What the paper is

Nada Tawfig Hashim, Bakri Gobara Gismalla, Ayman Ahmed and six colleagues, affiliated with RAK Medical & Health Sciences University and Ajman University in the United Arab Emirates and dental schools in Khartoum, published “USAG-1/SOSTDC1 as a Candidate Target for Periodontal Regeneration: Biological Rationale, Knowledge Gaps, and Future Directions” in Molecules on 23 September 2026 (doi:10.3390/molecules31193389; open access, CC BY). It is a perspective, not a research article: the data-availability statement reads “No new data were created or analyzed in this study.” The authors are dental faculty, mostly periodontists, with no declared funding and no declared conflicts of interest, and they are not part of the Toregem BioPharma or Kyoto University program that developed the anti-USAG-1 antibody TRG-035. The paper’s stated motivation is the clinical momentum of that antibody, which it describes as first-in-human Phase 1 testing in congenital tooth agenesis reportedly initiated in late 2024; the trial’s completion and the Phase IIa preparation are sponsor-reported developments recorded on the program page, not findings of this paper, and no peer-reviewed clinical results existed at the time of writing.

The rationale, as the authors grade it

The paper’s most useful feature is self-discipline. It sorts every central claim into four grades, summarized in its Table 1: established USAG-1 biology (largely from tooth development and kidney studies), established periodontal BMP and Wnt biology (from non-USAG-1 work), indirect evidence, and purely hypothetical applications. USAG-1 (SOSTDC1) is a secreted antagonist that binds BMP-2, BMP-4, BMP-7, and BMP-10 and also blocks the Wnt co-receptors LRP5 and LRP6; knocking it out in mice produces supernumerary teeth by reactivating rudimentary buds. The only evidence that USAG-1 is even present in the adult periodontium is transcript-level: a peer-reviewed re-analysis of public single-cell RNA-sequencing data found USAG-1 transcripts in two subsets of human gingival fibroblasts and in basal gingival epithelial cells, in non-diseased tissue, without protein-level confirmation and without any comparison to periodontitis-affected tissue (Moradi et al., Clinical and Experimental Dental Research 2026, cited as reference 9). Whether USAG-1 protein is secreted and functional at the periodontal interface is, the authors say, an open empirical question.

The comparator that is not a prediction

The strongest quantitative anchor in the paper belongs to a different molecule. Osteocyte-specific deletion of Dkk-1, another Wnt antagonist, reduced alveolar bone loss by 28.5 percent in a murine ligature-induced periodontitis model (Goes et al., Frontiers in Immunology 2019). The authors use this strictly as proof of principle that modulating a Wnt antagonist can move alveolar bone biology, and they state explicitly that USAG-1 and Dkk-1 are not interchangeable targets and the number cannot be assumed to predict anything about anti-USAG-1 therapy. The BMP side carries the same caution in a different form: in cultured human periodontal ligament stem cells, BMP-4 at 10 ng/mL sustains multipotency while 100 ng/mL pushes tenogenic differentiation and suppresses osteogenic commitment (Li et al., 2025), so even if USAG-1 blockade raises local BMP signaling, the direction of any shift in progenitor behavior cannot be predicted from current evidence.

Delivery and safety, treated as engineering problems

The authors argue the systemic intravenous dosing used in the TRG-035 tooth-agenesis trials is the wrong model for a periodontal application, partly because USAG-1 has a physiological role in renal BMP signaling and systemic inhibition could endanger the kidney. They propose local delivery instead, in rough order of feasibility: antibody incorporated into a collagen guided-tissue-regeneration membrane, antibody loaded onto a bone-graft carrier, nucleic-acid silencing (siRNA or AAV), and small-molecule inhibitors. Each is flagged as untested; the small-molecule option rests on a 2022 bioRxiv preprint with no experimental validation. The only local USAG-1 silencing data anywhere come from tooth-development work: topically applied Usag-1 siRNA in cationized gelatin partially rescued arrested tooth development in Runx2-deficient mice (Mishima et al., Scientific Reports 2021), a developmental model with no periodontal readout. The safety section additionally lists root resorption and ankylosis (documented risks of supraphysiological BMP-2 delivery), the possibility that Wnt reactivation favors epithelial proliferation over repair, and the theoretical dysplasia risk of sustained local Wnt signaling near oral epithelium.

The research agenda, and where it starts

The paper closes with a six-step agenda, and its first step is telling: protein-level profiling of USAG-1 in healthy versus Stage II and Stage III/IV periodontitis tissue must come before any animal work, because the entire hypothesis assumes the target is up in disease, which nobody has measured. Steps two through six run from PDLSC experiments under inflammatory conditions to a ligature-induced periodontitis model with local antibody delivery, combination studies with existing regenerative materials, renal and epithelial safety profiling, and only then a first-in-human periodontal trial, positioned where regenerative surgery sits, at Step 3, in the EFP S3 stepwise treatment algorithm. The authors also write in explicit falsification criteria, including the possibility that USAG-1 expression falls, rather than rises, in periodontitis.

Boundary, and what it changes

For the anti-USAG-1 / TRG-035 program, this paper does what a good perspective should: it shows the target biology may matter in a second disease context, periodontitis, and it sketches what a development program would have to prove. It adds nothing to the program’s evidence column. There is no USAG-1 expression dataset from periodontitis lesions, no periodontal animal experiment with an anti-USAG-1 agent, and no clinical signal; the paper says all three things itself, repeatedly. The field assessment does not change on this record. No press coverage of this paper exists as of 25 September 2026. If it is covered, the likely frame, that the tooth-regeneration drug might also regrow gums, will outrun a paper that grades its own case as hypothetical and names its first required experiment. The record supports a narrower sentence: a nine-author group with no program affiliation has published a carefully graded argument that USAG-1 inhibition is worth testing in periodontal regeneration, and the testing has not started.

Provenance: grounded in the full text of Hashim, Gismalla, Ahmed et al. (2026), Molecules 31(19):3389, published 23 September 2026, doi:10.3390/molecules31193389, retrieved from the publisher’s HTML on 25 September 2026; author names confirmed against the Crossref record for the same DOI. See /method/.