Griffin, Matthew D.

Mesenchymal stem/stromal cells (MSCs) facilitate repair in experimental diabetic kidney disease (DKD). However, the hyperglycemic and uremic milieu may diminish regenerative capacity of patient-derived therapy. We hypothesized that DKD reduces human MSC paracrine function. Adipose-derived MSC from 38 participants with DKD and 16 control subjects were assessed for cell surface markers, trilineage differentiation, RNA sequencing (RNA-seq), in vitro function (coculture or conditioned medium experiments with T cells and human kidney cells [HK-2]), secretome profile, and cellular senescence abundance. The direction of association between MSC function and patient characteristics were also tested. RNA-seq analysis identified 353 differentially expressed genes and downregulation of several immunomodulatory genes/pathways in DKD-MSC versus Control-MSC. DKD-MSC phenotype, differentiation, and tube formation capacity were preserved, but migration was reduced. DKD-MSC with and without interferon-γ priming inhibited T-cell proliferation greater than Control-MSC. DKD-MSC medium contained higher levels of anti-inflammatory cytokines (indoleamine 2,3-deoxygenase 1 and prostaglandin-E2) and prorepair factors (hepatocyte growth factor and stromal cell–derived factor 1) but lower IL-6 versus control-MSC medium. DKD-MSC medium protected high glucose plus transforming growth factor-β–exposed HK-2 cells by reducing apoptotic, fibrotic, and inflammatory marker expression. Few DKD-MSC functions were affected by patient characteristics, including age, sex, BMI, hemoglobin A1c, kidney function, and urine albumin excretion. However, senescence-associated β-galactosidase activity was lower in DKD-MSC from participants on metformin therapy. Therefore, while DKD altered the transcriptome and migratory function of culture-expanded MSCs, DKD-MSC functionality, trophic factor secretion, and immunomodulatory activities contributing to repair remained intact. These observations support testing of patient-derived MSC therapy and may inform preconditioning regimens in DKD clinical trials.

Drawing from basic knowledge of stem-cell biology, embryonic development, wound healing, and aging, regenerative medicine seeks to develop therapeutic strategies that complement or replace conventional treatments by actively repairing diseased tissue or generating new organs and tissues. Among the various clinical-translational strategies within the field of regenerative medicine, several can be broadly described as promoting disease resolution indirectly through local or systemic interactions with a patient’s cells, without permanently integrating or directly forming new primary tissue. In this review, we focus on such therapies, which we term disease-modulating regenerative therapies (DMRT), and on the extent to which they have been translated into the clinical arena in four distinct areas of nephrology: renovascular disease (RVD), sepsis-associated AKI (SA-AKI), diabetic kidney disease (DKD), and kidney transplantation (KTx). As we describe, the DMRT that has most consistently progressed to human clinical trials for these indications is mesenchymal stem/stromal cells (MSCs), which potently modulate ischemic, inflammatory, profibrotic, and immune-mediated tissue injury through diverse paracrine mechanisms. In KTx, several early-phase clinical trials have also tested the potential for ex vivo –expanded regulatory immune cell therapies to promote donor-specific tolerance and prevent or resolve allograft injury. Other promising DMRT, including adult stem/progenitor cells, stem cell–derived extracellular vesicles, and implantable hydrogels/biomaterials remain at varying preclinical stages of translation for these renal conditions. To date (2021), no DMRT has gained market approval for use in patients with RVD, SA-AKI, DKD, or KTx, and clinical trials demonstrating definitive, cost-effective patient benefits are needed. Nonetheless, exciting progress in understanding the disease-specific mechanisms of action of MSCs and other DMRT, coupled with increasing knowledge of the pathophysiologic basis for renal-tissue injury and the experience gained from pioneering early-phase clinical trials provide optimism that influential, regenerative treatments for diverse kidney diseases will emerge in the years ahead.

Objective Activin A, an inflammatory mediator implicated in cellular senescence-induced adipose tissue dysfunction and profibrotic kidney injury, may become a new target for the treatment of diabetic kidney disease (DKD) and chronic kidney diseases. We tested the hypothesis that human DKD-related injury leads to upregulation of activin A in blood and urine and in a human kidney cell model. We further hypothesized that circulating activin A parallels kidney injury markers in DKD. Research design and methods In two adult diabetes cohorts and controls (Minnesota, USA; Galway, Ireland), the relationships between plasma (or urine) activin A, estimated glomerular filtration rate (eGFR) and DKD injury biomarkers were tested with logistic regression and correlation coefficients. Activin A, inflammatory, epithelial-mesenchymal-transition (EMT) and senescence markers were assayed in human kidney (HK-2) cells incubated in high glucose plus transforming growth factor-β1 or albumin. Results Plasma activin A levels were elevated in diabetes (n=206) compared with controls (n=76; 418.1 vs 259.3 pg/mL; p<0.001) and correlated inversely with eGFR (r s =−0.61; p<0.001; diabetes). After eGFR adjustment, only albuminuria (OR 1.56, 95% CI 1.16 to 2.09) and tumor necrosis factor receptor-1 (OR 6.40, 95% CI 1.08 to 38.00) associated with the highest activin tertile. Albuminuria also related to urinary activin (r s =0.65; p<0.001). Following in vitro HK-2 injury, activin, inflammatory, EMT genes and supernatant activin levels were increased. Conclusions Circulating activin A is increased in human DKD and correlates with reduced kidney function and kidney injury markers. DKD-injured human renal tubule cells develop a profibrotic and inflammatory phenotype with activin A upregulation. These findings underscore the role of inflammation and provide a basis for further exploration of activin A as a diagnostic marker and therapeutic target in DKD.

Abstract CTLA-4 (CD152) engagement can down-regulate T cell activation and promote the induction of immune tolerance. However, the strategy of attenuating T cell activation by engaging CTLA-4 has been limited by sharing of its natural ligands with the costimulatory protein CD28. In the present study, a CTLA-4-specific single-chain Ab (scFv) was developed and expressed on the cell surface to promote selective engagement of this regulatory molecule. Transfectants expressing anti-CTLA-4 scFv at their surface bound soluble CTLA-4 but not soluble CD28. Coexpression of anti-CTLA-4 scFv with anti-CD3ε and anti-CD28 scFvs on artificial APCs reduced the proliferation and IL-2 production by resting and preactivated bulk T cells as well as CD4+ and CD8+ T cell subsets. Importantly, expression of anti-CTLA-4 scFv on the same cell surface as the TCR ligand was essential for the inhibitory effects of CTLA-4-specific ligation. CTLA-4-mediated inhibition of tyrosine phosphorylation of components of the proximal TCR signaling apparatus was similarly dependent on coexpression of TCR and CTLA-4 ligands on the same surface. These findings support a predominant role for CTLA-4 function in the modification of the proximal TCR signal. Using T cells from DO11.10 and 2C TCR transgenic mice, negative regulatory effects of selective CTLA-4 ligation were also demonstrated during the stimulation of Ag-specific CD4+ and CD8+ T cells by MHC/peptide complexes. Together these studies demonstrate that selective ligation of CTLA-4 using a membrane-bound scFv results in attenuated T cell responses only when coengaged with the TCR during T cell/APC interaction and define an approach to harnessing the immunomodulatory potential of CTLA-4-specific ligation.

Abstract The differentiation of double-positive (DP) CD4+CD8+ thymocytes to single-positive CD4+ or CD8+ T cells is regulated by signals that are initiated by coengagement of the Ag (TCR) and costimulatory receptors. CD28 costimulatory receptors, which augment differentiation and antiapoptotic responses in mature T lymphocytes, have been reported to stimulate both differentiation and apoptotic responses in TCR-activated DP thymocytes. We have used artificial APCs that express ligands for TCR and CD28 to show that CD28 signals increase expression of CD69, Bim, and cell death in TCR-activated DP thymocytes but do not costimulate DP thymocytes to initiate the differentiation program. The lack of a differentiation response is not due to defects in CD28-initiated TCR proximal signaling events but by a selective defect in the activation of ERK MAPK. To characterize signals needed to initiate the death response, a mutational analysis was performed on the CD28 cytoplasmic domain. Although mutation of all of CD28 cytoplasmic domain signaling motifs blocks cell death, the presence of any single motif is able to signal a death response. Thus, there is functional redundancy in the CD28 cytoplasmic domain signaling motifs that initiate the thymocyte death response. In contrast, immobilized Abs can initiate differentiation responses and cell death in DP thymocytes. However, because Ab-mediated differentiation occurs through CD28 receptors with no cytoplasmic domain, the response may be mediated by increased adhesion to immobilized anti-TCR Abs.

Abstract We report here the first association between vitamin D–resistant rickets, alopecia, and type 1 diabetes in a child with compound heterozygous mutations in the VDR gene. Transfection studies suggest dissociated effects of VDR gene mutations on the regulation of genes involved in vitamin D metabolism and dendritic cell maturation. Introduction: Whereas vitamin D may play a role in the immune tolerance process, no patient has been reported to associate hereditary vitamin D–resistant rickets (HVDRR) and an autoimmune disease, and no attempt has been made to delineate the outcome of mutations of the vitamin D receptor (VDR) on the transcription of genes controlling immune tolerance. Materials and Methods: The VDR gene was analyzed in a child with vitamin D–resistant rickets, total alopecia, and early childhood–onset type 1 diabetes. Patient's fibroblasts and COS-7 cells transfected with wildtype or mutant VDRs were studied for ligand-binding capacity, transactivation activity using two gene promoters [CYP-24, a classical 1,25(OH)2D3-responsive gene, and relB, a critical NF-κB component for regulation of dendritic cell differentiation], VDR-RXR heterodimers association to CYP 24 VDREs by gel mobility shift assays, and co-activator binding by Glutathione-S-transferase pull-down assays. Results: Two novel compound heterozygous mutations (L263R and R391S) were identified in the VDR ligand-binding domain in this child. Both mutations significantly impaired VDR ligand-binding capacity but had dissociated effects on CYP-24 and RelB promoter responses to vitamin D. CYP 24 response binding to SRC-1 and RXR-heterodimer binding to CYP24 VDREs were abolished in L263R mutants but normal or partially altered in R391S mutants. In the opposite, RelB responses to vitamin D were close to normal in L263R mutants but abolished in R391S mutants. Conclusions: We report the first clinical association between HVDRR, total alopecia, and early childhood–onset type 1 diabetes. Mutations in the VDR ligand-binding domain may hamper the 1,25(OH)2D3–mediated relB responses, an effect that depends on the site of the VDR mutation and cannot be anticipated from VDR ligand-binding ability or CYP-24 response. Based on these results, we propose to survey the immune function in patients with HVDRR, including those with moderate features of rickets.