Primary attributes of study participants
During Jan 2017 - June 2019, 268 BM examinations were done in the Institute of Liver and Biliary Sciences for various clinical indications. One hundred forty-five (145) were cirrhotic patients, and twenty-nine non-liver disease cases without pathology were considered controls. The rest of the cases (n=94) belonged to other diseases and hence were excluded. BM of six cirrhosis patients and three controls were suboptimal, and 12 cirrhotic patients had associated neoplastic pathology and excluded from the study. [Study Participants Summarized in Fig S1].
Amongst the cirrhosis group, 28.3% patients belonged to CTP A (n=36), 42.6% to CTP B (n=54), and 29.1 % to CTP C (n=37) classes. The most frequent etiology was alcohol-associated cirrhosis (41.1%). These basic parameters amongst the CTP classes and controls succinctly summarized in Table-S3.
Bone marrow transcriptomics showed Down-Regulation of CSF3R
Bone marrow transcriptomics analysis showed that the immunological signatures are affected in cirrhotic patients. Especially, those related to innate immune responses become downregulated in advanced cirrhosis, i.e., CTP class C [Fig S2, S3]. Gene set enrichment analysis showed 294 down-regulated genes [Fig.S4]. Specifically, 34 genes were downregulated across the group (Control> CTP A> CTP C) including CSF3R [Fig.1A]. Further, it was confirmed by qRT-PCR. Whereas, the associated genes like HCK and SYK were comparable amongst the CTP classes. [Fig. 1B]. Immunohistochemistry showed reduced CSF3R+ cells but not HCK and SYK positive cells/20X with cirrhosis progression. [Fig. 1C, D] These results indicate the reduced CSF3R expression in the BM precursor cells.
CSF3R in Peripheral Blood
Since bone marrow is routinely not done in cirrhotic patients, we decided to test the CSF3R levels in the peripheral blood plasma. We assessed the levels of both ligand (G-CSF) and CSF3R in the BM and peripheral blood plasma. The plasma levels of G-CSF were increased [Fig.2A], whereas the receptor levels were found to be lowered [Fig.2B], with the advancement of cirrhosis stages.
There was no difference in BM and peripheral blood of CSF3R (p=0.439 and 0.850) amongst various cirrhosis etiologies. Also, BM and peripheral blood CSF3R (p=0.539 and p=0.131) were comparable among male and female patients.
During a follow-up of 6 months, 26 had naturally acquired infection, and of these, seven had pneumonia, urinary tract infection (06), spontaneous bacterial peritonitis (10), and other infections (03). Those patients who had developed infection had lesser BM-CSF3R (p=0.056) and peripheral blood CSF3R (p=0.022) levels as compared to the patients who did not. [Fig. 2C]. Similarly, patients with peripheral blood leukopenia (total leukocyte count <4x10^6/L, n=31) also demonstrated lower levels of CSF3R in the BM plasma (p=0.001) and peripheral blood (p=0.217) [Fig. 2D].
PB-CSF3R correlated with total leukocyte count (ρ=0.303, p=0.022) and absolute neutrophil count (ρ=0.431, p=0.01). Baseline PB-CSF3R showed moderate sensitivity and specificity for the occurrence of infection and severe neutropenia (<2000/cmm and neutrophils<1000/cmm) with an area under the curve (AUROC) of 0.677 [Fig. 2E] and 0.707 [Fig. 2F], with cut-off values of ≤ 55 pg/ml and ≤ 58 pg/ml, respectively.
Overall, the results show the lower levels of circulating CSF3R in BM and PB plasma with cirrhosis advancement and association with occurrence infection and leukopenia.
Low CSF3R levels relates to both decreased stem cell population
and downregulation of surface receptors
We have earlier reported that the level of HSCs declines in advanced cirrhosis patients. [7] The lower levels of CSF3R receptors could be due to decreased BM progenitor cells. Hence, we enumerated these cells in various classes of cirrhosis patients. As expected, we found lower CD34+ cells in CTP class B and C than CTP A and controls [Fig. 3A, B]. Further cell assessment revealed that the % population of CSF3R+ cells out of CD34+ cells also showed a declining trend with advancing cirrhosis [Fig. 3A, C].
The reduction of a stable pool of CD34+ cells could be due to higher G-CSF levels in the circulation. The mobilized HSCs lead to the formation of CFU and BFU in BM. We found that the CFU-GM and BFU-E were more pronounced in CTP A or B patients. [Fig.3 D].
This data indicates that the low CSF3R in advanced cirrhosis was related to decreased CD34 cells in BM and downregulation of CSF3R in the remaining CD34 cells in the BM.
CSF3R inhibitory protein: Carcinoembryonic antigen cell adhesion molecule-1 (CEACAM1) in Cirrhosis
CEACAM1 (biliary glycoprotein) acts as a coinhibitory molecule for CSF3R and downregulates the CSF3R-STAT3 pathway. [16] BM transcriptomics data revealed that the CEACAM1 was upregulated in CTP C than CTP A (2.26; q value= 0.00033). On validation, by qRT-PCR, the CEACAM-1 was upregulated in cirrhosis BM compared to controls. [Fig. 4A] On IHC, CEACAM1 positive BM precursor cells were more pronounced in CTP C and B than CTP A and control [Fig. 4B]. Further, the estimation of the circulating level of CEACAM1 in BM plasma [Fig. 4C] and peripheral blood plasma [Fig. 4D] also showed a similar trend (p<0.001 in both), with the highest level being in the CTP C class.
The CEACAM1 in BM and peripheral blood plasma levels negatively correlated with the CSF3R (ρ= -0.668, p<0.001 and ρ= -0.729, p<0.001, respectively). Whereas, BM-GCSF and PB-GCSF levels correlated positively with BM-CEACAM1 (ρ=0.726, p<0.001) and PB-CEACAM-1 (ρ=0.719, p<0.001), respectively.
CEACAM-1 is expressed mainly in the biliary and colonic epithelium. So we did IHC in this cohort's available liver biopsies {n=14, (Control/CTP A/B/C=6/3/3/2)}. Interestingly we noted that in cirrhosis, especially in advanced cirrhosis, increased hepatic expression of CEACAM-1. [Fig. S5]
The results suggest the increased levels of CSF3R inhibitory protein CEACAM-1 in advanced cirrhosis.
CEACAM-1 downregulates CSF3R in the Bone marrow precursor cells:
In vitro, bone marrow mononuclear cultured cells treated with CEACAM-1 for 24 hours revealed a significant mean reduction (-21.8%, p=0.031) of CD34+CSF3R+ cells compared to untreated cells. [Fig. 4E]
CSF3R downregulation due to CEACAM in BM precursor cells occurs possibly due to lysosomal degradation
Due to elevated CEACAM1 levels, it is likely that the CSF3R receptor may get degraded in lysosomes and cannot be recycled. To test this hypothesis, we assessed the lysosomal contents in sorted BM CD34 cells by CXCR4 immunocytochemistry. We noted that the lysosome contents increased in cirrhosis as compared to controls. Moreover, the incremental changes noted with the advancement of cirrhosis [Fig. 5 A, B]. Further, on flow cytometry, the lysosomes were assessed by TLR 3 in the CD34 cells. CD34+ CSF3R- TLR3+ cells showed increasing (p<0.001) [Fig. 5C] and CD34+CSF3R+TLR3- had a declining trend (p=0.001) [Fig 5D] with the severity of liver cirrhosis. Likewise, BM precursor cells show incremental ubiquitin expression with cirrhosis advancement (p=0.007) [Fig 5E, F].
CD34+ CSF3R- TLR3+ positive cells and ubiquitin positive cells correlated with BM cellular CEACAM-1 (ρ=0.642, p<0.001 and ρ=0.459, p<0.001), respectively.
Thus the increasing lysosomal contents in CD34+ cells and increased ubiquitin in BM indirectly suggest that the CSF3R is degraded, possibly due to elevated CEACAM1.
Phase-2: Validation Studies of CSF3R
- CSF3R and Response to G-CSF in Cirrhosis
We took the stored plasma of patients (n=22) who received G-CSF treatment in an earlier study. (11) Fourteen were responsive, and eight were nonresponsive to G-CSF Table S4]. The baseline CSF3R levels were lower in BM and PB in patients who eventually did not respond to the therapy [Fig. 6A]. Contrarily, G-CSF at baseline was higher in non-responders in comparison to those who responded. [Fig. 6B] Moreover, post GCSF leukocyte count (ρ=0.48, p=0.02), neutrophil count (ρ=0.42, p=0.043) and CD34 cells/20x in liver biopsy (ρ=0.25, p=0.055) correlated with baseline CSF3R in these patients. ROC analysis of CSF3R in peripheral blood identified a cut-off value of <6.2 pg/ml for non-response with area under the curve 0.893, p=0.001 with a sensivity of 87.5% and specificity of 85.7%.
- CSF3R and Response to G-CSF in Cirrhosis related Neutropenia
G-CSF therapy was given to 15 patients with neutropenia from June 2019- June 2020. Six of these did not show improvement in leukocyte count. In comparison, it was noted that non-responders had lower CSF3R (p=0.015) in blood, and of them in four patients, baseline CSF3R was almost undetectable [Fig. 6C] The circulatory G-CSF was higher in non-responders, although it was not statistically significant (p=0.071). [Fig. 6D]
Phase-3: Single nucleotide polymorphism (SNPs) in CSF3R gene
Variation in the GCSF response could also be due to the genetic polymorphism of CSF3R. So we tested for SNPs of the CSF3R gene. In our study set, no SNPs were detected.