1393 Human TMEM2 is not a hyaluronidase but a regulator of hyaluronan metabolism

Hyaluronan (HA) is a high molecular weight linear glycosaminoglycan and abundant in the skin extracellular matrix. Cutaneous HA is first depolymerized to intermediate sizes and then further fragmented in regional lymph nodes. High molecular weight HA is anti-inflammatory and anti-angiogenic, whereas fragmented HA is pro-inflammatory and pro-angiogenic. We have reported that HYBID (HA-Binding protein Involved in HA Depolymerization), also known as KIAA1199/CEMIP, is responsible for the first step of HA depolymerization, but it was recently shown that mouse TMEM2 (mTMEM2) with high structural similarity to HYBID, is a membrane-bound hyaluronidase. We previously showed that HYBID was essential for HA depolymerization in normal human dermal fibroblasts (NHDF), whereas knockdown of human TMEM2 (hTMEM2) enhanced HA depolymerization. The purpose of this study is to elucidate the HA degradation activity and functions of hTMEM2. HYBID and TMEM2 expression plasmids were transfected into HEK293T cells, and each HA depolymerization activity was confirmed. hHYBID and mTMEM2 degraded HA, but hTMEM2 did not, indicating that hTMEM2 does not function as a hyaluronidase. Then, we focused on amino acid residues that are conserved in the HA-degrading hHYBID, mHYBID, and mTMEM2 but substituted in hTMEM2. Simultaneous replacement of the corresponding amino acid residues (H248N and A303F) in the GG domain of mTMEM2 abolished HA-degrading activity. In addition, stimulation of NHDF by IL-1β increased mTMEM2 mRNA expression and subsequently decreased HYBID mRNA expression along with an increase in HAS2-dependent HA production, which were reversed by hTMEM2 knockdown. Taken together, these results indicate that hTMEM2 is not a hyaluronidase but a regulator of HA metabolism.