps on enlarging and, as the distal wall of the marrow space recedes, it is intensely immunostained with both antisera indicating that both MMPs and aggrecanases are involved in this resorption. We conclude, that both enzyme subfamilies contribute to the lysis of aggrecan. However, the results suggest that the respective subfamilies target different sites and even stages of development in the tissue, suggesting some diversity in the mode of aggrecan lysis during the excavation of a secondary ossification center.

Active gelatinase B is identified by histozymography in the cartilage resorption sites of developing long bones

In order to determine which proteinases mediate the resorption of endochondral cartilage in the course of long bone development, a novel assay called "histozymography" has been developed. In this assay, frozen sections of tibial head from 21-day-old rats are placed for 4 hr at room temperature on light-exposed photographic emulsion (composed of silver grains embedded in gelatin). We report a localized but complete digestion of emulsion gelatin facing two tissue sites which are, therefore, presumed to contain an active proteinase. One of the sites is localized at the growth plate surface forming the epiphysis/metaphysis interface. The other consists of small patches located within the epiphysis at the edge of the marrow space. Both sites are engaged in the resorption of endochondral cartilage. In both sites, inhibitor tests have established that the involved proteinase is a gelatinase. Furthermore, the use of neutralizing antibodies against gelatinase A or B have demonstrated that only those that are specific for the latter block the reaction. That gelatinase B is present in the two sites has been confirmed by light microscopic immunohistochemistry. Finally, when immunoelectron microscopy is used for fine localization of the cartilage structures that form the epiphysis/metaphysis interface, the enzyme is detected within the 0.5-microm thick edge of the cartilage, and outside the cartilage, it is present in debris composed of type II collagen-rich fibrils in various states of digestion. It is concluded that gelatinase B attacks the edge of an endochondral cartilage and helps to solubilize the type II-collagen-rich fibrillar framework, which is then released as debris for further digestion. This final step opens the way to invasion by capillaries, thereby making possible the replacement of cartilage by bone. Dev Dyn 1999;215:190-205.

[Increase of renal dopamine production induced by nifedipine in hypertensive patients. Double blind vs placebo study]

Dopamine is synthetized and excreted by kidneys, this amine exerts its natriuretic and diuretic effects by inhibition of sodium reabsorption on kidney convoluted tubules. The objective of this study was to verify the changes of dopamine urinary excretion induced by nifedipine-LP treatment in hypertensive patients. Twenty four patients with essential hypertension (stages 1, 2) were included in this double-blind, placebo controlled study. Twelve patients received nifedipine (average daily dose, 21.5 mg/day) for 4 weeks, and 12 patients received placebo for the same time period. No significant changes were detected upon nifedipine treatment neither in plasma biochemical nor hematological parameters. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) was significantly reduced from pretreatment values 168.0 +/- 8.7 mmHg and 102.0 +/- 5.2 mmHg respectively, to end-treatment values 140.0 +/- 6.6 mmHg and 88.0 +/- 5.6 mmHg (p < 0.05). Placebo treatment did not modify SBP and DBP. Urinary dopamine excretion increased by 53% from 679.5 +/- 80.1 micrograms/24 h prior to treatment to 1040.0 +/- 110.1 micrograms/24 h after treatment (p < 0.009. 95% Confidence Interval of the Difference: -538.9 to -183.6). Urinary volume of nifedipine treated patients increased from 1613 +/- 85 mL/24 h to 1920 +/- 160 mL/24 h post-treatment (p < 0.05). No significant changes were observed in urinary noradrenaline and adrenaline excretion in nifedipine or placebo treated patients. Analysis of fluorescent light excitation and emission spectra (200 nm to 800 nm) of dopamine extracted from patient's urine submitted to nifedipine treatment did not reveal any interference when compared to chemically pure dopamine. If is concluded that nifedipine treatment of hypertensive patients increases kidney dopamine production which in turn can exert a natriuretic and diuretic effect besides its well known vasodilator properties.