Background Impaired fracture healing represents an ongoing clinical challenge, as treatment options remain limited. Calcitonin gene-related peptide (CGRP), a neuropeptide targeted by emerging anti-migraine drugs, is also expressed in sensory nerve fibres innervating bone tissue. Method Bone healing following a femoral osteotomy stabilized with an external fixator was analysed over 21 days in αCGRP-deficient and WT mice. Bone regeneration was evaluated by serum analysis, µCT analysis, histomorphometry and genome-wide expression analysis. Bone-marrow-derived osteoblasts and osteoclasts, as well as the CGRP antagonist olcegepant were employed for mechanistic studies. Findings WT mice with a femoral fracture display increased CGRP serum levels. αCGRP mRNA expression after skeletal injury is exclusively induced in callus tissue, but not in other organs. On protein level, CGRP and its receptor, calcitonin receptor-like receptor (CRLR) complexing with RAMP1, are differentially expressed in the callus during bone regeneration. On the other hand, αCGRP-deficient mice display profoundly impaired bone regeneration characterised by a striking reduction in the number of bone-forming osteoblasts and a high rate of incomplete callus bridging and non-union. As assessed by genome-wide expression analysis, CGRP induces the expression of specific genes linked to ossification, bone remodeling and adipogenesis. This suggests that CGRP receptor-dependent PPARγ signaling plays a central role in fracture healing. Interpretation This study demonstrates an essential role of αCGRP in orchestrating callus formation and identifies CGRP receptor agonism as a potential approach to stimulate bone regeneration. Moreover, as novel agents blocking CGRP or its receptor CRLR are currently introduced clinically for the treatment of migraine disorders, their potential negative impact on bone regeneration warrants clinical investigation. Funding This work was funded by grants from the Else-Kröner-Fresenius-Stiftung (EKFS), the Deutsche Forschungsgemeinschaft (DFG), and the Berlin Institute of Health (BIH).

Tight junction (TJ) formation is vital for epidermal barrier function. We aimed to specifically manipulate TJ barriers in the reconstructed human epidermis (RHE) by claudin‐1 and ‐4 knockdown (KD) and by claudin‐binding fusion proteins of glutathione S‐transferase and modified C‐terminal fragments of Clostridium perfringens enterotoxin (GST‐cCPE). Impedance spectroscopy and tracer permeability imaging were employed for functional barrier assessment and investigation of claudin contribution. KD of claudin‐1, but not claudin‐4, impaired the paracellular barrier in vitro. Similarly, claudin‐binding GST‐cCPE variants weakened the paracellular but not the stratum corneum barrier. Combining both TJ targeting methods, we found that claudin‐1 targeting by GST‐cCPE after claudin‐4 KD led to a marked decrease in paracellular barrier properties. Conversely, after claudin‐1 KD, GST‐cCPE did not further impair the barrier. Comparison of GST‐cCPE variants with different claudin‐1/claudin‐4 affinities, NHS‐fluorescein tracer detection, and immunostaining of RHE paraffin sections showed that GST‐cCPE variants bind to extrajunctional claudin‐1 and ‐4, which are differentially distributed along the stratum basale–stratum granulosum axis. GST‐cCPE binding blocks these claudins, thereby specifically opening the paracellular barrier of RHE. The data indicate a critical role for claudin‐1 in regulating paracellular permeability for ions and small molecules in the viable epidermis. Claudin targeting is presented as a proof‐of‐concept for precise barrier modulation.

Genome-wide association studies have discovered hundreds of associations between common genotypes and kidney function but cannot comprehensively investigate rare coding variants. Here, we apply a genotype imputation approach to whole exome sequencing data from the UK Biobank to increase sample size from 166,891 to 408,511. We detect 158 rare variants and 105 genes significantly associated with one or more of five kidney function traits, including genes not previously linked to kidney disease in humans. The imputation-powered findings derive support from clinical record-based kidney disease information, such as for a previously unreported splice allele in PKD2, and from functional studies of a previously unreported frameshift allele in CLDN10. This cost-efficient approach boosts statistical power to detect and characterize both known and novel disease susceptibility variants and genes, can be generalized to larger future studies, and generates a comprehensive resource (https://ckdgen-ukbb.gm.eurac.edu/) to direct experimental and clinical studies of kidney disease.

Genome-wide association studies have discovered hundreds of associations between common genotypes and kidney function but cannot comprehensively investigate rare coding variants. Here, we applied a genotype imputation approach to whole exome sequencing data from the UK Biobank to increase sample size from 166,891 to 408,511. We detected 158 rare variants and 105 genes significantly associated with one or more of five kidney function traits, including genes not previously linked to kidney disease in humans. The imputation-powered findings derive support from clinical record-based kidney disease information, such as for a novel splice allele in PKD2, and from functional studies of a novel frameshift allele in CLDN10. This cost-efficient approach boosts statistical power to detect and characterize both known and novel disease susceptibility variants and genes, can be generalized to larger future studies, and generates a comprehensive resource (https://ckdgen-ukbb.gm.eurac.edu/) to direct experimental and clinical studies of kidney disease.