GPCR kinase knockout cells reveal the impact of individual GRKs on arrestin binding and GPCR regulation

G protein-coupled receptors (GPCRs) activate G proteins and undergo a complex regulation by interaction with GPCR kinases (GRKs) and the formation of receptor-arrestin complexes. However, the impact of individual GRKs on arrestin binding is not clear. We report the creation of eleven combinatorial HEK293 knockout cell clones lacking GRK2/3/5/6, including single, double, triple and the quadruple GRK knockout. Analysis of β-arrestin1/2 interactions for twelve GPCRs in our GRK knockout cells enables the differentiation of two main receptor subsets: GRK2/3-regulated and GRK2/3/5/6-regulated receptors. Furthermore, we identify GPCRs that interact with β-arrestins via the overexpression of specific GRKs even in the absence of agonists. Finally, using GRK knockout cells, PKC inhibitors and β-arrestin mutants, we present evidence for differential receptor-β-arrestin1/2 complex configurations mediated by selective engagement of kinases. We anticipate our GRK knockout platform to facilitate the elucidation of previously unappreciated details of GRK-specific GPCR regulation and β-arrestin complex formation.

Renal comorbidity after solid organ and stem cell transplantation

After transplantation of solid organs or hematopoietic stem cells, a significant acute decrease in renal function occurs in the majority of patients. Depending on the degree of kidney injury, a large number of patients develop chronic kidney disease (CKD) and some develop end-stage renal disease requiring renal replacement therapy. The incidence varies depending on the transplanted organ, but important risk factors for the development of CKD are preexisting renal disease, hepatitis C, diabetes, hypertension, age, sex, posttransplant acute kidney injury and thrombotic microangiopathy. This review article focuses on the risk factors of posttransplant chronic kidney disease after organ transplantation, considering the current literature and integrates the incidence and the associated mortality rates of acute and chronic kidney disease. Furthermore, we introduce the RECAST (REnal Comorbidity After Solid organ and hematopoietic stem cell Transplantation) registry.

Protocol biopsy-driven interventions after pediatric renal transplantation

The therapeutic value of protocol biopsies (PBs) in renal transplant recipients remains unclear. We performed protocol biopsies in 57 children six months after transplantation. We increased the CNI dose in patients with borderline findings. In cases of Banff grade Ia, six prednisolone IV-pulses were given and the CNI dose was increased. CNI toxicity and polyomavirus nephropathy led to a reduction in the CNI dose. GFR was compared with a control group of 51 children with no PBs transplanted in the same period. Forty-two percent of PBs had no pathological changes, 24% IF/TA. Borderline findings were detected in 11%, Banff grade Ia in 15% (CNI), toxicity in 8%, and one case showed polyomavirus nephropathy. GFR after 1.5 and 2.5 yr was similar in both groups. GFR 3.5 yr after transplantation was significantly higher in the intervention group (57 ± 17 vs. 46 ± 20). Patients treated with low-dose CNI and everolimus had a significantly lower number of pathological findings in PBs. The performance of protocol biopsies followed by a standardized treatment algorithm led to better graft function 3.5 yr after transplantation. Prospective randomized studies to confirm our findings are needed.

De novo therapy with everolimus, low-dose ciclosporine A, basiliximab and steroid elimination in pediatric kidney transplantation

The number of acute rejections and infections after pediatric kidney transplantation (KTX) could not be reduced in the last years. To reduce these events, we investigated a new immunosuppressive protocol in a prospective trial. After KTX, 20 children (median age 12 years, range 1-17) were initially treated with Basiliximab, ciclosporine A (CsA) (trough-level = C0 200-250 ng/mL) and prednisolone. After 2 weeks, CsA dose was reduced to 50% (C0 75-100 ng/mL, after 6 months: 50-75 ng/mL) and everolimus (1.6 mg/m²) /day) was started (C0 3-6 ng/mL). Six months after KTX prednisolone was set to alternate dose and stopped 3 months later. All 20 protocol biopsies 6 months after KTX showed no acute rejection or borderline findings. Indication biopsies resulted in no acute rejections and two borderline findings. Mean glomerular filtration rate (GFR) 1 year after KTX was 71 ± 25 mL/min/1.73 m². Without cytomegalovirus (CMV)-prophylaxis, only two primary CMV infections were seen despite a donor/recipient-CMV-constellation pos./neg. in 10/20 children. In pediatric KTX, de novo immunosuppression with low-dose CsA, everolimus and steroid withdrawal after 9 months led to promising results according to numbers of acute rejections and infections. Further follow up is needed. Future larger trials will have to confirm our findings.

Differential effects of neuropeptide Y (NPY) on leukocyte subsets in the blood: mobilization of B-1-like B-lymphocytes and activated monocytes

Sympathetic nervous system activation mobilizes leukocytes but it is unknown whether the concomitant neuropeptide Y (NPY)-release also alters blood leukocyte counts. Using chronic intravenous (i.v.) cannulation of freely moving rats and flow cytometry, time-, dose- and subset-specific effects of NPY on blood leukocytes were investigated 1-15 min after injection: High-dose NPY increases leukocytes numbers by preferentially mobilizing CD4(+) T-cells, activated NKR-P1A(+) monocytes and NK-cells. Low-dose NPY significantly decreases B-lymphocyte and NK-cell numbers. Furthermore, NPY dose-dependently mobilizes a previously undetected IgM(low)CD5(+)CD11b(+) B-cell subpopulation in rats ("B1-like" B-lymphocytes). These data suggest a role for the sympathetic neurotransmitter NPY in neuroimmune alterations in vivo.

No leucine(7)-to-proline(7) polymorphism in the signal peptide of neuropeptide Y in Japanese population or Japanese with alcoholism

We have screened 200 Japanese workers and 105 Japanese patients with alcoholism for the mutation in the signal peptide of pre-pro-neuropeptide Y resulting in a substitution of proline for leucine at position 7. This polymorphism was reported in the Finnish and Dutch populations recently. None of our subjects displayed the mutation at this site. Therefore, this allele does not play any role in the development of alcoholism in the Japanese population.

Leukocyte mobilization induced by hypervolemia is due to a combined alpha- and beta-adrenoceptor activation

A phenomenon of leukocytosis induced by hypervolemic stress was discovered. Although a single injection of 350 microl of saline (equivalent to approx. 70 ml in humans, 1 ml/kg of body weight) did not have an effect on the leukocyte counts in long-term intravenously cannulated, freely behaving rats, a single injection of 750 microl of saline (equivalent to approx. 150 ml in humans, 2.1 ml/kg) induced rapid leukocytosis of 160% within 1 minute followed by a gradual increase up to 180% after 1 hour. Measurement of serum norepinephrine concentration revealed a significant increase in rats of the hypervolemic group, compared with those of the low volume group. Pretreatment with either the beta-adrenoceptor antagonist nadolol or the selective alpha2-adrenoceptor antagonist yohimbine prevented both leukocyte peaks in the high volume group, suggesting a combined receptor activation. This critical dependence of leukocyte counts on changes in blood volume should be taken into consideration in experiments with laboratory animals (the quantity of volume applications can falsify results of experiments).