The stakes of the question are enormous. Diabetic foot ulcers affect a substantial fraction of the world’s more than half a billion people living with diabetes, and their consequences rival those of many cancers. Previous research cited by the authors has shown that five-year mortality and direct costs of care for people with diabetic foot complications are comparable to those faced by cancer patients. Kerala, a state with one of India’s highest diabetes burdens and a well-documented ten-year cohort documenting the incidence of type 2 diabetes and prediabetes, offers a particularly important setting for this kind of investigation. Yet until now, genetic risk factors for foot ulcers in this population had been barely explored.

The research team focused on the vitamin D system for good reason. Vitamin D is far more than a bone-building nutrient; its active form, calcitriol, binds to the vitamin D receptor to regulate hundreds of genes involved in immune defence, inflammation, insulin secretion and tissue repair. Wound healing is an intricate biological process that depends on precisely coordinated cell migration, matrix remodelling and antimicrobial activity, all of which are influenced by vitamin D signalling. Small variations in the VDR gene, known as single nucleotide polymorphisms, can subtly alter how strongly the receptor is expressed or how efficiently it responds to its hormonal ligand, potentially shifting the balance between effective healing and chronic, non-healing wounds.

Reveendran and colleagues examined four of the most widely studied VDR polymorphisms, each named after the restriction enzyme originally used to detect it: rs7975232 (ApaI), rs731236 (TaqI), rs1544410 (BsmI) and rs2228570 (FokI). These variants sit at different points in the gene. The BsmI, ApaI and TaqI sites lie in or near the three-prime untranslated region, where they may influence messenger RNA stability, while FokI sits in the start codon region and is famous for creating two physically different versions of the receptor protein: a longer 427-amino-acid form and a shorter 424-amino-acid form that differs in its ability to activate target genes.

The study compared three groups: patients with diabetic foot ulcers, patients with type 2 diabetes but no foot ulcers, and non-diabetic controls, all recruited in Kerala. The researchers measured serum levels of 25-hydroxyvitamin D, the standard clinical marker of vitamin D status, and genotyped participants for the four polymorphisms. The mean 25-hydroxyvitamin D levels were low across the board, at 17.7 plus or minus 14.2 nanograms per millilitre in the foot ulcer group, 19.5 plus or minus 12.4 in the diabetes group and 20.6 plus or minus 13.9 in the controls. Those averages did not differ significantly between the groups, but when the researchers looked at deficiency as a categorical state rather than a continuous measurement, a clear signal emerged: the prevalence of vitamin D deficiency was significantly higher in the foot ulcer group than in either the diabetes or control groups, a difference the authors report with a chi-squared statistic of 6.03 and a p-value of 0.04.

The genetic findings were even more intriguing. Two of the four variants showed significant associations with foot ulcer risk. For rs731236, the TaqI polymorphism, carrying the AG genotype was associated with a reduced risk of diabetic foot ulcer compared with both the diabetes-only patients and the non-diabetic controls, with an odds ratio of 0.51 and a p-value below 0.05. In other words, people carrying that genotype were roughly half as likely to develop an ulcer. A strikingly similar protective pattern appeared for rs1544410, the BsmI polymorphism, where the TC genotype was associated with reduced risk, with an odds ratio of 0.51 and a p-value of 0.0219. The other two variants, FokI (rs2228570) and ApaI (rs7975232), showed no significant associations with ulcer susceptibility in this population.

To probe the biology behind the FokI variant, the team turned to computational molecular docking, a technique that predicts how strongly two molecules bind to each other. They modelled the binding of calcitriol, the active hormonal form of vitamin D, to both protein isoforms generated by the FokI polymorphism. The docking analysis indicated favourable calcitriol binding to both receptor versions, with a slightly higher affinity for the shorter 424-amino-acid variant, at minus 7.8 kilocalories per mole versus minus 7.7 for the longer form. Although the difference is small, such subtle changes in ligand affinity can, in principle, translate into differences in receptor signalling output, and previous studies have linked FokI variation to oxidative stress and wound outcomes in diabetic foot patients in other populations, including work in Iran and Indonesia.

The protective associations of the TaqI and BsmI variants fit into a growing international literature. Meta-analyses have examined VDR polymorphisms in susceptibility to type 2 diabetes itself, and systematic reviews of genetic polymorphisms and diabetic foot risk have catalogued associations across multiple ethnic groups. A recent prospective observational study at a South Indian tertiary care facility also explored the interplay between vitamin D status and VDR genotype in foot ulcer patients. The Kerala findings add population-specific evidence from a region where diabetes prevalence is exceptionally high and where earlier clinical surveys have documented the heavy burden of foot complications in both hospital podiatry clinics and rural communities. Because genetic associations can vary substantially between populations owing to differences in allele frequencies and environmental exposures, regionally grounded studies like this one are essential for building a complete global picture.

What makes the study particularly compelling is the convergence of two independent signals: a higher burden of vitamin D deficiency among ulcer patients and a protective effect of specific VDR genotypes. Together, they suggest that the vitamin D axis may influence not just whether someone develops diabetes, but whether the disease culminates in its most disabling complication. The authors caution, however, that these findings require validation in larger, multicentre studies and that functional investigations will be needed to establish exactly how the TaqI and BsmI variants alter receptor biology and wound healing. The study was supported by the Department of Science and Technology’s Science and Engineering Research Board and the Department of Biotechnology of the Government of India, and involved collaboration between the National Institute of Technology Calicut, the Nutrition Research Centre in Thiruvananthapuram, the Kerala University of Health Sciences and the Rajiv Gandhi Centre for Biotechnology.

If the associations hold up, the implications could be significant. Vitamin D status is modifiable through supplementation and sensible sun exposure, and genetic screening could one day help identify patients with diabetes who carry a heightened risk of foot ulcers before the first wound appears, allowing intensified preventive care for those who need it most. With diabetes prevalence projected to double globally by 2050 and foot ulcers already consuming a disproportionate share of diabetes-related healthcare spending, even modest advances in risk prediction could translate into many thousands of limbs and lives saved. For now, the Kerala study stands as a reminder that the answer to one of diabetes’ oldest clinical puzzles may lie partly in the fine print of the genome, written in the language of a sunshine vitamin.

Subject of Research: Association of vitamin D receptor gene polymorphisms and vitamin D deficiency with diabetic foot ulcer risk in type 2 diabetes

Article Title: Genetic Association of VDR Polymorphism with Diabetic Foot Ulcers in Type 2 Diabetes: Evidence from Kerala, India

Article References: Reveendran, R., Thankam, S. K., Anish, T. S., Jose, L., Jones, S., & Vasu, S. T. (2026). Genetic Association of VDR Polymorphism with Diabetic Foot Ulcers in Type 2 Diabetes: Evidence from Kerala, India. Biochemical Genetics. https://doi.org/10.1007/s10528-026-11450-x

Image Credits: AI Generated

DOI: 10.1007/s10528-026-11450-x

Keywords: diabetic foot ulcer, type 2 diabetes, vitamin D receptor, VDR polymorphism, vitamin D deficiency, Kerala, genetic association, single nucleotide polymorphism, TaqI, BsmI, wound healing, calcitriol

Cutaneous melanoma is the most lethal and aggressive cancer of the skin, arising from malignant transformation of melanocytes and marked by rapid proliferation, high metastatic potential, and notorious resistance to conventional therapies. The latest epidemiological estimates from the International Agency for Research on Cancer counted 331,722 new cases and 58,667 deaths worldwide in 2022, and even as targeted therapies and immunotherapies have transformed the landscape, low response rates and acquired resistance continue to frustrate effective management. That unmet need is precisely why the study’s authors turned their attention to two signaling systems increasingly recognized as vulnerabilities in tumors: purinergic signaling, the extracellular communication network built on adenosine triphosphate and its breakdown products, and the inflammatory axis involving interleukin-6 and the NLRP3 inflammasome.

Purinergic signaling, first proposed in 1972, operates through P1 and P2 receptors that respond to a ladder of molecules: ATP, adenosine diphosphate, adenosine monophosphate, and adenosine. Depending on which molecules dominate the extracellular space, the same pathway can drive cell proliferation or push a cell toward apoptosis. In the tumor microenvironment, the balance tilts dangerously. Extracellular adenosine, generated in abundance, acts as a potent immunosuppressant, blunting the anti-tumor immune response. The levels of these signaling molecules are controlled largely by ectonucleotidases, membrane-bound enzymes known as CD39 and CD73, along with adenosine deaminase, which breaks adenosine down into inosine. CD39 converts ATP into ADP and AMP; CD73 then hydrolyzes AMP into adenosine. Overexpression of CD73 has been documented in pancreatic adenocarcinoma, thyroid cancer, and melanoma itself, and both CD39 and CD73 have been flagged as next-generation checkpoint targets for cancer therapy.

Against that backdrop, calcitriol offered an intriguing candidate. Previous work had shown that 1-alpha,25-dihydroxyvitamin D3 induces apoptosis in melanoma cells, enhances the anticancer effects of classical chemotherapy, inhibits proliferation and migration in breast cancer models, and can modulate IL-6 expression. Yet its mechanism of action on the purinergic system in melanoma had never been systematically explored. The research team hypothesized that calcitriol exerts a potent antineoplastic effect on cutaneous melanoma by modulating the activity and expression of ectonucleotidases, thereby rewiring the extracellular nucleotide landscape in favor of tumor cell death.

To test the hypothesis, the investigators cultured two human cutaneous melanoma cell lines, A375 and SK-MEL-28, treating them with calcitriol at 1, 10, and 50 nanomolar concentrations for 24 hours. The A375 line, which displays epithelial morphology and an invasive, metastatic profile, and SK-MEL-28, a polygonal melanoma line, were subjected to a battery of assays: MTT and fluorescence microscopy viability tests, measurements of mitochondrial transmembrane potential using the TMRE dye, detection of apoptotic bodies by acridine orange staining, wound-healing migration assays, and enzymatic quantification of ATP, ADP, and AMP hydrolysis alongside adenosine deaminase activity. Gene expression of CD39, CD73, IL-6, and NLRP3 was assessed by RT-qPCR, normalized to the housekeeping gene GAPDH and analyzed with the comparative delta-delta-CT method, with one-way ANOVA and Dunnett’s post hoc test applied throughout.

The results were striking and, in one respect, unexpectedly selective. In A375 cells, calcitriol significantly reduced viability at every concentration tested, with the MTT assay yielding P values of 0.0004 at 1 nM and below 0.0001 at 10 and 50 nM. Fluorescence microscopy independently corroborated the viability loss across all doses. Crucially, the treatment also collapsed the mitochondrial transmembrane potential of A375 cells at all concentrations, with statistical significance reaching P < 0.0001, a disruption consistent with the initiation of intrinsic apoptosis. Matching that mitochondrial signature, the treated cells showed marked nuclear fragmentation: apoptotic bodies rose significantly at all three doses, while cell counts fell in a dose-dependent manner. Wound-healing assays added another dimension, revealing that calcitriol inhibited A375 migration and wound closure at every concentration tested within just 24 hours, with P < 0.0001, a finding with obvious implications for blocking metastasis.

The SK-MEL-28 line told a different story. Calcitriol produced no significant reduction in its viability and left its mitochondrial potential untouched; at 1 nM, viability even increased slightly. The researchers point to a well-documented explanation: SK-MEL-28 cells express functionally lower levels of the vitamin D receptor than several other melanoma lines, rendering them resistant to calcitriol’s antiproliferative effects at nanomolar concentrations, with prior studies noting sensitivity only at much higher doses. The contrast between the two cell lines underscores that calcitriol’s anticancer activity depends on functional vitamin D receptor signaling, a caveat that will shape which patients might ultimately benefit from a calcitriol-based adjuvant strategy.

The deepest technical insight, however, came from the purinergic analysis. Calcitriol left ATP hydrolysis unchanged but significantly decreased ADP hydrolysis at 1 and 10 nM, with a modest increase at 50 nM, and reduced AMP hydrolysis at 10 and 50 nM. Because CD39 and CD73 jointly convert ATP down the cascade to adenosine, dampened AMP breakdown means less substrate for adenosine production. Consistent with that logic, adenosine deaminase activity, which depends on adenosine availability, dropped sharply at 10 and 50 nM. At the gene level, calcitriol downregulated CD39 expression at 10 and 50 nM and exerted a strong suppressive effect on CD73 at those same concentrations, P < 0.0001. Together, these changes describe a coherent suppression of the AMP-to-adenosine axis, the very pathway tumors exploit to generate immunosuppressive adenosine in their microenvironment. By throttling adenosine generation, calcitriol may indirectly loosen the tumor’s grip on local immunity.

The inflammatory arm of the study completed the picture. Extracellular nucleotide signaling is intimately connected to inflammation, and both IL-6 and NLRP3 have dual, sometimes controversial roles in cancer, with evidence linking them to tumor progression, chemoresistance, immune cell infiltration, and poor prognosis in melanoma. Calcitriol significantly downregulated IL-6 expression at 10 nM and 50 nM, and produced an equally robust reduction in NLRP3 gene expression, with P < 0.0001 at both doses. Given that IL-6 targeting has been proposed to abrogate melanoma growth and progression, and that NLRP3 is increasingly viewed as a therapeutic target capable of reducing chemoresistance, these transcriptional effects suggest calcitriol acts on multiple fronts at once: killing tumor cells directly, impairing their migratory capacity, starving the immunosuppressive adenosine pathway, and calming the pro-tumoral inflammatory circuitry.

The authors are careful about scope. Their analysis covered gene expression rather than protein levels, and only two cell lines were examined, which they acknowledge as a limitation given the distinct metabolic profiles of A375 and SK-MEL-28. They also stress that while the nanomolar concentrations used appear practical for in vivo applications, safety testing is required, and future animal studies should monitor calcium levels to guard against hypercalcemia, the classic toxicity of active vitamin D compounds. Encouragingly, the adjuvant concept already has clinical footprints: calcitriol has been shown to enhance the effects of cisplatin and dacarbazine in melanoma cells, to combine favorably with the VEGFR inhibitor Cediranib, and, in a prospective phase Ib study, to be well tolerated in metastatic melanoma patients receiving high-dose encapsulated calcitriol alongside temozolomide, with no significant secondary side effects reported. Combined with prior evidence that calcitriol can sensitize melanoma cells to proton beam irradiation, the new purinergic mechanism adds a mechanistic rationale to an accumulating clinical case. If subsequent in vivo work confirms that calcitriol’s ectonucleotidase modulation translates into restored anti-tumor immunity, the sunshine vitamin’s most potent form could find itself written into the melanoma treatment algorithm.

Subject of Research: Antineoplastic effects of calcitriol on cutaneous melanoma cells via purinergic signaling modulation

Article Title: Calcitriol, the active form of vitamin D, induces cell death and purinergic signaling modulation in cutaneous melanoma cells

Article References: da Silva, G. B., Narzetti, R. A., Dallagnol, P., Ozelame, B. C., Manica, D., Ramos, V. H. M., Kempka, A. P., & Bagatini, M. D. (2026). Calcitriol, the active form of vitamin D, induces cell death and purinergic signaling modulation in cutaneous melanoma cells. Medical Oncology, 43(10), Article 288. https://doi.org/10.1007/s12032-026-03412-5

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03412-5

Keywords: calcitriol, vitamin D, cutaneous melanoma, purinergic signaling, ectonucleotidases, CD39, CD73, apoptosis, mitochondrial membrane potential, IL-6, NLRP3, adjuvant therapy

The research team, led by Qingqing He and Junlin Liu, set out to map the molecular targets through which calcitriol exerts its anti-psoriatic effects. Calcitriol is best known for its role in calcium homeostasis and bone mineralization, but it also regulates cell proliferation, differentiation, oxidative stress, angiogenesis, immune modulation and antimicrobial peptide production. When calcitriol binds the vitamin D receptor, it dampens excessive T cell activation, particularly of Th17 cells, reducing interleukin-17 secretion, and it suppresses pro-inflammatory cytokines such as interleukin-6 and tumour necrosis factor-alpha. The enzyme CYP24A1 then hydroxylates calcitriol at the C-23 or C-24 position, converting it into less active metabolites that are eventually excreted, a safeguard against hypercalcaemia. What remained unclear was which downstream genes calcitriol might regulate to produce its therapeutic benefit in skin.

The researchers focused on CHI3L2, also known as YKL-39, a member of the chitinase-like protein family. Unlike its better-known relative CHI3L1, or YKL-40, CHI3L2 has been comparatively neglected in inflammatory disease research, although it is expressed in macrophages, chondrocytes and epithelial cells and can be induced by interleukin-6 and tumour necrosis factor-alpha. The protein displays chemotactic activity, growth factor activity, the ability to induce cytokine secretion and the capacity to stimulate angiogenesis. Previous work had connected CHI3L2 to the ERK1/2 signalling pathway in glioblastoma, and to STAT3 phosphorylation in invasive ductal carcinoma, where its role appears to depend on the molecular subtype of breast cancer. Because STAT3 is a critical transcription factor downstream of interleukin-6, interleukin-17, interleukin-22 and epidermal growth factor, and because persistent STAT3 activation in psoriatic keratinocytes and immune cells drives hyperproliferation, anti-apoptosis and inflammatory cytokine production, the team hypothesized that calcitriol might relieve psoriatic inflammation by suppressing CHI3L2 through inhibition of STAT3 signalling.

To test this idea in living animals, the researchers used the imiquimod-induced mouse model of psoriasis, in which topical application of the toll-like receptor 7/8 agonist activates the interleukin-23/interleukin-17 inflammatory axis that closely mirrors human disease pathogenesis. In a unilateral ear model, BALB/c mice received daily topical calcitriol solution before imiquimod cream for seven consecutive days. The treatment significantly reduced the clinical hallmarks of erythema, scaling and thickening, and histological examination showed markedly attenuated epidermal hyperplasia. Real-time quantitative PCR of ear tissue revealed substantially reduced expression of the pro-inflammatory cytokines interleukin-1alpha, interleukin-6, interleukin-17A and interleukin-23A. Importantly, serum calcium levels rose only to 2.500 millimoles per litre, comfortably within the normal physiological range of 2.0 to 2.6, and body weight, haematological parameters and organ histopathology remained unremarkable, indicating an excellent safety profile at the dose used.

The most striking finding emerged from a bilateral ear model designed to test whether local treatment could influence distant lesions. After seven days of calcitriol and imiquimod application to the right ear, the untreated left ears of the same mice were challenged with imiquimod alone for five days. Remarkably, even though only the right ear had ever received calcitriol, the left ears showed only mild psoriasiform changes compared with controls, with attenuated epidermal hyperplasia and reduced cytokine expression. Serum calcium returned to normal within five days of stopping treatment. This systemic effect suggests that calcitriol or its downstream mediators may enter the circulation and act at distal sites, although the precise circulating factors responsible remain to be identified. The observation raises intriguing questions about whether topical vitamin D therapy could benefit psoriatic lesions beyond the site of application in patients.

To dissect the cellular mechanisms, the team turned to HaCaT human keratinocytes stimulated with a five-cytokine cocktail, abbreviated M5, comprising interleukin-17A, interleukin-22, interleukin-1alpha, oncostatin M and tumour necrosis factor-alpha, which mimics the psoriatic inflammatory milieu. In psoriasis, the intermediate filament protein KRT1 is downregulated, marking impaired differentiation, while KRT6 is upregulated, indicating excessive proliferation and inflammatory activation. Calcitriol reversed both changes, restoring KRT1 and suppressing KRT6. CCK-8 and colony-formation assays showed that calcitriol counteracted the abnormal proliferation induced by M5, wound-healing assays demonstrated reduced aberrant migration, and quantitative PCR confirmed downregulation of interleukin-1alpha, interleukin-6, interleukin-17A and interleukin-23A messenger RNA.

The pivotal clue came from RNA sequencing of M5-stimulated cells treated with or without calcitriol. The analysis identified 537 differentially expressed genes, 344 upregulated and 193 downregulated. As expected, CYP24A1, the canonical calcitriol-metabolizing enzyme, was the most significantly upregulated gene, confirming that the vitamin D pathway was engaged. But the most significantly downregulated gene was CHI3L2, a result the researchers validated by quantitative PCR. When the team silenced CHI3L2 using short hairpin RNA, the effects phenocopied calcitriol treatment: KRT1 and KRT6 levels normalized, cell viability and colony formation declined, migratory capacity was impaired, and pro-inflammatory cytokine expression dropped. These loss-of-function experiments position CHI3L2 as a pro-inflammatory and pro-proliferative factor in psoriatic keratinocytes and a critical downstream effector of calcitriol.

Next, the researchers asked which signalling pathway mediates the CHI3L2 effect. KEGG pathway enrichment analysis of the downregulated genes pointed strongly to the STAT pathway, with no significant enrichment of the ERK pathway. Western blotting confirmed this: silencing CHI3L2 reduced phosphorylated STAT3 at both Tyr705 and Ser727 as well as total STAT3 protein, while phosphorylated and total ERK1/2 remained unchanged. Comparing the two STAT3 phosphorylation sites revealed that Tyr705 was the dominant regulatory node, with Ser727 showing a smaller, less pronounced change. Tyr705 phosphorylation is essential for STAT3 dimerization, nuclear translocation and transcriptional activity, so CHI3L2 appears primarily to facilitate STAT3 activation at this residue. The reduction in total STAT3 protein upon CHI3L2 knockdown also raises the possibility that CHI3L2 stabilizes STAT3 or enhances its expression, a hypothesis the authors flag for future investigation.

The authors are careful to acknowledge the limitations of their work. The imiquimod model, while widely accepted, does not fully capture the chronic, relapsing nature of human psoriasis and involves TLR7/8-driven inflammation that may not perfectly mirror the human disease. The in vitro experiments relied on HaCaT cells, an immortalized keratinocyte line, and validation in primary human keratinocytes or organotypic skin models would strengthen physiological relevance. Crucially, the study does not establish whether STAT3 or the vitamin D receptor directly binds the CHI3L2 promoter; chromatin immunoprecipitation and luciferase reporter assays would be needed to determine whether the regulation is direct or mediated through secondary transcription factors. It also remains unknown whether CHI3L2 interacts with STAT3 directly or acts through upstream receptor-mediated signalling. The systemic improvement seen in the bilateral ear model demands further exploration of circulating factors such as calcium, vitamin D metabolites or soluble inflammatory mediators.

Nevertheless, the study delivers a compelling new framework for understanding how vitamin D-based therapies work in psoriasis. By identifying CHI3L2 as a previously unrecognized downstream effector of calcitriol and demonstrating that its suppression depends on inhibiting STAT3 phosphorylation at Tyr705, the research links vitamin D signalling to chitinase-like protein regulation for the first time in cutaneous inflammation. The findings suggest that CHI3L2 could serve as a biomarker predicting response to vitamin D treatment, and that combining CHI3L2 inhibition with calcitriol administration might yield additive or synergistic benefits. With psoriasis prevalence rising worldwide and no cure in sight, uncovering a druggable node in the STAT3/CHI3L2 axis offers both mechanistic insight and a tangible target for the next generation of anti-psoriatic therapies.

Subject of Research: The mechanism by which calcitriol suppresses psoriatic inflammation and keratinocyte hyperproliferation through downregulation of CHI3L2 via the STAT3 pathway

Article Title: Downregulating CHI3L2 via the STAT3 Pathway: The Mechanism of Calcitriol in Suppressing Psoriatic Inflammation and Keratinocyte Hyperproliferation

Article References: He, Q., & Liu, J. (2026). Downregulating CHI3L2 via the STAT3 Pathway: The Mechanism of Calcitriol in Suppressing Psoriatic Inflammation and Keratinocyte Hyperproliferation. Journal of Cellular and Molecular Medicine, 30(18), Article e71367. https://doi.org/10.1111/jcmm.71367

Image Credits: AI Generated

DOI: 10.1111/jcmm.71367

Keywords: psoriasis, calcitriol, vitamin D, CHI3L2, STAT3, keratinocytes, imiquimod model, inflammation, HaCaT cells, CYP24A1, interleukin-17, drug mechanism