Idiopathic Focal Segmental Glomerulosclerosis (FSGS) is a progressive and proteinuric kidney disease that starts with podocyte injury. Podocytes cover the external side of the glomerular capillary by a complex web of primary and secondary ramifications. Similar to dendritic spines of neuronal cells, podocyte processes rely on a dynamic actin-based cytoskeletal architecture to maintain shape and function. Brain Derived Neurotrophic Factor (BDNF) is a pleiotropic neurotrophin that binds to the tropomyosin-related kinase B receptor (TrkB) and has crucial roles in neuron maturation, survival, and activity. In neuronal cultures, exogenously added BDNF increases number and size of dendritic spines. In animal models, BDNF administration is beneficial in both central and peripheral nervous system disorders. Here we show that BDNF has a TrkB-dependent trophic activity on podocyte cell processes; by affecting microRNA-134 and microRNA-132 signaling, BDNF upregulates Limk1 translation and phosphorylation, and increases cofilin phosphorylation which results in actin polymerization. Importantly, BDNF effectively repairs podocyte damage “in vitro”, and contrasts proteinuria and glomerular lesions in “in vivo” models of FSGS, opening a potential new perspective to the treatment of podocyte disorders.

The TLR3/IRF3/Fkn signaling pathway may, at least in part, mediate immune and inflammatory responses against viral infection in MCs.

Proteinuria is a common symptom of glomerular diseases and is due to leakage of proteins from the glomerular filtration barrier, a three-layer structure composed by two post-mitotic highly specialized and interdependent cell populations, i.e. glomerular endothelial cells and podocytes, and the basement membrane in between. Despite enormous progresses made in the last years, pathogenesis of proteinuria remains to be completely uncovered. Studies in the field could largely benefit from an in vitro model of the glomerular filter, but such a system has proved difficult to realize. Here we describe a method to obtain and utilize a three-dimensional podocyte-endothelial co-culture which can be largely adopted by the scientific community because it does not rely on special instruments nor on the synthesis of devoted biomaterials. The device is composed by a porous membrane coated on both sides with type IV collagen. Adhesion of podocytes on the upper side of the membrane has to be preceded by VEGF-induced maturation of endothelial cells on the lower side. The co-culture can be assembled with podocyte cell lines as well as with primary podocytes, extending the use to cells derived from transgenic mice. An albumin permeability assay has been extensively validated and applied as functional readout, enabling rapid drug testing. Additionally, the bottom of the well can be populated with a third cell type, which multiplies the possibilities of analyzing more complex glomerular intercellular signaling events. In conclusion, the ease of assembly and versatility of use are the major advantages of this three-dimensional model of the glomerular filtration barrier over existing methods. The possibility to run a functional test that reliably measures albumin permeability makes the device a valid companion in several research applications ranging from drug screening to intercellular signaling studies.

Background: The optimal long-term treatment for lupus nephritis (LN) in pubertal patients remains to be determined. Tacrolimus (Tac) inhibits T cell activation, and is therefore expected to be effective in patients with LN. However, little has been published about the long-term efficacy and safety of Tac-based immunosuppressive treatment of young patients with LN in daily clinical practice. Methods: Nineteen consecutive patients with biopsy-proven LN were recruited for an open-label, prospective, long-term Tac-based treatment regimen. Tac was administered once daily at a dose of 3 mg as induction- or reinduction-maintenance treatment. Four patients (21%) with new-onset LN received mizoribine at a dose of 150 mg once daily in addition to Tac. Treatment outcomes were defined by the European Consensus Lupus Activity Measurement (ECLAM) index, urinary protein/creatinine ratio (Up/cr), serum creatinine and serological lupus markers (complement C3, complement hemolytic activity, CH₅₀, and anti-dsDNA antibody titer). Data on these parameters were collected prospectively. The median follow-up was 42 months. Results: Baseline characteristics of the patients were as follows: mean age, 18 years; Up/cr, 0.89 ± 1.17; serum C3, 68.1 ± 23.2 mg/dl (normal, 79–152 mg/dl); serum CH₅₀, 26.4 ± 10.5 U/ml (normal, 23–46 U/ml); serum anti-dsDNA antibody titer, 69.3 ± 67.5 IU/ml (normal, <12.0 IU/ml); serum creatinine, 0.55 ± 0.18 mg/dl, and ECLAM index, 4.6 ± 1.9. Despite gradually tapering the dose of concomitantly administered prednisolone, a marked improvement compared with baseline values was observed in all outcome measures as early as 3 months after the initiation of treatment, and the favorable changes persisted throughout the treatment period in most of the patients. Sustained improvements in the outcome measures compared with the baseline values were confirmed after a mean of 42 months of treatment: ECLAM index, 1.1 ± 1.1; serum CH₅₀, 36.0 ± 12.8 U/ml, anti-dsDNA antibody titer, 22.5 ± 26.5 IU/ml (all p < 0.01); Up/cr ratio, 0.35 ± 0.58, and serum C3 level, 79.7 ± 17.6 mg/dl (both p < 0.05). Serum creatinine level remained within the normal range in all the study participants. Complete response was achieved in 12 patients (63%), and a partial response was achieved in 5 patients (26%). The remaining 2 patients showed no response. No serious adverse effects were observed. Conclusion: The data suggest that long-term, relatively low-dose Tac-based immunosuppressive treatment is beneficial and has low cytotoxicity, and therefore represents an attractive option for the treatment of young patients with LN in daily clinical practice. Further studies involving a larger number of patients are needed to confirm these results.

Since viral infections activate type I interferon (IFN) pathways and cause subsequent release of IFN-dependent proinflammatory chemokines and cytokines, the innate immune system plays an important role in the pathogenesis of lupus nephritis (LN). It has been reported that human myxovirus resistance protein 1 (Mx1), a type I IFN-dependent transcript, acts against a wide range of RNA viruses. Although the expression of Mx1 in biopsy specimens obtained from patients with dermatomyositis and cutaneous lupus has been described, the expression of Mx1 in human mesangial cells (MCs) has remained largely unknown. We treated normal human MCs in culture with polyinosinic-polycytidylic acid (poly IC), an authentic double-stranded RNA, and analyzed the expression of Mx1 by reverse transcription-polymerase chain reaction and western blotting. To elucidate the poly IC-signalling pathway, we subjected the cells to RNA interference against IFN-β. We also conducted an immunofluorescence study to examine mesangial Mx1 expression in biopsy specimens from patients with LN. Poly IC-induced Mx1 expression in MCs are shown both time- and dose-dependently, and RNA interference against IFN-β inhibited poly IC-induced Mx1 expression. Intense glomerular Mx1 expression was observed in biopsy specimens from patients with LN, whereas negative staining occurred in specimens from patients with IgA nephropathy or purpura nephritis. These preliminary observations support, at least in part, the theory of innate immune system activation in the pathogenesis of LN.