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The ability to differentiate sporadic primary hyperparathyroidism (sPHPT) caused by a single parathyroid adenoma (PTA) from multiglandular parathyroid disease (MGD) preoperatively, as well as definitely diagnose sPHPT in difficult patients, would enhance surgical decision-making. This work aimed to identify miRNA (miR) signatures for MGD, single- and double-PTA, as well as cell-free miRNA (cfmiR) in plasma samples from patients with single-PTAs to use as biomarkers. A total of 47 patients with sPHPT (single-PTA n = 32, double-PTA n = 12, MGD n = 9). Preoperative plasma samples from 16 single-PTA and 29 normal healthy donors (NHDs). All specimens were processed and analyzed for 2083 miRs using HTG EdgeSeq miR whole-transcriptome assay and normalized using DESeq2 to identify differentially expressed (DE) miRs. MiR classifiers were identified using Random Forest. Main outcome measures were receiver operating characteristic curves and areas under the curve. MiR signatures distinguished normal parathyroid from MGD and PTA as well as MGD from PTA in tissue samples. Common miRs were found in the single-PTA and double-PTAs. Data integration identified a 27-miR signature in single-PTA tissue samples compared to the rest of the tissue samples. In plasma samples analysis, significant cfmiRs were DE in single-PTA patients compared to NHD. Of those, only 9 miRNAs/cfmiRs were found DE both in tissue and plasma samples from patients diagnosed with a single PTA (AUC = 76%). Twenty-seven miRs were consistently found DE in single-PTA tissue and plasma samples. Data integration showed a 9-cfmiR signature with potential clinical utility to preoperatively diagnose sPHPT caused by a single PTA, which could decrease more invasive parathyroid explorations.

The parathyroid hormone receptor-1 (PTH1R) is a class B G protein–coupled receptor central to calcium homeostasis and a therapeutic target for osteoporosis and hypoparathyroidism. Here we report the cryo–electron microscopy structure of human PTH1R bound to a long-acting PTH analog and the stimulatory G protein. The bound peptide adopts an extended helix with its amino terminus inserted deeply into the receptor transmembrane domain (TMD), which leads to partial unwinding of the carboxyl terminus of transmembrane helix 6 and induces a sharp kink at the middle of this helix to allow the receptor to couple with G protein. In contrast to a single TMD structure state, the extracellular domain adopts multiple conformations. These results provide insights into the structural basis and dynamics of PTH binding and receptor activation.

Formation of functional skeletal tissues requires highly organized steps of mesenchymal progenitor cell differentiation. The dental follicle (DF) surrounding the developing tooth harbors mesenchymal progenitor cells for various differentiated cells constituting the tooth root–bone interface and coordinates tooth eruption in a manner dependent on signaling by parathyroid hormone-related peptide (PTHrP) and the PTH/PTHrP receptor (PPR). However, the identity of mesenchymal progenitor cells in the DF and how they are regulated by PTHrP-PPR signaling remain unknown. Here, we show that the PTHrP-PPR autocrine signal maintains physiological cell fates of DF mesenchymal progenitor cells to establish the functional periodontal attachment apparatus and orchestrates tooth eruption. A single-cell RNA-seq analysis revealed cellular heterogeneity of PTHrP⁺ cells, wherein PTHrP⁺ DF subpopulations abundantly express PPR. Cell lineage analysis using tamoxifen-inducible PTHrP-creER mice revealed that PTHrP⁺ DF cells differentiate into cementoblasts on the acellular cementum, periodontal ligament cells, and alveolar cryptal bone osteoblasts during tooth root formation. PPR deficiency induced a cell fate shift of PTHrP⁺ DF mesenchymal progenitor cells to nonphysiological cementoblast-like cells precociously forming the cellular cementum on the root surface associated with up-regulation of Mef2c and matrix proteins, resulting in loss of the proper periodontal attachment apparatus and primary failure of tooth eruption, closely resembling human genetic conditions caused by PPR mutations. These findings reveal a unique mechanism whereby proper cell fates of mesenchymal progenitor cells are tightly maintained by an autocrine system mediated by PTHrP-PPR signaling to achieve functional formation of skeletal tissues.

Abstract Context Primary hyperparathyroidism (PHPT) is an endocrine disorder that is treated surgically, and some correlation between the size of the responsible lesion and preoperative clinical data is assumed. Objective The purpose of this study was to predict tumor volume of the lesion responsible for PHPT from preoperative clinical data. Methods Participants comprised patients with surgically treated PHPT who underwent initial surgery in our department between January 2000 and December 2021. The volume of parathyroid gland removed was used as the primary outcome and associations with preoperative clinical data were assessed by multivariable analysis. Results A positive correlation was identified between parathyroid tumor volume and both preoperative intact parathyroid hormone (PTH) (Spearman's r = 0.503) and calcium values (Spearman's r = 0.338). Data for intact PTH value and tumor volume were logarithmically transformed (ln-PTH = log-transformed intact PTH value; ln-volume = log-transformed tumor volume). Multiple regression analysis revealed male sex, ln-PTH and calcium values as significant predictors of ln-volume, with standardized regression coefficients of 0.213 (95% CI 0.103-0.323), 0.5018 (95% CI 0.4442-0559), and 0.322 (95% CI 0.0339-0.149), respectively. The adjusted R2 for this model is 0.320. Conclusion Preoperative serum intact PTH value is associated with tumor volume of the lesion responsible for PHPT. A rough estimation of the tumor size would provide responsible physicians with opportunities to add further imaging tests or plan appropriate surgical strategies.

The thymus and parathyroid glands share a common embryological origin from the third pharyngeal pouch, yet their potential morphological and functional interconnections remain insufficiently explored. We conducted a comparative study integrating immunohistochemistry (IHC) and SEM on human thymic tissue, parathyroid adenomas, and parathyroid tissue excised during thyroidectomy. IHC staining targeted Thymosin-α1, CaSR, and PTH1R, with semi-quantitative evaluation of staining intensity and distribution. SEM analysis was performed at multiple magnifications to assess stromal organization and microvascular relief. Non-parametric statistical tests (Kruskal-Wallis with Mann-Whitney post hoc comparisons) were applied to clinical and laboratory data across the three cohorts. Scanning electron microscopy (SEM) revealed convergent ultrastructural features between thymus and parathyroid, including reticular stromal meshes and vascular grooves suggestive of comparable microcirculatory organization. IHC demonstrated robust Thymosin expression in thymus, with heterogeneous/apical distribution in parathyroid tissue; CaSR showed strong membranous and cytoplasmic expression in parathyroid, but weak diffuse signal in thymus; PTH1R exhibited low-to-moderate expression in thymus and moderate heterogeneous expression in parathyroid, with apical accentuation in adenomas. Statistical analysis confirmed significant differences in ionized calcium, PTH, and anti-AChR titers among the three cohorts (all < 0.001), while TSH and calcitonin did not differ significantly. Our findings strengthen the hypothesis of a morpho-functional parathyroid-thymus axis. The robust parathyroid expression of CaSR and PTH1R aligns with established roles in calcium-PTH homeostasis, while the novel detection of Thymosin in parathyroid tissue suggests an expanded functional repertoire. These results highlight a continuum between embryological proximity and adult tissue cross-talk, with potential clinical implications for parathyroid pathology and immune regulation.

Abstract Parathyroid hormone (PTH) and the paracrine factor, PTH-related protein (PTHrP), have preserved in evolution sufficient identities in their amino-terminal domains to share equivalent actions upon a common G protein-coupled receptor, PTH1R, that predominantly uses the cyclic adenosine monophosphate-protein kinase A signaling pathway. Such a relationship between a hormone and local factor poses questions about how their common receptor mediates pharmacological and physiological actions of the two. Mouse genetic studies show that PTHrP is essential for endochondral bone lengthening in the fetus and is essential for bone remodeling. In contrast, the main postnatal function of PTH is hormonal control of calcium homeostasis, with no evidence that PTHrP contributes. Pharmacologically, amino-terminal PTH and PTHrP peptides (teriparatide and abaloparatide) promote bone formation when administered by intermittent (daily) injection. This anabolic effect is remodeling-based with a lesser contribution from modeling. The apparent lesser potency of PTHrP than PTH peptides as skeletal anabolic agents could be explained by lesser bioavailability to PTH1R. By contrast, prolongation of PTH1R stimulation by excessive dosing or infusion, converts the response to a predominantly resorptive one by stimulating osteoclast formation. Physiologically, locally generated PTHrP is better equipped than the circulating hormone to regulate bone remodeling, which occurs asynchronously at widely distributed sites throughout the skeleton where it is needed to replace old or damaged bone. While it remains possible that PTH, circulating within a narrow concentration range, could contribute in some way to remodeling and modeling, its main physiological role is in regulating calcium homeostasis. Graphical Abstract Graphical Abstract

The 2022 WHO classification reflects increases in the knowledge of the underlying pathogenesis of parathyroid disease. In addition to the classic characteristic features of parathyroid neoplasms, subtleties in histologic features which may indicate an underlying genetic abnormality reflect increased understanding of the clinical manifestations, histologic, and genetic correlation in parathyroid disease. The importance of underlying genetic aberrancies is emphasized due to their significance to the care of the patient. Traditionally, the term “parathyroid hyperplasia” has been applied to multiglandular parathyroid disease; however, the concept of hyperplasia is generally no longer supported in the context of primary hyperparathyroidism since affected glands are usually composed of multiple “clonal” neoplastic proliferations. In light of these findings and management implications for patient care, the 2022 WHO classification endorses primary hyperparathyroidism-related multiglandular parathyroid disease (multiglandular multiple parathyroid adenomas) as a germline susceptibility-driven multiglandular parathyroid neoplasia. From such a perspective, pathologists can provide additional value to genetic triaging by recognizing morphological and immunohistochemical harbingers of MEN1 , CDKN1B , MAX , and CDC73 -related manifestations. In the current WHO classification, the term “parathyroid hyperplasia” is now used primarily in the setting of secondary hyperplasia which is most often caused by chronic renal failure. In addition to expansion in the histological features, including those that may be suggestive of an underlying genetic abnormality, there are additional nomenclature changes in the 2022 WHO classification reflecting increased understanding of the underlying pathogenesis of parathyroid disease. The new classification no longer endorses the use of “atypical parathyroid adenoma”. This entity is now being replaced with the term of “atypical parathyroid tumor” to reflect a parathyroid neoplasm of uncertain malignant potential. The differential diagnoses of atypical parathyroid tumor are discussed along with the details of worrisome clinical and laboratory findings, and also features that define atypical histological and immunohistochemical findings to qualify for this diagnosis. The histological definition of parathyroid carcinoma still requires one of the following findings: (i) angioinvasion (vascular invasion) characterized by tumor invading through a vessel wall and associated thrombus, or intravascular tumor cells admixed with thrombus, (ii) lymphatic invasion, (iii) perineural (intraneural) invasion, (iv) local malignant invasion into adjacent anatomic structures, or (v) histologically/cytologically documented metastatic disease. In parathyroid carcinomas, the documentation of mitotic activity (e.g., mitoses per 10mm 2 ) and Ki67 labeling index is recommended. Furthermore, the importance of complete submission of parathyroidectomy specimens for microscopic examination, and the crucial role of multiple levels along with ancillary biomarkers have expanded the diagnostic workup of atypical parathyroid tumors and parathyroid carcinoma to ensure accurate characterization of parathyroid neoplasms. The concept of parafibromin deficiency has been expanded upon and term “parafibromin deficient parathyroid neoplasm” is applied to a parathyroid neoplasm showing complete absence of nuclear parafibromin immunoreactivity. Nucleolar loss is considered as abnormal finding that requires further molecular testing to confirm its biological significance. The 2022 WHO classification emphasizes the role of molecular immunohistochemistry in parathyroid disease. By adopting a question–answer framework, this review highlights advances in knowledge of histological features, ancillary studies, and associated genetic findings that increase the understanding of the underlying pathogenesis of parathyroid disease that are now reflected in the updated classification and new entities in the 2022 WHO classification.

Abstract Context Conventional therapy for hypoparathyroidism aims to alleviate symptoms of hypocalcemia but does not address insufficient parathyroid hormone (PTH) levels. Objective Assess the long-term efficacy and safety of TransCon PTH (palopegteriparatide) for hypoparathyroidism. Design Phase 3 trial with a 26-week, double-blind, placebo-controlled period followed by a 156-week, open-label extension (OLE). Setting Twenty-one sites across North America and Europe. Participants A total of 82 adults with hypoparathyroidism were randomized and received study drug and 78 completed week 52. Intervention(s) All OLE participants received TransCon PTH administered once daily. Main Outcome Measure(s) Multicomponent efficacy endpoint: proportion of participants at week 52 who achieved normal serum calcium (8.3-10.6 mg/dL) and independence from conventional therapy (≤600 mg/day of elemental calcium and no active vitamin D). Other efficacy endpoints included patient-reported outcomes and bone mineral density. Safety was assessed by 24-hour urine calcium and treatment-emergent adverse events. Results At week 52, 81% (63/78) met the multicomponent efficacy endpoint, 95% (74/78) achieved independence from conventional therapy, and none required active vitamin D. Patient-reported outcomes showed sustained improvements in quality of life, physical functioning, and well-being. Mean bone mineral density Z-scores decreased toward age- and sex-matched norms from baseline to week 52. Mean (SD) 24-hour urine calcium excretion decreased from 376 (168) mg/day at baseline to 195 (114) mg/day at week 52. Most treatment-emergent adverse events were mild or moderate and none led to trial discontinuation during the OLE. Conclusion At week 52 of the PaTHway trial, TransCon PTH showed sustained efficacy, safety, and tolerability in adults with hypoparathyroidism.

Abstract Context Abaloparatide is a US Food and Drug Administration-approved parathyroid hormone-related peptide analog for treatment of osteoporosis in postmenopausal women at high risk of fracture. Objectives We assessed the cardiovascular safety profile of abaloparatide. Design Review of heart rate (HR), blood pressure (BP), and cardiovascular-related adverse events (AEs), including major adverse cardiovascular events (MACEs) and heart failure (HF) from: (a) ACTIVE (NCT01343004), a phase 3 trial that randomized 2463 postmenopausal women with osteoporosis to abaloparatide, teriparatide, or placebo for 18 months; (b) ACTIVExtend (NCT01657162), where participants from the abaloparatide and placebo arms received alendronate for 2 years; and (c) a pharmacology study in 55 healthy adults. Results Abaloparatide and teriparatide transiently increased HR relative to placebo. Following first dose, mean (standard deviation [SD]) HR change from pretreatment to 1 hour posttreatment was 7.9 (8.5) beats per minute (bpm) for abaloparatide, 5.3 (7.5) for teriparatide, and 1.2 (7.1) for placebo. A similar pattern was observed over subsequent visits. In healthy volunteers, HR increase resolved within 4 hours. The corresponding change in mean supine systolic and diastolic BP 1 hour posttreatment was –2.7/–3.6 mmHg (abaloparatide), –2.0/–3.6 (teriparatide), and –1.5/–2.3 (placebo). The percentage of participants with serious cardiac AEs was similar among groups (0.9%-1.0%). In a post hoc analysis, time to first incidence of MACE + HF was longer with abaloparatide (P = 0.02 vs placebo) and teriparatide (P = 0.04 vs placebo). Conclusions Abaloparatide was associated with transient increases in HR and small decreases in BP in postmenopausal women with osteoporosis, with no increase in risk of serious cardiac AEs, MACE, or HF.