Coincident pre- and postsynaptic activation induces dendritic filopodia via neurotrypsin-dependent agrin cleavage.

The synaptic serine protease neurotrypsin is essential for cognitive function, as its deficiency in humans results in severe mental retardation. Recently, we demonstrated the activity-dependent release of neurotrypsin from presynaptic terminals and proteolytical cleavage of agrin at the synapse. Here we show that the activity-dependent formation of dendritic filopodia is abolished in hippocampal neurons from neurotrypsin-deficient mice. Administration of the neurotrypsin-dependent 22 kDa fragment of agrin rescues the filopodial response. Detailed analyses indicated that presynaptic action potential firing is necessary for the release of neurotrypsin, whereas postsynaptic NMDA receptor activation is necessary for the neurotrypsin-dependent cleavage of agrin. This contingency characterizes the neurotrypsin-agrin system as a coincidence detector of pre- and postsynaptic activation. As the resulting dendritic filopodia are thought to represent precursors of synapses, the neurotrypsin-dependent cleavage of agrin at the synapse may be instrumental for a Hebbian organization and remodeling of synaptic circuits in the CNS.

MYO9A deficiency in motor neurons is associated with reduced neuromuscular agrin secretion.

Congenital myasthenic syndromes (CMS) are a group of rare, inherited disorders characterized by compromised function of the neuromuscular junction, manifesting with fatigable muscle weakness. Mutations in MYO9A were previously identified as causative for CMS but the precise pathomechanism remained to be characterized. On the basis of the role of MYO9A as an actin-based molecular motor and as a negative regulator of RhoA, we hypothesized that loss of MYO9A may affect the neuronal cytoskeleton, leading to impaired intracellular transport. To investigate this, we used MYO9A-depleted NSC-34 cells (mouse motor neuron-derived cells), revealing altered expression of a number of cytoskeletal proteins important for neuron structure and intracellular transport. On the basis of these findings, the effect on protein transport was determined using a vesicular recycling assay which revealed impaired recycling of a neuronal growth factor receptor. In addition, an unbiased approach utilizing proteomic profiling of the secretome revealed a key role for defective intracellular transport affecting proper protein secretion in the pathophysiology of MYO9A-related CMS. This also led to the identification of agrin as being affected by the defective transport. Zebrafish with reduced MYO9A orthologue expression were treated with an artificial agrin compound, ameliorating defects in neurite extension and improving motility. In summary, loss of MYO9A affects the neuronal cytoskeleton and leads to impaired transport of proteins, including agrin, which may provide a new and unexpected treatment option.

Denervation drives mitochondrial dysfunction in skeletal muscle of octogenarians.

KEY POINTS: Mitochondria are frequently implicated in the ageing of skeletal muscle, although the role of denervation in modulating mitochondrial function in ageing muscle is unknown. We show that increased sensitivity to apoptosis initiation occurs prior to evidence of persistent denervation and is thus a primary mitochondrial defect in ageing muscle worthy of therapeutic targeting. However, at more advanced age, mitochondrial function changes are markedly impacted by persistent sporadic myofibre denervation, suggesting the mitochondrion may be a less viable therapeutic target. ABSTRACT: Experimental denervation modulates mitochondrial function, where changes in both reactive oxygen species (ROS) and sensitivity to permeability transition are implicated in the resultant muscle atrophy. Notably, although denervation occurs sporadically in ageing muscle, its impact on ageing muscle mitochondria is unknown. Because this information has important therapeutic implications concerning targeting the mitochondrion in ageing muscle, we examined mitochondrial function in skeletal muscle from four groups of humans, comprising two active (mean ± SD age: 23.7 ± 2.7 years and 71.2 ± 4.9 years) and two inactive groups (64.8 ± 3.1 years and 82.5 ± 4.8 years), and compared this with a murine model of sporadic denervation. We tested the hypothesis that, although some alterations of mitochondrial function in aged muscle are attributable to a primary organelle defect, mitochondrial dysfunction would be impacted by persistent denervation in advanced age. Both ageing in humans and sporadic denervation in mice increased mitochondrial sensitivity to permeability transition (humans, P = 0.004; mice, P = 0.01). To determine the contribution of sporadic denervation to mitochondrial function, we pharmacologically inhibited the denervation-induced ROS response. This reduced ROS emission by 60% (P = 0.02) in sporadically denervated mouse muscle, which is similar to that seen in humans older than 75 years (-66%, P = 0.02) but not those younger than 75 years. We conclude that an increased sensitivity to permeability transition is a primary mitochondrial defect in ageing muscle. However, at more advanced age, when muscle atrophy becomes more clinically severe, mitochondrial function changes are markedly impacted by persistent sporadic denervation, making the mitochondrion a less viable therapeutic target.

Plasma total C-terminal agrin fragment (tCAF) as a marker for kidney function in patients with chronic kidney disease.

BACKGROUND: Total C-terminal agrin fragment (tCAF) is a new biomarker that was previously correlated with kidney function. This article studies the validity of tCAF as a biomarker for kidney function in chronic kidney disease (CKD). METHODS: Plasma tCAF, serum creatinine (Cr), cystatin C (CyC), blood urea-nitrogen (BUN) concentrations and estimated glomerular filtration rate (eGFR CKD-EPIcrea-cystatin) were assessed in 426 individuals [71 without CKD (CKD 0°) and 355 CKD patients]. In addition to descriptive statistics, univariate correlation between tCAF and biomarkers/eGFR was calculated; multiple linear regression modeling was applied between logarithmic (log) tCAF and log eGFR and adjusted for demographic data. The same methods were used to analyze the association of demographic factors and the different biomarkers adjusted for eGFR. RESULTS: Mean tCAF levels were 1012.2±789.9 pM. tCAF correlated with all biomarkers/eGFR in univariate analysis (eGFR: r=-0.77, Cr: r=0.74, BUN: r=0.66, CyC: r=0.75). Linear regression modeling revealed an excellent coefficient estimate between log tCAF and log eGFR (CKD-EPIcrea-cystatin) (-0.91, p<0.001). tCAF was the parameter least associated with demographic parameters in both univariate and multivariate regression modeling (only with age, coefficient estimate r=-0.159, p=0.001 in multivariate regression). CONCLUSIONS: In conclusion, tCAF is a promising biomarker for the assessment of kidney function in CKD patients showing an excellent correlation with eGFR and being less influenced by demographic parameters compared to conventional biomarkers. These preliminary results encourage further evaluation of tCAF in larger CKD cohorts and other clinical settings such as acute renal failure.

Early postoperative C-terminal agrin fragment (CAF) serum levels predict graft loss and proteinuria in renal transplant recipients.

BACKGROUND: C-terminal agrin fragment (CAF), cleavage product of agrin, was previously correlated with kidney function in renal transplant patients. This article studies the predictive value of CAF for long-term outcomes in renal transplant recipients. METHODS: In this observational cohort study, serum CAF, creatinine and blood-urea-nitrogen (BUN) concentrations and eGFR (CKD-EPI) were assessed 1-3 months after transplantation in 105 patients undergoing kidney transplantation. Cox regression models were used to analyse the predictive value of all parameters concerning all-cause mortality (ACM), graft loss (GL), doubling of creatinine/proteinuria at the end of follow-up. RESULTS: Median follow-up time was 3.1 years. The mean concentrations were 191.9±152.4 pM for CAF, 176±96.8 µmol/L for creatinine, 12.6±6.2 mmol/L for BUN and 44.9±21.2 mL/min for CKD-EPI formula, respectively. In univariate analysis CAF and BUN concentrations predicted ACM (CAF: HR=1.003, 1.1-fold risk, p=0.043; BUN: HR=1.037, 1.3-fold risk, p=0.006). Concerning GL, CAF (HR=1.006, 3.1-fold risk, p<0.001), creatinine (HR=2.396, 2.6-fold risk, p<0.001), BUN (HR=1.048, 1.7-fold risk, p=0.001) and eGFR (CKD-EPI) (HR=0.941, 0.45-fold risk reduction, p=0.006) showed a statistically significant association. CAF was the only parameter significantly associated with doubling of proteinuria (HR=1.005, 1.7-fold risk, p<0.001). In multiple regression analysis (CAF only) the association remained significant for GL and doubling of proteinuria but not ACM. CONCLUSIONS: Early postoperative serum CAF appears to be a useful tool for the assessment of long-term outcomes in renal transplant recipients. Most importantly it represents a promising predictor for the development of proteinuria.

Comparison of Peritoneal Low-Molecular-Weight-Protein-Removal in CCPD and CAPD Patients Based on C-Terminal Agrin Fragment Clearance.

BACKGROUND/AIMS: This study compares the peritoneal elimination of the low-molecular-weight-protein (LMWP) C-terminal agrin fragment (tCAF, size 22 kDa), a promising biomarker for kidney function, in continuous cycling peritoneal dialysis (CCPD) and continuous ambulatory peritoneal dialysis (CAPD). METHODS: 103 sets of serum, 24h-urine and dialysate samples were obtained in 15 CCPD (63 sets) and 11 CAPD (40 sets) patients. Total, renal and peritoneal substrate removals/clearances were measured/calculated for tCAF, creatinine, blood-urea-nitrogen (BUN), cystatin C and albumin and correlated with the peritoneal transport type. RESULTS: Serum und urine concentrations of all biomarkers did not differ between both groups, urinary substrate removal was higher in CAPD patients for all biomarkers due to better residual renal function. Peritoneal substrate removal of tCAF and albumin were significantly higher in CAPD (tCAF: 35.3 vs. 19.3 µg/d, p<0.001; albumin: 4.3 vs. 3.7 g/d, p=0.001), whereas cystatin C and creatinine did not differ between CAPD and CCPD (cystatin: 7.7 vs. 6.1 mg/d, p=0.08, creatinine: 423.9 vs. 456.7 mg/d, p=0.241). BUN was better removed by CCPD (4846.6 vs. 3393.4 mg/d, p<0.001). CAPD patients with high-transporter characteristics had a higher peritoneal tCAF removal compared to high-average-transporters (49.8 vs. 28.4 µg/d, p<0.001), no differences could be detected in CCPD patients between these groups. CAPD patients using icodextrin twice/day had higher peritoneal clearance of tCAF compared to once daily (4.4 vs. 2.8 l/wk/1.73 m2 body-surface-area, p<0.001). CONCLUSIONS: CAPD was superior to CCPD concerning peritoneal tCAF removal. This finding was pronounced in high-transporters and CAPD patients using icodextrin twice daily.

C-terminal agrin fragment (CAF) reflects renal function in patients suffering from severe sepsis or septic shock.

BACKGROUND: One of the main causes of acute kidney injury (AKI) in patients treated on an intensive care unit (ICU) is sepsis. The identification of new biomarkers indicating the early development and future course of AKI are of utmost medical interest. The C-terminal agrin fragment (CAF) is measurable in blood serum and might reflect kidney function. Therefore, this study evaluates CAF in patients presenting to an internal ICU with severe sepsis or septic shock. Serum levels of CAF are correlated with biomarkers of kidney function, markers of systemic inflammation, and the presence of AKI and renal replacement therapy (RRT). METHODS: 61 patients suffering from severe sepsis or septic shock were included during the first 24 hours of ICU treatment and blood samples for biomarker measurements, i.e., CAF, creatinine, cystatin C, procalcitonin (PCT), interleukin 6, C reactive protein (CRP), and white blood cells (WBC) were collected on the first day of intensive care treatment. The number of RRT days and the incidence of AKI were documented. RESULTS: 13% of the patients (8/61) suffered from SIRS/sepsis, 20% (12/61) from severe sepsis, and 67% (41/61) from septic shock. Serum levels of CAF significantly correlated with creatinine (r = 0.623, p < 0.001) and cystatin C (r = 0.578, p < 0.001). Multiple linear regression analyses adjusting CAF for inflammatory parameters (i.e., WBC, CRP, interleukin 6, PCT), age, and gender showed a strong correlation between CAF and creatinine (r = 0.643, p < 0.001). Serum levels of CAF were significantly associated with the need of RRT (area under the curve (AUC) = 0.772, 95% CI: 0.641-0.903, p = 0.002) and the incidence of AKI (AUC = 0.721, 95% CI: 591-0.850, p = 0.004) as indicated by ROC analysis. CONCLUSIONS: In patients suffering from severe sepsis and septic shock, serum levels of CAF were significantly associated with kidney function and RRT and were not influenced by severe septic conditions.

C-terminal agrin fragment--a new fast biomarker for kidney function in renal transplant recipients.

BACKGROUND: The C-terminal agrin fragment (CAF) is a cleavage product of agrin, the major proteoglycan of the glomerular basement membrane. This article studies if CAF could serve as a biomarker for renal function in renal transplant recipients. MATERIAL AND METHODS: We measured serum CAF and creatinine concentrations and calculated estimated glomerular filtration rate (eGFR) (MDRD) in 96 healthy individuals and in 110 end-stage renal disease patients undergoing kidney transplantation before and after transplantation. Correlation between CAF and creatinine concentrations/eGFR was calculated as within-patient (cWP) and between-patient correlations (cBP). Moreover, we evaluated the association of CAF with delayed graft function (DGF). The diagnostic value of CAF for early detection of DGF compared to creatinine was evaluated by receiver operating characteristics (ROC) analysis. RESULTS: CAF concentrations strongly correlated with creatinine (r = 0.86 (cWP), r = 0.74 (cBP)) and eGFR (MDRD) (r = 0.86 (cWP), r = 0.77 (cBP)). Pre-transplant (pre-Tx) CAF concentrations were 19-fold higher than in healthy individuals (1,115.0 (258.4-3,990.0) vs. 56.6 (20.0-109.5) pM). After transplantation, CAF decreased significantly faster than creatinine (postoperative days 1-3 (POD 1-3): 562.8 (101.6-2,113.0) pM; creatinine: pre-Tx 6.9 (3.1-15.7), POD 1-3: 6.4 (1.7-12.7) mg/dl, p < 0.001). Stable concentrations were reached 1-3 months after transplantation for CAF and creatinine (CAF 145.1 (6.7-851.0) pM; creatinine 1.6 (0.7-8.0) mg/dl). CAF concentrations at POD 1-3 were significantly associated with DGF and outperformed creatinine in early detection of DGF (area under the curve (AUC) CAF 80.7% (95% CI 72.3-89.1%) vs. AUC creatinine 71.3% (95% CI 61.8-81.1%), p = 0.061). CONCLUSION: CAF is a promising new and fast biomarker for kidney function and may serve as a new tool for the early detection of DGF.

Embolic events caused by aortic thrombi: an underestimated entity?

Stroke and other thromboembolic events are mainly caused by emboli from heart, aorta and other arteries. In this paper we describe a group of 5 middle-aged patients suffering from emboli caused by large thrombi in the aorta. Since the development of giant thrombi under high flow conditions in the aorta is a pathophysiological process which is not well understood, a model of flow distribution by numerically simulating the Navier-Stokes equation for an incompressible fluid was generated. This model simulated how such thrombi may develop in the aorta. We hypothesize that large thrombi issuing from the aortic vessel wall represent a underestimated entity in middleaged persons and are probably overlooked as the cause of stroke or other embolic events in some cases.

Modulation of the Acetylcholine Receptor Clustering Pathway Improves Neuromuscular Junction Structure and Muscle Strength in a Mouse Model of Congenital Myasthenic Syndrome.

Introduction: Congenital myasthenic syndromes (CMS) are a diverse group of inherited neuromuscular disorders characterized by a failure of synaptic transmission at the neuromuscular junction (NMJ). CMS often present early with fatigable weakness and can be fatal through respiratory complications. The AGRN gene is one of over 30 genes known to harbor mutations causative for CMS. In this study, we aimed to determine if a compound (NT1654), developed to stimulate the acetylcholine receptor (AChR) clustering pathway, would benefit a mouse model of CMS caused by a loss-of-function mutation in Agrn (Agrn nmf380 mouse). Methods: Agrn nmf380 mice received an injection of either NT1654 or vehicle compound daily, with wild-type litter mates used for comparison. Animals were weighed daily and underwent grip strength assessments. After 30 days of treatment animals were sacrificed, and muscles collected. Investigations into NMJ and muscle morphology were performed on collected tissue. Results: While minimal improvements in NMJ ultrastructure were observed with electron microscopy, gross NMJ structure analysis using fluorescent labelling and confocal microscopy revealed extensive postsynaptic improvements in Agrn nmf380 mice with NT1654 administration, with variables frequently returning to wild type levels. An improvement in muscle weight and myofiber characteristics helped increase forelimb grip strength and body weight. Conclusions: We conclude that NT1654 restores NMJ postsynaptic structure and improves muscle strength through normalization of muscle fiber composition and the prevention of atrophy. We hypothesize this occurs through the AChR clustering pathway in Agrn nmf380 mice. Future studies should investigate if this may represent a viable treatment option for patients with CMS, especially those with mutations in proteins of the AChR clustering pathway.

Neurotrypsin cleaves agrin locally at the synapse.

The synaptic serine protease neurotrypsin is considered to be essential for the establishment and maintenance of cognitive brain functions, because humans lacking functional neurotrypsin suffer from severe mental retardation. Neurotrypsin cleaves agrin at two homologous sites, liberating a 90-kDa and a C-terminal 22-kDa fragment from the N-terminal moiety of agrin. Morphological analyses indicate that neurotrypsin is contained in presynaptic terminals and externalized in association with synaptic activity, while agrin is localized to the extracellular space at or in the vicinity of the synapse. Here, we present a detailed biochemical analysis of neurotrypsin-mediated agrin cleavage in the murine brain. In brain homogenates, we found that neurotrypsin exclusively cleaves glycanated variants of agrin. Studies with isolated synaptosomes obtained by subcellular fractionation from brains of wild-type and neurotrypsin-overexpressing mice revealed that neurotrypsin-dependent cleavage of agrin was concentrated at synapses, where the most heavily glycanated variants of agrin predominate. Because agrin has been shown to play an important role in the formation and the maintenance of excitatory synapses in the central nervous system, its local cleavage at the synapse implicates the neurotrypsin/agrin system in the regulation of adaptive reorganizations of the synaptic circuitry in the context of cognitive functions, such as learning and memory.

Plasma C-terminal agrin fragment and rapid kidney function decline in chronic kidney disease patients.

C-terminal agrin fragment (tCAF) is a promising biomarker for glomerular filtration. Data regarding biomarkers that have the ability to predict rapid progression of chronic kidney disease (CKD) are sparse but necessary in order to identify patients at high risk for rapid progression. This study addresses the value of tCAF as a predictor of rapid kidney function decline in CKD patients.We measured plasma tCAF in a retrospective observational cohort study of 277 prevalent CKD patients stage I-V. Using multivariable Cox proportional hazards regression analysis, we evaluated the association of tCAF with end-stage-renal-disease (ESRD), ≥30%-decline of estimated glomerular filtration rate (eGFR) and the composite endpoint of both, adjusting for eGFR, age, systolic blood pressure, proteinuria and diabetes.The median age was 58 [interquartile range 47, 71] years, 36% were female. Median tCAF level was 822 [594, 1232] pM, eGFR was 32 [19, 48] ml/min/1.73 m. tCAF was correlated to eGFR and proteinuria (r = -0.76 and r = 0.49, P < .001 resp.). During a follow-up of 57.1 [42.9, 71.9] weeks, 36 (13%) patients developed ESRD and 13 (5%) had an eGFR decline of ≥30% (composite endpoint: 49 (18%)). In multivariable analysis, each 100 pM higher tCAF was independently associated with ESRD (hazard ratio (HR) 1.05 (95%-CI 1.02-1.08)), ≥30% eGFR decline (HR 1.10 (1.03-1.18)) and the composite endpoint (HR 1.07 (1.04-1.1)).Plasma tCAF may identify CKD patients at risk for rapid kidney function decline independent of eGFR and other risk factors for eGFR loss such as proteinuria.

Modulation of Agrin and RhoA Pathways Ameliorates Movement Defects and Synapse Morphology in MYO9A-Depleted Zebrafish.

Congenital myasthenic syndromes (CMS) are a group of rare, inherited disorders characterised by impaired function of the neuromuscular junction (NMJ). This is due to defects in one of the many proteins associated with the NMJ. In three patients with CMS, missense mutations in a gene encoding an unconventional myosin protein, MYO9A, were identified as likely causing their disorder. Preliminary studies revealed a potential involvement of the RhoA/ROCK pathway and of a key NMJ protein, agrin, in the pathophysiology of MYO9A-depletion. In this study, a CRISPR/Cas9 approach was used to generate genetic mutants of MYO9A zebrafish orthologues, myo9aa/ab, to expand and refine the morphological analysis of the NMJ. Injection of NT1654, a synthetic agrin fragment compound, improved NMJ structure and zebrafish movement in the absence of Myo9aa/ab. In addition, treatment of zebrafish with fasudil, a ROCK inhibitor, also provided improvements to the morphology of NMJs in early development, as well as rescuing movement defects, but not to the same extent as NT1654 and not at later time points. Therefore, this study highlights a role for MYO9A at the NMJ, the first unconventional myosin motor protein associated with a neuromuscular disease, and provides a potential mechanism of action of MYO9A-pathophysiology.

Specific cleavage of agrin by neurotrypsin, a synaptic protease linked to mental retardation.

The synaptic serine protease neurotrypsin is thought to be important for adaptive synaptic processes required for cognitive functions, because humans deficient in neurotrypsin suffer from severe mental retardation. In the present study, we describe the biochemical characterization of neurotrypsin and its so far unique substrate agrin. In cell culture experiment as well as in neurotrypsin-deficient mice, we showed that agrin cleavage depends on neurotrypsin and occurs at two conserved sites. Neurotrypsin and agrin were expressed recombinantly, purified, and assayed in vitro. A catalytic efficiency of 1.3 x 10(4) M(-1) x s(-1) was determined. Neurotrypsin activity was shown to depend on calcium with an optimal activity in the pH range of 7-8.5. Mutagenesis analysis of the amino acids flanking the scissile bonds showed that cleavage is highly specific due to the unique substrate recognition pocket of neurotrypsin at the active site. The C-terminal agrin fragment released after cleavage has recently been identified as an inactivating ligand of the Na+/K+-ATPase at CNS synapses, and its binding has been demonstrated to regulate presynaptic excitability. Therefore, dysregulation of agrin processing is a good candidate for a pathogenetic mechanism underlying mental retardation. In turn, these results may also shed light on mechanisms involved in cognitive functions.

Increasing Agrin Function Antagonizes Muscle Atrophy and Motor Impairment in Spinal Muscular Atrophy.

Spinal muscular atrophy (SMA) is a pediatric genetic disease, characterized by motor neuron (MN) death, leading to progressive muscle weakness, respiratory failure, and, in the most severe cases, to death. Abnormalities at the neuromuscular junction (NMJ) have been reported in SMA, including neurofilament (NF) accumulation at presynaptic terminals, immature and smaller than normal endplates, reduced transmitter release, and, finally, muscle denervation. Here we have studied the role of agrin in SMAΔ7 mice, the experimental model of SMAII. We observed a 50% reduction in agrin expression levels in quadriceps of P10 SMA mice compared to age-matched WT controls. To counteract such condition, we treated SMA mice from birth onwards with therapeutic agrin biological NT-1654, an active splice variant of agrin retaining synaptogenic properties, which is also resistant to proteolytic cleavage by neurotrypsin. Mice were analyzed for behavior, muscle and NMJ histology, and survival. Motor behavior was significantly improved and survival was extended by treatment of SMA mice with NT-1654. At P10, H/E-stained sections of the quadriceps, a proximal muscle early involved in SMA, showed that NT-1654 treatment strongly prevented the size decrease of muscle fibers. Studies of NMJ morphology on whole-mount diaphragm preparations revealed that NT-1654-treated SMA mice had more mature NMJs and reduced NF accumulation, compared to vehicle-treated SMA mice. We conclude that increasing agrin function in SMA has beneficial outcomes on muscle fibers and NMJs as the agrin biological NT-1654 restores the crosstalk between muscle and MNs, delaying muscular atrophy, improving motor performance and extending survival.

The C-Terminal Fragment of Agrin (CAF), a Novel Marker of Renal Function, Is Filtered by the Kidney and Reabsorbed by the Proximal Tubule.

Agrin, a multidomain proteoglycan and neurotrypsin, a neuronal serine protease, are important for forming (neuromuscular) synapses. Proteolytical activity of neurotrypsin produces a C-terminal fragment of agrin, termed CAF, of approximately 22 kDA molecular size which also circulates in blood. The presence of CAF in urine suggests either glomerular filtration or secretion into urine. Blood levels of CAF have been identified as a potential novel marker of kidney function. Here we describe that several nephron segments in the mouse kidney express agrin and neutrotrypsin in addition to the localization of both protein in the glomerulum. Agrin mRNA and protein was detected in almost all nephron segments and mRNA abundance was highest in the inner medullary collecting duct. Neurotrypsin mRNA was mostly detected in the thick ascending limb of the loop of Henle, the distal convoluted tubule, and the inner medullary collecting duct. Moreover, we show that the proximal tubule absorbs injected recombinant CAF by a process shared with receptor-mediated and fluid phase endocytosis. Co-injection of CAF with recombinant human transferrin, a substrate of the receptor-mediated endocytic pathway as well as with FITC-labelled dextran (10 kDa), a marker of fluid phase endocytosis, showed partial colocalization of CAF with both markers. Further colocalization of CAF with the lysosomal marker cathepsin B suggested degradation of CAF by the lysosome in the proximal tubule. Thus, the murine kidney expresses agrin and neurotrypsin in nephron segments beyond the glomerulum. CAF is filtered by the glomerulum and is reabsorbed by endocytosis by the proximal tubule. Thus, impaired kidney function could impair glomerular clearance of CAF and thereby increase circulating CAF levels.

Failed reinnervation in aging skeletal muscle.

BACKGROUND: Skeletal muscle displays a marked accumulation of denervated myofibers at advanced age, which coincides with an acceleration of muscle atrophy. METHODS: In this study, we evaluated the hypothesis that the accumulation of denervated myofibers in advanced age is due to failed reinnervation by examining muscle from young adult (YA) and very old (VO) rats and from a murine model of sporadic denervation secondary to neurotrypsin over-expression (Sarco mouse). RESULTS: Both aging rat muscle and Sarco mouse muscle exhibited marked fiber-type grouping, consistent with repeating cycles of denervation and reinnervation, yet in VO muscle, rapsyn at the endplate increased and was associated with only a 10 % decline in acetylcholine receptor (AChR) intensity, whereas in Sarco mice, there was a decline in rapsyn and a 25 % decrease in AChR intensity. Transcripts of muscle-specific kinase (21-fold), acetylcholine receptor subunits α (68-fold), ε (threefold) and γ (47-fold), neural cell adhesion molecule (66-fold), and runt-related transcription factor 1 (33-fold) were upregulated in VO muscle of the rat, consistent with the marked persistent denervation evidenced by a large proportion of very small fibers (>20 %). In the Sarco mice, there were much smaller increases in denervation transcripts (0-3.5-fold) and accumulation of very small fibers (2-6 %) compared to the VO rat, suggesting a reduced capacity for reinnervation in aging muscle. Despite the marked persistent denervation in the VO rat muscle, transcripts of neurotrophins involved in promoting axonal sprouting following denervation exhibited no increase, and several miRNAs predicted to suppress neurotrophins were elevated in VO rat. CONCLUSIONS: Our results support the hypothesis that the accumulation of denervated fibers with aging is due to failed reinnervation and that this may be affected by a limited neurotrophin response that mediates axonal sprouting following denervation.

Evaluation of C-terminal Agrin Fragment as a marker of muscle wasting in patients after acute stroke during early rehabilitation.

BACKGROUND: C-terminal Agrin Fragment (CAF) has been proposed as a novel biomarker for sarcopenia originating from the degeneration of the neuromuscular junctions. In patients with stroke muscle wasting is a common observation that predicts functional outcome. We aimed to evaluate agrin sub-fragment CAF22 as a marker of decreased muscle mass and physical performance in the early phase after acute stroke. METHODS: Patients with acute ischaemic or haemorrhagic stroke (n = 123, mean age 70 ± 11 y, body mass index BMI 27.0 ± 4.9 kg/m(2)) admitted to inpatient rehabilitation were studied in comparison to 26 healthy controls of similar age and BMI. Functional assessments were performed at begin (23 ± 17 days post stroke) and at the end of the structured rehabilitation programme (49 ± 18 days post stroke) that included physical assessment, maximum hand grip strength, Rivermead motor assessment, and Barthel index. Body composition was assessed by bioelectrical impedance analysis (BIA). Serum levels of CAF22 were measured by ELISA. RESULTS: CAF22 levels were elevated in stroke patients at admission (134.3 ± 52.3 pM) and showed incomplete recovery until discharge (118.2 ± 42.7 pM) compared to healthy controls (95.7 ± 31.8 pM, p < 0.001). Simple regression analyses revealed an association between CAF22 levels and parameters of physical performance, hand grip strength, and phase angle, a BIA derived measure of the muscle cellular integrity. Improvement of the handgrip strength of the paretic arm during rehabilitation was independently related to the recovery of CAF22 serum levels only in those patients who showed increased lean mass during the rehabilitation. CONCLUSIONS: CAF22 serum profiles showed a dynamic elevation and recovery in the subacute phase after acute stroke. Further studies are needed to explore the potential of CAF22 as a serum marker to monitor the muscle status in patients after stroke.

C-terminal agrin fragment (CAF) as a serum biomarker for residual renal function in peritoneal dialysis patients.

BACKGROUND: C-terminal agrin fragment (CAF, size 22 kDa) is a promising new biomarker for kidney function. This study evaluated the usefulness of CAF as a serum biomarker for residual renal function (RRF) in patients undergoing automated peritoneal dialysis (APD). PATIENTS AND METHODS: Serum, urine and dialysate samples were obtained in 12 end-stage renal disease patients undergoing APD. Total, renal and peritoneal clearances were calculated for CAF, creatinine, blood urea nitrogen (BUN) and cystatin c. kt/V was computed, and RRF (in ml/min) was calculated as the arithmetic mean of creatinine and BUN clearance. Correlations between the biomarkers' serum concentrations, clearances, kt/V and RRF were computed. RESULTS: Serum CAF concentrations were highly correlated with serum concentrations of creatinine (r = 0.806, p = 0.002), BUN (r = 0.727, p = 0.007), cystatin c (r = 0.839, p = 0.001) and inversely to 24-h urinary output (r = -0.669, p = 0.017). RRF was inversely correlated with serum concentrations of CAF, cystatin c and creatinine being highest for CAF (r = -0.734, p = 0.007) followed by cystatin c (r = -0.65, p = 0.022) and creatinine (r = -0.606, p = 0.037). Serum BUN was not significantly associated with RRF (r = -0.497, p = 0.101). Age, weight and gender did not significantly affect serum CAF concentrations. CONCLUSION: Serum CAF provides a robust serum biomarker for RRF in peritoneal dialysis patients undergoing APD, possibly outperforming the value of conventional biomarkers.

C-Terminal Fragment of Agrin (CAF): A Novel Marker for Progression of Kidney Disease in Type 2 Diabetics.

BACKGROUND: Diabetes is the leading cause of CKD in the developed world. C-terminal fragment of agrin (CAF) is a novel kidney function and injury biomarker. We investigated whether serum CAF predicts progression of kidney disease in type 2 diabetics. METHODS: Serum CAF levels were measured in 71 elderly patients with diabetic nephropathy using a newly developed commercial ELISA kit (Neurotune®). Estimated glomerular filtration rate (eGFR) and proteinuria in spot urine were assessed at baseline and after 12 months follow up. The presence of end stage renal disease (ESRD) was evaluated after 24 months follow-up. Correlation and logistic regression analyses were carried out to explore the associations of serum CAF levels with GFR, proteinuria, GFR loss and incident ESRD. Renal handling of CAF was tested in neurotrypsin-deficient mice injected with recombinant CAF. RESULTS: We found a strong association of serum CAF levels with eGFR and a direct association with proteinuria both at baseline (r = 0.698, p<0.001 and r = 0. 287, p = 0.02) as well as after 12 months follow-up (r = 0.677, p<0.001 and r = 0.449, p<0.001), respectively. Furthermore, in multivariate analysis, serum CAF levels predicted eGFR decline at 12 months follow-up after adjusting for known risk factors (eGFR, baseline proteinuria) [OR (95%CI) = 4.2 (1.2-14.5), p = 0.024]. In mice, injected CAF was detected in endocytic vesicles of the proximal tubule. CONCLUSION: Serum CAF levels reflect renal function and are highly associated with eGFR and proteinuria at several time points. Serum CAF was able to predict subsequent loss of renal function irrespective of baseline proteinuria in diabetic nephropathy. CAF is likely removed from circulation by glomerular filtration and subsequent endocytosis in the proximal tubule. These findings may open new possibilities for clinical trial design, since serum CAF levels may be used as a selection tool to monitor kidney function in high-risk patients with diabetic nephropathy.