Impact of urinary calcium excretion on kidney, bone, and cardiovascular systems in patients with bone biopsy proven osteoporosis: a longitudinal long-term follow-up study.

The impact of urine calcium on kidney, bone, and cardiovascular systems in osteoporosis is not well-known. In this 7-year-follow-up study, high urine calcium did not affect kidney function but increased risk of kidney stones, while low urine calcium increased cardiovascular diseases. Maintaining normal urine calcium is beneficial for bone health. PURPOSE: Hypercalciuria is common in patients with osteoporosis. However, the long-term effect of urinary calcium excretion (UCaE) on patients' health is not well-examined. The current study aims to assess the impact of UCaE on kidney, bone, and cardiovascular outcomes in patients with bone biopsy proven osteoporosis. METHODS: Longitudinal study of all patients with osteoporosis who underwent bone biopsy and 24-h urine collection between 2008 and 2015 in the University of Kentucky. DXA scans, serum markers, kidney function, and cardiovascular events were recorded until last clinic visit in 2021. Exclusion criteria were secondary osteoporosis or conditions that might substantially impact UCaE. The significant results in univariate analysis were confirmed in multi-variable regression models involving clinically important covariates that might impact patients' outcomes. RESULTS: Study included 230 patients with mean follow-up of 7.2 ± 2.9 years. The mean age was 61 years, and the mean eGFR at baseline was 85 ± 19 ml/min/1.73 m2. Low bone turnover (LBT) was present in 57% and high bone turnover (HBT) in 43% of patients. Hypercalciuria was found in one-third of patients with no difference between LTB and HTB. UCaE correlated positively with eGFR but did not affect the rate of eGFR decline over time. Higher UCaE predicted kidney stones development. We observed U-shaped effect of UCaE on bone health. Hypercalciuria predicted loss of BMD at all sites, but also hypocalciuria was associated with higher loss in total hip BMD. Upper limb fractures were the most observed fractures, and their incidence was higher in patients with hyper- or hypo-calciuria. Lower UCaE independently predicted development of major adverse cardiac events (MACE) and cardiovascular disease (CVD). CONCLUSION: UCaE correlated with eGFR but it did not affect the change of eGFR over time. Patients with normal UCaE had lower incidence of upper limb fractures and less reduction in BMD. Low UCaE predicted MACE and CVD.

Management of osteoporosis in patients with chronic kidney disease.

Patients with CKD have a 4-fivefold higher rate of fractures. The incidence of fractures increases with deterioration of kidney function. The process of skeletal changes in CKD patients is characterized by compromised bone strength because of deterioration of bone quantity and/or quality. The fractures lead to a deleterious effect on the quality of life and higher mortality in patients with CKD. The pathogenesis of bone loss and fracture is complex and multi-factorial. Renal osteodystrophy, uremic milieu, drugs, and systemic diseases that lead to renal failure all contribute to bone damage in CKD patients. There is no consensus on the optimal diagnostic method of compromised bone assessment in patients with CKD. Bone quantity and mass can be assessed by dual-energy x-ray absorptiometry (DXA) or quantitative computed tomography (QCT). Bone quality on the other side can be assessed by non-invasive methods such as trabecular bone score (TBS), high-resolution bone imaging methods, and invasive bone biopsy. Bone turnover markers can reflect bone remodeling, but some of them are retained by kidneys. Understanding the mechanism of bone loss is pivotal in preventing fracture in patients with CKD. Several non-pharmacological and therapeutic interventions have been reported to improve bone health. Controlling laboratory abnormalities of CKD-MBD is crucial. Anti-resorptive therapies are effective in improving BMD and reducing fracture risk, but there are uncertainties about safety and efficacy especially in advanced CKD patients. Accepting the prevalent of low bone turnover in patients with advanced CKD, the osteo-anabolics are possibly promising. Parathyroidectomy should be considered a last resort for intractable cases of renal hyperparathyroidism. There is a wide unacceptable gap in osteoporosis management in patients with CKD. This article is focusing on the updated management of CKD-MBD and osteoporosis in CKD patients. Chronic kidney disease deteriorates bone quality and quantity. The mechanism of bone loss mainly determines pharmacological treatment. DXA and QCT provide information about bone quantity, but assessing bone quality, by TBS, high-resolution bone imaging, invasive bone biopsy, and bone turnover markers, can guide us about the mechanism of bone loss.

The first survey of the Saudi Acute Myocardial Infarction Registry Program: Main results and long-term outcomes (STARS-1 Program).

BACKGROUND: Prior acute coronary syndrome (ACS) registries in Saudi Arabia might not have accurately described the true demographics and cardiac care of patients with ACS. We aimed to evaluate the clinical characteristics, management, and outcomes of a representative sample of patients with acute myocardial infarction (AMI) in Saudi Arabia. METHODS: We conducted a 1-month snap-shot, prospective, multi-center registry study in 50 hospitals from various health care sectors in Saudi Arabia. We followed patients for 1 month and 1 year after hospital discharge. Patients with AMI included those with or without ST-segment elevation (STEMI or NSTEMI, respectively). This program survey will be repeated every 5 years. RESULTS: Between May 2015 and January 2017, we enrolled 2233 patients with ACS (mean age was 56 [standard deviation = 13] years; 55.6% were Saudi citizens, 85.7% were men, and 65.9% had STEMI). Coronary artery disease risk factors were high; 52.7% had diabetes mellitus and 51.2% had hypertension. Emergency Medical Services (EMS) was utilized in only 5.2% of cases. Revascularization for patients with STEMI included thrombolytic therapy (29%), primary percutaneous coronary intervention (PCI); (42.5%), neither (29%), or a pharmaco-invasive approach (3%). Non-Saudis with STEMI were less likely to undergo primary PCI compared to Saudis (35.8% vs. 48.7%; respectively, p <0.001), and women were less likely than men to achieve a door-to-balloon time of <90 min (42% vs. 65%; respectively, p = 0.003). Around half of the patients with NSTEMI did not undergo a coronary angiogram. All-cause mortality rates were 4%, 5.8%, and 8.1%, in-hospital, at 1 month, and at 1 year, respectively. These rates were significantly higher in women than in men. CONCLUSIONS: There is an urgent need for primary prevention programs, improving the EMS infrastructure and utilization, and establishing organized ACS network programs. AMI care needs further improvement, particularly for women and non-Saudis.

Outcome of kidney transplant in primary, repeat, and kidney-after-nonrenal solid-organ transplantation: 15-year analysis of recent UNOS database.

The number of nonrenal solid-organ transplants increased substantially in the last few decades. Many of these patients develop renal failure and receive kidney transplantation. The aim of this study was to evaluate patient and kidney allograft survival in primary, repeat, and kidney-after-nonrenal organ transplantation using national data reported to United Network for Organ Sharing (UNOS) from January 2000 through December 2014. Survival time for each patient was stratified into the following: Group A (comparison group)-recipients of primary kidney transplant (178 947 patients), Group B-recipients of repeat kidney transplant (17 819 patients), and Group C-recipients of kidney transplant performed after either a liver, heart, or lung transplant (2365 patients). We compared survivals using log-rank test. Compared to primary or repeat kidney transplant, patient and renal allograft survival was significantly lower in those with previous nonrenal organ transplant. Renal allograft and patient survival after liver, heart, or lung transplants are comparable. Death was the main cause of graft loss in patients who had prior nonrenal organ transplant.

Posterior urethral valves: Metabolic consequences in a cohort of patients.

BACKGROUND: Despite the improvements in diagnosis and management of posterior urethral valves (PUVs), about one third of patients develop chronic kidney disease (CKD). Children with PUVs might have abnormal calcium, phosphorus, vitamin D and parathyroid hormone levels, which could affect their bone growth and overall health. OBJECTIVE: The aim was to determine the relationship between kidney function, vitamin D deficiency and secondary hyperparathyroidism in children with PUVs. PATIENTS AND METHODS: Sixty-four children with PUVs were followed for a period of 3.64 ± 2.50 years after their initial presentation and management. Their laboratory parameters were compared with 20 age-, gender- and race-matched children in a control group, including: serum calcium, phosphorus, intact parathyroid hormone (iPTH), 25-hydroxyvitamin D levels, and kidney function. RESULTS: Children with PUVs had significantly lower estimated kidney function (P = 0.006) and vitamin D levels (P < 0.001) and higher iPTH levels (P = 0.042). There were no significant between-group differences in serum calcium, phosphorus, alkaline phosphatase, sodium, potassium, and bicarbonate levels. There was a strong correlation between the degree of vitamin D deficiency and hyperparathyroidism and the degree of kidney dysfunction (r = 0.52 and -0.52, respectively) in the PUV group. On a multivariate analysis, the kidney dysfunction was the only independent predictor of vitamin D deficiency (ρ = 0.271, P < 0.001), while kidney dysfunction, serum calcium and alkaline phosphatase were independent predictors for hyperparathyroidism (ρ = 0.925, P<0.001, ρ = 0.933, P<0.001 and ρ = 0.913, P < 0.001, respectively). DISCUSSION: The prevalence of CKD in children with PUVs ranges from 30 to 60%. Patients with CKD are more likely to have vitamin D deficiency and display more-prominent hyperparathyroidism. Compared with a control group with normal kidney function, the present cohort had lower 25-hydroxyvitamin D and higher iPTH serum levels. Abnormal kidney function was a major predictor for both serum levels. In this cohort, there were no significant differences in serum calcium and phosphorus between children with PUVs and the control group, and also between those with and without CKD. On the contrary, vitamin D level decreased early in the disease and progressively declined thereafter, while iPTH was the opposite. These findings were comparable to previous studies. This study had some limitations because it was a single center cross-sectional non-randomized study. However, the findings in this study can be extrapolated to children with PUVs and CKD from other origins because the unit is considered as a referral center in the Middle East region. CONCLUSION: Abnormal kidney function, vitamin D deficiency, and secondary hyperparathyroidism are prevalent in children with PUVs. Kidney function is the main determinant of vitamin D and parathyroid hormone levels. Efforts should be directed toward managing CKD, and controlling vitamin D deficiency and hyperparathyroidism in children after ablation of PUV.

Postsynaptic scaffolding molecules modulate the localization of neuroligins.

Previous work has shown an important role for neuroligins in promoting the formation of synaptic connections in cultured cells. Although neuroligins enhance both excitatory and inhibitory synapse formation, individual neuroligin isoforms have been shown to preferentially localize to either glutamatergic or GABAergic synapses. Current evidence points to an important role for both the extracellular and intracellular domains of neuroligins in their synaptic localization. Although postsynaptic density protein 95 (PSD-95) has been shown to be involved in the recruitment of neuroligin 1 to excitatory synapses, the localization of neuroligin 2 (NL2) and neuroligin 3 (NL3) to excitatory and inhibitory synapses is less well defined. We assessed the roles of gephyrin and PSD-95, postsynaptic scaffolding molecules exclusively localized to inhibitory and excitatory synapses, respectively, in localizing NL2 and NL3 in primary neuronal cultures. We demonstrate that knockdown of gephyrin results in a significant shift of NL2 from inhibitory to excitatory synaptic contacts, while knockdown of PSD-95 leads to a partial shift of NL2 and NL3 from excitatory to inhibitory contacts. Furthermore, analysis of specific domain deletions within the C-terminal, intracellular domain of NL2 reveals that the region between amino acids 716 and 782 is required for the normal synaptic clustering of this protein. Together, these data suggest that intracellular mechanisms are involved in the targeting of different neuroligin family members to synapses (216).

The neuroligin and neurexin families: from structure to function at the synapse.

Proper brain connectivity and neuronal transmission rely on the accurate assembly of neurotransmitter receptors, cell adhesion molecules and several other scaffolding and signaling proteins at synapses. Several new exciting findings point to an important role for the neuroligin family of adhesion molecules in synapse development and function. In this review, we summarize current knowledge of the structure of neuroligins and neurexins, their potential binding partners at the synapse. We also discuss their potential involvement in several aspects of synapse development, including induction, specificity and stabilization. The implication of neuroligins in cognitive disorders such as autism and mental retardation is also discussed.

Als2-deficient mice exhibit disturbances in endosome trafficking associated with motor behavioral abnormalities.

ALS2 is an autosomal recessive form of spastic paraparesis (motor neuron disease) with juvenile onset and slow progression caused by loss of function of alsin, an activator of Rac1 and Rab5 small GTPases. To establish an animal model of ALS2 and derive insights into the pathogenesis of this illness, we have generated alsin-null mice. Cytosol from brains of Als2(-/-) mice shows marked diminution of Rab5-dependent endosome fusion activity. Furthermore, primary neurons from Als2(-/-) mice show a disturbance in endosomal transport of insulin-like growth factor 1 (IGF1) and BDNF receptors, whereas neuronal viability and endocytosis of transferrin and dextran seem unaltered. There is a significant decrease in the size of cortical motor neurons, and Als2(-/-) mice are mildly hypoactive. Altered trophic receptor trafficking in neurons of Als2(-/-) mice may underlie the histopathological and behavioral changes observed and the pathogenesis of ALS2.

Regulation of ErbB4 phosphorylation and cleavage by a novel histidine acid phosphatase.

Signaling by a variety of ligands including epidermal growth factor, betacellulin and neuregulin is mediated by the ErbB family of receptor tyrosine kinases. Studies on the prostate have shown that ErbB2 phosphorylation and signaling can be regulated by prostatic acid phosphatase, a histidine acid phosphatase which can dephosphorylate phospho-tyrosine residues in the ErbB2 receptor. Here we report that the histidine acid phosphatase ACPT (testicular acid phosphatase), which is highly homologous to the prostatic acid phosphatase, can dephosphorylate the ErbB4 receptor, which is known to play important roles in neuronal differentiation and synaptogenesis. ACPT and ErbB4 are both expressed in the brain where they are enriched at post-synaptic sites, and furthermore they can be co-immunoprecipitated from brain. We demonstrate that ACPT can inhibit basal and neuregulin-induced tyrosine phosphorylation of ErbB4. We also show that ACPT-dependent dephosphorylation can regulate the proteolytic cleavage of ErbB4, and this process can be reversed by applying the tyrosine phosphatase inhibitor, pervanadate. Furthermore, neuregulin-dependent differentiation of PC12 cells expressing ErbB4 is prevented by co-expressing ACPT. These results indicate that ACPT acts as a tyrosine phosphatase to modulate signals mediated by ErbB4 that are important for neuronal development and synaptic plasticity.

Renal transplantation in children with abnormal lower urinary tract.

OBJECTIVE: This retrospective study reports the outcomes as well as pre- and posttransplant urologic treatments of renal transplantation for children with an abnormal lower urinary tract (LUT). METHODS: Between March 1981 and December 2001, 195 children (< or =18 years of age) received live-donor kidney transplants. The 15 recipients (14 boys and 1 girl, mean age 13.5 +/- 3 years) who had lower urinary tract disorders included posterior urethral valves (PUV) with valve bladder (n=12) and neuropathic bladders secondary to meningomyelocele (n=3). These children were evaluated by voiding cystourethrogram, cystourethroscopy, and cystometry. The children with PUV were maintained on clean intermittent catheterization (CIC) and a detrusor relaxant at least 3 months before transplantation. Augmentation ileocystoplasty or continent cutaneous diversion were used in three patients. The graft and patient survivals as well as complications in this cohort was compared with a group of children with normal LUT, who underwent renal transplantation during the same period. RESULTS: One child died in the early posttransplant period due to rupture of the external iliac artery. Follow-up ranged from 6 months to 16 years (mean=4.5 years). During the same period the graft and patient survival rates were comparable between the group of children with versus without abnormal LUT. Furthermore, mean serum creatinine and creatinine clearance values were also comparable. The group with an abnormal LUT showed a higher incidence of urinary fistula (3/14) and recurrent UTI and/or bacteremia (4/14). CONCLUSIONS: Renal transplantation is feasible with good results for children with abnormal LUT. Pre- and posttransplant urologic management is critical for a successful outcome. However these children display a high incidence of urologic and infectious complications.

Bone loss in pediatric renal transplant recipients.

The factors that affect bone mineral density (BMD) and the long term progress of BMD after transplantation in children is still unknown. Therefore we performed a cross-sectional study to determine BMD in 83 recipients who received living renal allotransplants in Mansoura Urology & Nephrology Center between 1981 and 2001 (mean age at transplantation 13.2 +/- 3.1 years) by dual energy x-ray absorptiometry at various time intervals up to 16 years after transplantation (mean duration after transplantation was 48 +/- 34 months, range 6-192 months). The Z-score for lumbar spine was -2.28 +/- 2.06 and -1.44 +/- 1.44 for the total body. Osteopenia/osteoporosis were present in about two thirds of our kidney transplant recipients. The significant predictors for osteopenia/osteoporosis by univariate analysis were cyclosporine based immunosuppression, the cumulative steroid dose/m2 surface area, graft dysfunction and the urinary deoxypyridinoline. Using logistic regression analysis the cumulative steroid dose/m2 surface area and the urinary deoxypyridinoline were the major significant predictors for bone loss.

Impact of clinical and histopathological factors on outcome of Egyptian patients with crescentic glomerulonephritis.

This study included 128 patients with crescentic glomerulonephritis (CGN) having sufficient clinical and histopathological data and were followed up in our institute for a mean period of 34 +/- 28 months. There were 49 males and 79 females with mean age 22.7 +/- 14 years. We studied the effect of clinical, laboratory and histopathological parameters on kidney function and patient survival at the end point of the study. The multivariate analysis revealed that serum creatinine at presentation, nephrotic range proteinuria during the follow up period, percentage of glomeruli affected by crescents, percentage of fibrous crescents and absence of cellular infiltration were significant risk factors affecting the kidney function at termination of the study. The only risk factor which correlated significantly with the patient mortality was the serum creatinine at last follows up.

Polarized targeting of peripheral membrane proteins in neurons.

Differential targeting of neuronal proteins to axons and dendrites is essential for directional information flow within the brain, however, little is known about this protein-sorting process. Here, we investigate polarized targeting of lipid-anchored peripheral membrane proteins, postsynaptic density-95 (PSD-95) and growth-associated protein-43 (GAP-43). Whereas the N-terminal palmitoylated motif of PSD-95 is necessary but not sufficient for sorting to dendrites, the palmitoylation motif of GAP-43 is sufficient for axonal targeting and can redirect a PSD-95 chimera to axons. Systematic mutagenesis of the GAP-43 and PSD-95 palmitoylation motifs indicates that the spacing of the palmitoylated cysteines and the presence of nearby basic amino acids determine polarized targeting by these two motifs. Similarly, the axonal protein paralemmin contains a C-terminal palmitoylated domain, which resembles that of GAP-43 and also mediates axonal targeting. These axonally targeted palmitoylation motifs also mediate targeting to detergent-insoluble glycolipid-enriched complexes in heterologous cells, suggesting a possible role for specialized lipid domains in axonal sorting of peripheral membrane proteins.

Cloning and characterization of a gene (RNF22) encoding a novel brain expressed ring finger protein (BERP) that maps to human chromosome 11p15.5.

We have recently identified a novel RING finger protein expressed in the rat brain, which associates with myosin V and alpha-actinin-4. Here we have cloned and characterized the orthologous human BERP cDNA and gene (HGMW-approved symbol RNF22). The human BERP protein is encoded by 11 exons ranging in size from 71 to 733 bp, and fluorescence in situ hybridization shows that the BERP gene maps to chromosome 11p15.5, 3' to the FE65 gene. The human BERP protein is 98% identical to the rat and mouse proteins, and we have identified a highly conserved potential orthologue in Caenorhabditis elegans. BERP belongs to the RING finger-B-box-coiled coil (RBCC) subgroup of RING finger proteins, and a cluster of these RBCC protein genes is present in chromosome 11p15. Chromosome region 11p15 is thought to harbor tumor suppressor genes, and deletions of this region occur frequently in several types of human cancers. These observations indicate that BERP may be a novel tumor suppressor gene.

PSD-95 involvement in maturation of excitatory synapses.

PSD-95 is a neuronal PDZ protein that associates with receptors and cytoskeletal elements at synapses, but whose function is uncertain. We found that overexpression of PSD-95 in hippocampal neurons can drive maturation of glutamatergic synapses. PSD-95 expression enhanced postsynaptic clustering and activity of glutamate receptors. Postsynaptic expression of PSD-95 also enhanced maturation of the presynaptic terminal. These effects required synaptic clustering of PSD-95 but did not rely on its guanylate kinase domain. PSD-95 expression also increased the number and size of dendritic spines. These results demonstrate that PSD-95 can orchestrate synaptic development and are suggestive of roles for PSD-95 in synapse stabilization and plasticity.

Ion channel clustering by membrane-associated guanylate kinases. Differential regulation by N-terminal lipid and metal binding motifs.

The postsynaptic density protein PSD-95 and related membrane-associated guanylate kinase (MAGUK) proteins assemble signal transduction complexes at sites of cell-cell contact including synapses. Whereas PSD-95 and PSD-93 occur only at postsynaptic sites in hippocampal neurons, SAP-102 also occurs in axons. In heterologous cells, PSD-95 and PSD-93 mediate cell surface ion channel clustering, but SAP-102 and SAP-97 do not. This selective ion channel clustering activity by MAGUKs is explained by differential palmitoylation, as PSD-93 and PSD-95 are palmitoylated though SAP-97, and SAP-102 are not. Rather than being palmitoylated, we find that N-terminal cysteines from SAP-102 tightly bind to zinc. And, appending the N terminus of SAP-102 to PSD-95 results in localization of the chimera to both axons and dendrites. These data suggest that lipid modifications and heavy metal associations with the N termini of MAGUKs mediate differential functions and subcellular localizations of these synaptic scaffolds.

BERP, a novel ring finger protein, binds to alpha-actinin-4.

We recently identified BERP as a novel RING finger protein belonging to the RBCC protein family. It contains an N-terminal RING finger, followed by a B-box zinc finger and a coiled-coil domain. BERP interacts with the tail domain of the class V myosins through a beta-propeller structure in the BERP C-terminal. To identify other proteins interacting with BERP, the yeast two-hybrid strategy was employed, using the RBCC domain as bait. Screening of a rat brain cDNA library identified alpha-actinin-4 as a specific binding partner for the N-terminus of BERP. This actinin isoform could be immunoprecipitated together with BERP from HEK 293 cells transfected with expression constructs for BERP and alpha-actinin-4. These proteins could also be colocalized immunohistochemically in the cytoplasm of differentiated PC12 cells. We suggest that BERP may anchor class V myosins to particular cell domains via its interaction with alpha-actinin-4.

Dual palmitoylation of PSD-95 mediates its vesiculotubular sorting, postsynaptic targeting, and ion channel clustering.

Postsynaptic density-95 (PSD-95/SAP-90) is a palmitoylated peripheral membrane protein that scaffolds ion channels at excitatory synapses. To elucidate mechanisms for postsynaptic ion channel clustering, we analyzed the cellular trafficking of PSD-95. We find that PSD-95 transiently associates with a perinuclear membranous compartment and traffics with vesiculotubular structures, which migrate in a microtubule-dependent manner. Trafficking of PSD-95 with these vesiculotubular structures requires dual palmitoylation, which is specified by five consecutive hydrophobic residues at the NH(2) terminus. Mutations that disrupt dual palmitoylation of PSD-95 block both ion channel clustering by PSD-95 and its synaptic targeting. Replacing the palmitoylated NH(2) terminus of PSD-95 with alternative palmitoylation motifs at either the NH(2) or COOH termini restores ion channel clustering also induces postsynaptic targeting, respectively. In brain, we find that PSD-95 occurs not only at PSDs but also in association with intracellular smooth tubular structures in dendrites and spines. These data imply that PSD-95 is an itinerant vesicular protein; initial targeting of PSD-95 to an intracellular membrane compartment may participate in postsynaptic ion channel clustering by PSD-95.

Cypin: a cytosolic regulator of PSD-95 postsynaptic targeting.

Postsynaptic density 95 (PSD-95/SAP-90) is a membrane associated guanylate kinase (GK) PDZ protein that scaffolds glutamate receptors and associated signaling networks at excitatory synapses. Affinity chromatography identifies cypin as a major PSD-95-binding protein in brain extracts. Cypin is homologous to a family of hydrolytic bacterial enzymes and shares some similarity with collapsin response mediator protein (CRMP), a cytoplasmic mediator of semaphorin III signalling. Cypin is discretely expressed in neurons and is polarized to basal membranes in intestinal epithelial cells. Overexpression of cypin in hippocampal neurons specifically perturbs postsynaptic trafficking of PSD-95 and SAP-102, an effect not produced by overexpression of other PDZ ligands. In fact, PSD-95 can induce postsynaptic clustering of an otherwise diffusely localized K+ channel, Kv1.4. By regulating postsynaptic protein sorting, cypin may influence synaptic development and plasticity.