Establishment of a conditionally reprogrammed primary eccrine sweat gland culture for evaluation of tissue-specific CFTR function

BACKGROUND

Sweat chloride concentration is used both for CF diagnosis and for tracking CFTR modulator efficacy over time, but the relationship between sweat chloride and lung health is heterogeneous and informed by CFTR genotype. Here, we endeavored to characterize ion transport in eccrine sweat glands (ESGs).

METHODS

First, ESGs were microdissected from a non-CF skin donor to analyze individual glands. We established primary cultures of ESG cells via conditional reprogramming for functional testing of ion transport by short circuit current measurement and examined cell composition by single-cell RNA-sequencing (scRNA-seq) comparing with whole dissociated ESGs. Secondly, we cultured nasal epithelial (NE) cells and ESGs from two people with CF (pwCF) to assess modulator efficacy. Finally, NEs and ESGs were grown from one person with the CFTR genotype F312del/F508del to explore genotype-phenotype heterogeneity.

RESULTS

ESG primary cells from individuals without CF demonstrated robust ENaC and CFTR function. scRNA-seq demonstrated both secretory and ductal ESG markers in cultured ESG cells. In both NEs and ESGs from pwCF homozygous for F508del, minimal baseline CFTR function was observed, and treatment with CFTR modulators significantly enhanced function. Notably, NEs from an individual bearing F312del/F508del exhibited significant baseline CFTR function, whereas ESGs from the same person displayed minimal CFTR function, consistent with observed phenotype.

CONCLUSIONS

This study has established a novel primary culture technique for ESGs that allows for functional ion transport measurement to assess modulator efficacy and evaluate genotype-phenoytpe heterogeneity. To our knowledge, this is the first reported application of conditional reprogramming and scRNA-seq of microdissected ESGs.

Fascia Layer-A Novel Target for the Application of Biomaterials in Skin Wound Healing

As the first barrier of the human body, the skin has been of great concern for its wound healing and regeneration. The healing of large, refractory wounds is difficult to be repaired by cell proliferation at the wound edges and usually requires manual intervention for treatment. Therefore, therapeutic tools such as stem cells, biomaterials, and cytokines have been applied to the treatment of skin wounds. Skin microenvironment modulation is a key technology to promote wound repair and skin regeneration. In recent years, a series of novel bioactive materials that modulate the microenvironment and cell behavior have been developed, showing the ability to efficiently facilitate wound repair and skin attachment regeneration. Meanwhile, our lab found that the fascial layer has an indispensable role in wound healing and repair, and this review summarizes the research progress of related bioactive materials and their role in wound healing.

A novel organotypic 3D sweat gland model with physiological functionality

Dysregulated human eccrine sweat glands can negatively impact the quality-of-life of people suffering from disorders like hyperhidrosis. Inability of sweating can even result in serious health effects in humans affected by anhidrosis. The underlying mechanisms must be elucidated and a reliable in vitro test system for drug screening must be developed. Here we describe a novel organotypic three-dimensional (3D) sweat gland model made of primary human eccrine sweat gland cells. Initial experiments revealed that eccrine sweat gland cells in a two-dimensional (2D) culture lose typical physiological markers. To resemble the in vivo situation as close as possible, we applied the hanging drop cultivation technology regaining most of the markers when cultured in its natural spherical environment. To compare the organotypic 3D sweat gland model versus human sweat glands in vivo, we compared markers relevant for the eccrine sweat gland using transcriptomic and proteomic analysis. Comparing the marker profile, a high in vitro-in vivo correlation was shown. Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5), muscarinic acetylcholine receptor M3 (CHRM3), Na⁺-K⁺-Cl^- cotransporter 1 (NKCC1), calcium-activated chloride channel anoctamin-1 (ANO1/TMEM16A), and aquaporin-5 (AQP5) are found at significant expression levels in the 3D model. Moreover, cholinergic stimulation with acetylcholine or pilocarpine leads to calcium influx monitored in a calcium flux assay. Cholinergic stimulation cannot be achieved with the sweat gland cell line NCL-SG3 used as a sweat gland model system. Our results show clear benefits of the organotypic 3D sweat gland model versus 2D cultures in terms of the expression of essential eccrine sweat gland key regulators and in the physiological response to stimulation. Taken together, this novel organotypic 3D sweat gland model shows a good in vitro-in vivo correlation and is an appropriate alternative for screening of potential bioactives regulating the sweat mechanism.

Serum is an indispensable factor in the maintenance of the biological characteristics of sweat gland cells

The tolerance of sweat gland cells for in vitro amplification and subcultivation is low as they are somatic cells. The present study aimed to formulate an optimal medium for the culture of human eccrine sweat gland cells (HESGCs) and to establish a method for induction of HESGCs proliferation, whilst maintaining the characteristics of sweat gland cells. HESGCs cultured in sweat gland (SG):keratinocyte growth medium-2 (KGM-2) (1:1) medium had a higher proliferation rate and a stable morphology compared with cells cultured in SG and KGM-2 medium only. Reverse transcription-quantitative polymerase chain reaction indicated that cells cultured in the SG:KGM-2 (1:1) medium exhibited higher expression levels of α-smooth muscle actin, keratin (K)77, carcinoembryonic antigen, K8, K18, ectodysplasin A receptor, c-Myc, Kruppel-like factor 4 and octamer-binding transcription factor 4 compared with cells cultured in SG only or KGM-2 only medium. Three-dimensional culture analysis revealed that HESGCs cultured in SG:KGM-2 1:1 medium differentiated into sweat gland-like structures, whereas cells cultured in KGM-2 only medium underwent cornification. The present study also determined that the maintenance of the biological characteristics of HESGCs occurred due to the presence of fetal bovine serum (FBS). Cells cultured in medium without FBS differentiated into keratinocytes. Therefore, the SG:KGM-2 (1:1) medium may be a suitable culture medium for HESGCs. In conclusion, this mixed medium is a valuable compound and should be considered to be a potential supplemental medium for HESGCs.

Isolation, culture and phenotypic characterization of human sweat gland epithelial cells

Sweat gland epithelial cells (SGECs) have been identified as essential for the regeneration of sweat glands and for the construction of skin substitutes containing skin appendages. Consequently, the isolation, culture and phenotypic characterization of SGECs are of paramount importance. In the present study study, human sweat glands were isolated by pipetting under a phase contrast microscope following digestion with collagenase type I. Subsequently, a microscopic organ culture technique was used for the primary culture of human SGECs, and the culture conditions were modified in order to achieve optimal cell growth status. Primary SGECs were identified based on their expression of markers specific for sweat glands, including carcinoembryonic antigen (CEA), CK7, CK8, CK14, CK15, CK18 and CK19. We explored the possible presence of stem cells in human sweat glands by detecting their expression of leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5). Primary SGECs achieved a good growth state when cultured under serum-free conditions. After one passage, the cells cultured in keratinocyte serum-free medium with 1% fetal bovine serum (FBS) still showed a prominent proliferative activity. Phenotypic analysis by immunofluorescence microscopy, reverse transcription-polymerase chain reaction (RT-PCR), and western blot analysis demonstrated the expression of sweat gland-specific markers, including CEA, CK7, CK8, CK14, CK15, CK18 and CK19. In addition, RT-PCR and immunochemistry detected the expression of LGR5. In comparison with traditional serum-containing conditions, serum-free culture provides the preferred culture conditions for human SGECs. LGR5 is a novel marker that identifies human sweat gland-derived stem cells.