IL-1β-Induced Inflammatory Transcriptome and TGF-β1 Attenuation of Chemokine Expression in ACL Remnant Fibroblasts.

Abstract

The high incidence of posttraumatic osteoarthritis after anterior cruciate ligament (ACL) injury and reconstruction suggests that biological mechanisms beyond joint instability contribute to disease progression. After injury, ACL-resident cells are exposed to inflammatory mediators within the joint and may influence the local inflammatory microenvironment; however, their global transcriptomic responses to inflammatory stimuli remain underexplored. Interleukin-1 beta (IL-1β) induces inflammatory transcriptomic responses in ACL remnant-derived (ACLr) fibroblasts, and transforming growth factor beta 1 (TGF-β1) attenuates these responses. Descriptive laboratory study. Primary ACLr fibroblasts were isolated from ACL remnants (n = 10) collected at the time of knee surgery. Near-confluent cultures were treated with IL-1β (10 ng/mL) for 24 hours to model an inflammatory joint environment. Genome-wide transcriptional changes were assessed by RNA sequencing using an Illumina NovaSeq-6000, with selected targets confirmed by microfluidic digital polymerase chain reaction (PCR). To evaluate the effects of TGF-β1, ACLr fibroblasts pretreated with IL-1β were exposed to TGF-β1 (10 ng/mL) for 48 hours, and chemokine transcript levels were assessed using digital PCR. IL-1β induced broad inflammatory transcriptional responses characterized by upregulation of chemokines (<i>CXCL6</i>, <i>CXCL8</i>, <i>CXCL5</i>, <i>CCL20</i>, <i>CXCL1</i>, and <i>CXCL3</i>), cytokines (<i>IL33</i>, <i>IL1B</i>, and <i>IL6</i>), and matrix-degrading enzymes (<i>MMP3</i> and <i>MMP12</i>), while suppressing extracellular matrix-associated genes (<i>KRT14</i>, <i>COL21A1</i>, <i>POSTN</i>, <i>COL1A1</i>, and <i>COL6A3</i>). Functional enrichment analysis demonstrated activation of immune and inflammatory responses, cytokine and chemokine signaling, and cell activation. TGF-β1 reduced the expression of all assessed IL-1β-induced chemokines, with reduction of up to 50%, with statistically significant suppression observed for 13 of the 16 chemokines. Concomitantly, TGF-β1 treatment reduced expression of <i>CEBPB</i>, <i>NFKBIA</i>, and <i>NFKBIZ</i>, transcripts implicated in inflammatory gene regulation. ACLr fibroblasts mounted a robust inflammatory transcriptomic response to IL-1β, characterized by marked induction of chemokines and inflammatory pathways. TGF-β1 attenuated many of these responses, supporting its role as a regulator of inflammatory signaling in ACL-resident cells. ACL-resident cells respond to injury and may contribute to the post-injury inflammatory microenvironment. Therapeutic modulation of inflammatory signaling in these cells could represent a strategy to mitigate early molecular events associated with post-traumatic osteoarthritis following ACL tear.