Integrative multi-omics analysis identifies endocrine-disrupting chemical-related molecular mechanisms in migraine.

Low back pain is a highly prevalent clinical condition, affecting more than 600 million people globally []. Discogenic low back pain accounts for 26–42% of all back pain cases [] and represents the most common underlying diagnosis among individuals with low back pain [,]. Well-known risk factors for intervertebral disc (IVD) degeneration (IDD) include aging, genetic predisposition, aberrant mechanical loading, a sedentary lifestyle, and poor diet [,]. IVDs consist of three distinct tissues: the nucleus pulposus (NP), a hydrated, gel-like core enriched with the proteoglycan Aggrecan, which binds water and enables the tissue to withstand compressive forces; the fibrocartilaginous annulus fibrosus, which consists of concentric lamellar layers that provide mechanical stability [,]; and the cartilaginous endplates that anchor the IVDs to adjacent vertebral bodies []. Signs of spontaneous IDD first occur in the NP and are characterized by increased production of pro-inflammatory cytokines and progressive extracellular matrix (ECM) degradation by increasing the expression of matrix metalloproteases (MMPs). Major cytokines implicated in this process include tumor necrosis factor-α (TNFA), interleukins, and chemokines [,,]. Among cytokines, TNFA, IL1B, and IL6 are the most extensively characterized in IVDs [,,]. This pro-inflammatory and catabolic environment further accelerates IDD by increasing the expression of ECM-degrading enzymes [,,] and phosphatases [,,]. We previously showed that the phosphatase PH domain leucine-rich repeat protein phosphatase 1 (PHLPP1) is highly expressed in degenerated human IVD tissues [] and that its deficiency in mice decelerated age- and injury-induced IDD by promoting ECM production and cell survival, while decreasing apoptotic cell death [,]. In other musculoskeletal tissues, PHLPP1 has been shown to induce osteoclast-mediated bone resorption [], cartilage degradation [], and post-traumatic osteoarthritis []. Consistent with these catabolic effects, evidence also supports an association between PHLPP1 and inflammation in osteoarthritis [] and bone homeostasis []. Building on these observations, the aim of the present study was to determine whether PHLPP1 functions as an upstream regulator of inflammatory signaling networks in NP cells, and if its deficiency can inhibit inflammatory signaling and catabolic pathways in NP cells. We examined lumbar IVDs from aged global knockout (KO) and wild-type (WT) mice for age-related IDD. Bulk RNA sequencing was performed to assess the transcriptomic profile of degenerated human NP cells after knockdown, and the results were validated using RT-qPCR. Degenerated human NP cell cultures were treated with IL1B to simulate the pro-inflammatory environment of degenerated IVDs and to assess the protective effect of knockdown against inflammatory stimuli. Degenerated human NP cells and IVDs of aged knockout mice were used to determine the role of PHLPP1 as an upstream regulator of inflammatory signaling networks during IDD (). Mouse lumbar spines were harvested from 20-month-old female and male WT and KO mice and processed for IDD and immunohistochemical analysis of IL1B and IL6. Degenerated human NP cells were transfected with either non-targeting small interfering RNA (si-NT) or -targeting siRNA (si-PHLPP1) to assess the transcriptomic profile after knockdown and to identify whether deficiency inhibits inflammatory signaling after IL1B stimulation.